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PUBLIC lie;;.-.: Y; 





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FBOmaOU OF CBEXUTB* DI OWMB OOLLIOI. MAHDHIiTni,; ■ ■ -_ ; _- ■..•-• 


" Chymia, alias Ahhtmia et Spagirica, est an eotfora nrf mixta, vel eomposita, vet 
aggregnta cliam, in prineipia tua nmlvtndi, avt tx prineipiu in talia com- 
biiuiitdi."~SrAML, 1728. 






"Til:; i.'KW Y':./<^ 

■ y ; / 


It has been the aim of the authors, in writing the 
present treatise, to place before the reader a fairly com- 
plete, and yet a clear and succinct, statement of the 
facts of Modem Chemistry, whilst at the same time 
entering so far into a discussion of Chemical Theory 
as the size of the work and the present transition 
state of the science permit. Special attention has been 
paid to the accurate description of the more important 
processes in technical chemistry, and to the careful 
representation of the most approved forms of apparatus 
employed. As an instance of this, the authors may 
refer to the chapter on the Manufacture of Sulphuric 
Acid. For valuable information on these points they 
are indebted to many friends both in this country 
and on the Continent. 

The volume commences with a short historical sketch 
of the rise and progress of cliemical science, and a few 
words relative to the history of each element and its 
more important compounds prefaces the systematic dis- 
cussion of their chemical properties. For this portion 
of their work, the authors wish here to acknowledge 
their indebtedness to Hermann Kopp's classical works 
on the History of Chemistry. 


In the part of the volume devoted to the description 
of the non-metallic elements, care has been taken to 
select the moat recent and exact experimental data, 
and to give references in all important instances, as it 
is mainly by consulting the original memoirs that a 
student can obtain a full grasp of his subject. 

Much attention has likewise been given to the repre- 
sentation of apparatus adapted for lecture-room experi- 
ment, and the numerous new illustrations required for 
this purpose have all been taken from photographs of 
apparatus actually in use. The fine portrait which 
adorns the title-page is a copy, by the skilful hands 
of Mr. Jeens, of a daguerreotj'pe taken shortly before 
Dalton's death. 

Mi^•CHE3TER, Julj/, 1877. 



Historical Iktroductiok 3 


Lava of Cliemiotl Combination S9 

Gases and Vapours 74 

The CoDtiuuity of Liquid and Gas«oaa States 78 

The Kinetic Theory of Gases 80 

DiSusion of Gases 8i 

Chemical Nomenclature 87 

The Non-Metallic £I.EME^'TB 95 

Hydrogen fiS 

ChloriQB 110 

Chlorine and Hydrogen 124 

Bromine 142 

Bromine end Ilj'drogeu ......... 146 

Chlorine and liromine ......... 151 

Iodine 151 

Iodine and Hydrogen 158 

Iodine aod Chlorine 143 

Fluorine 185 

Fluorine and Hydrogen 167 

Oxygen 167 

Oiygen and Hydrogen ......... 202 

Oiygen and Chlorine 262 

Orygen and Bromine 278 

Oxygen and Iodine 280 

Sulphur 284 

Sulpliur and Hydrogen 294 

Sulphur and Chlorine 301 

Snlphur and Bromine 30J 

Sulphur and Iodine 304 

Sulphur and Fluorine 305 

Sulphur and Oiyjcen . 305 

Chlorides and Bromides of Sulphuric Acid 345 

Selenium , ... .351 

Seleuium and Hydrogen 857 



Selenium and Chloride SfiS 

Seleoium and Bromine 859 

Seleniam and Iodine SflO 

Seleoinm and Fluorine 360 

Solenium and Oxygen 361 

Sslenium and Suipbnr 364 

Tellurium S66 

Tellnrium and Hydrogen 867 

Tellnrium and Chlorine 368 

Tellurium and Bromine 869 

Telhuiiun and Iodine 360 

Tellurium and Fluorine 370 

Tellurium and Oxygon 370 

Tellurium and Sulphur 373 

Nitrogen ST3 

Nitrogen and Hydrogen 377 

Nitrogen and the Elements of the Chlorine Group .... 395 

Nitrogen and Oxygen S90 

Compounda uf Nitrogen with Sulphur and Selenium .... 430 

The Atnjospliero 434 

Phosphorus 457 

Phosphorus and Hydrogen - . 474 

Phosphorus and Chlorine 480 

Phosphorus and Bromine ■ , . . 484 

Phosphoius and Iodine 486 

Phosphorus and Fluorine 486 

Oxides and OxyaciJa of Phosphorus 487 

Phosphorus and Sulphur S09 

Phosphorus and Nitrogen 618 

Arsenic 6t7 

Arsenic and Hydrogen 619 

Arseuic and Chlorine 621 

Arsenic and Bromine 522 

Arsenic and lotlina 623 

Arsenic and Fluorine 623 

Oxides and O.iyacida of Arsenic 623 

Arsenic and Sulphur 531 

Arsenic and Suknium 634 

Arsenic and Phosphorus 634 

Boron 641 

Boron and Chlorine 644 

Boron and Bromine ...,,.,... 646 

Boron and Fluorine ....,...,. 616 

Oxides ami Oxyacids of Boron 648 

Boron and Sulphur 654 

Boron and Nitrugen 664 

Silicon or Sillcium .......... 665 

Silicon nnJ Hydrogen 668 

Silicon and Chlorine 659 

Silicon and Bromine 662 



Silicon and Iodine . . 663 

Silicon and Fluorine S6i 

Silicon and Oxygen C66 

Silicon and Snlphnr S74 

Silicon and Nitrogen fi75 

Carbon 678 

Carbon and H;drogpn 603 

Carbon and Chlorine 617 

Carbon and Oxygen ^ . 618 

Carbon and Sulphur 6fl 

Carbon and Nitrogen 666 





In looldng back at the history of our Science, we find that 
although the ancient world possessed a certain empirical know- 
ledge of chemical facts derived chielly from an acquaintance 
with pharmaceutical and manufacturing art, the power of COQ' 
necting or systematizing these facts was altogether wanting. 

The idea of experimental investigation was scarcely under- 
stood, and those amongst the ancients who desired to promote a 
knowledge of Nature attempted to do so rather by pursuing 
the treacherous paths of speculation, tiian the safe though tedious 
route of observation and experiment. They had no idea of the 
essential differences which we now perceive between elementa 
and compound substances, nor did they understand the meaning 
of chemical combination. The so-called Aristotelian doctrine 
of the four elements. Earth, Water, Air or Steam, and Fire, 
bore no analogy to our present views as to the nature and pro- 
perties of the chemical elements, for with Aristotle these names 
rather implied certain characteristic and fundamental properties 
of matter than the ideas which we now express by the terra 
chemical composition. Tlius " Earth " implied the properties 
of dr}'ne33 and coldness ; " Water," those of coldness and wet- 
ness ; " Air or Steam," wetness and heat ; " Fire," dryness and 
heat All matter was supposed to be of one kind, tlie variety 
which we observe being accounted for by the greater or less 
abundance of these four conditions which were supposed to be 
essential to every substance, that which was present in the 
greatest degree giving to the substance its characteristic pro- 

perties. To men holding Bticb views, a change of one kind of 
DiAlUtr into a totally difTercnt kind appeared ptttbaMe and 
oaturaL Tbus, the fonuatioa of wat«r from air or vice vend 
U described 1>y Piiiiy as n usual phenomenon scfin in tlui 
rormation and disajipearance of clouds, whilst the onliiiaiy 
experience, Utat cold acts as a soUiUfyiug and liordeuio;; 
agent, bears out Pliny's view, tliat rock crj'sta! b produced 
from moisture, not by the action of heat, but by that of cold, 
fio that ib is, in fact, a kind of ice. A tmttsfoniiation of ouo 
Bort of substance into another qnito diBerent thus appears 
not only poHHible but probable, and we are not Hurpri:«ed to 
Iflarn that, under the influence of the Aristoteliao pliilosophy, 
which throughout \hf. middle ages wan acknon*ledged to be the 
hi^^hest expression of scientific truth, the question of the traus- 
nititabtlily of tlio base ioto tlie noble tuetaU vtaa coueidured 
to l)e perfectly open. 

To tliis ppriod of the practice of alchemy, the search after 
the artilicial proJiiction of the noble metals, we may o^tgn 
the earliest dswn of our science ; and ftlchemy appears to 
have hfld its orijj;iii in Egypt. In the Byzantine writers of the 
fourth centut)' tlio word chemia Brst occurs as the name of the 
art which treats of tlie production of gold and silver,' and as 
all these authors were clostly coiiuecletl with the celebrated 
•chooU of Akxnudria, the last restmg-plare of the proscribed 
secrets of the Egyptian priests, it appenrs prohiible that oar 
science was first pnictised in Egypt I'Kilarch. indued, slAten 
that the old name for F^'jpl was Chcmia, luid tluit this aame 
VM given to it on aceount of the black colour of its soil 
The same word was used to designate Hie black of the eye. 
09 th« symbol of the dark and mysterious. It is, therefore. 
pretty certain that chemijitry originally iDeaut ^-ptian.— or 
B6crct — knowledge, as it wns nfteru'arda termed tlie Secret or 
Black art 

The Aristotelian phiIoRr.phy booamo known to and was ex- 
tended by the Arahinns, who, in the year 040, overran Ejrj-pt. 
fuid thence, throii)-!! NVirllu'vni Africa, penetrated into Spain. 
They firet liecaine actiuninted with cheniistry in F^vpt.iui<l pre- 
fixed tlie Arabic article to the original nnnie, so that the word 
nlcheniy has from that time Ix-cn used to signify the art of 
DMking gold aud silver. 

Tlw works of Gobcr, the most celebrated of Arabian 

• K-aff. SeiMlfi wr GtMfhulUe dtr CAemM. 1 Sliiok. p. (0. 


alcbetui»ui, are handed <.lown to ns tliroagh I^tin translations. 
In thcw VooTts, whicli may with trutli he considered to bo tlie 
oldest chemical wrtttDgs, vte lenra thnc llic sim of the science 
of which Gebcr tn»ta is the truiisiimtiitiou of the base iiito 
the noble metals. He describes initnT chemical openitions, 
s)ich &8 filrmtion. distillation, ciystalliKAtion, nn<) »il>iimation ; 
and by tliexu be prepoi-cs ucw substances or ))urifii» the old 
ones. Bodies each as alum, green vitriol, saltpetre, and aal- 
aninioninc iin- employed ; and we find tiiat he was alilc to pre- 
pure nitric acid, or a^ua fui-tu. and trom it the valuable solvent 
for gold, aipta rcyia. It is probable ttiat even sulphuric ncid 
vas knovn to Geber, and certainly a iittmbcr of nictallio 
compounds, amongst which were mercuric o:iidc and corrosive 
sublimate, the preparation of which he describe*, were known. 
Geber was the first propounder of a chemical theoiy. He aat^erts 
that tlie essential differences lietween the melals are duR to the 
prejmndeniuce of one of two principles, inercurjr and sulphur — 
of whii'h all tl« wptals SM composed. The first pTiiioij.Io is 
cliamuterislic of tlie truly metallic qualities, whilst the latter 
canses the peculiar changes noticed when the metals are ex- 
posed to heat The noble metals were snpjiftsed to contain a 
very pure mwrcary, and are, tliereforc. unalturaWe by heal, whilst 
the baee metals contain so much sulphur that they lose their 
metallic qiialitioa in tiie tire. These conHtihieiits may. how- 
ever, not only lie pre^nt in dillerent proportions, hut also in. 
dilTcrcut degrees of purity of in different slates of division ; 
and thus it micht naturally bp supposed that, if not by a varia- 
tioti in their relative (jimntity. at any rate by a change in their 
condition, such an nitcmtion in the properties of one metal 
may Iw brouijht; aliout ns would produce from it some other 
known niclal. Thus gold and silver contain a very pure mer- 
cury, which in the one instance is combined u-ith a red and in 
tltc other wiUi a white sulpliur; and he explains tlie fnct that 
these two metuls amtlj,'amate so easily because tliey already 
coiilaiu a livi;ge C[unutity of mercury, aud are therefore (|ii>ckly 
atlmcted by the liquid metal 

Whilst Greece and Italy sank depper sod deeper into har- 
bariam, arts and science Houriflhed under Arabian dominion, 
and the aeadeniies of S\mn were throntied with studeuts 
from all parts of the Christian worhl, TIic knowledj^'w of 
atcheiny spretid from thlt source over Western Kiirope, and in 
the thirlecQih century we find alchemists of the Arabiaa school 


Bisi'OBiCAL DrrfiODOcrnoH. 

in dU the chief countries of Kurofie. la Climtion Spain lived 
tliu ctilebratod JRaymuiid LuUy ; iu Kmace we bear of Arnold 
ViUauoraniu; Albertas Magrttis nourished in Germany. Then 
Thomas Aquinu, pupil of Alliertus, was &ho aa alchemiat, 
as «-as oar own Koger Bacon (12li-I'J94). h-Iio vras tried at 
Oxfonl for sorcery, aiiU wtio. tu tlixpTwe Iliesu cliarge& wnile 
the celebrated tTcatiae,' in vrhich Jiu sbows tliat appearaocos 
than atlribute-.! to supcmulunil ft<^iii-y were due to common and 
natural chillies. It nas Jto^r Bacon, from his rare accomplish- 
ments and Icaniiug termed DocHot Mimbilis, wtio first pointed 
out tho possible distinction between tbeoretical alchemy, 
orchomistry slmlied fur ils own sake, on the one hami, and 
practical alchemy, or the atrlving after ceitain iuuuudiately 
useful i-nds, on the atli«r. 

Altlioii-ih all these men a<^eedthAttbfl tnuismuUtionormetnlg 
vna not only pos«it>le bat Uiat it was an acknowledged fact, and 
tliAt for the prepftration of gold and silver tlie pbilaiophcr's stoiiu 
was iieetlw), it is dilKcult, not to say iiu[)osi<il]o, now to under- 
stand th«ir methods or procvs«cfl, inasmuch as all that tliey 
have written on Ibis subject is expressed in tlic nxubi^uoits and 
infliit<?d diction of the Ityzantine and Arabian authors. 

T\fi fourteenth century tiiida the study of olchumy widely 
spreail over tbe civilized world, and the geucral attention which 
Uie subject aUracted gave n.-«e to the disi:over>' uf a lai^ number 
of chemical subatances. By tbe «nd of tbe Dltccntb century, 
altbongh the knowledge of chemical facts had continued to iu- 
crease, Iht old views respcclin^ tlic ultimate cotn[K»itioTi of matter 
were still accepted. In addition, however, to the sulphur and 
mercury, suppoaed by Geber to he the tmiversal eoustitiienta 
of nutter, wc find Basil Valentine adoptiiip: a tbird couslituiMit, 
viz. sail. We must bear in mind liowc'Vi-r that, these three prin- 
ciples like tho four Aristotoliftn elements, were not suppowd 
to be identical with the comDiou substances which bear bhetr 
Danies. , 

Abuut this time the new em of mcdieal chetoistTy liegiiu. 
Its connection with ths past is readily recognised in tho 
ftenrrli after the elixir vitc, a panacea for all the ills that 
fli'sh ia heir to. This search, however, led to the discovery 
of many potent medicines, for we find that BasU Valentine, 
whilst seekinfT for the philosopher's stone, taught much respecl- 
io;> the toedicnl value of many of his preparaUoos ; as is sccu 


in Ma remarfcable irvestisations on the grey ore of antin»ny, 
published uiiilcr the riinlastic title of the Triumpk-fy^affcn dr$ 
AtUivujnii, la this wovk the characteristic properties of the 
antimony conipoutitU are so completely given that up to thu 
bcj'inning of this centnry hanlly any further knowledge of this 
sulywt had been gaitie<l. Bn.sil Vnlwutine iippcBrs to linvc been 
llie first to employ reactions in the wet way, for he eays ; 
" Zulctzt mcrko, dass die Philosophic xwcif n Wc^ gchaU, den 
nassnt \V«g, welchen ich gebntuclit hahe, so datin den trockneu 

That men of audi wide exjierience and great powcra could 
bring tlicniselvca to believv in tho possibility of the diacovGiy of 
the jiliiiosophBr's stone, a substaiiee of such potency lliat wlieit 
thrown on the base metals In a state of fusion (moment of pro- 
jection) it tmnsiiiiit«s tlieni into gold and silver, appears to ns 
very remarkable. No one douUcd tho possibility of such a 
traiutmutotion, and th« explanation niiiy bo found in the 
f&rt, at that time well known, that the colour of ceitain tnetol^ 
can be nlti<red by the addition of other bodies. Thns Gobor 
knew that when red copper is melted with tntty. on impure oxide 
of zinc, the golden -yulluw bni^ is obtftiiicd ; and abo that oilier 
minenla (those which we now know to contain arsenic) give to 
copper a silver-white colour. Still the difleicncc between these 
alUtys and the noble metals muse soon have been discovcretl, and 
the pos.<!ibility of the transmutation luy rather in t!ie notion 
already alluded to> that the dirri>ient metals contaiucd the same 
ron»Litiient« arranged either in different quantities or in different 
fltatea of purity. Nor were experimental proofs of this new 
wanting. Thus Gel)er believed, tlial by adding mt-rcury to load 
tJi« met4i1 tin wnjt formed, and the solid anmlgnm does closely 
Tesemble tin in its appearance. Then ngain the nictnllurgicnl 
processes were in days very impiTrect, and the alchemists 
saw proof of their theory in tlie fonnatiou of a bead of pure 
silver from a mass of galena, or in the extraction of a few 
grainsof gold out of aqiiautily of pyrites. It was not until the 
beginning of tho seventeenth century that Basil Valentine proved 
tliat gnlena frequently cnntnina silver, and thnt traces of gold 
are often found in iron pyrites. Even so late as ITOff we 
find IToinlierg statin;; Ihnt piiru silver after welling with pyrites 
is found to contain gold, and it was only aRer scvciiil chemists 
hnd peiformcd the experiniimt with n like result Hint the miuenil 
itself was ackoowledgcd to contain tmces of gold. 


Again, it was uot until tlus time that salts were recognised to 
to metallic compounds, and the precipitation of copper from a 
aolutJoii of t>hie-stoiie by metallic iron was supposed to be a 
tronsniut&tion of iron into copper. Tlicse apparent expcnmciital 
proofs of tlic truth of the nlclicuiicjil doctriiio were ftcconipanicd 
iiy u mass uf liislorical evideiict' ; tlmt is, of Blorius lioudt'd down 
from generation to gL-ncratioii, in wliicli cum.-* of tlie tmasitiuta- 
tinn of niet:iU arc circumstanlially iinitutcd. Thus tiiv belief in 
the fundHiiiciiUl principle of alchcrii]' hccnuie lirmly cjstabiished.^ 

A sa-tUfaciory explsnatiun of the belief in the power of the 
pliilosophcr's stone to heal diBease aiid to :iet aa tlie elixir ttfir, 
the j^raiid panacea for hiiman ills, is more difficult to find. It 
inny possibly have at first ariaen from a lou liletal iiiterpretation 
of ilic oriental imagery found in the early Arabian wntere, wh«re, 
attbougli the peculiar doctrioo of elixir vita^ is unkuonii, we 
find suuh I'iissages aa the following ; " If thou carriest out my 
proscriptiou with due care thou sbalt heal the bad disea&e of 
porcrty," The Anibinna called the biiac luutuls "diseased." 
Thua Gober say». " Urin^ n)e the six lepers, so that I may heal 
them;" — that is, trau&uiult! the other niix kuowu nietala into 
gold. The belief iu the healing power of the philosopher's stone 
was also much atron;^thene J by the di.icoverj', about this time, of 
many substances Mliich produce remarkable rttl'ect^ oo the 
humaa f^me, aod of these the alchemists of tho thiitcentb 
century write in the most fantastic ami oxaltod terms. 

The man who etTected the iiioatiiiialde union between, chemistry 
and mediciae was ParuoelMiu (l-iDS-lSil). like his prede- 
CGSsore. ho Bssuiued the existi^nee of the tliree components nt all 
inorganic suljstances, but he was the first who included animal 
and vegetable iKKlies in tlio same clnssiGcatian, and he helil that 
the health uf the organism depends on tho continuance of 
the tnie priipfjrlions between these ijigredicnts, whilit disease is 
due to a di.'^turbiuicu uf this proper relatiou. 

The em thus inauyurated by Piiracelsus continued up to the 
end of tJie scvr-nt«cntJi centurj', Chemistry was the handmaid 
of medicine, and r^uentions respecting tlic ulumute conipofll- 
tion of matter were considered of Beeondarj' importance to those 
relating to the preparation of drugs. Of the contfni]>orane8 
of I'amcetsus, Agricola (1490-1555) was one of the must 
(listiiigui&lied, and his remarkable work Ih Re Mttalliea, con- 

* For runliiT iiir<47i]atioti on Uii» WitTwt Kopp's daasloil work, Dcr OeKMMi 
(ter Chimk, or Thoiuwu't MiMery of CAcrnutry, uiny bu coikiuIleiL 



tains n complete treatise ontu«talhii;ny and niininj> vfaichdid much 
to adviiuirc the proctsaM of leclioical eliemialrj', many of tlie 
melbod^ wliicli Iio tlc^-ribc-; Inriiig iu uw uvcri at tlie preseut 
dny. Wliilsl A^ticok tlevuk-il liuuaelf to llit; Aludy of tnetalliugy, 
bis countrymaQ, Ubavius, greatly usaiatod tbc gCDcml progress 
of w-ieui-e, iiiasniucb as lie collected U^lher in writioj^ 
wtiich are cbaract«rised by a clvar and vigorous iitylc, a]l the 
main facts of chemistry ; so tliat ha AUhaiiia, publishud in 
JyS5. may be rej^arvKul as tlie fiiat liiuidlHXik of clicniistiy. His 
chief obji«t was the preparation of medicines, but li(j Blill main- 
tained tliu scicnco in ilti old tUroction iind difltiuctly belicvt^d 
in tUfi liuiusmiitaLion uf nietaU. 

The lirst who formHlIy di'clinRd to nccopt the Anslotellnu 
doctrine of the four elements, or tliat of Paracelsus of the ttirae 
c«nslitii*.'iit» of matter, was Van Hclnioub (I577-16i4). He 
denied that l)ie bad any oiaterial existence, or that earLh can be 
considcnxl as an clumvnt, for it can, he says, be converted 
into water, but he admitted ibe elementary untnrti of nir 
and water, and he gave great jirominence to th<> laltcr in its 
gencntl distribution througliout animate nud inanimate nature. 
Vuii Hfhnout's a^kiiuwli.ii^'itioiit uf air as an element is the more 
remaikable. ai he was tbe lii-st lo rttogiUse the exisleiicB of dif- 
ferent kinds of air and to use tlio t«nn gas. Thns, his "gas 
■ylvwtre." whirh he clearly dislinguislied from common air, is 
carlwiiio acid >;as. for be states that it b given off in the piwx-sn 
of fvmiviiUition, nnd also formed during combustion, and that 
it ia found in the "Orotto del Cane." ncai" Naplea. He also 
mviilious a "gas pinj^iie " wbirh is evolved from diini:, and ia 
inilammable. It wn-s Ynn Helmont who first showed that if a tio distolvod in an acid it is not destroyed. ns was fonncrly 
believed, but can as«in be olituined from solution as nietid by 
suitable means; aitd be coDsidcrvd ttic higbrst aim of the 
science to Ixt the discoverv' of a general solvent which Mould at 
the same time sene as a universal medicine, and to which 
tlie name of "ulkitliest" was given. 

Alllwu;;li Van Hclmnnt aceompUshecl much towards tho over- 
lliruw iif the rnraceUmn doctrine, his ilisrovcrics of the dilfercnC 
gases were foij^tten, and even up to llie mtdtUe of the sevcii- 
leeiilfa ccntnry much divergence in opinion ou fundamental 
questions prvvailod m many caaes. TIiohb who were interceted 
in the ooiincc'ion of fheniistrj* with medicine fltill believed in 
tlie dn^Euns of the alchemist, and held to the old opinions ; whibtt 



those who, odvaDcing with the times, soo<;1itr to further the 
Bciunoc Tor its ovrn sake, or for tlie eoke of its iinpvitant t«chmiuil , 
applications, often upheUl views more in ii'.-c»r(litiice witb those 
whirh wc now know to be tlie true onea Among Uic nami-a of 
the men who, iliirin^ l.hi.4 jHsriofl, Lilioiireil MiccessfiiUy to pro- 
mot* the knowleilj-a of clicmistry, that of Glauber (1603-1668) 
must bo first mcQlionotl. Uc was both alcbemifit and medicinal 
chemist, and discovered maay valuable medicines. Auothi^ auuiu 
of iniporunce at this epuch in thai ot \. Letuery (1045-1716), 
He, OS well as Lefebre atid Willis, believed in tiie existence of 
five elements j muruury or spirit, sulpiiur or od aud salt are the 
active principles ; wator or phlegm, and caith arc tlic passiv«- 
oucs. I^eincry'a ideas and teachiiijp became well known tlxrough 
the publicaliou of his Courx dc Chijmie (1675) wliicll was tnuis- 
kted into Latin, as also into uioal modern langaages, and exerted 
a great influence on the progress of science. In tltis work 
the dJstinctiftu between mineml and ven;ctrible lioilies was firet 
oloftriy pointed out. and thus for llie first time the distinction 
between Tiiorganic and Oi^nic chemistry woa realized. 

Pre-eminent amon^t the far-seeinj; philtwophera of his time 
stands Itobort Boyle (1627-1691). It'is to Boylo that wc owe the 
complete overthrow of the Aristotelian as well as the Ftiiucelsian 
doctrine of the elements, so that, with him we begin a new 
chapter in tlio history of our science. In his SMptital CkymiM? 
ho upholda the view that it is not possible, oa Imd liithcrto Itecn 
supposed, to state at onco the exact number of tbe elements ; that 
on the contrary all iMxlJas are to be considered as elements which 
ore themselves not capable of further seiwiraliou, but which can 
be ohtaiiied (1*0111 a combiiiod bo<iy, ami out of which the com- 
pouml can lie aj^in prepared. Thus he stales, "That it may 
aa yet be donbted whether or no there be any detonninato 
numiter of elements; or, if you plcuso, whelber or no all com- 
pound bodies do consist of the eame number of elementary in- 
gredients or materiid principles." * iloyle. it is clMr, was the Orst 
to grasp tlie idea of the (li^til]ctio^ between an elementary and a 
oomponnd body, the latter boiiis a more complicated substance 
produrcd by the union of two or moreRimple bndiefland differing 
altogether fixiiu thcie in its properties. Uo also held that chemical 

1 711* flfrftitai Chymt* or f^mtm-fAffJtal DouUi and Pitnwfoara, IvtteAlnf rte 
Erprrimtn'ii if^fv^v rvlffar Sptt^TfriM art imnt fo fKittamnr Ic <ivii« (A*ir Sclt, 
SuiiAur. ifrrmm, tn U M< (rue Principtu o/ T/ungi, l\nt liuIiUatwtl in 1S6I 
<Hoylr'* Woik*. 1772. niL t., p. Hi.) 

* Ibtil Toi i , p, SOO. 



eambination consistii of an approxitniition of the smoUest particles 
ormuuer, and that a deoiiiiptMiiiuD uikt's jilacc when a third 
body is present, capable of exerting on the particlos of the one 
eleuieut a ^teater attrac-tiou than Die particles of the cillier 
dcjuent vt'itli which it is comtjitiud. Marv. ht>wvvcr, tluin for his 
vievrs ou the miturc of the elemenCflr is Bcieiice iudehted Id Boyle 
for his clear stntcmciit of the valuo of scieiititic invcstij^ition for 
its own sake, allogftiier indt-pumlcnt nf any upplicution for 
the purposes either of the alchemist or of tlie pbyajcian. It 
was Iktvlu who first felt and luuf'lit that chemistry vms not to he 
the handmaKl of any art or profc^ion, hut that it formed an cssen- 
tiiil |>»rt of the grcut .study of Nature, and who sltowod tliut From 
this independent point of view alnne cuiild the science attain to 
-vigorous growth. Ho was. in fact, the first tnie scientific cheniia, 
and with him we may date the comnicncement of a new era for 
our science when the hi^hc^st aim of chemical research was 
acknowledged to Itc Hial which it is siill upheld to be, viz., the 
simple adviincenient of natural knowledyo. 

In spccinl directions Boyle did mni-h to advance chemical 
science (hia publiahed writinj^s and experiments fill six thick 
quarto vohiiiics). particularly in the ltor<lerland of chemistry and 
physics; thus in the investJHatious on the "Spring of the Air," 
he dtEcoTCrcd the great law of the relation existing botweoD 
volumes of f^ses and the preflsures to which they arc subjected, 
which still bears his name. 

AtUiough Boyle was nworc of the fact that many metals when 
healed in the air form calces wliiuh Moigh tnoic than the ni»lala 
tiiemselves, and although be Aiaiiiined the suhjectexperimcutally 
with great care, hia mind was m much biassed by the views he 
held respecting tht> niutorinl niitiiro of fliime ami fire that he 
ignored tiie Inie explanation of the iucroaae of weight as behig due 
U the absorption of h ponderable constituent of the atmosphere, 
and looltcl iipim the giiin as a proof of the pondemblu natUM 
of fire and flsinie, k'^'*"K niauy experiments haviny for their 
object the •' limiting and weigliing of igneous corpuscles." * 

Similar views are found ex pressed in his essay "on the 
mechanical origin and prtxluctiou of BxeduCM,"' written iu 
1075, where Boyle, speaking of the formation of mercuric oxide 
from the metal by expimure to the air at a hij^h trmperatare, 
»ys» "chomifits and pbysicinns who agree in aupiiosiiig this prc- 

■ Knrl*'* 'VaAt. vol iiJ., fp. 70S— 718. 

■ iMk. vol. ir., p. 3«0. 

oipitate to be made without uiiy additatnent, will, pcrctuincc, 
ficaiue Us able to ;Hvu a more !iki;l_v uccouut of tlie coiuistency 
nod <U>gn« uf tixity, thiit is oLtaiiind in Ihe innifury ; in 
wUicli, since iio budy is added to it, Ibcrc nppcurs not to be 
wroiiglit any but a niochuidoul chanj^. lod tliougli I confess I 
Iiave not been n'illiout suspicions that in phitoeophical strict* 
l)CS3 lliis precipitate may not lie made p^r at, l>ut tJint sotno 
penetrating ifjnoous Tvarticloit, (-.spooinlly Mlino, may have aaso- 
clateil tlieniselves witli tliu mcrcmicJ forimscW 

We owe the ne.\t advances in cliemistry to tlie remarkablo 
viuwa and cxpcriiiicntj* of Honkft {Miero^apkia, 1665), and of 
his BUC«asor John Mayow (Opera Onniia Alcdko-physica, ItiSl). 
The forotor nnnouncvil n tlicory of vontbustioii, wbicb althougb 
it ha-s nttracted but littlv tiotico. mora n<}arly approai^liod tb« 
tnie explanation Ibjin luaiiy of tlio Bubseqnetit attempts. He 
pointed out tlie similarity of tlie actions produced by air and l»y 
nitre or saltpetre, anil ha conclinlol that coinbiisLion is efl'cctod 
by that coiistitiient of the air wliich is fixetl or cumbiued in tlie 
nitre. Ilooke did not complete liid theory or gWo tbo dctaU of 
his experimcnta, but this work waa undertaken by Mayow, who 
in ICfi!) published a pajicr, De Sale N'itro ct Spiritn Ji'itro-afrto, 
in whiuli hi! jtointa out that condruntion in cnrrii'd on by means 
of tliia "spiritUR nilro-;iTeH3 " (another, nnd not an inappropriate 
name for what we now coll oxy»eu). and he also distinctly states 
thiit when metals arc cnkiiifl, the incrtmso of weight oWrvwl is 
due to the combination or the- laeUl with thia " spiritu^" Stayov 
voa one of tlie fir^l lo dencTibe experiments mnde with fiases 
collected over watt>r, in wliich he showial thnt air is diminished 
in bulk by combustion, and thnt tbc rospinitiou of animals pro- 
duces the mme efieot^ He proved thnt it in the nitre-air wliich 
is alMorhed in Ixilti i\v.-n<t processes, and tliat an inactive kos 
remains, and he drew the conclusion tliat respiration and com- 
bastinn are fitrictly nnalo«oua plionomcna. There, themforc, is no 
doubt thnt Mayow clearly deinon^tratod Uie hetero^neous nature 
of air, although his conoliiRions weio not admiuud by his co- 

AnDther theory which woa destined greatly to inlliicncc nnd 
Vnent eheniieal (li»i:overy, was advanced about this time by 
J. J. Uecher (16:15—1081), and subsequently much developed 
and alterwl by (;. E. Stahl (I66(t— 1734). It made s|>eeial 
referent-o lo the allcrability of Imdics by firt-. and to tho 
explanation of tb« fitcta of combusUon. Bcchcr nssnnie^l tluic 

•11 Domlittflttbla tNxlies sre compoandfi, so thiit tbcy nact 

eontoiu nt least two coustiiuents, oiio of wliicti cscnpra ihiriii); 

BambtutioR. whilst the othpr n;iuu.ia» bahiitd. Thus wlien 

meuls atu iuilcititMl, au eanUy residuu or a luetulliu c:i1x: remoJits ; 

ntiabure tUctcroi^:; (;nni[>uuivld of Ih'is calx with a coutbiulililo 

frianiplu, wliilftl rtul|>liur or ]>lio«|il)orufl aj« roiii{iotiii<l8 coiiUiii- 

inc n prtiicipli! vrhidi c&ne^ tlieir eombustioa Bodies uiialt«r- 

lUe liT Qm arB conaidcnnl U) biivu alnuhly tintliTgoiie combtis- 

liofii to this class of bodies quickUmc was etipposcd to lioloiig, 

iGil it wiu assumed tliiit if the !tulx«tance wtiicb it liJid lost in 

the liiv were a;^iu uddeti & metAlHo body would resnltL The 

rpeation as to wbtthcr Lhrre bo only ouo ur Nevvrul ]>niici]>U'» of 

nmliuitiUIity was fraely discussed, and StAbl diM^idcd in favour 

M the first of these alternatives, and gnvc to tliiis combnstible 

pnunplit the name Pliloj;i-ilon (^Xoyisf o?, burnt, combustible). 

Aa exAinpIu niay serve lu illiistratti thu rcosouii^ of tho 
ti|4)«lil«re of the riilo^nstic Llictiry. >Stjihl knew that oil 
■ftitiiol tit a p^j-iuel of ibo coiiibimtion of sitl|iliur; hcnco 
nlfhnr is a coinbinatioit of oil of vitriol and phlo^ston. 
Ibt lliiB latter ia nUo contained in charcual. so thiit if wo can 
t)lt«tke pKInj^staa ouL of tlic chareoal and add it to tlio oil of 
^F»l. gulphur imigt rcstdt. in order tliat ttiis disDge iniiy lie 
hsB^ about, tlie oil of vitriol must be fixed (Le. retideied 
Llun-\'oUtilc) by combiiiing it vrith potash; if tli«n, the Hilt tliiM 
il4uaed is hoated with charcoal, a hqmr aulI^fluns (a compound 
>I»jrD'lac©d by fusing polash with sulphur) is obtained. Tlie 
PtBCDt slio'ws that when charcoal is heated with oil of vitriol 
tpklo^stoti of ttie cliarcottl coml>iDC3 viUi the oil of vitriol, 
*alsul|>hur is the r«suH. The phlofftston contained in suljihur 
t* Wt only identical with that contaijicd in cliurcotil. but ulso 
I tltiit existing in the metab, and in all or^auic bodies, for 
lUwan obtained by heating Ibntr calces with chiLn:oal. or witli 
»fl«r(rther combustible oi^nic bodias. 

Tbf atnouiit uf phlogiston contained in bodies was, according 

la Etahl. very sumll, and the greatest quantity was contained in 

^' iU;(l from burning oil. It was likewise tuusidcicd 

11*1 , ■.;^&t(tn given off by combuafion is taken up again 

6wi ilie air by jilants ; and the phenomena of fernipntnlion and 

iia-r were Iwlwved to dt'iJcnO upon a loss of phlofiistou which, 

oratwr. in IliU ea«o only «scnpc8 slowly. Stahl explains 

»hy cowbttsUon can only oct;nr in pr«ence of a goo<l supply 

rf tit. itttxvm ia thia com the phlogiMou assumes a very 

rapid wbirling motioa, atid this catuiot take place in a closed 

Kowev^er false from our present positiou ve see the phlogistic 
theory in certain dii'cetioiis to l>c; and although w© may now 
believe tliat the cxt^nsioD aud corroboration of the positive views 
enunciated hy Huoku luiil Mayow niigtil Imve led to a reixp^nition 
of a truu tlicory of choiuislry mora speedUy tliiui the adoption 
of the tliL'ury uf plUo;,'ision, we must admit lUat it« rapid 
general adoption showed tkat it supphcd a ical want. It was 
titiit theoty which for the iirst time established a comtnoa 
point of view from whicti all cbcRiical changes could he observed, 
cnubliii^ chuuustd to iutroiiuce sonietbinj^ like a system by class* 
itig lo^'tlher phenoiufna which arc analogouo aiitl are prohaWy 
produced by tlie same cause, for the firat lime making it pos* 
sible for them to obtain a gcuerul view of the whole nu^ 
of cimniinal science as then known. 

It may appear singular tliat the meaning; of tiio fact of the 
increase of woi};bt which the metals undei^o on heating, which 
lud been proved by Boyle and others, should hnvc been wholly 
ignored by Slahl, \iut we niuat remember that he considered tlieir 
/om ratlier tlian their vxijkt to he the iuiportiiut and ohatacter- 
istic projietty of bcMlies. 

Stabl also, perhaps independently, arrived at the same OOQ* 
dunon whicli Boyle bad reached, concemiug tlte truUi of tits i 
Qxistened of a vm'icty of elf^montar}* Iwdics. asoppoMsd to the 
Aiistoteliaii or Turacclsiau doctiiiie. and the iutlueiice which a 
clear statement of thia great faut by f>taU and Ids pupils — 
amongst whom must be mentioniKl Pott (1692 — 1777) and 
Maigrall (ITO'J— 1783)— exerted on the pro^Tesa of tlie science 
was iiamenso. It is oiUy aflcr Slahl'it luboui'« that a scientific 
chemistry Ik-coiiil-s, for the first time, passible. 'l1io c^sscutinl 
difference lM_'lwfL-n the teaching of the science then nud now 
being that ihc phcnomeun of combustion wore theu believed to 
be due to a chemical decompoaition. phlogiston being supposed 
to esca|w, whilst we account for the same phi'iioiucim now by a 
chemical combinallon, oxygen or same element being taken up. 

Tlnis Stahl prepared the way for the birth of raodt?m chemis- 
try. ItWM on August 1st, 1774, that Josepl) I*riestley dis- 
covered oxyf^en gas. 

Between the date of the establishment of the phlogistic theory 
by Stahl. and of its complete overthrow by Lavoisier, miuiy 
distinguislted men helped to build up the new science — Block, 



Priestley, and Cavendish in our own cottntiT'. Scheele in Sireden, 
and Ma<M]uer in France. Tlie clasncnl researches of Blitvk on the 
Kxed nlkalipii (lIsA) ■ not only diii much to shake the foiuidatio]) 
of the iihloyUiic theory, hut tlicy uiny be deicrihod with initli 
as the first beginnings of a tiuontitadve chemistry, for it was by 
meoiu of the balance, the essential inHtnnnent i>f all chcmicnl 
research, that Black established hia conchi.'>ioii<). Up to this lime 
the mild (or carbonated) allcnti was believed to be u more simple 
coiapoond than the caustic alknli. Wiieu mild alkali (jiotashcA) 
was hrought into contact with hiirnt ((uiustic) liiat;, the mild alkali 
took up the principle of combust ihility, obtained by the lime- 
stone in tlie fire, and it liecanie catiKlic Blnuk xhowdil lliat in 
the case of magnesia-alba the disftpjiear^nce of the effervescence 
on treatment with on acid aA«r hiMiting, was accompanied by a 
loss of weijjiit. Moraovor, as Van Helmonl's older observations 
were ((uite fnr^ottvn, lie vna the first clmrty to establish tlie 
axistonoe of n kind of air or gta, termed fixed air (1152) totally 
distinct Inth from common atmospheric nir and from modifica- 
tions of it. by iiii[iiinLy or uthent-iae. sucb as the various 
gases hitherto prepared were holieved to be. This fixed air^ 
then, is given off when mild alkalies become caustic, and 
it is taken up when the rever&e change occiira. 

Tbia clear statement of a fact which of jtself in a powerltil 
aigumcot against tlie truth of the theor)' in which he had been 
hrougbt np, was sutScient to make the iiajne of Black illus- 
trions, but ho becaaie iminoTtal by his di«»verics of latent 
and specific beau, itie principles of nhich he tjiu^flit in his 
claisaca at (ilus'^w and Edinburgh from 1763, The sinj;ulurly 
unbiaased cluiracter of Black'a uiinil is shown iii the fact that 
he was the only chemist of his j^e who completely and openly 
avowed his ooavefsion to Che new Lavoisienan doctrine of com- 
bostion. From an interesting com-sijoiidcnce which In*."! only 
recently lieeome known between Black and Lavoisier, it is dear 
that the (;reat French chemist looked to Block its bis nmtttvr and 
tcadier, speaking of Black'^ having first thrown hght upon the 
doctrines which be more fidly carried out.'' 

This period of the history of our science has been called that 
of pneumatic ch*miatr>', because, following in the wake of 
Black'a discovery of ttxed air, chemists were now chiefly eni,'ag€d 

1 " Exfmiintnto iip«n Mii]pMu»-aIb«. Qnirk1iin«, wd otbr Alk«lift* ni^ 
•tanrflL*'— /Uin- Phftf. and tittmrtf X—ayM, llfilt. 
* £rSL Ansc. JUfirU, ISil. Eainb. p. 1S9. 



in the cxRminatioTi of the properties ami modes of preparatkm 
of tlio rlifTweiit kimls of iiii-s or gftses, the striking and voiy 
difTtiiv'nt natures of whitth nnturally nttmcti'Ll iiitcrcst oud fitimu- 
ktcil rCMcaitili. 

No one obtained more important resiJts or thrflw more tifjlit 
npfin ihc chemical existence nl a iiumher of ditftitent gases than 
Joseph lYiestlcy. In 177:i Priestley waa engaged in the esamiu- 
tttion of the uhumiciLl ofTect |iioducetl by the liurning of coin- 
1)ufltil>le bodii'S ((.iiiidieA) and Che reepiratiou of animals upon 
ordinary air. He proved that \k}(\\ ihescj detcriomled tlie air 
and dimiiiUlied its volume, nnd to the residual air he gave the 
name of iililogisticated air. Priestloy next investigated the action 
of living plants on the air, and found to hta astoniRhmcnt Uiat 
tliey posHcu the powur iif ri;iHU*riii;{ the air deteriorated by 
ftnimaU again capable of supportiiLg the combuation of a candle. 

Fig. 1, a reduced facsimile of the frontispiece to Priestley's 
colebrated Ols^rvationa on Dijircnt Kinds of A ir, shows tlis 
primitive kiml of apparatus with which thin fLither of pnenmatje 
chemialry obtained bi-s re.'snlts. llie mode adopted for generating 
and collecting goaes is seen ; hydrogen is \mag prepared in the 
phial by the action of oil of vitriol on iron fihnga. and the gas is 
being collected in the large cylinder slaiiding over valer to the 
pneumatic trough ; round this tiougli are arranged various other 
pieces of apparatus, as, for instance, the bent iron rod lioMing 
a small crucible to contain the substances whicli I'riestley 
desired to expase to the action of the jj"^- ^i^ the front is seen 
a large cylinder in which he preserved the mice, which he used 
for ascertaining how far an air was impure or unfit for respiration, 
and standing in a anmller trough is a cylindtr containing living 
plants, the action of which on air had to be ascertained. 

On August Ist, 1774, hiestley obtainetl oxygen gas by 
heating nJ precipitate by means of the sun's mys coiiccnlmtod 
with a bnming-glas,i, and he teimed it depiiUffUiicnted air, 
because he found it to be so pure, or so free from phlogiston, 
that ill comparison with ii common air appeared to bo impiu^. 
I'riestley also first prepared nitric oxide (nitrous air or gas), 
lutmns oxide (dcphlogisticated nitrous air), and carbonic oxide ; 
he likewifle collected many gases for tlic first time over mercuiy, 
thus anunoniucal gas (alkaline air), hyilroi;hloric acid gas 
(marine acid air), snlphuroiu acid gus (vitriolic acid aJr), and 
silicon tetrafluoride (tluor acid air).' He also obser^'ed that 

' rriMtlty'i Obttrmtiinu im IKgertRt limit <yf Mr, vol. i., p. 828. 

when a series of electric sparks ia allowed to pass tlmiugh am- 
mooittcal gaa, an iiKrreaae of volmaa occurs, and a combustible 
gas U fomipd, wljiUt on beating aramoiiia with caJi of le«d 
phiogiaticBted air (nitrogen gaa) is evolved. 

Prio«U«y'a was a mind of rare quicknfss niid pMceptire 
powers, wlUeh led him to the rapid discovery of nmnerous new 
clicmicfU Biihstanoee, bat it was not of a philosophic or dulibcra- 
tivo cast. Hence, altbough he luul firet prepared oxj'gfiD, and 
liad obwTved (HSl) the fonnalioii of water, when inikmittaWe 
air (hydrogen) ajid aimoppherjc air iirc mixed and burnt together 
in a copper veaael, he was unable to gni»ii the true explanation 
of the ptit-uomeiion, and he rpmaininl to the ead of his days a finu 
believer ill llie truth of the phlo!,'istic theory, which he liud don« 
niorc than any uuo else to do^lroy. 

Piieatloy's notion of oriyiual research, which seems quite 
forcijpi to our present ideas, may be excused, perhaps jnstified, by 
the state of the Miente in hU day. He believed that all dia- 
coveries are made by chant-e, and he compares the iavesti^lion 
of nature to a hound, w-ihlly running after, and h(.'rc and ibew 
chancing on game (or aa James Watt called it, " his randotu 
hnphazardins.") whilst we should rather be disposed to compare 
the uiiiii of science to the fi|iorl8niaii, who liavinn, after persLttenl 
clfort. laid out a distinct phui of operations, makes reasonably 
aure of hia quarry. 

In soTiio respecta the scientific labours of Henry CavaadUll 
(1731-1810) seeia to be the eountiirpaii of thfwe of Priestley ; t^ 
work of Uie lattvr wm quick and brilliiuit', that of the former was 
slow anil tliorough. I'riestley passed tijo rapidly IVoin subject to 
8ril>jecteven lo notice the great truths which lay under the surface; 
Cavendish made but few discoveries, but his nwcorthisi were 
exbauntive, and for tliu iQo<;t part quaTititativc. His inveatiga- 
tion on the inflammable air ' evolved from dilute acid and zinc, 
tin, or iron, is a most remarkable one. In this memoir we find 
that ho first determined the speciiic gravily of gases, and used 
materiala for drying gafica, making correctioDB fot alterati(m of 
volume, and for cliangea of pressure aad temperature. He like- 
wise proved Hint by the use of a given weight of cocli one of these 
riiutaU, the Hume volume of inilaininaUe gta can always be ob* 
tuincd no matter which of the aci<Is lie employed, whilst equal 
weights of the metals gave unetjual volumes of tho gas. 
Cavendish also found that when the above metals ore dissolved 

* Ot AutittMU Air. Hon. Hmry CnenMOt. PhiL Tram. 17«S, p. 141. 



'in nitric acid, an incombustible air is rn'olv^d, whilst if 
they are heated with strong eulyjliuric acid suljihumus uir is 
fonned. He concluded that vrhva tb«s« un'tala are dissolved in 
hydroclUoric or in dilute sulpliuriu acid their [ihlogisUm Hies 
off, whilist when heated with nitric or strong sulphuric acids, 

bthe plilfif^'fitan goes ofT in combiiiHtion with on HciJ. This is 
tlio lirst occasion in which wo tlrid the view expressed that 
ioflaminable air is phlogiston^a view whifh was generally held, 
although C;iVL*udii«li himself substqueiitly changed his opinion, 
legardlng iiiflamniablB nir as a conijKinnd of phlogiston and 

The discovery of oxygen by Pricstky, iind of nitrogen by 
jtlterford, naturally directed the attention of choniists to tJio 
idy of the ctuospberc, and to the various methods for osccr- 
taicing its composition. 

Alihou^h Ilieslley's Du^thod of estimating the depldo^ti- 

|cated ail by mcana of nitric oxide was usually cuiplo^tMl, 
lie results obtained in this lespeot by diffurent observers 

'were very different Hence it wia believed that the compoBition 
of the air varies at differeut places, and in ditTerent seasons, and 
this opinion was so geuismliy adoplt'd, tliat tbu iiis(ruiii'-iit usod 

,for such njeasu cements was U^ruied a eudiometer {tvlia, ti]ie 
readier, and n^Tpov, a mensiiie). Cavendtsh inreetigatMl tliis 

'eutijuct with liii« nooustoniod skill in the yeor 17^1, and found tliat 
when even' jiossible procaution is token in the analysis, "the 
qoantity of ]Hire air in common air iis j^," nr 100 volumes of air 
always contains !20'8 volumee of de]>blogisticated. and 79-2 
rolunws of pUogisticated air, and that, therefore, atiuuspliuric air 
hAB an onvarying composition. Ihii tl)e discovery which more 
tluiii any othtT is for <s\vt coatiecieA \rilh the nanin of Cavendish 
is that of the com|K«ition of n-itter (I7>S1).' lu making this dis- 

kcorcry Cavendish was Ictl by »uniu previous obsei'vatious of 

'Rieetley, and Ida friend Waltirc, They t-mployt-d u detonating 

'doeod glass or copper globe holding al»<nit thret; pints, ao 
anainied Uiat nu electric spark could be po^ed tlirough a mixture 
of billiiuiinable air (hydro^-n) uud common uir,^ but though 

[tbuy Iiiid ubeeired tlw pruductiuu of water, tliey not only over- 

' P\41. Tmns. (m ITSt. p. 110. ind for 178B, p. 875. Mr. CansudUb'i expert- 
nwnU on UT. 

■ A ■imilar kpiantna (oncinolly due ia VolU> WM u«d hj Cavmdiih. The 
pe«r->ha;>ifil jiju* Wtl" with atapcoi^k, tMiulI/ callod CkrDB<luh'« «ailioinel«r, 
mold tuc be noogniMd hj the (p«at c^porimonler. 

looketl its meuDing, but bulievecl Itiab the cbaiige wui aceoin- 
ponied by a loss of weight Cavendish saw tlic lull importauoe 
or Lhe phc-Qoiucnon uitl set to work witli care niul delilxiratiou 
to anawer Uie queatiou as to the caase of the fomiatioD or the 
water, ^ot only did lie detemiine the volumes of air and 
hydrogen, and of (i«phlogii<ticate«! air (oxygen) and iuflanimable 
air (hydrogen) Trliich must be mLted to form the maximum 
iiuunlity of waUir, Imt Ii« first sliowcd Ihiit no loss of weight 
ot'Ciirred in thia esperinient and that thti formfltiou of acid wi 
not an invariable accompaniment of the explosion. 

On lhi3 iiuporlaat subject it is interesting to Lear Cavea 
dish's own words ; in the I'kilMojiJiiatl Tranaactiotia for 1784, 
page 123, we read: — 

" From the fourth experiment it appears that 423 measures of 
inllamni&ble air are nearly sitflicient to ^ihlugisiicat^! 1,000 
of common air ; and that the bulk of the air remaiDtng after 
the explosion is tbvn very little uiorc ihua four-iifths of the 
common air employed ; so tliat, as common air cannot be reduced 
to a mucli less bulk than that by any mptlioil of phlogistication, 
wc muy safely conclude when they are uiixed in this pioportiou, 
and exploded, almost all Ht« injhtmmitbh: air and about ont-^/th 
pari of the rammon air, lose their eJasCiciti/ and are anuttiufd 
into a deny -ichich h>« thf t/ta8$." Since ],0Q0 volumes of air 
coutuiu 21(1 volume of oxygf^n and these require 4'20 volnm(»t of 
bydrogeu to combine with them, we see how exact Caveudish'a 
exporinicnls were. "Tliu butter," ho continue^), "to examins 
the nature of the dew, S00,000 giain measures of iullantniabia 
air were burnt with about ^^ times that qiuntity of common air 
and tJic burnt air made to pass throu^'h a tilass cylinder eight 
feet long and thrce-ciuai'terB of an inch iti diameter, in oi-det to 
deposit the dew .... By tliis meanit upwanls of l'^5 grains 
of wiiter were condensed Id the cylinder, which had tto laste or 
smell, and which Icit no seosibtu nediinQot wlien evaporated 
to dryness; uuitber did it yield any pungent smell during the 
evaporation; in short, it seemed pure water." Cavendish then 
sums up his conclusions from these two sets of expenmciits 
ns follows : — " By the experiments with the globe it appeared 
that whea inflammatlo and common air are exploded in a 
)>ropcr proportion, almost all the iiiiiammable air, luid near one- 
tifth of the common air, lose their ehisticity and are ooudentted 
into dew. And by this experiment, it appears tliat this dew is 
plain water, and consequently that almost all the inBanuiiahlo 




about oii«-iiftb of tlie corainoD air are turned into pure 

Still more coDclusive was tlic vxpcriniciit in which CaveDdish 
'intToduoed a mixture of dephlogisUcated air and iiiflaniiDaablo 
air nearly in liie proportions f)f one to tvo iuio a vacuous 
gUas globe, furniahod nith s stopcock tiud mcaiift of firing hy 
electricity. " Tito stopcoi-k vras theu shut and the included 
air lired hy electricity, by which moan<t ulina<<t nil of it lost 
elasticity. Ity reixmtin}; the operation the vliole of the 
lixtiire was let into the glol>e lUid exploded, without any bxwh 
JwJiauation of the globe." 

Priestley had previonsly been much led astray by the foct thflt 
bo found nitric cicid in tLu vutvr ol>t»inud by the union of the 
giaasa. Cavcudifili, by a careful etTtt-a of experiments, explained 
occurrence of thia acid, for he sluiwed that it did rot form 
unleK) an of depblogisticaled air vaa used, and he traced 
ils [irodaclion to the presence in tlic globe of a small qiiautit}' ol 
pUogisUcalcd air (nitrogen) derived fVom admixture of common 
air. Be likewise proved tlial the artificiid addition of phlogisti- 
eated air increased the quantity of acid formed in pre.'ience of 
Hephlogiftlicated air (oxygen), whilst if Uie latter air were re* 
Jaced by intlaturiinble air no acid was formed, even although 
plltogisticated air [nitrogen) be present In Ihui way he diowed 
that the only product of the explosion of pare dephlogisticatcd 
with pure inSnmniable air h pure water. Although Cavendish 
thus distinctly proved the fact of the composition of water, it 
bdoea not a[>[)ear from his writingx that he held clear views as to 
*lhe fi«;t that water is a ehemiettl eampoitnj of ita two elementary 
constituents. On the contrary, he seems to have rather inclined 
to Ihe opinion that the water formed wua already contaiucd in 
the inflammable air, notwiilist^nding the fact that in 1783 the 
oelehraled .Tuiues Watt hud already expressed the opinion that 
" water 13 composed of dephlogisticatcd and inflaDimable air."* 
Cavendiitli'd goui-ral coucluuions in this luutter may be brielly 
nunmed up in his own woi-ds as follows : — " From what has 
en said thi'ro seems tliu utmost reason to think that dcphlo- 
psticatcd air is only water deprived of its phlogiston, and that 
nmablo air, as wiu before said, is either phlogisticnted 
water, or else pure phlogiston; but in all probability the 
former." To the end of his dnys Cavendish remained a firm 
ipporter of the phlogistic view of chemical phenomena, but 
■ Letter (rom Wall to KticV, 9lKt Apnl. 1T&X 

after the overthrow of tliie theory by Lavoisiei's cxperimeDls 
the English philusophto- withdrew from any active participation 
in Kicutiflc reaeuTch. 

'Whilst Priestley and Cavendish were pursuing their great 
diBcoveries io EDgland, a poor apothecary iu Sweden was 
actively engq^d ia iuvestij^tiutis which wore to rnnki; the iiaiae 
of Scheele (1742-1786) botiouivtl tlirotighout Europe. These 
investigations, vihilattboj did not briog to light so mauy i)«w 
chvuiiail suWtiiiioes as those of Priestley, aud did iiot posseas 
the qiiautitative exactitude which is characteristic of the labours 
of (Cavendish, opened out groiujd which hnd l>eeii entirely 
neglected, and was perh^is unapproachable by the Kngliah 
chemists. Scheele's discoveries covered tlie whole range of 
rhcniicul acieucc. A etroug supporter of the pUoxistic theory, 
he held peculiar views (sl-i; hi:! ei-lubnitid truatisu L'bcr die 
I/uft vTid das Fcmr) an to the miit<*rial nature of heat and light, 
and their power of combining with phlogiston, and, hke Stahl, 
be considort-d iiiodiliouliuii in tin- foi'iii» of ititiUi'T t<j bu of much 
greater importauce than alteration iii its weight Iq experiment- 
ing upon the nature of common air he discovered oxygen gaa 
independeully of, but probably somewhat later than, Priestley. 

The investi*;atioiis which led Schoclo to this discovery are of 
interest us a, rcuiarkablu uxaiuple of exact obscrvntiuiis leading 
to erroneous conclusions. His object was to explain the part 
played by the air in tlie phenomenoD of combustioD ; and for 
this purpose, he examined the action cxertotl by bodiea, sup- 
posed to contaJD phlogiston, upon a coiUined volume ul air, 
Thug he found that wlii!ii a Kuhition of ktpar siUphurU (aa alka- 
line sulphide) was brought into contact with a given volume 
(if air, that volume gradually diiuiniEhed, the residual air being 
incapable of supporting the comliustinn of a taper. The aamo 
result was observed when moist iron tilings or the precipitate 
formed by the action of potash on a solution of green vitriol was 
eoaployed. Hence Soheele concluded that whenever air combines 
with phlogiston, a contraction occurs, and, therefore, the remain- 
ing air must be beavit^r tliau common uir. To bis astonishmeat 
ha found that this was not the case ; and he inferred that a poi^ 
tton of the common uirmust have disnppeared.and that common 
air must consist of two gases, one of wMch lias the power of 
uniting vitb phlogiston. In order to find out wliat had become 
of the portion of air which disappeared, Sclieele heated phos- 
phorus, metals, and other bodies iu closed volumes of air, and 



found tliAt tlieiie &ct just as the former kitid of sultftancee bad 
done. Uence he concluded that the compound formed by the 
imion of the pbloniatou u-ilh oue of tliu constituents of the air 
U noibiu^ inoro nor U-sa tlian heat or 6re which escapes through 
the glU3. In order to prove the truth of this li^-pothesis, 
Scbeeltt endeavoured to decompose heat into phlogistou and 
Gre-atr. Xitric acid liaO, to his belief, a great power of combin- 
ing with phlogistou, fotiniDg with it red fumes ; he, tlierefore, 
heated nitre iu a nttort, over a cliarcoal fire with oil of vitriol, 
■od obtained, ia addition to a fuiuiug acid, a colourleas air 
wlitch supported combtistiou much htilt«r than commoa air. 
This he explained by assuuiiiig that when charcoal burns, the 
phlogistou corubiue« with the fire-air to form heat, which pasi^n 
into the letort, and is there decompoAed, giving rise to the red 
nitroas fumes and pure fire-air. lie conceived that he had brought 
about the same chuuiicul ducoupoQitioii of heat b; warming 
Mack oxide of manganese with sulphuric acid, or still mora 
simply, t))' heating calx of mercury ; for here it is clear enough 
that by bringing heat and caU of mercur>' together, the phlo- 
giston combined with the latter, and iiie-air was UWrated, 
thus: — 



lMD(Moa-t TIcMtr >■ CiUof Mttwuy - 6«l»iif Marontr-f fhlacUWB-l- Wi a«te 

Iu the year 1774 Schcelo made bis great discovery of chlorine 
gas, vhich he termed dephlogifiticatud muriatic acid ; in the same 
year lie sliowed that baryta wan a peculiar earth ; shortly af);er< 
mida be proved the ecparate existeuco of molybdic and tungs- 
tic acids, whilut his invcstigntions of pnissian blue led to the 
iaolation of hydroeyanic acid, of which bo asccrtaiood the 
propertiea. It was, however, cai>GciiUly iu tbo domain ol 
aniuial and vegetable chemistry that Scheele's most numerous 
discoveries lay, as will be Jieen hy the fidlowing list of oi^nic 
acids lirat prepared or distinctly identitied by him: — tartaric, 
oxalic (by the action of uitric acid OD sugar), citric, malic, gallic, 
uric, lactic, and mucic. In addition to the ideutiTicatiou of ench 
of these as distinct sabstaaces, Svbeele discovered glycerin, and 
re may regard him not only 03 having given the first indication 
^ the rich harvest to be reaped by the investigation of the 
compounds of oiguiiio chemistry, but as having been the first 
todiacovor and make use of characteristic reactions by which 
closely allied substances can be detected and separated, so 

that he muRt be considered one of the chief founders of quanti- 
tative BnnlyaiB. 

We hiive nuw brought the liistoiy of our BcicDce to the point 
at which Lavoiaier placed it in the path which it lias ever sJDce 
followed. Before deacribing the overtlirow of tlie phlogistic 
theory it may be well shortly to review the position of the 
Huii'Due before the great cheuiist began hi» lubourx about one 
hundred ye^nra ago. Chemiiitry had long ceased to be tlie slave 
i>f the alchemist or the doctor; all scientific clieniists had 
adopUtd Uoylc's dffiiiitiou, aiid the science was valued for ita 
own sake as a part of the great study of iiaturc Stahl had well 
defined chemistry to be the science which was coijcfrnt-d with 
the resolution of ooiiipoiind bodies into their simpler con&ti- 
rtuonts, and with the building up of compounds from their 
Jements ; so that the diatiuction between pure and applied 
chemiati^" v&a perfectly tindenil'jod. Gehcr's dciiaitiou of a nll^tuI 
that it was a fusible, malleable substance, capable of luixiup 
Willi other metals, was still accepted ; gold and silver were coii- 
sidvrcd to he pure or uoblti uit^tals, whiUt the other nialleiible 
metals, copper, tin, iron, and lead were called the basb metala. 
Merciirj', on Ihe other hand, was thought to be only a nietal-Hkc 
body until it was fnwoii iu 17C0. After that ilate it waa oon- 
sidercd to be a true nietaJ in a inolteu state at the ordinary 
teiJijicrature. Arsenic, antimony, bismuth and ziuc, from being 
brittle, were classed sa semi -metals, and to these well-known 
bodies were added cobalt in 1735, nickel in 1751 and nmn- 
gansse in 1774, whilst platinum was recognised as a peculiar 
luetal in 1750, and inQlybdetiiiiu and tungsten were discovered 
about 17S0. Tlie several metals were ftupposed to he coupounda 
of phlogiston with metallic caice.1, whilst sulphur, phosphcirus. 
imd cnrboii were looked upon as conipouriils of phlogiston with 
tho acids of these elements. Of the simple gases the following 
were known: inflammable air (liydrogt-n), supposed to he either 
pure phlogiston or phlogiaticated water; dophlogisticated or fiie- 
air (oxygen) ; phlopisticated air (nitrogen), and dephlijyistioated 
mnriatic acid (chlorine). When the metals dissolve in acids the 
phlogiston was thought to escape (as inBamniable nir) uithcr in 
the pure state or combined with water. It was also known that 
when a metal is calxed, an increase of wei<>hl occurs, but this 
was cxpliiiuud either by (he nulal boDOmtnjj more dense, whit-li, 
in the opinion of some, would produce an increase of weight, or 
by the absorption of fierj- particles, or again by the escape of 



plilogiston, a nuI^Htaact: wbicti iiisteiul of hdng attriLCted is rc- 
polled by the. earth. In short, con^sion and difference of 
Bpinion in the (lunntitativc relatintis of ch«inii^tty reined su- 
preme, and it was not until Lavoisier brought (lis gi-cui [lowera 
to bear on tb« subject Umt light vraa uvokud from the darkness 
snd Ibe tnie und simple nature of tli« plieiiomeiia waa rendered 

la the year 17+3 CAvoiirivr was born. Carefutly educated, 
endowed witli ample uieaus, Lnvuiiiitir deapisinjj the luiual occu- 
putimis of the Kreuch youth of his lime, devoted himself to 
scieooe, his genius aided by a caivful iQatbemntical and physical 
training. rendt-Tinj? it posaible for him to bring about a complete 
rcvolatitm in ths; science of chemistr)-. Before his time, 
Uie quanUtalive methods aud processes which be introduc<!d 
were considered to be purely pbysicfll, though thoy now ore 
ackuowlud^ to bti chemical, and of all these, the determina- 
tion of tbo wei;>lits of bodies taking part in chemical change, 
as ascertained by the bnlance, is the most important. Others, 
indeed, before him, bad made quantitative inTestigetiona. 
Black and Cavendish almost exceeded Lavoisier in the exact- 
itude of their experiment:^ but it is to the ^Wuch philosopher 
IhHt llie glory of having first distinctly asserted the git;at priii- 
cipJa of the iudcfttruclibilily of mutter belongs. Every chemical 
chaugv, according tn him, coiisi.<*t.4 in u tmnsferenco or an 
, exchange of a portion of the mutfrial constituents of two or 
aotis bodies; the sum of the weights of the substances under- 
oing chemical change always lomaius conxtitnt, and the balance 
: the instrument by which this fimdomeDtal fact is made knowu. 

Jq his first important research (L770), Lavoisier employs 
tbo lAlance to iuvostigate the question, much discussed at Lbu 
time, as to ulit-ther water on being hnited becomes convened 
into earth. For one hundred and one days ' he heated water in 
a closed and weighed vosstil ; at the oud uf tlio L'xperimont the 
weight, uf llie closed vessel remained imallered, but on pouring 
out (be water he found thai the vessel Imd lost 17'4 grains, 
kwliilat on evaporating the \vat<*r, he uscortMim-d that it had dis- 

Ived 20'4 grains of solid matter. Taking llie excess of 3-0 
as duu to unavoidable experimental errors, lifi uoucludes 

it water when heated is not converted into earth. Shortly 
this, the Kime question was examined independently by 
Setieblc, who obtained the eomo results by help uf quulitutivo 

> CEuTTMik LtfiNMrr, tome ii.. p. 32> 



aualyfiis whicli sliowcd that tb» wnter had takeu up a constitueut 
of tho glass, vLe., ihv uUuUiDu silicatits. 

li^lien bo became acquainted with the novel and unexpected 
diBCoreries of Black, Priestley, and Cavendish, a new lifjht buraft 
upon the mind of Lavoisier, and he tlirevr himself insbantly 
with f'reah ardour into the study of specially cbomical 
phenomena. He sav at once that the old theory was in- 
capable of explaining tlie facts of comhustion, and by help 
of his own experimeDts, o» well a.» by nialcing use of the 
experiments of othera, he Buecoeded io finding the oomict 
exi^lunutton, dtstroyiiif,' fur ever the tboory of pldogiatyn, and 
rendering his name ilJusfrious aa having placed the science of 
chemistry oD its true basis. Oa looking back in tlie liLitory of 
our science n'e find indeed that others had made experiments 
wLiuh could only be explained by tlii.'^ new theory, niiil in cer- 
tain isolated tustances the true ejcplaiiatioii may have previously 
occurred to the niiuda of otherH. Tims in I'm Cuyen showed 
that calx of mei-cnry loses weiiglit, cvolvinj; agfiA etinal iiiweiglit 
to what is lo&t, and be concludf^s that either the theory of phlo- 
giston ill incorrect, or Lliia culx can be ivduccd without additJoa 
ofphloyiston. This, however, in no way detracts from Lavoisier's 
glory OS having been the first to cany out the truB ideas oousis- 
teotly and deliberately through the whole science. It ia tbe 
syatematic application of a truth to evvry part of « science which 
constitutes a theory, and this it was that Lavoisier and no one 
else acoompUshed for chemistry. 

VThen a man has done so much for science as T^voisier, it 
seems almost pitiful to discuss his shortcomings and failings. 
But it is impossible in any sketch of tho histoid' of chemistry to 
Ignore tiie education liow far I.avoisier'a great concluaions, the 
authorship of which no one questioos, were drawn from his 
own diacoverie-'*, or how fur he was iudebted to the orisiual 
iuvestigutioofl of his contemgioraries for tho facts iipua wliich 
bis conclusions are based. Tlie dispute hss recently assumed 
fresh interest. Certain chemists assert that to him alone the 
fouudiUiuii of modern cheuiistiy in to be ascribed, liolh as 
regards material and deducliou, whilst others athnn that 
Lavoisier made use of the dhicovurtes of his prctlvcefQOn, 
and especially of the discovciy of oxygen by Priestley, 
without ackuowledfi^ent, assert tliat he went so far as to 
claim for himself a participauon in tliis discovery to which 
he had no right whatever, and iusist that imtil he had tlius 



i«btflin«d, from another, the ki-y tn tho proMem, his vievra npon 
le quustiou or oimbualioii vi:tk nltuout as vague os tiiose of 
the pUogUtotusts themaelvea To enter into a full disfcussion 
of the subject would lead ua into a historical criticism which 
would outnui our space. Suffice it to say Unit iuhdj' of tlie 
c1)ai;gc« which luivc lii^n brought agniiiKt Lavoisier's good 
fiuth utUbrtuiiately turn out upon iiivestij^tiou to be well 
founded, CO that whilst we roust greatly admire the clear sight 
uf the pbiloHopher, we cnniiot feel the same degree of respect fur 
tbo moral character of the luan. 

His tnvcstigatJODS on the phenomena of conibitstion began in 
the year 1772. In a first memoir ' LAvoisier finds not only that 
when sulphur and phosphorus iiru burnt no losa of weight 
occurs, but that an JQcreaae of weight ia observed. Honc« lie 
couclijdi>« that a Ui:ge quantity of air becomes iixed. This dia- 
covtiiy leads him to the conclusion that ii similar nhsoriition of 
air Cakes place whenever a body increases in weight by combus* 
ttoii or calctnatioii. In order to coiiRrni this vtow, he ivduccfl 
litharge with charcoal, and finds that a considerable rjiiftDti^ 
of air is liberated. This, he ossertn, appears to him to be 
one of \hti motKt iutereiiting expcriuieuts made »nc« the time 
of StahL 

Lavoisier's next publication was his Opuxvlea jA.y$iqius tt 
thymines, commenced in (774. Id tlic.<«c memoirs he flrst 
examines the kind of air given off in the pioccsfiefi of brcatliing, 
comlmstion, and furmentatioa. The views which he expresses ore 
exactly those put forward long bt-fon) by Black, yet he never 
uontions Black's name, and th«; omission is the more remarkable 
ail we leacn from an interesting correspondence, lietweeii 
lAroisier and Black which has n^oontly been made known* that 
the tonaer acknowledged the latter as his teacher and master, 
and as having fint tJirown light upon the theory which he 
bad carried out and perfected. 

In the year 1774 he describes experiments on the calcination 
of lead and tin, whicli he, like Boyh^, hcat« in closed glass 
globes ; so long as the vu^el is closed it does not change in 
wsi^it, but when the neck of the fliii<k is broken, air nislies in. 
snd the weight increases. He further shows that only a por- 
itioo of the ait is taken up by the iiioUfn nn-lnl, and that tlie 
llMidual air is diilerent from common air, and also from fixed air. 

* Air la CmiMifi raugmmialiim Jn Pads. (Eutki, ii %i. 
■ BritiiJi AiacdatuM HtptrU. EfUnborgh, ISTl. ISU. 



From these statements it is clear lliat Lnvoisier cousidered tlmt 
the air ooiisLitj* of Iwo difTmvut elastic tluitk, Lut thnt be wa» 
not iit!iiU!iiiilt!il with I*riiistK'y'8 UUtovery of oxygen. \or were 
Ills views at this time so precise or well defined as we should 
gaUiL-r from ivjitidinj^ liis papi^i-s jniMLslurd in thw iii(.-iiiuini 
of tlie French Acaduray fur 1774. The ex|tIaimlion is 
simple enough, inoHiuutili us owing to the careless and tardy 
iitaiiiier ill which the memoirs of the French Acndoniy were 
at that time cdiled. changes in the original commuiucatious 
were freci^uently made by the writera beforc publication, so that 
the papers printed in the memoirs weitj corrected to suit 
altei'ntion in view or in fuel which had liuaome ktiovi'u to the 
autliora between the times of reading and of ptibhcalioo. 
Tliiiis for imiuuce, it ia clonr thnt the pnjicT ' detailing the 
results of his ex[>eTiinentB on the cutciDntion of the metala 
aliove refeiTcd to, which was read before the Acudoiny in 
Nov, 1774, does not express the same views which we find 
given in the o.ttettde(l description of hu experim(>nt^ con- 
tained in tho Yoluniu of the inemuirs for 1774, which how- 
ever wiih not publislied till 177:^. So that altliou;;!) Ijivoisivr 
in 1774 considered air to bo niiuie up of severiil ditlirrentnlftstio 
fluids, it is certain that he was uot tiien acquaiiitinl with the 
kind oE' air which wiis ubxorbcd in cutcination, that his vievs 
on the subject were in reality vvry siniikr to those expressed 
a century before hy Jean Key (1630), Mayow (IGtiO), and later, 
by Poll (1750), and that they were far fmtn bL-iitg as precise 
and true us we should gather them to have been from the penisoJ 
of his extended memoir, prlnti^d in t77S and corrected so m 
to harmonize with the position of the science at that date. 

It is not until we KOtne to a paper, Sur la natutv du 
princijic qui se combine unc /•'« m^tuc pendant tear ealctna- 
lian, iini read in 1775 aud i-c-rcad on Aug. 8, 1778, Uiat 
we find a distiuct meniion of oxypen crs, whicli he first tenued 
"fair imincmstenl irapirablcy" or " Vair pur" or "lair vital," 
and that we see that the whole theory of combustion is clear to 
IjtvoLsier. He shovs that this gas is necessary for tlie cal- 
ciuBliou of metaia, he prepares it from prtdpUatum per ae, 
as Priestley lind previously done, and in the year 1778 wo 
find the first mention of OKf/gen or the nci Jifiant principle. The 
name was given to it because ho observed that combined with 
carbon this aubatanue forms carbonic acid, with sulphur ntrioUo 
1 JoKmai dt Pky^iu for Dm. 1774. 



acid, vith nitrous air nitric acid, witli phosphortu pbospboric 
acid, and witb the inetuls in general lut-tallic calces. In his 
Elhncnis de Ckimict publislied in X'i'A'i, vro liod the following 
words under oxygeu gas: — "Ctt air qtu nous avom r/Avwtvrf 
prttque tn vtime tcmjts, Dr, PriaUtry, M. SckecU tt mot."''' 
Now there irt no doubt whatever Uiat in October, 1774, Dr, 
FriasUey iururaied I^voisier iu Paris, of the diicovcry he 
bad lately made, and that I^Toiaier was at that lime unac- 
I qnainted witli the fact tliat jrrf^ipilaium ptr sc yields tliis new 
pas ou hfMttiu^. Hence we cannot admit Laroiaior's ctuim to 
thu joint discovt'Ty of oxygen, a claim, it is to be remembered, 
not tnade until ei^ht years sfWr th« event luid occurred. In 
corroboration of this conclusion wo tind in rrio6Ue3''s last worif, 
published iu 1800, and sin^^uhirly cnougli untitled The Doetrim 
of J'hlojision EstahtUh^, the following; succinct account of tlio 
luatler. '• Xow tliat 1 am on the subject of th& right of dia- 
coverifs," he saya, " I will, as the Spaniards say, loivc no ink of 
thi£ kind behind in my ink-hom, hoping it will bo the last time 
] shall liuYC any ocuisiun to trouble the public about it. M. 
Lavoisier saya (£lemfiUs of ChtviiHr^, En>{li8h edition, p. 3fi) 
* TIii» spocieo of air (meaning depblogisticaicd) was diacovered 
fllmoat at tlie same time by Wt. Priestley, if. Sclieelc, and 
myself ' The case was this : haring made the discovery some 
time before I woa in Paris in 1774, 1 mentioned it at tho tabic 
cf M. Lavoisier, when most of tho phtluuipliical people in the 
city were present ; 8ayin<; that it was a kind of air in which a 
candle burned mnch bttU-T than in common air, but I had not 
then given it any name. At thia all the company, and >Ir. and 
\lSn. Ijtvoisier as much ns any, expressed great surprise ; I told 
tlient iheu I had gotten it from prtcipUatun ptr se and aUo from 
ttd Ittui. Speaking b't'Otidi very inipcTfcctly. and being Uttle 
|licquaint«d with the terms of c)i«iiustry, I said plomb rovge and 
firas not understood till M. Maci[u^r siiid, ' I must mi-an Tnintum.* 
SI. Sclicete's discovery wna certainly independent of mine, though 
I believe not made quite so early." 

The two memoirs in which Ijivoi.-sier clearly put« fora-ard 

Ilia viewa on the nature of combustion and respiration arc, fiKt, 

Jooe read before the Academy in 177S, Sut la comlmslion en 

: gfnfral, and aecoiid. one entitled Jt^JUxicru siir If Phhsi/^iqvt, 

published by the Academy in 1783. In tlio first of thesa 

memoirs, he does Dot attempt to subntitute for Stahl'a doctrine 

' <£Bvtei, lam« i-i p^ IS. 



a rigoioualy demonat rated theory, bnt only nn hypothesis vbich 
•ppean to Uim raoro coiifonnnblfi to the Uw« of nature, and 
less to contradict known facts. In the second memoir lie 
developB his thoor>\ denying the existence of any *' principle 
of combustibility," as upheld hy Sfcflhl, stating th«t the 
metals, and sueJi substances as carbon, RulphuT, &e.. flM simple 
hnttics wliicrh on ccjtiibiutiuii enter into coiubiuatiou with oxygun. 
ami cQiicIudiii;;; that Stalil'a supposition of thu existence of 
phlogiston in tlio metals, tc, is entirely gmtuilooB, and more 
likely to retard thnn tn advance tbe progrcsH of science. 

The Iriniijph of the antiphlogistic (Lavoisiflrian) doctrines 
was. however, not complete until the discovery of the compound 
Qoturo of water by Cavendish in 1783 became fully known. 
Tbe cxpuriiuent concenitng t'tw ctMobinatlon of hydtogun (phlo- 
giston) and oxygen to forai water was at once repealed and 
conHrmcd by Liivuiaiur and I^])1uue on the 24th Juno, 1783( 
ant] tken Lavoisier v/as able aatiafoctorlly to explain tJie changes 
which take place wlieii inutnU dissolve in acids, and to show 
that the nietals are simple bodies which take up oxygen on 
combustion, or on tiulutioii in acid, tlio oxygen biiing derived 
in the latter case either from the acid or fj-um ttie water 

Ilere. again, if we investigate tlie poaiLion occupied by I^voiwct 
respecting the diHCOvery of tiie comiHisitioa of water we shall see 
that, not content wiih the filory of liuviny l»e(;n the fii:sL to 
givetltutniu cxplauatiun ui' the pbcuumoim, he appears to claim 
for himself the first quantitative dulermination of the fiict.' 
although it is clear that he had been previously informed by 
Blagdeii of Cavendish's experiments.'' 

The venlicl coiicerning the miirh vexed question as to liie 
rival claims of Cavendish. Watt, and Lavoisier, cannot be more 
forcibly or uiorc concisely giwn than in the following words of 
Professor Kopp — Cavendisli first ascertained the facts npon 
which the discuvery of the comjio^i^ition of water \n-u« iHisod, 
although wu uni uiiuble to prove tliat he first deduced from Uicsu 
facts the cotiijioiiii(l nature of water, or Uiat he wu<t the lU^t 
rightly to recognise its constituent component parts. Walt was 
the first to argUB from these facta cuuceiiiing the compound 

■ (Ennrav *°"** ^t, 33S. 

* F<ir«>rxlinu)tiveili«.iiwii'n of ttri' i-ibjwl we wuiil wfti th« rndcr bo Oeomv 
Wilwn'i Li/r of CartiidM, 1H9, M well us tu Vtot II. Kot])! BeiMtje mp at- 
KfttEoto dtr Chanu, DU EnlAakuof 4tr ZiMit»,mnmtui^ de» Women, Ticmg 
anil fiohn, 1S7S. 



nature of viu«r, although lie did not arrive At a snttsfitctory 
ooocluaion reapi-cluig ibc oatiue of tbc ooiu|:roncat& Lavoi- 
sier, also from ihesa &cts> first clcurly recognised the compoiiDd 
nature uf water, and di>t«!nuiiie(l nxaclly tbu aaiount of iw 

Althou;;h at tbifi period the experimental bBEis of lite true 
theoiy of comhustioa vrua cuuiplttc, it was sjome time before Ui« 
clear statements of Lavoisiur v-'hk accepted hy chemiabt. !litaity 
of Uiose who Ten moat diHtinguish(><t by tjieir discoveries 
reauuued to the last wcddcHl to the old ideas, but bj de;<:rees, an 
froab and iiiiprejudiced minds come tu sludy tliu dubjvct, Uie 
new views Wi-rm nniversally ndr>pt«(!. 

In coudidtinii;^ tlm great discuciHiim from our pnssent point 
of view, wu caunot but reuogniso in the phlogistic theory th« 
expression of an important fact, of wliich, hoT«v<!r, thu true in- 
teiiirotatioa was unknown to the exponents of the theory. Tbv 
phlogiatotuBts aasert that something which they tenn phlogiston 
escapes when a body bums ; the antiphlogietooista prove, on the 
other band, tliat no escape of material substauce tbeu occurs, but 
that, on tlio contrary, aii addition of o:«yg«n (or some other 
clement) always takes place, lu thus correctinf; from oue aepoct 
the Cilsu Btutcmciit of the fullowcra of Stabl, Lavoisier and his 
diecipl«s overlooked an iutet^iiflation which may tiiily be 
placed upon the stttlements uf ttie phlojiriKtoiiiKts, for if in place 
ttf the wird "pblogiaton," we read "energy/' this old theory 
becoioes llie expression of tlie laU*at developuieut of scientific 
inTegtigation. \Ve now know that when two elements combine, 
SnfTfjy, gviicrally in the form »if heat, is evolved, whilst iu 
order to nssolvo tliu compound into its constituent elements an 
expenditure or abaoriition uf an etjual amount of energy in 

The fact that every diatinct chemical compound posses.«e« a 
fixed and unalterable composilioti. was first proved by the 
endeavour to ii.\ the compoeition of certain ueutrul anlt«. 
Betgniatin from the year I77i>, and Kii-wnn from 1780 were 
occupied with this experimental inquiry, but their re-snlts did 
not agree sutllciently well to enable chemists to come to a satis* 
facloiy conoluaion, and it was to Cavendish that we owe the first 
proof lliat the conibiuinj; proportion between base and acid obeys 
a distinct Liw, wliilst to Lim we also owe the introduction of the 
word "equivalent" into the science. It is. however, to Kichtt-r 
(1763-1807) that we are indebted for the full explanation of the 


rout, that wbea t^'O Qeutral ealta luidcTigo tuiituul dc>oom[Ki6it)Oii, 
the two newly-rormvd salts urn nlto neutral. He sbovra in ha 
"St6c!iioinetry."thal Ihe jiruportions by weight of different 
wbkli saturate the same weight of a given acid viU also sttunb 
a tlifierent hut ft coiistant weight of ft tecoud acid. So that 
we have (iKturniioed wlint veigtit of a given base is needed 
Biitunite a given wvi^^'ht of scveml diUutvat acids, and also if we 
know thti weights of Uie diflei-ent bases wliich aro needed for '■ 
nciitraJizaliiJii of a given weight of any one of these acids, w< 
can calculate in what propurlioii each of these huscs will uuit« 
witli any onp of these acida. Richt«r aI§o showed that when tlie 
difTeivnt uietaU are separately dissolved in tiie same qnanlity 
of sulphuric acid, caul) one tak&i up the same quantity of 
onygen ; or, aa ne may now exprves il. the ^-arj'ing (quantities of 
th«e diHercnt o>:id<>.s wliiuh niintndize one luid the aanio 
({unulity of any acid, all contain Ibe same quantity of oxygen. 
These important ubscTvations atiiuct«.'d hut liltlo attvnlion or 
consideration fmm Kichter's contemporaries, all of whom wore 
busily ensured Ln canying on the phlogistic war, 

Ttie inv(?8tigatinnR of Rieliler and his predecessors hod 
reference nia.inly to the proportions by weight in which those 
bodies unitui, wlucli, according to Liivoister's theory, are not 
simple substances, whilst Lavoisier recognised the tact tliat the 
eleinenta themselves coiiihitie in defiaite proportions by weight. 
In opposition to this view of combination in dcliuite nualteraUe 
quantities, L Claude liurthollet ptibliiihui] in 1803 his cele- 
brated A'ssdi dt sUttiifut Ch-imiqtui, in ivbich lie refers the 
phenomena of chemistiy to certain fimdauieatal properties of 
matter, endeavouring to explain clie.iniea] changes hy tlie niotioti? 
of the particles of matter on the same principle aa Newton'8 
theory of gravitation accounts for the siiupler motions of tlie 
heavenly bodits. Cunsidering chemical change from this mechan- 
ical point of view, }iertli»llet pointed nutthecircumstanoesiinder 
which we can accomplish the higlieat development of the science, 
namely, prediction of the j-lieuomcna ; and, if, in his assumed 
identity of the laws of gravitation and chemical action, he was 
mistaken, the aim which he set before himself is that which has 
remained, and will ever remain, the highest ideal of the science. 
The intluenco which Borthol let's views oxorcised on the progien of 
the Bcience was less powerful than it othcnriee would have been 
owing to the fact that he, considering chemical combination to 
be based upon purely mechanical laws, was obliged to admit 



lluU ftn alteration of the physical conditions, ench iw mow, must 
' ptoduoe an alteration in the chemical compound. &nd vaa there- 
fore forecd to ignore, Or vvwi to 'Icny, tli« fact of conil>iDation 0( 
the elements iu a sinalt number of dctirute fixiM) proportions, vhich 
bad been flRl distinctly proved by hia countryman Proust 
Thia led to a keen debut* botwuon the two French philosophera 
which hwted from the year 1801 to tlie year 1808. In the «nd. 
howenrer, Proust proved concUisively that BertlioUet's views were 
iDCOiTOCl inusiuiich as lie sliowcd that vhen one metal gives rise 
to tn-o oxides, the weight of the metal v-hicb combines vith the 
same qoantity of oxygen to form the various oxides is a different 
but a fixed quantity, so that combination docs not take place by 
the gradual nddition of one eleniont, but by Enddvu incrcinents. 
This observation ought in fact Ut have led to the recognition by 
Proust of the law of corabiDiDf; prnportions, but his analysu 
V.-CTO not sufficiently accurate for tliLt purpose,' so (hat neither 
Proust nor Richter arrived at the true expression of the facts 
of chemical combination, and it -was reserved for Jolrn Dultoo, 
k(17G6 — 1844) clearly to state tlie great law of chemical com- 
fbination in multiple proportions, and to found upon this a theory 
whinh folly t-xplains the observed Gacts. 

DemocrituA, and after him Epicnrua and Lucretius, had lonif 
la^o taught that matter is made up of small indivisible particles, 
and the iOca of the atomic constitution or matter, and even the 
ht'Iiof that clicmical combiuation consists iii the npprosimatton 
of the unlike particles, had been ainjady expnissed by Kirwan in 
Kl71^ as well oa by Hii.'gins in 17$f>. I>alton v/aa, however, the 
^ first to propound a tndy cJiemkai atomic tlicoiy, tht- only one 
hitherto proposed which explains the facta of cliemical combina- 
Htion in a sati-<ractory manner. The cnnliiiul point upon which 
^■Dolton's atouiio thi-ory reats, and in whicli it difTt^rs from all 
^vprc%'ious sa^estifms, is that it is a quantUtUivt theory respecting; 
llie confititntion of matter, whereas all others are simply quali- 
tative views. For whilst all picvioua nplioldi^rs of au iitoniic 
Ibeoiy, including even Hi^ns, had supposed that the rohitive 
■ wci^htit of the atoms of Uie various elernvnl^ uru tho sumo, 
l^lJalton at onoe decliitt!<] thul tlie iitonin of the different elemcnta 
MO not of the sune woifilit ; and that the rtlative atonic wcighti 
t>f lAe eitmeats are tht prvportiona bif wti^ht in vikieh tkf tlements 

Id 1803 Dolton published his first table of atomic weigbta of 

) Jtwml A /«y»fiv, t Kx. pp aao ud 321. 


fxfjt^ •s^f:zjrc^jt kiii 'l^rhi <^^>:<=iit. «s ss ^fioidix to a paper 

O'.t- 22, 1 '.•yi. '.1. tLe fc"'«.'.r^i:i«i rf £**** Ijr vu^ aod other 
li'-'^ii^- A- i ;^si*-.c. f vr i::^r-ji -:=c liies* --ssisis. Dahon Elata 
\zj£, *.;* c,?*:?*:.! %.; -''-ilitT ci ^=4^ ia -wiz^ff 'iejcnds i^on the 
ir*;;^* a^i l";~'.'^ -vf '^^ r'----.ii-j- janiires c^ uie scToal gases. 
"Ti.*; Lv,'.ir>/ L*: 'y. Ltii-;^, ~i:;w iLc r^iiire -resells (rf the 
t;]'.:::;^*^ jar*.; .If:^ '.' '•'.■iiiH i= & rTi'.i^c &£ ikra$ I knov, entii^^ 
r**nr : I Lavt !*•>:>.- >.*:r:ii j-Tn/i^-mn::^ tii; iaiiciiy wiih ranaik- 
ai/l*: ¥'j-y>^,-t. T:.^ j-:iz.;:ilt eirji'.'i be eiii>Entl n{:«» in this 
ji^j^iT, h'l: I ^''-oll r^r-,'::a :L^ pe:^^ as Car as thev- i^^ieat 
asosnaiii^i :>v cv fea:j'rrx;-;iiii'' 

Ifa/t/yht f'irff T'fhk r,/ the £/.'f.tiri Wti^hU of Oi£ UitiauiU 
/'a/iv.ln </ Qatt</aiand other Bodia. 

llyApyjhu 1 Xilrcius oxide . . . 13-7 

AvA 4-2 Sulphur l-ll 

Carlx/D 4-3 Hj-po-nitric acid . . 15-2 

Ariitiionia 52 Sulphuretted bvdiogeD I5'4 

Oxyg':a 5-5 CarliODic add . . , 15"3 

WaUir C5 Alc-uhol 15'1 

rh'^plionis . . . . 7'2 Sulplmreous acid . . 19'9 

I'Ii'/-;pliijr(;lt'::<lliy'lr';^'en 82 .Sdpliaric acid . . .25-4 

}fitmij.=j (jJi't , , , . !);i Carburetted hydrogen, 

Ktli<;r 90 from stagnant water. 63 

Gaw^jUHoxidwof carlion &3 defiant gas .... 53 

'I'liuH tli';ri, at tlie end of a paper on a physical subject, does 
Daltoii ni!(k<: known a principle the discovei^- of which at once 
pl;u:<^l tlj<i w;if;ii';(; of chemistry ui>oa its true basis, and has 
n:n'li!ri:<i tin; nanir; of its discoverer second only to that of 
LiivoiHier annjn;^t the founders of the science. 

It JH not eawy to follow in detail the mental or experimental 
\>TiH-A:muv. by which Dalton arrived at this great theoiy. Certain 
it Ih, liowiivnr, thiit tin; idea which lay at its foundation had long 
Iwain in Iuh mind, wlijih wna essentially of a mathematical and 
UKtcliiinical tnni, and tliat it was by his own experimental deter- 
minations, and not by cointjining any train of reasoning derived 
fiijui tlie previous conclusions of otlier philosophers, that he was 
alili! til prove the correctness of his theory. Singularly self-reliant, 
iuxustuiHcd from ehildltood to depend on his own exertions, 

Balboa vras a miui to whom original work was a oecesgity.' la 
the prefacu to the second part of hia Neu> Sgghm of CJumical Phil- 
o$opkif, puldislittil ill 181(1, he clctriy sliows his independence 
and even disreganl (»f the laboms of otliera, lor lie siiys — " Iliiviny 
IXiCQ in my i>r<ij;rc-s-s so otiva misled by taking ior gnuited the 
resulu or others, 1 have del«niiiued t^i write m Httlo as possihie 
but what I can attest by niy own experieuce." 

A3 early us 1802, 111 an experimental iiiquiiy into tlie pi'Wpor- 
tious i]i wliich the several gases coiistiliitiii;; thu atmospheie 
occur, DjilUtii clearly points out "thiit tJi<; rlt-mnilA of oxygon 
may combine vitli a cortaiu portion of nitrutia gns" (our nitric 
oxide) "or %vitli Iwiro thnt pni-tion, I>ut with no intennodinto 
qtuiiiUty," aud this olviervatiuii wan vk-orly the fii-st whicii IimI to 
the possibility of drawing up llie table already given.' Iri that 
tabl», it will be seen that the relative weights of the smallest 
panicle of iiilmufl gns is given aa y.i, thiit of Ar.ot (nitrogen) 
being 4*2, and lliat of oxygen 5'd. Daltoa clearly intending by 
this to cxpre^ that the gas is n compound of one otom of nitro- 
gen with 0110 atom of oxyf.'ca, whilst the suletoiicu to uhich 
he gives the name of liypo-uitric auid (now called nitrogen 
peroxide), i» a coiDiiound in which one atom of nitvo^n is 
eiiuiLiiuetl nilh two of oxygen, and thereforo having tlie rela- 
tive atomic wviglit of I5'3.' 

The first public annoiincomciit of the atomic theory, and of the 
lav of comtiiiiatidii in multiple jTojiorlinnn upon which it was 
founded, was, siugnlarly enough, not made by Dalton hini»elf, but 
by Ills friend, I'rofesmr Thomas Tlionisnn, of (ilasgow, who pnb- 
liiilied ill l8U7an account of I>alton's discovery in the third edition 
of his Syatcm of Chtwi:Ur}/. In the following year (1808) DaU 
ton tnadp known hk own views in the roiniu-kable book entitled 
A A'ftt- b'lfstem of Chemical Philonephy, in which (Part i. p. !il3) he 
says — " It is one gre-at oVywt of this work to show the importiuioe 
and advantage of u&ceTtaining the relative weights of the 
ultimate portidiit, both uf aiuiple and compound IxkUos, the 
number of simple elemunttuy particles whifh constitute one 
compound particle, and the number of less c'oui{)ouud particles 

> lj)aml»lii'» Lift of Daiim. LonicmBii*! l^?'- 

■ Mimdialef Mfmoin, 'JmI iVriK*, vi^. i. |i. 250. 

■ Cfftatn iuw^mrttrir* in thn vuhini of the wviffbts of sima of ihn comitoundf 
MTur in Ihiii Ubli? ; iliu^ *t *■ 5'A = B*?, toliilxl 9^ sppmn otniunta iiiu«ni 
o^de. WbcUivr tin^v ato nirrvly printM't <xnoT» or hn to b« eiptaiiwd ill sang 
ntW nv tv» now on1)r bo ooiiiri^liiivit 8m Roar<e4i on I>alt«ii'« Find Ttbla of 
Atooiic Wrights, iAouAotn- LiL »ml PKU Hoe. Utm. 3r1 Scric^ vol. v. p. «Si 

which enter into the fonnation of one more compound particla" 
T])oni!K>ii RtiLU!.H tltut (luring; the yciiis 1803 ujkI 1804 Dalum 
wna occupied with the examination of the composition of the 
two gaseous hydro-cnrhons. moish gna anil oletiant gas. nnd the 
results of this examiimtiou led hiiu to the adoption of the 
atomic theory. He lound ihat both tiitutti bodice consist 8ol«l]r 
of carbon and hydrogen, and that the first of tbeee gases contains 
twice as much hydrogen to a givnn qnnntity of cartmn as the 
second. Henco liu concUided thnt r>leflaiit gas contains ouu 
atom of carbon ooin1>ined with one of hydroj>en, whereoa marah 
gas couaiatrt of one aE<n« of carbon coml)i!i<Hl with two atoms 
of hydrogen. The same idea and method of investigation he 
tlieti applied to the osiiles of oarlmn. oxides of suliJinr. oxides 
of nitrogen, to ammonia and other Ifodies, and he showed that the 
compo^ittun of thf^^i; might bo most simply explained by the 
iissum]>tion tlmt otl^ aUna of one elemeat is att^urhed to 1, 2. 3, 
&c. atoms of iinf)th(!r. The novelty luid importance of his view 
of the composition of chemical compouud-i induced Dulton to 
introduce a method of graphio leprest^nliition of the almns of 
the elements, and the aystem he adopted was as follow* : — 

B*liilive Wriaht 
Symbol. of tbt ittim. 

Oxygen O 7 

Hydrogen 1 

Nitrogen CD 5 

Carl:ion # 6 

Wnler ©O 8 

i\miJioiiia 0® 6 

Carbonic oxide O • ■ 12 

Carbon dioxide O • O 10 

Oleflaiit yas • 6 

Marsh yas ♦ 7 

Nitrous oxide O CD O 17 

Nilrii; oxide O CD 12 

Nitrous acid jOOOl og 

^'^^^'-^ {too} 26 

These atomic weights, it is evident, are for from being those 
which wo now accept as correct, indeed they arc different from 
thoM given in hia first table, for Halton not only frequently 




altered and amended tlit'se numbers, according as his experi- 
meots ehowod t)tom tci l>e faulty, but even distinctly asserts 
tUc doubtful accuiucy uf some. Cbomisls at tliat time did uoC 
pofiseaa the means of making uccuititu dtiUirmiiiaUouH, and wlicn 
we Imuomti anjuaintvd with tlid mu^h uietliudii wliiuh Daltoti 
adopt«d, and tlie imperfect apparatius lie had to employ, we c&u- 
tiol bttt be struck with the c]ciinii!!«^ of \u» vistuii nnd the 
boIdu«s8 of graep wbicti enabled him, thus poorly e'iuip{H-'d. to 
cstabliBti a doctrioo which further investigation lias only mora 
firmly eatablislied, and wliich, from tliat time forward, lias served 
as the pule star round which tdl otJicr chcniical phenomena 

Ainunnst those to whose labours we are indebted for advancing 
Dftlton's jitoiiiic theory i»re Thomas Thomson and Wollaston, hnt 
before all, the f^reat Swedish cheiniat Beritelius, to ^ihom we owe 
the fir«t really ex&ct valucM for ihvso priinitry clicuiiad con»tant«. 
With a rfuiiukublf auiounl of perss^vurauce he aacwrtiuued the 
exact compusitiuu ul'a luxge number of compounds, and wus, there- 
fore, able to calt-iilate the eonihiiiing weights of many elementa^ 
thus kyiii<; liie foundation-stones of the science as it at present 
exist& In 1818 BctZtfUus published his tht-orj' of tbeiuical pro- 
portions, and that of the chviuical action of electricity, and in 
tlieae remarkable workfi ho made utie of tht! clieuiical symbols and 
f<;niiula- such as we nuw i-inpluy, to deuutc nut only the qiuilila- 
tivo.but abothcijuantitativ^couijMiHition of uhciioical compounds. 
Trom tiiis time forwanl it was satisfactorily proved and generally 
aoknowb:dge<| thnt the elem«'>itary Vjodte-^ vomUiue tn^jether 
cither iu certAin giveu proportions by weiglity or in simple 
multiples of Ibesn; jrroportions ; and, tlirongh tlm researches of 
BerzeUus and others, the list of elements, wluch at the time 
of lAvoisier amountwl to twc:ity-threc in nimil>er, was now con- 
aidembly iocreastsL 

Next in order wnics Ilnmphrcy Davy's discovery of the com- 
pound nature of the alkalies (ISOS), proving that they are not 
simple subatancea Ixit oxideH of pectiliar metals, nnil thus entirely 
Teroluttoniitiug the views of chemiste as to the constitution of a 
Isrge and iin^iortant class of compounds, including the xalts of 
the alkaline earths. Hie discussion in 1810 as to the constitti- 
tinn of cblon'iitr — tlion termed oxytiMwIod muriatic acid — decided 
by D&vy and tiay^Lnsssc in favour of iU elcmontsry nature, was 
likewise a step of tlie greatest importance and of vide applica- 
tion. In 1811 iodine was discovered by Couttois, and most 


carefully iuvcaliguted by Gay-Lnssac, who proved the close 
analnj^' existing bebvecn this element and chlorice. The dis* 
covciy of many irtliKi' eleniHnu now opened out frt'-sh fields for 
invcsstijjulion, and pave the means of ciosaifyiug those already 
ktiowu. The names nod propuitics of thusu will be fomiil in 
the iiortions of tliia book specially dovoled to their description. 

If Ualtoa, fLS wu have sucii, &uccvc-dcd ia plttcing the laws of 
chemical combination by vxi^t on a firm basis, to Oay-Lussac 
belongs the great lionour of having discovered the law regulating 
the combination of gaseous bodies by volume. In the yenr 18U3 
Gay-LusMC and Alexander von Huinboldt found that ouo volmne 
of oxygen comhiiies with exiictly two volumes of hydrogen to 
form water, and that these exact proportions hold good at wliat- 
cvvr temperature the gases are brought into contacL Tliis 
observation waa ox^nded by Guy-Lussac. who in 1 808 publtslied 
his cdubratcil iiiftuoii on tliu cuiubiliatiuii of gaseous bodies,' in 
which he proves that gafi«a not only combine in very simple 
relations by volume, but also tliat tlie alteration of volume which 
those gnses undei'go in the act of combination olwys a very 
simple law, Ilenco it foUovi-8 that the densities of gases must 
bear a simple rehition to tlieir combining weights. The tmo 
explanation of these foct^ was Qrat given by Avogadro in 1811, 
and his hypothesis is now \inivci«aUy admitted both hy 
cheniiKts and pliy«cists. According to the Itahan philo- 
sopher the uunUwr of smallest pai-ticles or molecules con- 
tained in the same volume of every tiiid of gas is the same, 
similar circumstances of pressure and temperature being of 
course prcsitppOH-d. Tlie giMuuds for tiuch an assumption 
will be fomid fully discussed in the tlieoretical portion of 
this work. 
The discovery by Ony-Lnsaac of the law8 off volame- 
ibiiiatioii, togetlier with Avogadi-os expliiimtion of the law, 
' served do doubt as most valuable supports of Oaltoo's atomic 
tlK^ury, hut the truth of this latter theory was still further 
at^erted by a discovery made by Dnlong and Petit in 1819. 
Tlieae French chemiata detennined the specific lieat of tliirteen 
elementary bodies, and found tbat the niimhera thus obtained, 
when compare*! with the atomic weights of the same bodies, 
showed tliat the spe^tjie htaia of tlie several olomonta are 
universally proportional to their atomic weights, or in oilier 
words, the atom of eacli of thpse elements possesses the same 
> HhniAnt d'AmHO, L iL p^ 20T. 






capacity for lieaL Altliougb subat;<]u(:itt resmrch has shovrii 
that this lav doos not apply in every case, it stJU lenialns a. 
Talual>to meaiiJ) of controlling the atoniic-weiglit d(!t«rminfi- 
tioiu of 111007 elemente. 

Tn the tmma year a tltsoo^'ciy of tiquul imjKirttiucc was in- 
nomieed 1)y MitBcberlieli — that or tli« law of Immorphitm, 
^cemding to thia law. ctiemicEilly analogniiB elements can t«- 
ptac« each oUier in numy orystalline compounds, either wholly 
or iu port, without any ebaiig« occurring In tbc crystollino form 
of tlic compound. Thia lav, like thai of atoniic liuats, baa pruVL-d 
of great value ia Iho dvtonninatiou of atomic vroigbts. For a 
full dexcripUoti of this applicatiou the tbooreticul chiipteni uf 
this book muBt also be conHitlted. 

Gruduolly the new basis ^vou by Daltori to onr scicuco was 
widolT ^xtoided' by these discoveriea and by tlio resoarclies of 
other chcmista^ and a noblo struRtura aroaei towaixls the coni- 
plvlion of which a numerous hand of men devoted the whole 
encp^ea of their lives, 

Eijieciiilly alriking was the progress made during these years 
in the domain of Ot^gaoic Chumistry, or the choiniatr}' of the 
mtbatanccs found in, or outlined from, vf?};eLii))le or animal 
bodice. Dulton bad iu vain endeavoured to oUtain aniLl>'t)ca] 
nsnltft to pruvu tlint the coniplicatud Organic bodies obL'yed the 
same lawn as tlie moro simple Iuor<,iinic conipouudg. ft is ta 
Hentelius that we owe the pnnif that this is reiilly the case, and 
bis exact analy-ses placed organic chemistry iu this respect on a 
firm and satisfactory basis. There still remained, however, much 
doubt us to tha strict idctility of tint Iuwb nvcordiog to which 
organic and inoi^anic compounds were sevemlly formed. Most 
of tbe compounils met with in niineml choniistry could ho easily 
prepared by the juxtaposition of their constituents; they were 
of comparatively simple constitution, and tould as a rule be pre- 
pared hy Rynthe^is from Ibeir constituent elements. Not 8» 
with oipinic bodies j they appeared to be produced nnder cir- 
conutancca wholly difr«rent from those giving rise to mineral 
oompotinda : tbe myatcfious phenomena of life seemed in some 
way to influence the prodnclioti of tliiisc substances and to 
preclude the possilwlity of their artificial preparation, A grent 
step was therefore made in otir science when, in 1S28, Wiihier 
artificially prepared urc«, a body which up to that time hail Iwen 
thought to Ix' a product peculiar to luiiuial life. Tliis discovery 
broke down at once Uie supposed impassable barrier lietweaii 


organic and mineral chemistry, pointed out the ridi harvest of 
discovery since so largely developed, especially by Liebig, in the 
synthesis of oi^anic substance-s, and paved the way to the know- 
ledge which we have gained, chiefly throngh the labours of the 
last-named cheraiat, that the science of Physiology consists 
simply ill the Chemistry and Physics of the body. 


I Mattes is capable of asaunimg three difTercnt states or cod* 
dUiona: — the eolid, the liquid, and the gasuuiis stale. Of tlieso, 
tbo first two htvo, for obvious TeasonB, been fecognised from the 
earliest ages as acconipiinying very dtfTercnt kinilA of substances. 
It is, however, only nitbin » coni^^anitively ^hort time that men 
have come to undcnttand that jtiat m tliore are tnonjr distinct 
kiads of solids and liquids, so tlierc arc many distinct kiuda of 
gast» (Van Hi^liuont), Thrao may, indeed, be colourless and 
inrisible, but, nevertheless, they can readily be aho\sii to diflTer 
one from another. Thus, Itlack, in 1750, collwled a peculiar 
gas, vrhieli we now know tut ciirhonic acid gas, or carbon dioxide, 
by tlic action of dilute acids on marble; to this fjn.^ ho t^avethc 
name of" fixed air," Iiccause it is fixed in the alkaline carbonates, 
which at that time were called the mild alkalies, in contradis- 
tinction to the I'nn^tie nlkalies. This inviBible gas does not, like 
air, siip]Kirt the combustion of a taper, and, unlike air, il readers 
■Jear liuie-water turbid ; it is also much header than air, as can 
he slio^Ti by pouring! it downwards from one voeeel to another, 
by drowing it out of a vessel by means of n syphon, or by pouring 
it into a beaker gliLs.^ previously equipoised at one end of the 
beam of a Imlanco (see Fi?. 2). Tlint the gns has actually been 
ponrttl out is Mxn either by a burniii;j taper being exlinyuhibed 
when dipped into the beaker glass, or by addiug some clear 
liine-wntM, wbioh then turns milky. 

In, 17013. Cavendish sliuwed that the fias termed by him in- 
flanunablo air, aud obtained by the action of dilute acids on 
metallic zinc or iron, is al^o a pet^diar and distinct snbstanoo, 
to which nc no\T {(ire the name of hydrogen gas. It is so much 
li];hter than air tliaC it may be poured upwards, and takes firo 
when & lif^ht is brought in contact with it. burning with a pale 
flame, boap-bubblea bloiru with hydrogcD ascend in the air, 


and if hydi'Oguu Im poured upwards into ttm equipoised 1)cll-jar 
hung tnouth downwards on the arm of the balance (Fig. 3), the 
cqiiilibriiim will be distuvljod, and the ann with the bell-jar wil! 

3 On August l»l^ 1774, Priestley heated some red precipi- 
tato (oxide of raerciiiy) aiid obtainod from it a new colour- 
less gas called oxygen, aud this, although iuyiaihle, poasesses 

Pio, S. 

properties quite different from tliose of nir, carbonic acid gas, or 
hj'drogHQ ffo. A red-hot chip of wood is at oneo rekindled 
when plunged into this gas, aud bodiua such aa iron wire or steel 
walcli-8priiig, which do not biim in tho air, bum with brilliaDcj 
in oxygen. 

Tliese examples suffice to show that invisible gases exist 
which differ in the widest de^ee from each other, though many 
more iilastrationa of tlie s&me principle might be given. 



3 The nKthod which we have bad to adopt in order thos to 
difloem diflcrericcs between these invisible gases, is termed the 
SxjMTimttttiU Jfttkod. Eiperiments may be »ml to bo qiics- 
tioua put 1o luittUT, and n ecteace ig tortned experimental, aa 
opposed to obiKrvBlioiial, wbca we are able, so to control and 
niodily tbi! conditions under wliicb tlio phenomeoa occur aa to 
produce results wliicb are difTereut from those which are 

Pia a. 

letwise met with. Chemistry is, therefore, one of several 
experimental sciences, coch of which has the atudy of natuml 
, phencnnena for its aim. Thesu scivnccs aiu most intimately con- 
Faected, or, mtb^r, the division into separato sciences is quite 
arbitrary, so that it is not possible cxuctly to say where tlie 
phenomena bp.lougiug to on« science begin and those appertaining 
to another Bclwnce end. Nature is a coimecled wliole, and the 
diviaioua whidi we are accnstomed to make of natural phenomena 

into sepaiate eciencea serve only to aid th« liuman mind in ita 
efforts to arrange a subject wlitcli is too vast in its complete 
mago fur tbe individual to grasp. AUhou^^h it oiay uot be 
posaible exactly to duKue tliu nature of tlie plienonieiia which 
ve ciaas m ehxmieat, m distin^nmlied from tliose tenned phytiaU, 
ic is not (liHicult, by mostu of examples, to obtain a clear idea 
of tlitt kind of observations with wliicb the chemist lias to do. 
Tims, for ijistane«, it is foiuid thnt wbcD two or more given 
yiibeUucts arc brou^Iit togcllier, under ccitain coiiditiuus tbey 
ma^y change their properties, and a new Bubstance^ diBeting 
altogether from the originni ones, may make its appeonuioa 
Or, again, a given salstance may. when placed under certain 
conditions, yield two or nioru tttilistanccs difRtring eiitii-ely from 
the original one in their essonttal properties. In both these 
cases the cbangu which occurs is termed a chemical cbau^^e ; U 
several distinct substanceis have coalesced to form cue new 
substance, nn net of ehemiotU e<mhinalt9n is said to occur ; if one 
substance is made to yield two or more dist-inct new bodies, a 
ehemic^ dt^ffrnpasition has taken plactx Tliese acts of chemical 
union and disruption occur alike amonfrst solid, liquid, and 
gaseous bodies; they arc rq^lated in the first place by the 
eneutiol nalure of the Hubstajices, and seeoiiilly, by the circura- 
ataaees or conditions under wliicb thoy are brought together. 
It is also to be obs(;rvcd Lliat these actions of clieinical union in 
the first place do not occur when the compcnent materiaU axe 
sitaated at a distance from each otlier, close contact being nc- 
oessaiy in order that such changes should take place; wliilst 
sucuudly, vru ulniast invnriaUy uolico that such a combination 
U flttendi'd with an evolution of bout anii, aometimea. of light 

4 Some sim|>lc illusirations of chemical action may here be 
cited: — If powdered tralplmr and line copiwr-filJiigs Vjc well 
mixed togetlier, a yreen -coloured powder will result, in which, 
however, a powerful microscope will sliuw tin; particles of sulphur 
lying by the side of the parliclos of copper. On heating this greea 
powder in a test tube, the mass suddenly booomes ted-hot. and, 
on coaling, a nnifomi blaclv ])owder is found. This is neither 
copper nor 8ul]>bur, but a chemical cotnpound of the two, in 
which no particle of either of the sulwtanccs can be seen, how- 
ever high ft nuLj^itying jiower be employed, but from which, by 
the etuployrocut of certain chemical means, both copper aiid 
sulphur can again be extracted. Here then wo hare a ease 
of chemical oombiaatioD. An experiment similar to that made l^ 



Priestley wh*ii he discovered oxygeo, may serve as an illualta,. 
tioD of a cbemical decomposition. 2*16 grams' of red oxide of 
nmrcmj- ure Iicated iti a small retort provided -witb a receiver, 
and tt }^ delivery tube passing to the toj>of a gratliiatftil cylinder 
611ed with water to the begiDtmig of the gradaatioDa, and standing 
in the pneumatic trrtuglmver water (Fig. 4). On hi-Atinfj thu rod 
oxide by meamt of the Biinsen's gas flame, it fii^t becomes dark* 
coloured and then svon bcgioft to decompose into metallio 
mercuij'. which eollecta in small bright dpf>pa in the neck of the 
retort gradually running down into cbc rcceiver, aud into oxygen 
gaa, which pas9ea through the deliver)' liihe and collects iu the 
graduated cyliudor. After the heab baa beca continued for 
Bome time, the vhole of the red powder will have disappeared, 
having been changed by heat into metalhc mercoiy and oxygen. 

Fid. i. 

On nlloving the retnrt to cool, a volume of 112 cubic centi- 
tnetres of gas hn been collected, and thin, on application of the 
red-hot chip test, ia shown to be oxygen. If this experiment 
is properly coiiductcd, the volume of oxygen obtained ia always 
fonnd Ui be the same from the same wei|^ht of oxide (provided 
the teai[>eniture and pressure at which the ga« i^ mcusurcd are 
tha Name in the dilTerent esporimcnte), viz., 112 cubic centi- 
metres from 216 fimms of oxide. 

Another intorcstiny case of chemical change is the decompo- 
sition of water hy galvanic electricity as discovered by Nicholson 

' Poratthl« of eqiiinleDt rahiMof iVcntnmcinRii^lUhwMithUftiiilnMUirM 
«tlk that tt tbe netricftl arMaai, mi Appondix to thu toluin& 



and Carlisle in iSOi), For tlic purpose of exhibiting tbia ve 
oaXy iiuod to pa^is a curreiit of electricity from four vr 8LX 
Cirove'a or nuiiReii's elements \>y means of twa platinum 
poles through some water ncidulatcd witb sulphuric acid 
(Fig. 5). The iiistaot contact is mtuiv, biiltblw of gas begin to 
ascend from each platinum plate and collect in the graduated 
tubes, which at fiwlare filled with tlie acidulated water. After 
a little time it will be Been that the plate which is ia con- 

-^i _ 

Fio. » 

nection vriih Q19 zinc of the battery evolves more gw Uian tlie 
one which is in contact with the platiitum or carbon of tlt« 
battery ; and after the evoltilion has continued for a few uiinates 
one lube will be seen to contain twice as mucli gas as the 
other. On examination, tlie larger volume oF giui will be found 
to b« hydrogen, becauso it takes liic and burns when a lif'ht 
is brought to the eod of the tuljc in which it was ooUfxled, 

whilst ihd smallHT volume af (!U is seen to be oxygen, because 
a glowing <;lii]> of vrooil is rekindled when plunged inlo tlic pts. 

5 In niany cases of clieiuical action, tlie prodacta &k gaseous, 
whilst one or more of the materials acted upon are solid or liquid. 
Heuce, in tbeae caws, a diaappeftraLce or apptireiit loss of niauer 
occuni. It liiia, however, been shown by many Bccurat« experi- 
ments that in these cases the loss of matter is only apparent, so 
tliat cltcnvisU Lnv« came to the conclusion that matUr it iti- 
deitruetibU, and that in all cases of cltemical action in which 
matter (ILsappwin), the loss is apparent only, the solid or Ii<iniJ 
Iteing changed iiito an iii^'inilile gas, the weight of wtiich is, liow- 
evei, exactly identical with tlmt of its component parts. "U'a 
only reqain] to allow a candle tu burn fur a fi^w miiiut«s in 
a dean tiaek filled with air in order to show that the materials 
of the candle, hydrogen and carbon, iinil« with tliA oxygen of 
tite air to fonii, in the tint place, water, nhich is aeon in small 
drops bedewing the bright sidus of thu llask, nud io Ibo liccoud, 
earbun dioxide or carboniu acid gas. whose presence is revealed 
to iiff by lime-water being tnmecl milky. The fact that the sam 
of the weights of the proOucta of combostion (water and oarboa 
dioxide) is greater llian the logs of weight sustained by the candle 
is clearly shown by uii ox]H;riint:nt uutde by niuiiis uf Hil- uppa- 
ratus (Fig. 6), which consists of a tube equipoised on the arm oF 
a balance. In the long vertical tube a taper is placed, the other 
end of the system being attached to a gasholder QJled with 
water, which, on being allowed to run out, causes a current of 
air to pass tliroiigh the tube, and thus tnaintnins the combustion 
of tlic taper. TltB water and carbunic acid gas which are formed 
are ab^orlKid by the bent tube, which contains caustic potash. 
After the taper has burnt for a few minute!, the apparatus is 
disconnected fi-om tbe i^-asholder aud allowed to vibrate freely, 
when it will be found to be appreciably h(?avicr than it wa* 
before the taper had burnt, the explanation being that the excess 
of weight is due to the combination of the carbon and hydrogen 
of thu wax with the oxygen of tlie air. 

6 Another series of experiments which also show plainly the 
fact of the indestnictibility of nuittcr, and are of historical in- 
terest, are tho^ by which it has been clearly deraoDEtrated that 
the nir consists of two diiTerent gases, oxygen and nitrogen. 
The fact of the composite nature of air was prored by Priestley 
in 1772 by setting fire, thiougb the moans of a burning glass, to 
charcoal contained in a vesnel of air. He showed that fixed air 


(carbonic acid gas) was produced, and that on the absorpUoa of 
this fixed air by lime-water, one-tifth of the original bulk of 
the air disappearud, niui a coloiirluss gas recoained, which did 
not support oombuation or respiration. It was not, however, 
till the year 1775, aftiirhehad discovered oxygen, tliat Prieet- 
ley distinctly stated that this gas was contained iu common 
air, and about tho same time Scheele came to ao identical 

Fw, a. 

conclusion from independent experiments. Rut the method, 
by which the existeoco of oxygon in the air was first demon- 
strated in tlie clearest way. ia tliat adopted by LavoJBier, aiid 
diacribial iu his Traits de. Chimu:^ Into a plitss balloon fFig. 7) 
having a long .ttraight neck, I^voisier broiiglit 4 ounces of purs 
menmry ; he then bent the neck so that when the balloon naiod 
on the top of the furnace, the end of the bent neck appeared 
above the surface of tbu mercury contained in the trough, thus 
> iWt i., cbsp. Ui. 



pUcitijiC tlic A<r i" t-''^ bell-jkr ia cotumtiuicaltou with that in 
,tlw ballooiL Tli« volnine of the air (reduwU to 28 iiieht-s of 
inerctu7 Mid h teinp^r^ture of ID") containwJ in tli« ItL-lI-jar and 
kalloon nmoiinted to 50 cubic incliv^. Tiit* nicrciiry id tlit- IhlIIoud 
was now h«ate<I, 1>y n fiio ptncsil in the furnace, to near its boil- 
incpoiDl. Fnr the first lew hours no clianpe occurred, but then, 
ri'd-coloiiret! specks and suuli-s bc<,iiD lo iiiiike tlieir appearance. 
Up to a CdtlAin point theae increased in nnmber. but after n 
wliilc nofurtJi^r fomialioD of this red .tub^Dtmiicc could be noticed. 
Afler heating for twelve days the tire wtw removed, and tlto 
volume of tlie air was »ccn to hnvc undergone a Kni&rknblo 


rio. 7. 

ditnmution : the Yolumc, measurwl under tlie same conditions ns 

Wfope, hanng bfen reduced ft'om 50 to between 42 and 43 cubiu 

inches. Tlie red particles were next cnrefully collected, and on 

woi(;hing, were found lo nniotuit to 45 grains, Tliesu 4-5 grains 

wen* next introduced into a sniall rttort connected vrilh a 

j.7»du8ted gliLss cylinder (Fig. 8), and, on heating, they yielded 

4 1 i gmins of Toelallic mercuiy and from 7 to 8 cubic iiiclies of 

, a gas which was found to be pare oxygen. Thus, the vibole of 

ilie oxygen, whetht^r measured by volume or hy weight, whieb 

WHS witlidrawn from the air by the raercnry, was obt«ined again 

whi^u t1ie oxide formed w.vs deoonipOM?d by heitL. 

7 U 18 not merelv to the invesiigatiou of changes occHrring in 




the essentin] properties of inorgnDic or mineral matter that the 
cheaiiat bas to direct liia aUcutioiL The study of mnny of Ibo 
phenomena observed iu tlic vog(-t(t,b1L^ or auimaluoiKl tiUo claira 
his notice. So much so, iudeecl, ia this the case that the gc-ieaoe 
of physiology has been delined as t^e pbyaica and chemistry 
of the boiJy. The simplest as well as tlie most complicate! 
changes which accompany life are, to a great, extent, dependent 
upon clieiiiicsl laws, and, iiltliongb wc aro etill tiimlik fully tc 
expUiin matiy of these cbaogea, yet each year brings oB addi- 
tional aid, no that we may expect some day to pusvess an exact 
knowledge of the cheuii-^try of Ufe. Iu onlur to cou'>'iuce a 


Fiij. 8. 

iner that vita.1 actions are (Jos«ly connected with chemical 
pbenomcDa, we ouly n^ed to blow the air from our lungs through 
clear Ume-wnter t» »ee from Xhe ensuing turbidity of Lbv w-nt^fr 
that carbonic acid gas is evolved in lai;<^e quantities during the 
process of the rcspinitioii of nniiiinls, oiid wlieii wo furtlier 
observe that tlie higher aniiuuis arc all wannor than sorroumling 
objects, we couie to the .conclusion that tlie procesa of respiratioQ 
is accompanied by oxidation, and that the breathing auimal 
resembles tbe buruinjj citudlc, uot only in the products of this 



combuetioD, tu., water and carbon dioxide, liut in the beat 
whicli lliat coR)1)Uiiiion evolves, the diflercncc being that in tlic 
one case the oxidation goes ou C|iuckly and is confined to one 
SjiuL (the wick of tho ctodlc) whereas in the oth^r it goes on 
slowly and takes place throughout the ixxly. In like mnnner 
tbe living plant is constantly undergoing changes, wiiich are as 
necessary for its existence as tbe act of breitthing is for uiiiiunls. 
One of tbe must fundamental of iheso chan>;e3 is readily seen if 
we place some freeh giren leaves in a bell-jar tilled with spring 
water and expose the whole to stinliglit. Utihbles of gas are 
observed to ris« from the leaves, and these, when collected, prove 
to be oxygL-n. Id presence of the suiiliglit the green Icnf lias 
decomposed the carbonic acid j^ held lu solution in tbe spring 
water, assimiliiting the carkni for ilie growLh of its Imdy and 
bTxrmting lite O-xygen as » gas. Nor, indeeii, are tbe iuvesLiga- 
tiona of tlio cliL-miHt now conflm-d to the orgniiic and iuorgunic 
materials of tbe earth which we inheibit Kecent research has 
enabled him. in t^njimctinu with his colleague the physicist, to 
obtain a knowledge of the chemistry its well as of the physics 
ei the ean and far distaDt stars, and thus to found a truly 
eostnical science. 

8 It 18 tbe aim of tlie chemist to exambie tbe properties of 
all the different substances which occur in nature, so far as they 
act upon each other, or can be made to act ao as to jiroduce 
something totally dilTi-renl from the substances tbtrmsclvcs ; 
to fisoertaintlie circumstances umlt^r which sticli chemical cliaiijres 
occur, and to (tisoover tho laws upon which they are based, 
In thus investigating terrestrial matter it is found that all the 
various forms of matter with nhii-li we nro sunoundcd. or 
which have been cxamiued, cuu bu divided into two great 

1. ELEMENTAKy BoDtES.— Klenicnts, or simple suljstances, out 
of which no other two or more tsaeutioUy diflering substouces 
have been obtuluod. 

il. CowpnusB Boorea, or compounds/ out of whioli two or 
oKiTC essentially differing substances have been obtained. 

Only twenty-three elements were known rlnriny the lifetirae 
of Livcisier ; now we are acquainted with no less than sixty-four. 
Of these, or compouods of these with ciicli other, the whole 
mass of our globe, solid, liquid, and gaseous, is composed, and 
these elements contribute the material oat of which the fabric 
of our science is built. The scieoce of chemistry has for ita 



nim the ezperimeDtal examination of the elements and tfaeir 
compounds, and the investigation of the laws which regulate 
their comhinatiOQ one with another. 

The following is a complete alphahetical list of the elemen- 
tarj- bodies known at present (1876) : — 


Atomic weif{ht. 

Atomic ireigbt 


. 27-3 

Mercury . . 

. 199-8 


. 1220 


. 95-6 

Arsenic . 

. 74-9 

Nickel . . 

. 58-6 

Barium . . 

. 136-8 


. 940 


. 90 

Nitrogen . 

. 14-01 

Bismuth . 

. 210 

Osmium . . 

. 198-6 

Boron . . 

. 110 


. 15-96 

Bromine . 

. 79-75 

Palkdium . . 

. 106-2 

CaHmium . 

. 111-6 


. 30-96 


. 1330 


. 196-7 


. 39-9 

Potassium . . 

. 3904 


. 11-97 

Khodiiim . 

. 1041 


. 35-37 

Gubidium . 

. 85-2 


. 141-2 


. 103 5 


. 52-4 


. 780 


. 58-6 

Silver . . 

. 107-66 


. 630 

Silicon . . 

. 28-0 


. 1470 

Sodium . . 

. 22-99 


. 1690 

Strontium . 

. 87-2 

Fluorine . 

. 19-1 


. 31-98 

Gallium . 


Tantalum . 

. 1820 

Gold . . 

. . 196-2 

Tellurium . 

. 1280 

Hydrogen . 

. . 10 

Thallium . 

. 2036 

Indium . ' 

. . 113-4 


. 231-5 

Iodine . . 

. . 126-53 

Tin . . . 

. 117-8 


. 1967 


. 48-0 

Iron . . 

. 55-9 


. 1840 


. . 1390 


. 240-0 


. . 206-4 

Vanadium . 

. 51-2 


. . 7-01 

Yttrium . . 

. . 930 


. . 23-94 

Zinc . . . 

. 64-9 


. . 54 8 

Zirconium . 

. 900 


For the sake of convenience it 13 customary to divide the 
elements into two classes — the Metals and the Non-Metals, or 
Metalloids, a distinction which was first made about the time of 
Lavoisier, when only a few elements were known. Now the 
division is a purely arbitrary one, as it is not possible to draw 
an exact line of demarcation between these two groups, so that 
there are cases in which an element has been considered 
as a metal by some chemists and as a non-metal by others. To 
the first class belong such substances as gold, silver, mercury, 
and tin; to the second substances which are gaseous at the 
ordinary temperature, auch as hydrogen, nitrogen, and oxygen, 
together with certain solid bodies, as carbon and sulphur. The 
Dumber of metals is much larger than that of the non-metals : 
we are acquainted with forty-nine metals, and with only Sfteen 

The elements occur iu the most widely differing quantities on 
the earth, and their distribution is most irregular. Some are very 
abundant, and are widely distributed, whilst others have hitherto 
been found only in such minutfi quantities and so seldom, that 
even their properties have not yet been satisfactorily examined. 
Thus oxygen is found throughout the air, sea, and solid earth in 
such quantities as to make up nearly half the total weight of the 
crust of our planet, whilst the compounds of CEesium, although 
tolerably widely distributed, occur only in very minute quan- 
tity, and those of erbium have as yet been met with only iu 
very small quantities, and in vury few localities. 

9 In this treatise the elements will be considered in the follow- 
ing order, although another system of classification, termed the 
natural system, based upon the eheuiical properties of tlie 
elements, will b; discussed and explained in the chaptcra on 
theoretical chemistry. The natural system, however, cannot 
at present be employed iii a manual It is as yet imperfect, 
and its value can only be properly appreciated when a fuller 
knowledge of the properties of the elements has been gained. 



I. — Non-metals. 


3,™.v 1 Atomic 
Symbol. ^^;^(^j^ 



Hydrogen . 

, H 

= 1 

Nitrogen . 

. N : 





= 35-37 


. P 




. Br 

= 79-75 

Arsenic . 

. As 



Iodine . 

. I 

= 126-53 


. F 

= 190 

Oxyo;en . . 


= 15-96 

Boron . . 

. B 





= 31-98 

Carbon . . 




Selenium . 

, Se 

= 780 

Silicon . . 

. Si : 



Tellurium , 

. Te 

= 128-0 

II. — Metals. 

Potasaiutn . 


=* 3904 


. Mn 



Sodium . . 


= 22-99 

Iron , . 

. Fe 




, Li 

= 701 

Cobalt . . 

. Co 



Rubidium . 

, Rb 

= 85-2 

Nickel. . 

. Ni 




, Cs 

= 1330 


. Cr 




. Ca 

= 399 

Molybdenum. Mo 



Strontium , 

, Sr 

= 87'2 

Tungsten . 

. W 



Batium . . 

. Ba 

= 136-8 

Uranium . 

. u 



Beryllium , 

, Be 

= 90 

Tin . . . 

. Su 




. Mg 

= 23-94 

Titanium . 

. Ti 



Zinc . . . 

, Zu 

= 64-9 


. Zr 



Cadmium . 

, Cd 

= 111-6 

Thorium . 

. Th 




. Pb 

= 206-4 


. V 



Thallium , 


= 203 6 


. Sb 



Bismuth , 

. Bi 



Copper . 

. Cu 

= 630 

Tantalum , 

. Ta 



Silver . , 


= 107-6G 

Niobium . 

. Nb 



Mercury . 


= 198-8 

Gold . . 

. An 




, Y 

= 93 

Platinum . 

. I't 



Cerium . . 


= 1412 


. Ir 





= 139-0 

Osmium . 

. 09 





= 147 



- Ifi9 


. Ru 





= 27-3 

Rhodium , 

. Rh 





= 113.4 


. Pd 





Of Uiese elements only four occur in the air, about tliirty liave 
been detected iu tlic sua, wbilst all the sixty-four are foimd 
irregularly distributed throughout the solid maatt of mir [ilftnct.. 
In order to obtain an ideu as tu which elements form t)iu uiaru 
poitiuu of tlie solid crust of the curth, we ntay fxaininu the 
composiUoQ of all the different kinds nf granitic or emiitive 
rucks which constitute by far the greater part of the earth's 
ontsl. From analydes made by Busaen we find that all ^Tuuitic 
roclni poanou a composition varj-itig between the hmits given in 
the following table, so that tliese nuiufaers give a fair idea of 
wliat L3 kiiowu of the avcmgc chemical ooinpositioii of the mli<l 
globe. All the othar cluments occur iu ijuoutities less than 
any of Ikose iiientiuncd in the tiibla 

The. Compoaitian 0/ Uu EartKa Solid Crtut in lOO porta 
Jy Weit/iU. 

Oxygen . . 

44 to 48-7 

Calcium . . 

. 6-6 to 0-9 

Silicon . ■ 

22'8 „ 36 2 

Mngiiiftiuni . 

. 27 „ 01 

Aluminium . 

it-0 „ 6-1 

Sodium . . 

. 24 .. 2-5 

Iron . . . 

9-9 „ 2-4 

Fotusitiuin . 

. 1-7 ., 31 

10 In considering for the first time the subject of the elements, 
the (juestion will at once suggest ileelf — Are these sixty-four 
all the plcinents which make up our cai-tti, or i» it likely that 
other hitherto midiacovered elemeuta exist ? Jtidfjing fmm 
analog)', lemenihenng wtiat iim previously occurred, end looking 
lo tbu incoiiiplvtc Btste of our knowludgo concerning the com- 
jKtfilioii of Iho earth's craHt, we may fairly concladc that it 
is all but certaiu tliat other elementary bodies remaiu to be 
discovenrJ. Evci^' iinjirovcment in our methods of examin- 
nlion leads t»> thft detection either of wow elenifnts or of 
old ones in substances iu uhich they IduI juevionsly been 
overlooked. Ttius by the new methods of Spfrlrum Atuily- 
tia no lix«s thiin fivu (cu^itim, nibidium, thallium, indinni and 
gofliom') new ek-uienla liu\e been discovered. By help of 
this same method we are al&> enabled to como to certain con- 
clusions respecting the dintrit'ution nnd occurrence of these same 
elemejit^ iu some of tlie heavenly bodies, and wo lenra that 

I Thi« I««t nwUl bw }>t*B M TMtntlf iliMomviI. and i>, Ihetvrorr, m {np«r- 
(Mtljr 1bts*(^IoiI, Ibu wb do Dotoayoi knoir lo wliloli fuilly it beloi^ 

many of the metAls.and even non-metals, vhich are well known 
to lis on tlic earlli. urc found la tlio sua mid in tltv tixod Htant. 
The conclaaion tlml the teirestrkl ekmrnts exist boyond the 
bounds of our planet in borne out by tiie chemical examina- 
tion of the met-eoric stones wliicli come from aa extra-terna- 
trial source anil are cotistantly falling iii»o» tlie surlaoe of the 
earth. In bnndreds of these which Lave been examinetl, nu 
single case of the discovurj- of an unknown i-luiiient Las occuitc<L 
The eubstAnoGS of wliich mctooritcs have boon found to consist 
are iron, nickel, oxygen, calcium, iiiliuon, carbon, and other well 
known terrestrial eknients. 

Aiiuthur <)ii«slion wliich may here be iiskcd is — Arc theso 
elements ically uiidecomposaUe substiinces ? and to this vns 
may answer, that ho fur a« our uticinical knowledge enables tlfl to 
judge, we may assume, with a coii^idoi-able decree of probability, 
that by the application of more powerful means than at pre- 
sent are ktiown. chemists will succeed ia obtaining »tiU more 
aiuiplp bodies from the so-calted elementa. Indeed, if we 
examine Ihe history of our science, we find fn-ijticnt examples 
ocuurriug of bodies whiuli only a short time ajto were considered 
to be el(jmi-utary which, upon more CMCfol cxamiiiatiun, hav^ 
been sliowu to be coiupoimdg. 

CI A very remarkable fact observed io the case of ma^ 
elements is that they ai-e capable of existing in more than one 
distinct condition, presenting tfjtnlly diDVrenl itliysical <]uiilitie3. 
One of the most strikinf^ examples of these alhtrA/iic mottijiea- 
liatis or conditions of matter {a\Xot. nrother— Tpiire?. a way or 
mode) oc^'.ura with airlnia. which exists as Diamond, (haphiU, 
and Charcoal, bodies wUicli «« rcgiit-ds colour, hurdncss, specific 
piuvity, Ac, bwir ctjitainly but s slight resemMaiioe to e*ch 
other, but which, wIku they are burnt in oxygen, all give tb« 
same weight of the .suiiic pixMluct, viK,, carbonic acid, thereby 
proviujj thi;ir choiiicnl idciiitity. 

13 The £alanK. — As it is the aim of Ihe clwmist to examine 
the properties of tho elements and th<';ir compounds, and as the 
weight-determination of a substaiicR is of the gi'«at(!at importance 
it becomes necessary for him to ascertain with great precision the 
proportion hy wei;;Iit in which those several (^lenient-i combine, 
as well as that in which any one of them occurs in a givt-n com- 
pound, and for this jmrpuse tho Halancf is employed. By means 
of this instrument the weight of a given substance is compared 
with the unit of weigliL It ouiisisls esseutially of a light but rigid 

brass beam (JFig. 9). sospeoded on a fixed horixoDtal axis situatttd 
at its cerilre ; and llus twam is so hung as to assume a horizontal 
positioD when unloaded. Al eauh cud of thv beam scale-pans 
are hutig, ouc to rMeive the body to be weighed &ud tliv other 
for tJtt> wi^ii^lits. \VlivD Kddi jiuii is etiuidly wej^htt-d the buaiu 
must still retain its horizontal ptxsitioD, but when oue paa is 
tuure b«mvtly vretghUd than lh« utlivr, thv beam will iudiue ou 

the irictioD of tbv various part« must be reduced to a luinimQiiL 
This 19 uBualty accom^lishi^cl by euspending the beam from an 
Agate knire-edge, worl\itig on ngato planes, -vrhitst tbo puis are 
attnclictt to each end of the betuu by a somewhat simihir arran;^ 
ment shown ia Fig. 10. Tho position of the axis of eugpensioa 
relative to ttie centre of gravity of Ihu bcain is likuwiac a matter 
of con.sei)ueiica If tbe axis of auspciiaioa and the centre of 
gravity iu a balance wcro coincidoit, the beam would rvinain 
Btatiotiury in ull punitions in wbich it might be placed. If tbu 
axis of suspension be placed belovr tlte centre of grnvttv tbe 
beam would be in n condition of unstable vquilihriuui. Henco 
the only case in wlucli the bulanee am be used is tliat in which 
the {mint or axis of fluspen^ioii is above the centre of gravity, 
for in this case alouc will the beam Ktum to a horisontal 
positioa adei- niukiii^ un ouicillaiiou. and in this cose the bahiuce 

fid. 10. 

may be consicknd as a pendulum, tho whole weight of Ihe 
beam and paua being t«giir<l<Hl os conceDtrated in the centre 
of gravity. In onbir tliat tlie weight of tbe siilstmico and the 
SDUi o( tbe measuring weijjhts in tiie acale-pnn may he equal, 
it is evident tliat the axis of 8ii«i]>en8ii>u must be exactly in the 
omtTc of the b^nm. or in other words, that the balance tnast 
liuva arms of i-quul li;n^th. It is also necessary that the 
balance may have great sensibility; that in, that it may he 
moved by the sinaliHSt ]KmsibIe wiMght; inr this end it i."* like- 
wise niquiisitc tliHt Uic vc-rticul distance of the cwitrc uf gmvity 
below tlie axis of suspension shall be as small as possible. Ab 
the whole weight of ihn instnimt>nt niuy U> regnrdotl as eon- 
ceulrated at the centre of gravity, it evidently requires a less 
foroa to tuA ei tbe end of the Wnin to move tlie tnatrutDCttt 
when the distance of the centre of jfravity from the point of 
sospenaion of the balance is small, than wlieo that UisUnce is 



greater, inasniucli as in the latter ca»e the nvigbt hits to bo 
lifted throagh n longer arc. Tbo sousibility of tlio Iwlance is 
hJso incnAscd, both by increasioj^ tbo length or tlie boaia and 
by diminialuDg thu weight of tlie beiiiu and of the load. When. 
however, the b«am is made eitlier too long or too liglit it ecftseft 
to be rigid, and a eerious source of error is iuiroduced. If great 
oocmaoy in Ute weigliiog U d«)iircd, it Is advis)d>lu to Imve 
reoouTM to tlio lUi'thod of wcigliing by vibration,' by whiuh 
tba excursiotia of- the moving beam are accarately observed 
instead of its approach to a borizontal position. \\y coiubiniii;^ 
this method of vihrations with thnt of double wTigbing, which 
oonsi&ts iu reversing the position of tlie wci};ht8 in the two 
pans, it is possible for a good balsnou which is loaded witJi a 
kilogram in eat-li puu, to turn wii)i 0*001)7 grni. or about 
the rnht m^^ of the weight in eitlier pan. 

Lxwa or Chemical CouuDCATtoii. 

13 The ootnpontion of a chemical componod can be ascertained 
in two ways, (1) by scpfimting it iuto it« conipunent eleinenis, 
an operation termed analysis (^\vw, I unloose), and (2) by 
brin^'ing the component elements under conditions favoumble 
to combination, an operation termed ^ntliais {uvyriStjiu, I 
place together). To carry out both of these operations the 
balance is needed; tlie wetgiit of the compound and of the 
component in each inshtnce must he oGCcrtained, eicept, indeed, 
in tlie caiie of eertain ga.tes of known specitic ^Tavitv, wliou a 
measiireuieut of the volume occupied by tlie gas may bo sub- 
stituted fin- a detenninatioR of its ivcight. 

Tlie fi rst great law concerning cheniital combination discovered 
by the uw of the balance is that of the unaltcnililc composition 
of ohcniical substances. In whatever way any given chemical 
compound is prepared, or in whatever monuei it is nccurntcly ana- 
lyteti, it is found always to contain a fixed and deSnite <]uantity 
of each of its conetitnent elements, and tliis is a dietingnishing 
eluuitctcri>t!c of « chemical compound as opposed to n mere 
meclienical mixttiTc, the constituents of which may be present 
in miy varying proportions. Thus the red oxide of mercury can 
l-e j>n;]>nred in several ways, but 100 parts by weight of each 
product yield upon being stmngly heated exactly 02-6 parts of 

< Sm Prat W. H. aiiUnr. PkiL Tnnis. I8M, p. 763. anil arliule " Btt]uK«," 
TMf* I/ittiomitty. 

metallic mercury and 74 parts of oxygeu gss; aiid nguio if 
wa briog oxyi,'eu aud mercury togcth«r uc a BomewUat lower 
teuipcrature, they combine exactly in the above proponious lu 
furin tliu red uxiiIlv 111 like iii»tin<.'r lUO part^ by weight uf 
wiiK-r are invariably found loeuiitaiu 88-86 parts of oxyyea aad 
1114 parts of hydmgcn ; UIH parts by weight of hydrochloric 
•t;id jifw contiiiii 07'20 parts of chloriiiR and 'JH of hydrogen, 
and so ou for all dctiaitc chemical conipouuds. If the cou- 
fititiipnt demftita of a compound arc btxiu^hc U>}{iither in dilTcrtMil 
proportions from those in which tliey are able to oorabine, tlie 
exccBs of the oiic clement remains in the free etnte; thus, if a 
niixtun; of 98-89 part-3 by wei«;ht of oxysen aud IMl pftils by 
weight of hydrogt'u are broMyhl together iiiidvr cireumiita.DCCS ia 
wliioh tlicy can combine, 8SS9 pHi'Ui of ihe oxygen will ooni- 
bine with nil the hydrogen to form IiHI parts of water, whilst 
10 parts of oxyyeii gn* tt-'iimiii in the free stiifc 

It is one of lii« aims of Analytical CheviiMnj to aai^crlain with 
great precision the pcrcwilagc composition of all chemical sub-j 
stunce-s aikI this brancli of iiKjuiry is teniied Quaiiliiattfe Amtlif 
m L-oiitradistinguiehc'd from tlmt which ha« only to invcsli<^t« llic 
iMtil of muttmal of which eubsLanccs urc composed, and wliich 
is hiMice tenncd Qua/Uatice Aaali/na. 

14 A. careful exnminntion of the qtiantitntiva composition of 
(I sl-Hl-s of clicintcal compouuds leads to a conclusiou respecting 
the nature of the laws ro<|^Utiiig chuuiicnl combionlion of the 
bi)^dii>!ct impnrtant;e. I^t ua examine the cotnposttiou of auy 
given s^-rie3 of compaunds a^ determined by analysis, 9ucli as tlio 
following : 


Bydrvgcn CliluriJ«. 
Chloriue .... 97-25 
Uydrogen. . . . 275 


Potudom Chloridft 
Chlorine .... 47-53 



100 00 

Chlorine .... 60-61 
Sodium .... SD-30 

Bflver Chloride. 
Chlorine .... 24'73 
SUver 75-27 






Hydragen Bromide. 
Bromine .... 9876 
Bydroyen .... 124 


Sodium Bromide. 
Bromine .... 7762 
Sodium .... 2238 


Potassium Bromide. 
Bromine .... 6713 
Potassium . . . 3287 


Sflrer Bromide. 
Bromine .... 42o5 
Silver 5745 



Hydrogen Iodide. 

Iodine 9922 

Hydrogen .... 078 


PotaBsiura Iodide. 

Iodine 7642 

Potassium . . . 2358 


Sodium Iodide. 

Iodine 8462 

Sodium .... 15-38 


Silver Iodide. 

Iodine 54-03 

Silver 45-97 


Arranged in this way we do not notice any simple relation 
existing between the components of this series, except that the 
quantity of hydrogen is always smaller than that of the chlorine, 
bromine, or iodine, whilst the quantity of sodium is always 
smaller than that of potassium, and this again is less than the 
quantity of silver. 

15 If, however, instead of examining a constant weight of 
the several compounds we ask ourselves, how much of the 
one constituent in each compound combines with a constant 
weight of that constituent which is common to several, we 
shall obtain at once a clear insight into the law which governs 
the formation of the compound. In the series of hydrogen 
compounds for instance, let us calculate (by simple proportion) 


how much chlorine, broinice, and iodine combine with the unit 
weight of hydrogen. We find that we obtain for the composition 
of these compounds : — 

. Hydrogen Chloride. 
Chlorine . . 35-37 
Hydrogen I'OO 


Hydrogen Bromide. 
Bromine . 79-75 
Hydrogen . 1-00 


Hydn^en Iodide. 
Iodine . 126-53 
Hydrogen . 1-00 


Continuing our calculation, let u3 next ask how much of the 
metah, potassium, sodium, and silver, unite with 35-37 parts by 
weight of chlorine to form chlorides ; with 7975 parts of bro- 
mine to form bromides, and with 126-53 parts of iodine to form 
iodides. The result is as follows :— 

PotasBinm Chloride, 

Chlorine . 3537 
Potassium . 39 04 



Sodium Chloride. 
Chlorine . 3537 
Sodium . 22 99 


Silver Chloride. 
Chlorine . 35-37 
Silver . . 10766 


Potassium Bromide. 
Bromine . 79-75 
Potassium . 3904 



Sodium Bromide. 
Bromine . 7975 
Sodium . 22 99 


Silver Bromide. 
Bromine . 7975 
Silver . . 10766 



Potassiam Iodine. 
Iodine . . 120-53 
Potassium. 3904 

Sodium Iodide. 
Iodine . . 12653 
Sodium. . 22-99 

Silver Iodide. 
Iodine . . 126-53 
Silver . . 10766 





Now for the first time a remarkable relation becomes apparent, 
for it is clear that tbe SAME weights of the metals, potassium, 
sodium, and silver, which combine with 35'37 parts of chlorine 
lo form clJorides, also combine with 7975 parts of bromine to 
jonn the bromides, and with 12653 parts of iodine to form the 
iodite. In other words, if we replace the 3537 parts by 
weight of chlorine in each of these compounds by 79 75 parts 
of bromine, we get the bromides, and if by 126'53 parts of iodine 
ve obtain the iodides of the metals. Hence one and the same 
weightof metals (39 04 of potassium, 22-99 of sodium, and 10766 
of silver) has the power of forming compounds with tlie precise 
quantities of chlorine, bromine, and iodine respectively, which 
unite with 1 part by weight of hydrogen, to form the hydrides 
of these element's. Thus we arrive at the conclusion that each of 
Iht tltmenls comhines with the oOters m aju^ and definite pro- 
portum bif tedgfU, or ; — 

[ 35-37 of cHorinel ^^ 
3flD4 of potassium combines with , 7975 „ bromine .- 'i,, 

1 126-53 „ iodine J "^'^'J"' 
22-99 „ sodium „ „ « » 

107-66 ., silver „ „ „ 

1-00 „ hydrogen „ . „ „ » , 

Tliis conclusion is home out by the examination of the com- 
pounds of all the other elements, so that a number attaches to 
^h element which is termed the combining weight or atomic 
•K*?^ of the element, and these numbers are found in the 
WKind colnmn of the table of the elements given on page 52. 

i6 Taking an example from another group of chemical com- 
Ponndswe find that the well-known oxides of lead, copper, 
mercury, and cadmium possess the following percentage com- 
poiition :— 

Metallic Oxides. 

Lead Oxide. Copper Oxide. 

I*»d 9^-82 Copper .... 7975 

0»fgen .... Y18 Oxygen .... 20-25 

10000 10000 



Hei>Bai7 Oxide. Cadmiom Oxide. 

Mercury .... 9260 Cadmium .... 8749 
Oxygen .... 7-40 Oxygen .... 125 1 



Wliilst the corresponding sulphides exhibit the following 
composition: — 

Metallic Sulphides. 

Lead Sulpliide. Copper Sulphide. 

Lead 8658 Copper .... 66-31 

Sulphur .... 13-42 Sulphur .... 3369 



Mercury Sulpbid*. 
Mercury .... 80-20 
Sulphur .... 1380 


Cadmium Sulpfaid*. 
Cadmium .... 7773 
Sulphur .... 22-27 


If, aa before, we now compare the quantity of each metal 
united with one and the same weiglit of oxygen, say lo'96 parts 
by weight, as found in the list of tlie elements, page 52, we 
get the following numbers; — 

Lead Oxide. 

Lead 206 40 

Oxygen .... 1596' 


Copper Oxide. 
Copper .... 63-00 
Oxygen .... 1596 


Mercury Oxido. 
Mercury .... 19980 
Oxygen .... 1596 


Ca'Iuiiura Oxide. 
Cadmiiiin . . . 111-60 
0.\ygyii .... 15-96 




And if we investigate the sulphides, wo find tliat one and 
the same weight of 8ulplmr, viz, — 31i'8 parts by weight unite* 
vitli the following t^iiantiUes of metal aa found already to fonn 
suljihtdcs. Thus «e have:— 

L<«>1 Sal[iliid«^ 

Lead 206-40 

Sulphur .... 31-9« 

CopiMr SnlpUdo. 

Copper 63-00 

Sulphur . . . 31-98 



BIcKsiy Sulphide 
Merctuy. . . . 199-80 
Sulpliur . . - . 31-98 

Okdmiam Stilphid& 
Cadmium . . . 111-60 
Sulphur .... 31-98 



Hence again we see that eacti of these metah umles in n 
fi-ted proportiou \nth both oxyj^en and Bulphur. so Miat 

206-4 part* by .-eight of le«d «o"biuewith[Jj|«^"f ^«;;>^° 

63-0 .. . copper 

1998 „ „ mercury 



and these numbers oio the eombiuing weights of the metala io 
question, as given io tlic Table on pugo 52. 

17 At a time wh«n the constancy in compoaition of chsmioal 
compounds vaa still under dl.'^eiisston, Joha Dultou's speeolative 
mind conceived an hypothesis which clearly explained the 
law of coinbiuatioii in constiitit proportiuns, uud solved 
the question as to tlii^ nature of the eampounda furnied by 
the union of two or more elements in several different 
proportions. Ttii.i liypothesiii, kDOwn »» Dalton's Atomic 
Thtory, uiay be ^id to hare bocome one of the most important 
fouDdatioQ stones of the science, and to have exerted an inQucnco 
on iU progress greater than that of any other geneialization, 
with, perhaps, tlie single exception of liivoi^ier's explanation 
of the phenomena of combustion, and the discovery of the 
indeatmctibility of matter. 

As has been said, the frequently occurs of two elements 
uniting to form scvcTal compounds. For each of these the la-w 
of constant proportion holds good. Thus the tvo element*. 


carbon and oxygen, unite to form two distinct compounds, 
carbonic oxide gas and carbonic acid gas, and 100 parts of each 
of these bodies are found by analysis to contain the following 
weights of the elements : — 

Carbonic Oxide Gu. Carbonic Acid Gas. 
Carbon .... 42-86 . . . 2727 
Oxygen .... 5714 . . . 7273 

10000 10000 

Knowing these facts Dalton asked himself what was the 
relation of one element (say of the oxygen) in both compounds 
when the other clement remains constant? He thus found that 
the one compound contained exactly double the quantity of 
oxygen which the other contained ; thus : — 

Carbonic Oxide Gas. Carbonic Acid Gaa. 
Carbon .... 1197 . . . 1197 
Oxygen .... 1596 . . . 3192 

27-93 43-89 

Thus again, analysis showed that two compounds which carbon 
forma with hydrogen, viz. : marsh gas and olefiant gas, have the 
following percentage composition : — 

Marsli fina, Oiefinnt Gas. 

Carb9n .... 7495 . . . 85-C8 
Hydrogen . . . 2505 . . . 1432 

100-00 10000 

Dalton then calculated how much hydrogen is combined in 
each compound with 11-97 parts by weight of carbon, and he 
found that in olefinnt gas there are two parts by weight of liy- 
drogen to 11-97 of carbon, whilst marsh pas contains four parts 
of hydrogen to the same quantity of carbon, or exactly double 
aa much. 

As another example we may take the compounds of nitrogen 
and oxygen, of which no less than five are known to exist The 


pereetttage compodtirm of thoso &vq boilies is touni b^ ftxperi- 
mcnt to be u$ TuUuws : — 

(I) m m It) (5) 

Nitrogen . . 63-71 4675 36-91 3051 25-99 
Oxjgeu . . 36-29 63-25 63-1)9 6949 7401 

100-00 100-00 lOO-flO 100-00 1 00-00 

IT then, like DalLoti, we ioquire how mucli oxygfin is con- 
tained in cuch of thuse fire coaipoiinds, combiucd villi a fixitl 
weight, say :*S-02 parts of nitrugou (it. twice the combining 
weifjht of nitrogen), we find tliaL t]iia is reprewDtcd by th« 
nuaiUnJ 159Q, 31-92, 47-33, 63-84. and 7&-8. la oUier worda; 
the relative quantities of oxygi'it itiii ia the rktJo of thu nimple 
Qumlera 1. 2, 3. 4, and 5. It luu not been fouud pwsibte to 
oUaia ttay cotapounde containing quantities of oxygeii iuler- 
mrdiutn to tlie above muiibtirsi thv conihiuatioa of the two 
filemt-nt^ in any ("iveu intenuediato qiin.ntitits resulting simply 
in thu forniutiijn of one (or more) of tho above compounds 
leaving tlie excess of tht> one olotiu-oi in the fntc »tatc. 

l8 These examples suiliee to iUiistmlc tlio Law o/ Combina- 
tion i» mttitijilc jmporiions, which is intimutcl^r coiinccicd 
with tho Lam o/conalitnt pmjMriioiis. Th«Be laws Simply atate 
that tlio idiMiictitJi unite togctti^r iu tho proportions of tbcir 
coinbiuing weights or in miilUples of tlicse wcif;hta. 

In orJcT to t-xphiin thu L-xisti^Dcv of these fiacts John Dolton 
pmpusul bia Auimic Tiieaty, whiuh follows tlie dovtiines of the 
Grevk philosophers so far oa it supposes that matter is not con- 
tinuous, but mado up of extremely smaU indivisible [mirticlea 
termt-d atoms (a privative and T£/ffu I cut) ; hut dtfTurs, hov> 
ever, from that of llie oiicients and becomes truly a chemical 
atomic theory inasmuch as it supposes the atoms of diiTLTcnt 
clement^ not to posses iLc same weights, but nj^urls tlial the 
reluLiuu bclwccn their weighta is represented by the com* 
bining wLiyhlM of tlifi clemonts. Tims the atom of oxygen 
18 liiHG times a« lieary as tlie atom of Iiydrogeu, and ihc 
weights of tlte atoms of oxygen and chlorine are aa 15-06 to 
35*37. Ihilton assumed,, in Um second place, that chemical 
oombiuatiou constste in the appioxiciation of tlie individual 
atoms to each other. Having mode these ftssumplions he was 
able to expUIn why all oompounda must eontnin their 



couslituetita either in their combiuiiig jiroiiortious or Ui uiulUpIca 
of them. 

Lvt us consider the case of the Bve cumpounds of nitrogt^n and 
o^tygen; the first compound consists of two atoms of uilrfj^t-u 
vthuso relative weight is I40I X ^ = 28-02, untte<l with <iiio 
single atom of oxyseii I'avin;^ a relative weight of 15 96. Tlie 
next possible c;i>mi)Qiuid vouUiuing more oxygua is one in which 
t)ie smallest indivisible portion of oxygen, or one atom weighiog 
1590, is added to the first a)mpnun(l The third possible com-jj 
pOHRcI must Irc farmed hy the approximation of u Ibinl atom ' 
oxygen. The next possible compound contuins four atoms of 
oxvji^en, nnil the ] fiv« atoms of oxyj^'fn united with the t«'c 
Atoms of iiitrogcu. It ts thus cleitr tliat the atoiiiic tlieor 
explains why no iiLtcrmvdiuto coniponiidit arc foimd to exist, 
but it is equally «videiil tlmt it in no way deeidea how many 
compouDdB can be formed by any two or more elemeots. This 
at present can only be learnwl by exppriment, but wo ore ik>1 
withont indications that a time approaclies when this further 
problem will receivt! a thvoreliciU suhiliou. 

Although the atomic theory satisractorily explains all the 
known laws of chemical comhination, the aettial existence of 
atoms is far from being thereby positively pi-ovud ; indeed 
from iiuroly t-homical considerations it appeals unlikely that the 
question will ever be solved.' Nevertheless, there is evidence, 
gradually becoming more cogent, connected with physical 
pheoomena, which compels ua to admit a limit to the divisi- 
bility of matter. The phenomena in question belong to the science^ 
of molecular physics, and have refureucc to such subjects as thol 
capiUar^' iittraction of litjuiils. the diffusion of gases, and the pro>| 
diictiou of electricity by the contact of metals. lEensoning from 
facts obser>'ed in the study of these subjects, phjaiciats have not 
only come to the cuuclusion that matter is disoontinuous and 
therefoi-e, tliat indivisible particles or molecules (nioA!ru/a,a small 
tnasi) exist, but they have even gone so far as to indicate the order 
of magnitude which these molucules otlaiii. ThuB Sir Willi* 
Thomson stales that in any ordinary liquid or transparent or'' 
seemingly opaquu soUd, the mean distance between tlie centres 
of contiguous molecules is }e»n tlian one Imndred-millionth, and 
greater than Uie two thousand -millionth of a centimctie. Or. ia, 
order to form a conception of this coarsv-griuuodncss wa ma] 

* WtlliaifiMn. " On th« Atomic Theoi^'," Cina. Soe. Joum., ml uciL (1988) 
p. 328 and p. 133. 



imagine a lain-drop or a glube of glnss ns large ns 8 ])Cfl to le 
uiagnilied up to the siz« o( tha caich, each ciiii^tituctii luolctulu 
liviug aiBgnified in Uie sauic proportion ; the magaitii'd structure 
tt*ouId b« coarser-graiued than a lieiip of siimll hIiuI, but proliably 
li!88 oourso-gminccl than a heap or cricket- bulls.' 

TIk- existence of the nioleculitr cuiiNtitiitiun of uiitttvr id Uke- 
wtso an Gseciilial condilioii of the uicchatiieiil theory ofgaaefi by 
means of which umrly cvciy Jcnorni mechanical pmperty of 
the gases caa be explained on dymuiiical prini^ipIeH, so that in 
this direction again, we have a coutinuatiou of the real existence 
of molecules. 

As, liowi'vtT, every chpTnical compound must consist of ut 
least two elmni^iiU, the moleaile of ti compound nuittl coiuii)>t 
of At least two smaller piitliclcs which aru most pinlinbly 
identical with the a/oms, 

19 The discovery by Gay-Losaac and Humboldt in 1805 of 
Iho aitnplu relation existing between the combinititf volumes of 
oxypen and hydrogen jmses, followed by ibnt of tlio general law 
of gaseous volumes enuncintod iu 18i)8 ly Cay-Lu^sac aleno. 
eerFed as a powerful argument in favour of Ihilton'a -Atomic 
TIi»;ory. Tliia law statec that the weifffUn of ifte cmnbimny 
rofvmcs of tie ijastons elements bear a simple ratio (0 their atomie 
veitfhia. Ttiua taking the ntiit volame of hydrogen gas to weigh 
1, as being tlio lightest substance known, wo find that 

The unit volume of nitm^tn gns wt'ij^he I4'0t 
oxvKm „ „ IfiaS 
.. 35-37 



wd these numbers are identical with the atomic vr^ighta of the 
elements In other words, nilrogcQ is 14-01 an<l tlie other sub- 
stances 15 9lj, 35-37, 797s, 126 53 times as heavy as hydrogen 
respectively. If comhiuation betwoeu thcso lUniieuls takca 
ploeo in ntomio propnrtinus, or in aimple umltiplcs of these 
proportions, it is clear that the volumes in which they combine 
roust bo either cijiial or tlutt tliey niiittt bear a simple relation 
to one another. This Gay-liissjc found by experiiiicnl to be 
tJie case. One volume of chloiim: wcijjitiing 3d-^7 combines with 
one voliiuie of hydrogen weighing one, to form hydrocli luiic acid 

■ Sir Williun Tkomioa, A'atwe, iittdi 81, 1870. 



gaa ; wliitst one volume of oxygen weighing 15'96 combines 
«ith two vohiiiiesor hydrogen weighing two, to fonn witer. Not 
only tlocs tliis simple volume-ratio liuld good with reganl to tin- 
gasc'8 nliiuh cumliiue, bnt iiko witb rMpect to Uio gaaeonii pro- 
ducts of tliuir combitintion. T\w voluia« of a compouud (^ 
bears a simple ratio to that of its gaseous constituCDt« ; thus 
one voluitiv of Iiydrogon anJ one volume of chlorino combine to 
form two volumes of JiyJrocbloric acid gas ; whilst two volumes 
of hydrogen and one volunio of oxj'gen, whcu tlicy unite, form 
two volumes of watpr-j^nis. 

The simple relations exhibited in the vohinies of comltitiing 
gases are clearly shown hy the following UiUe; — 

1 to), orddoiincnnil 1 vn). of hyilnij^ formS yoK of kydnchlinlc add. 
1 „ bromine und 1 „ ,, g B „ hydrobronuo Mid. 

I „ iodine and I „ „ „ 2 „ lifdriodic MikL 

t u oxj-geo uiitl 3 vols, of bjrilrogeD form S „ >t«iiin. 
I „ iiittogea und 3 „ „ „ S „ unmotuo. 

tc thus is clear thtiL Ike numltr of aioma which U contait 
in a given volume of «ny gaseota bodg, muM stand in a nmpit 
rtlation to that containtd in. tkc same voiumf. of tiny other g<Ui 
(measured under equal circumstances of t«mpemturc and j>r<?a-' 
sur<>)- I'li^ itimplcst ns well as the nio-st probabtu euppoeition 
reapectiiig this quostion is tlat put forward hy Avogndro in 181 1.' 
who »Gsumc<l that rqHal volumes of ail the di£vrfnt gasex, bulk 
elemtnlarff and compound, contain the same number of particles 
or vitfiirant moUcuirs. and tliis theory is uow generally accepted 
liy pliysicist^, who have urrived nt tlio tame cooclusion as the 
chemists have reached by nn iiidqieudent train of reasoning. If 
we take the simplest case of volume combination, that of one 
volume of chlorine and one volume of hydrogen unitins to form 
bydrocliloric acid gas. it ia clear that the number of particles of tli« 
compound hydrochloric acid contained in one volume can only 
be half 118 lai>^ as that of Uie uncooibiued chlorine or hydrogen. 
Huncc: to conl'umi to Avogudro's liiw, the iuLi'graut molecule of 
free chlorine ojid of flee hydrogen must cuusist of at least two 
Atoms joined together, and vro sliaU represent the combina- 
tion aa talrin}; place between two volumes (onu molecule) of 
chlorine, and two volumes (one mnlcculoj of bydrugen, forming 
four volumes (two molecules) of the compound hydrochloric 

■ Jivm. d* Phyi., Mr Do k Mttheri^ t. 73, Jui]|«t, 1811, p. S3-76. 
Vth. 1914. 

DErrxmoK ok atom and molfxule. 


acid gaa. Agsin, two volnnics of steam coritojn tvo YOlumcs of 
by<lrog«n and one volume of oxygen, Itcuce if lli«rc urn tbe same 
nambet of moteciUea of steam, of iiydrogcn, and of oxygen in 
the same volume of oacli gu», it i» cli»>r tlist iu the fomiatioD 
of vater fiom ita elemeota, eacli molecule of oxjgcii must be 
fiplit ttp into tvo similar parts. From this train of reasuniug 
it follows ibat a« a/ow* « (he »mn(list portion 0/ matter 
lehich ean enter inUt a (kemieal eompouiui, wliilst a tnolecale, on 
the other liaiKl, is the gmallat quantity of an. eleinent or of a 
eom/xntnd which can ejeitt m the fn< ftat<. Il must, however, 
be borne in mind tlial t)ic motcculca of tlie simple gases do not 
always coiiliitii tuo atoms. TLus, for instance, llio ni(>1eciil« 
of pliospborus vapour cotisista of four atoms, wliilst tliat of 
mercury va|»our consists of single atoms; 

20 Forllie lirst time we may uow eiiiploy tTtftimat symboh, 
a kiud of slioitli&ud, by ^^lli(;h wc cuii couvtrniuully express 
tlie various cheraicnl changes. To Mich element we give a 
symbol, usually the first letter of tlie lAtin. which is generally 
also tliat of the EogUsb name. TLus elands for oxygcu ; H for 
bydrngen; S for sulpliur; Au for gold (auium); Ag for silver 
(arf^nlnm). These letlen, liowevt>r, signify more than thai a 
punicular substance takes part in tlie reaction. Tliey serve 
also to {;ivc tbe quantity by weight in which it is present. 
Thus O does not stand for ony quantity, but for I j BG parts by 
weight (tbe couibiiiiu^ weight.) of oxygco ; H always stands for 
^e part by weight of hydrogen ; and in Mk^ manner S. Au, 
idAg Bland invariably for SIDB. l%-8, and Id? filJ porta by 
weight of the several elements respectively. By placing ^mbols 
of any elements aide by side, a combination oi' the elements is 
signified, thus : — 

nCl Hydrochloric acid IU llydriodic nctd 

HBr Hydrobromic add H<>0 Mercuric oxide. 

If the compound contains mors tlinn one cotabiuing weight, 
or, Rs we may now tenu it, more than one atom of any dement, 
tbi3 19 indicated by plat-ing a small number below th« symbol 
of tbti atom of ttio element, thus II^O aignifies iU parts by 
weight of a compound (water) containing two atoms or two 
paita by weight of hydrogen and one atom or 10 parts by 
weight of oxj-gen- Uenco it is clear tliat tfu atomic vxiijht of a 
compound is (he s*im of the atomic weights of the evmponent pOTU. 

IX the chemical fomuila of any compound is known, its 

composition by weight is »lso known. Thus KCIO, signifiea a 
body caUed jjotosaium chlorate hnving the following composi- 
tion OS ascertained by analysis ; — 

CMurine . 

Pftrta by wuigjit, 

. 39 04 . 

. 35-37 . 

47-83 - 


. . 31'J2 
. . 28-93 
. . 39-15 


Tt 19 usual to npnsant cbcniical changes in tht; form nf equa- 
tions; the niatcrtalfi taking part in ilic cliaugo being ploccti on 
one side and thu ptoducts foroiei], which must be i-^ual to tJie 
matc>riala in wciglit, beinr; plnced on thn olber. If we beat 
chlorate of potaali, or, us it ia now more freiiuenllj termed 
potus»tuiiicliloralc, it it) decomposed into oxygon aud potassium 
chloride, and this decomposition is represenlud by the eq,unUon 

KC10,= Ka + 0, 

in which the sign + connects the two products and signifies 
" togi'tliei Willi." Tills shows us that 12229 parla by weight of 
this salt leave bebind on htaling 7411 parte (3537 + 3904) of 
potassium chloride and liWrnte 47-88 parts of oxygen. IleDce 
it ts clear (hat the quantity of oxj^en wliieh \s obtained from any 
other weiyhl of the salt and vice rcrsA can Iw foniid by a siraple 
calciUntton when the equation representing the chemical change 
13 known. 

To take a more complicated cose, if we knew tliat the equation 
representing the change which occurs when wc heal pota^gium 
fwrrocyan ide K^C^NJ-'e with strong sulphuric acid H^SO, and 
water, is the following : — 


yielding carbon monoxide gas CO. pota*«ium sulphate K,SO,, 
ammonium sulphate (NIIjJ^Oj, and iron sulphate yeSO,, wo 
can easily falculnte how many grains of carbon monoxtdo p«s 
CO can be obtained from any given weight of the femicyanide 
K,CjN,Fe, inasmuch as analysis proves that the weiglit of u 
molecule of each of these substances is as follows: — 

Oxygen O 


FcrrocTnnidc of r<-U»intii. 


Iron . . 




The forcgoiug cquotiou then shows that one molecule of Uie 
furrocyiaide, or S67'94 p»rts by wtiglit, yields 6 molecules, or 
IC7'58 ports by weight or carbou tuonoxidi;, and bt-nce a sitiiplu 
proporliou gives thu (jiinntity yielded by any other weight Tlio 
illustratioii is, however, not yet i-^inspletc ; conimcrciitl poUissium 
ferrocyanide contains, as do many clieniical crj'sLalhue coni- 
})ouiids, a cerUiiii iitianttty of water of cnfstaUizatiaa, which is 
giveo o£f when the salt is heated, in consequence of which tlie 
crystals fall to a iH>wih'r. Diit, as the equation shows, a certain 
ciiuLUttty uf water takes partiu the reactiou, nud it ia, Ux^rcfuru, 
iunecessarj' to dry tlie suit previously if only we know how much 
rntcr of crj-stallizntion the salt coiilains. Analysis hns shown 
tli&t Uie commercial salt liaa the composition K^faNoFe + 3HjO ; 
heoce if wv udd 3 x 17 00, the wciglit of tt juolcculvs of water 
to 367H4, we ohtaiu the uuiub«i- 41^182, as the weight of 
the htfdroUii eitlt, wliich must he taken iu order to obtain 
367r>S paitJ* by weight of carlwii monoxide. 

As, however, the quantity of a gas is almost always eHtimat«iJ 
by RMwAuring ita volume, and from this volume calculating its 

eight, it becomes of the greatest importance to know how to cal- 
ilate the volume of a gas from its weight, or nix iTvsa. This can 
readily be done, for we iiud that the dcntHy of cver^ tompound in 
the gaaeoH* state is half ''' molecular teti^l ; or tli at ever}/ moltxuie 
in the gaseous ttaieoeenpiaOte volamsJUUd by two parts by teciifht 
^h/drmjen^ One litre of hydrogen gas at O^ond under 760""" of 
mercHF)' weighs 0-0S9378 gram, ; hence the weight of a litre of 
any other g:is meaauivd under the same circumEtaiic«s of tem- 
perature and pressure is obtained by multiplying the density of 
Uje gns, iiv hidf ilj* niolccuhir weight, by the above number, or by 
0-0896, wiifuabaolute accuracy is not reciiiired. Thus one litre 

.of ctubon mouoxide weighs " ^ X 00690 = 1-251 gnus., 

'■nd 167*58 grmfl. of this Eubstonee occupy a volame of "rryai" 
litres at n" and 700"'™. 



It is now easy to calculate what volume this weight will 
occupy at any otlior tt-niptrnture or pre«suiv, for wc Itnow that 
the coctiicient of espansion of all gases when raised from (i^lo VC. 
a Tfx (Law of Clmries), and that the volume of all gas» is 
inveraely jproportioiial U) llie ppcssure to wliicJi they are aubjected 
(Law of IJt'vle). Uence if tlie temperatiire at uluch the gas 
was coUecteil were 17* C.aiul if tJie lutromelcr then alood at 
750"" the volume (v) in litres of the carbon moaoxide collected 
would bfl 

ir>7-5 8x(273 + 17) x 760 
l'2ol X 273 x"V50. 

Oases a.ku Vapoubs. 

91 Tlie gaseous condition of matter is well dofinod to bo that 
in wliich it is capable of iudetiuite cxpausiuii. If a quantity 
of gas as small as wc pIcuM is plucod in a closed vacuous 
spacp, however large, the gaa will distribute it^telf uniformly 
tbTouglioiit that space. The relation between the vohinie and 
pressure of a gas, the temperature rfiiminiug constant, Is 
expressed by the well known kw of Koyle (16G2) viz., that 
the volume of gas varica inveraely lus the pressure, or, in otiier 
wonU, Uio preiMure of a gas is piopurtional to it« density; so 
that the pressure exerted on the containing vessel by two 
poitioHS of any given gas is the Buni of tJie jjresHures which 
each portion would exert if present by itself. I)altou extended 
this law itiasiiiUL'h n.i he showed that if different gases, which 
do not act chemically on each other, are mixed together, tJie 
pressure' cxeited is likewise the sura of the separate preasures 
of Hie diflerent gasea. Tlie law of Hoyle is, however, only 
approximately true, for it is found that no giis exactly obeys 
th is law under high pressures, al though under moderate variations 
of pressiue the deviations are iiiapiirpciahle. These gases wliieh 
have not as yet been condensed to hquids, fullil the law more 
nearly than tiioae which have been conilviiSL-d, and lIio higher the 
tompcnitiire at which the obser\'ations are made the tuore closely 
the experimental results agree with the law. I'lie deviations 
fiom tlic law wliich are thus obser^'ed under high ]>res.sure8 are 
seen in the following table exhibiting the experimental results 
obtained by batterer.' 

1 Pogg. Anit. xciv. iSS. 


TaiU of fkoiatiimi frtm 

tk* Lav 


PiBMBV ill 

Number or ralninn of fju coiprciJ into omr rolnintt. 











































'When U]e pressure is iDcrcosed bejond it given poiiit, Utile or 
no fimJicr cliaogo of volume is obeen'ed in the case of th« 
noa-coiidcnsable gase-«, whereas others under similar circum- 
Btancee ontltr^o a sudJen conttoccioii, the gao changing into a. 
liiiaiit. The tirst instance of a substance, wrbicli, under ordinary 
couditious, ia kuowu as a ^is, buing thus tnuuforini-d by pnea- 
snra into a liquid is cLloiinc gas. Tbift gttfi was first liquefied 
uodor presBure by Northmore' in 1806. Faniday investigated the 
subject fully shortly oftcncarda' Mhowing that many other gases 
Bitch as Biilphurous ncid, carbonii,' acid, ciichlorinc, nitrous oxide, 
cyaDAgen, ammonia, and hydrochloric acid gaaca can al^o be 
rudur«d to tlie liquid state. In these experimeBts Faraday em* 
jiloyeil bent tiilies made of strong kIi^^ ui the onu Unib uf wliicb, 
l«in]; closed at the end, materials were placed which ou being 
lieatcd wilt yield the gus; the open limli of the tube was then 
ltemieti{<ally sealed and the gas evolved by lieatJuj; the other 
end. The pressure or tension exerted by the ^as itself, when 
thus geDeTat«d in a closed space is suDicient to nmdenxe a pop* 
tioR into the liquid 8tat«. The following table ahows the 
nuixiniuni tensions of some of these lique&ahle gases at 0*: — 

Sulphurous acid 
Cyanogon . . 
Uydriodio ncid 
Ammonia. . . 
Chlorine . . 

Atmoaq>lion« Alntai|ili«m. 

IbH Sul])huretted hydrogen 1 U UU 

237 Hydrochloric acid . 26-20 

357 NiLrous acid ... 3200 

4-40 Carbon dioxide . . . 33'^ 

> NonkmoK^ b'iAOaM'* Jimntat. xU. MS : xUL SSI 
* Aii. 7V«w. 1623. p. 1«. /Ud,ie23.p.18». 



ir, therefon^ any of tUo above gases at 0° le expoeed to pn>3> 
fiun-3 fixueudiug tlioso givuti Id the taUo they will condeoee 
U> liquids. 

The liciuofaction of gases can 'he brought about not ooly by 
esposiire lo liigb |»i-easun: but aJsu to low h-mivcraturc ; ' llius, 
if we reduce the tompeiamre of eulphurous acid gas, uuder tint 
ordinary HtnioHphttric pTenmire, to— lU" it liquefies and tvhen 
Uie temperature eiiiks to - 70", tlie liquid freezes to an ice-liliv 
tatua. The fuUowin^ i» a list of tlic giiAi^ (1) whidi huve uot 
yet been coudciised to liquids, (2) wliicb liava been liquefied, and 
(3) wldch have been both liquefied aud solidified :— 

m (2) 


t^RTAtliicML Ltijueflcd. 

I.iqiuDr.Ll atid Soli>lifi«L 

I^lydiogea Cliloriue 

ilydrobroiuic acid 

Oxygen Hydtocliloric acid 

Jlydriodic acid 

Nitrogen Hydroflttoric Hcid 

Sulphun'lted hydrogen 

Nitric oxide Silicon iftrafiuoride 

f^ulphur dioxide 

Cirboiiic oxide I'liosphuruttcd Iiydrogpn 

Nitrous oxide 

Mariib gas Arseiiiurnlted liy()n)^uii 



C'arbouic acid 


32 i\iiother »iiup1e numerical law whitjb cburoclcmes tlto 
gaseous condition is known as tlie law of Charles, ofUin called 
tlie law of G«y-I,usRnc (IS02) or of Dalton (l«(Jl), but first 
experiuieuUdly di-iaoiistratvd by Charles. This states tliat aU 
gase« incfuurfd undor constant pTOssure, txpnud equally for c<iiui] 
iucremenu of litat, one voluino at 0° becoming i"3665 at 100* 
so tliat the coetlicient of pxpiui^ion of gaiics is 0'003G6S or neatly 
yls for an increase fion] 0* to 1" Cpnligrade Thti same law of 
wjualily iji expansion 1ms bppn found to hold good for all other 
tUQipcralures under which it baa bveu exuniinud. The lavs affect- 
ing the gasuousstate as regards pressure and beat are diatinguishMl 
by their siuipHcily and unifonnity from those governing the solid 
and liquid forms of matter. For iu the case of eolids and 
liquids the nction on the volume of pressure as well as Uiat 
of heat is rlilTer«^nt in «v6ry Kubstaiure, wliil&t gases ars all 
unifonnly afl'ected. Hence we are led to conclude that the 
;'aseou8 fonn of matter is that in which the constitution is 

> Fanday, Phil Ttwu., JSiS, p. ICS, 



iDDSt simple, an^ thus result is bome out by many other 

It is evident &ora vrliat has bvoii suid that tliv (listinotioti 
between gas tnd vapour is only une of de^n>e, fur a vapour is 
simply au easily condeiuabla j^as. The same laws wliich 
regulste the volume of gas«A uiidcr cluingn of toiuporntum 
and pressure apply Ut vapours, at any rate when they sra 
examined at tunipuTaturea (.oasidcrahly ahovo their points (tf 
conden.tatiun. When a gaA or vapour is near Uiia point ita 
density iucrvanes mote quickly than the pressure, and m Hoon 
B8 tliis point U rcachud the least iocroase of the preesure brings 
about a condenaation of t1>« whole to & liquid. The tempera- 
ture at which the liquid ai;aiD assuiues the ^'aseous fonn is 
Utrmeil tlic hinling-point of the liijiiid, uud at tlua tvinpcratuD 
the temioA of Ou vapour is egaal to Ike svpcrincurabeitt prta- 
sune. The fuUouin); table gives tlie hoilJng>pnint of some 
well kiiowo bodies under a preaanie of 760 mm. of mercury: — 

roUf ^ Doainj-PoiHti. 

Nitrous oxide 


Acetic aid . . 

I IS'' 

Catbojiic acid . . 


Pivpionic acid . 


p}'anOigoa . . . 


Butyric acid . . 


SulphurouR acid 


rheuol .... 


Ethyl chloride . 

+ l2*-5 

.Ajuline . . . 


Prussic acid . . 


Xnpllialene . . 


Kther .... 


Phosphorus . . 


Oubon distil phido 

. 4r-3 

Sulphuric auid . 


Chlocoforiu . . 


Mercury . . . 


Bromino . . . 


Sulphur . . , 


Alcohol . . . 


Cadmium . . 


Benzene . . . 

. 87' 

Zinc .... 


Wattr .... 


Liquids poeeces a notable tension below llieii boiliuj^-poiots ; 
thus water gives off vajmur at all tempemturfct, and even slowly 
evspcirates wljen in the solid slate, for tlie tension of the vapour 
coming irom ice at — 10° ia 0208 mm. AMording to tlie expen- 
nients of Faraday, there is. however, a limit to evaporution ; 
tlins he fonnd that mi-rcury which (jives out a jwrneptible 
amount of vapour during the euinmor emita none in the winter; 
aDd that certain compounds which con bo volatilised at 150* 


undergo do cTaporatioii wlma kept for years at. tbe onJinarj 
t^mpvratuiT. Tin- tcii^iou of tliv vnpour uF ii liijuitl is cuuslaot 
for a given temperntun?, and tbis amount whicli is always 
reached when an excess of the liiitiid is present ia termed the 
maxiuium teusiun vt' tliu valour. Dultt^u* iu 1801 discovci'ed 
tliat tliis umxinium tension or dfuaity of a vapour is not aUenn) 
by the presence or other gases, or, in otlier words, Lliat the 
quimUty of « liquid wUich will evajjomte iato a given e[)«oe is 
^e same wl)«tb«r tbe spac? is a vftcimm or is 6Ued with 
another giLs. T}ie same pliiluiWpbBr also l>eliev(!d tliat the 
vapoure of all liquids possessed an et|tial ten^itm at tenipera- 
taiv» equally tlisUuit front their buiJin^-iiointa. liet^nault* 
has, however, shown by exact expcrioieats that the above 
cooclusioDs ciui only be considurod aa approximately IruL-, imis- 
much as he found that about 2 per oenL more raponr asceitds 
into a spftce tilled with gas than into a vacuum, whilst at 
Considcmblu Iml equal distances from the hoiliiiy-point tlie 
t^mions of volatile liq^uids are by no niuans ci[uai. 

The CoxTiNumr of* the Gaseous ANn Liquid States of 


23 It is matter of everyday experience that the tfinsion of 
the vapour of waU>-r aiul of otlier lii^tiids hwitwd with excess 
of llio liquid in closed vessels, increiisws in a verj* nipiil ratio 
with lucruosc of tumpcntture, and that the diiosily of the steam 
or vapoar in such a ca&c undergoca a similar nipid itici'caee 
Thus at 2;ir the weight of a cubic metre of steam is ^j part of 
tbe "wcij^lit of the same bulk of water »t the pulut of maximum 
density of 4°. the weight of sloum at 100°, b«ing only xtW of the 
same bulk of water, so that at a ti-inpentture not very far above 
2^0" the wi-i^ht of the vapour will become equal to that of the 
liquid. Tho result of this muet I>q that iinder these circuta« 
Stances a change from the giucoiis to tho liquid state is oot 
accompanied by any condensation, and i[i such u case the 
distinctions wc have been in the habit of drawing between these 
conditiouB of matter wiise to have any meimiiig. So long ago as 
1822, Cugiiiard do la Tour^ made experiments upon tiie action of 

■ JfnivA. iftmoirt, in B(irieB,rol. v. p. SSS. 
* UfmiriTfa 4c TAtad. df* Sciinr^ xxi, 46S. 

■ ^•1. 6'Aim J%j., (2j ixL lit?, xxii. <ia 



liq^iiitls senlcd up ill [jlatw tulies of ti capacity Iml little gre&tiT tlinii 
that of the liquid '\VIicd a tube one-fourth tilled witli water 
was liititcd up to ulniut ^60" the wul^r uiiliroly (li«Ji}>]icureil, 
the tube appearing empty, aud as tlie vapour cooled a point was 
rtaclieil at which a kimi of cloud mnde its appearance, aod in a 
r«w moments afU-rwants tho liquid was again visible. Cagtiiard 
de la Tonp considered tliat the substance when thus heated 
assnmes the gnscous condition; but I>r Audrcn's' has shown 
tltnt in such an exfKTiiiiuiit the propcrtii^s of the Itc|uid and 
tliose of tho vapour constantly approach one another, so that 
above u given U-mpi-raliirc the propertip.'; of the two states 
caonot be distin^piishvd. Hcnvc it follows tlint at nil tem- 
pomtun>8 above tJiin particular one, no incrcaae of prc-^iirc can 
bring about the cliapye by coiidciistttion which we term lique- 
Eaction. This teuiperalnre la called by Andrews the crilleai 
point. In the case of the so-callod permanent gases siidj as 
oxyt^n. nitrogen, &c. the critical temperature is supposed to lie 
below — 166", the lowi'St. tompemturc whiL-h has jcl buen obtained, 
and consequently although tliese gafles have been redncod to 
1(33 than xJ» of their ordinary volume by pressure at tbis low 
temperature, Ihey have never been obtained in tlie liquid 
form. In tbc case, however, of condensable gases the crilitsil 
points BTC sitanted at practicable tetnpcretiires ; thus, for 
e^cainple, the critical Ipniperntinx! for uarbon dioxide (or cui^ 
bonic acid ga;^) ia 30''-l)2. and at all tfimpcratur&j above Ihia 
point no condensation rmm gas to liquid occunt; so that if the 
pressure on the gas be gradually increased up to 150 atmo- 
spheres a steady diminntion of volnnie occurs as the ]irc<<iiure 
■agnjents and no sudden diminution of volume will occur in 
nriy rtnge cif it, Tlie ti;mpi.'mture iimy tbi-ii bo gradtiiilly 
allowed to rail until the carbon dioxide has rt'acbcd the ordi- 
nary t^mpemtnre of the air when it is found to bti a liquid; 
thus br^niiing with a gns and by n series of gradual cluingcfl, 
presenting nowhere any abrupt altemtion of volume or sudden 
evolution of heat, it cads by being an undoubted liquid. This 
clearly shows that the pi-oportics of a gii« may be contimmlljr 
and imperceptibly cli£in|,i.>d into those of a liquid. 

I Fhii TfMLt.. nea. I'm 2. p. 575. 

> AndtcwH, £nL jtuae. Jlfp»rU. 1861. 


34 Tliviloctrinc UuitlicatisDiily a kind of mobiuD ieone which 
is DOW genetuUy udmitlcd, bo tliat altoi liudy may be 1%'artled. as 
posaessiiig a store of euergj-. some portiou of wliicli at any mte 
may bo niitJe use of to accoinplisli actual work. The eneigy of 
motion iii tflpmod Kiiielic (from Klyiai, I move), and tJiis cneigy 
ia comnjiinicated when the body po!*seesing it comes to rest by 
contact with some other bwly. Tlie other fyrin of rjiicigy 
depending on position witli i-cspect to other bodies and not 
iipcin the condition of matter is termed I'otontial pneTgy. It 
ha^i been shown that in a liol hody a very cnn.sidcra1>U portion 
uf the (inergy tiriscis frnm a motion of the parls of the body; so 
that^ every hot body is in motion, but this motion is not one 
affecting tlie motion uf the mass as a wholu but only tkut of the 
tnolcculos or email portions of the body. Tlieae molecules may 
consist of a collection or syuteni of &mall(;r parts or atoms 
which partake as a whole of this general motion of the molecule- 
Tln; subject of the motion of the smallest particles of matter 
attracted the atleuUoii of tlio ancients, and Lucretius held tliat 
the diflcrent properties of matter depended upon auch u motion. 
Daniel BeruuulU was the first to conceive the idea that the prcs* 
»ura of the air could be expltiiued by the impact of its par- 
tides on th<> walU of the containing vessel, wliiUt in tho ycor 
lft48, Joulo ' showed that these views were correct, and cal- 
culated tJie moan velocity -which the molecules must possess 
in order to brin^j about the observed pressure. Since the 
above date, Ciausius, Ma.TwelI, and other pbysicisls have 
extoodcd and completed the dynamical theory of gaaest 
Many of the phenomenn observed in gases and also in liquidii, 
especially diffusion, prove tkut the large number of amali 
particles, or molecules of which, these forms of matter are 
made up nre in a cunslaiit condition of change or ugitation, 
and the hotter a body is, the gtHftter is tho amount of this 
agitation. According to the kinetic tbeorv. these molecules 
are supposed to move with preat velocity nmongst one another, 
and, when not otherwise acted on by exlorual foi-ees, the direc- 
tion of this motion is a rectilinear one, and the velocity uniform. 
The molecules, however, come into frequent contact with one 
■□other, or as Jlilaxweil descnbes it, cncountei's between tvo 

> Brit. Amt. RferU, 18IS, Snd hurl, p. St. 


muleciilcs occur. Id th«se mcounlers, and aim vrhea the molecules 
strike tLe suifEiCti of thu coDUuiiin<j rBseel, ao loss of enet^gy 
takea place, provided of course that everything ia at the same 
tempenituro. so that the total enct;^ of the iiic1i»p(l system 
rvriiBiua unalU'rcd. Trom tlipse priuciples the uxpvrimoutal 
gnseoas lawt; proviotisly fi)lu<tvii to, as well as otiieis, can he 
thooreticnily dLtlucML Thus iii the Bn;t plauu the law eiiuiiciatcd 
by Ufty-I.u&9ac, viz. tliat the densities of gtises are prnportionnl 
Ic their iHolvcular weights is exprv^ssed Iiy saying that *heii tw« 
gKSea are at the same temperature and pioeijura tbo number of 
molecules in tho unit volume is thfl same in both gasea. Ilie 
Uw of tlie equal dilatation of ganea, the law of pressures, as 
frcU as the Iiitws of gaseous diffusion and eHiLsion can in like 
manner be deduced from the Kinetic tht^ury. Tbis subject will 
again be referred to in the cbapteis on Tlieoretic Chemistry. 


35 Early in the history of gaseous chemistry it was observed 
that when gases of ilifTrrcnt sixrcific gravities, wliich exert no 
mutual chemical action, are once thoroii;i;b1y mixed, they do not 
of themselves scpatate in the order of their several dcnaitira 
by long standing. On thi: contrary, they remuin uniformly 
distributed throughout thu ruasa, Priestley' proved this 
by very satisfactory experiments ; but he believed that if the 
differtnt ga^es wens very carefully brought together, the heavier 
one bctii}' placed beoeath and the lighter cue bciiit; brought 011 to 
tlte top without being mixed with the other, they would then, on 
being allowed to stand, not mix, hut continun separate one alM)ve 
tbc other. iJaUoii,' iu lUfJ'-i proceet'ed to iavesUgate this point 
and be came to the coucluaon that a lighter gas cannot rest 
upon a heavier, as oil upon water, hut tlmt the particles of the 
tVD gases are ooDstautly diffusing themselves through each othc-r 
, nntil an equilibrium is reached, and tbis witbotit any regard 
to their specific gravities. Tliia conclusion Dnlton regarded 
as a oeocssary consequence of his theory of tbo constitu- 
lion of matter, according to which the particles of all gaseous 
bodies exert a repulsive inlluence on each ntht^r, and each 
goa expands into the apace occupied by the otber as it woidd 
into a vacuum. In fact, however, it does not so expand, for 
the ratio at vrbich a gas dilfuses into anoiber gas is many 

* CittnaKau <n Air, vol. iL ji. Ill, 
■ J/imcA. Meirwin, UIM. p. •£&». 

thoumud times slower th&u tbat at which it rashes into a 
vncuuiii^ As was usual with )iun tlte appamtus used t^ Dallon 
in tlieae experimpnta was of tlie Bimplest kind. It consisted 
of a few p}iiids And tubes with peifoml'.'d eniks. "The tuh« 
mostly ufi»d was oue 10 inches long uud of ^V >"c^ bore ; in 
ftome cases a tube of 80 inches in length and J inch bore were 
u$ed ; Ui« phials held the gases which were ihu &iibji-cl of ex- 
periment and the twhe fornifd the connection. In all cas^ tlie 
hoavibr <:aa was in tlie lowur i^hiul mid the two were placed in 
a peipeiidicular position, tiiid sulTorod to remain ro during thu 
experinipTit in a stats cjf rest ; llms circumstanced it is evident 
that the effuct of agitation was eiifficiently guarded against ; for 
a tuhi; almost cnpillnry and 10 iiichoit long, could not be instru- 
menlal in propagatinj" an interniixtura from a momentary com- 
motioD at the comiiii'iicuincat of onch experiment." Tlw gases 
experimented on were atmospheric air, oxygen, Iiydrogtn, nitro- 
gen, nitrous oxidi? and carhonic aiiid ; and after the gasee had 
remained in contact for a certain len^tli of time the compositiou 
of tliat contaiuLnJ in each phial Wiis determined, anil invariably 
Bhowed that a passage of the hcavinr gas upwanis and the lighter 
gas downwarils, had occm-rcd. Similar expcriuicnlol results 
were nltio obtained by Berthollet in IROO.* 

The passagp of gase-s through fine pores was likewise ubsenrod 
by Priesllcy'iuthecoseof miglazed eai-tlmuwnre retorts which 
although perfectly air-tight so as not to allow of any ei^capo by 
blowing in, allowi^d the vapour of water to pass out whilst air 
eanic iu, even where the gas in the retort waa under u gn^iter 
pressure than that outside. Italton was tlie lirat to explain this 
fact '.la bL'iug due lo precisely the same cause «s that which brings 
about the cxchimgu of gases in the phials conutctcd with the 
long tubes, only that here wo have a laige number of small pores 
instead of one (the Itiire of tnlw) of sensible magnitude- 
la the year 18-*i Uobereiner'* made the remarkable obscivalioQ 
that hydrogen gas colleuted over water in a large flask whids 
happt-ned to have a fine crack in the glass, escaped through the 
crack into the air, whilst the level of the water rose in the ftask 
to a height of nearly throe inches above its tuvol in the trough. 
Air placed in the same flask did not produce a similar erfect, nor 
was this riae of the water observed with the flask full of hydro- 
gen when it was surrounded wilti a bell-jar lilled with the same gea. 

' nil, Aftv- 4. so, <')9. 

' ObKTtatUmr, dr., vul. iL p. 414. 

* .^lui. (Aim. ns*- 18J3, xxiv. 93:1. 


^ Ai in the former instance, tie discoverer of Ihu fuct was 
ntuiblc toexpUiu t}iei>1]«Dvai«iiu[t, and it was not imlil l§32 Ihat 
Tbonua Graham ' in repeatiog Doboreiner'n experimeiiU showed 
ttut no h}-dni}{Cn cuuIU escape by the cnick without some air 
cotniDg in, and enuDciated the lav of gaseous difTasion founded 
on the results of his «]qx!riuientfl,Tiz., tJiat the rat« at whiob guea 
diffuse is not the same fur all gases but that their rdative rates 
of dijiision are iuvertely prvpoHumal to (he square root$ of iJicir 
tUnsitiet, so tliat hydrogen and oxygen having the relation of their 
densities as 1 to IC the relative rates of diffu&ion are as 4 to 1. 

lostead of uulng cmvltod vessels Grtkhani employed a difution 
tuin consisting of a glass tub? open at eacli end and about .six to 
fourteeD inches in lengUi and ludf an inch in diameter ; a wooden 
(^lindvr is intrcxluced into the tube so ns to fill it with the exception 
of half an inch at one end, and this unoccupied space is filled with 
a plag of plaster of Paris; the cylinder being witbdrawn after 
the paste of plaster has set. With such a tube divided Into 
Tolmnes of cnpacity, filled with gas and placed ovor water, the 
rate of tlie rise or depression of the water, could be easily 
observ'ed and the composition of the gas both before and 
nflT the experiment ascertained. In this way the relative 
diffiisibiiity of various gases was deteiinined, the results 
of Graham's experiments being shown in tlie following tabic. 

DiFFUSiOK OP Gases. 


Oydrogpn .... 
Mulsh gus .... 


Carbonic oxide. . . 



Nitrio oxide .... 


Sufphnrettcd hydrogen 
Nitrous oxide . . . 
Carbon dioxide. . . 
Sulphurous acid , . 







11 056 






root of -T-i — ;-- 

Velociilj of 

of air = 1. 



1 -2:105 




1 0143 



> £JiH. Hil. Trant. aii 183(, S3S. nO. Hag. 183S, U. 175- 

The observed veloeilieB f>f diffiiejon agree very closely witlt] 
those oblained by cakuintiun. This is, liowever. only the caw] 
when the poroaa plate tltrough wliich tlte iliiTusioii ttilces place - 
in very tliin. Jf tho plates bo thick the gostte have to pass 
throiif;h a acrit^a of capJIIury lulies. and the rate of difliisioti is 
considerably diminished by tlie friction. 

The passage of the gases through capilkTy tnbcs has he«it 
krnied transpiration of gases, aud tliia a yovcrued by other laws 
thao tlio»6 of difTiiiuoi], as iii Irouspiratioa we Imve to do with a 
motion of the mnaa of the gas, whereas in ditfuhion the motion i«l 
parcly mflUTular. Thus when allowed to pass through capillaryj 
tubes the rate of transpiration ofeqti&l volm»03 of th« fultuwiugj 
guua was found by Grahaiii to bo represented by the numbers :- 

Osysen .... 100 
1 1 j'd royuii. . . . 0-44 
Cai'huii dioxide . . 0'T2 

Kumbers which bear do lelaUon to the sq^uare root4 of tfa< 
densities of the gassa. 

Of all suljstauces. that which fa beat adapted for exJiibiiinti the 
laws uf dill'ii.'tiuii lA a thiti phite of ai-tificiul grBplul-e. Wiilt a 
poraufl pUte of ;^phito 0'5 mtn. in thickness Ordtant* obtained 
the followin;;: ttmus of difTuaiou into air under a pressure o( 
100 mm. of mercury. 

Time of moltcuW iltjnara root of 
IHUMi^ •Icinity = 1. 

Hydrogea .... 0-2472 . . . l)L'ii(l2 

Oxj-geii 10000 . . . 1(HW0 

Carbon dioxide . . 1-188C . . . 11760 

When tlio sanic f^m were allowed to difTusG into a vumui 

the following wvcc the ttsulcs ; — 

Hydrogen . . 
Air ... . 
Oxygen . . . 
Carbon dioxide 

Time et iiial«iniUr 

0-2>'>()5 . 

Oii.'.Ol . 

1-0000 . 

MStiO . 

di'iuity = 1. 
. 02502 
. 0^9507 
. 1-0000 
. 11760 

Hence it appeam that a plate of artilicial grapbit« is practically _ 
iRipcrnK^nble to gas by tiaii»pim1inii liitt is njudily penetrated by 
gsses when in molecular or dill'ufiive movement, whether theyaaea, 

1 PklJ. Trant. Itei, f. VPS. 



under preseure into air or into a vdouiiui, and tliia stj\i- 

ICC, therefore, serves as. a kiml of " ptittiiuHtio sieve " which 

enaits th« posat^ of the molecales l^ut not the maaaes of Clic 

■7 The phenomena or (tilTusion can be strikint'ly deinonstrateU 

\ty ilw foUwwJDg expcriiBcnls : — 

1 FiriJ. To oue end of a glass tiiV.e ahoiit 1 raeire in length and 
fl a m. in dJanieter,[i;> a bulb blowa on to it. a cyliudiical 

porous cell (such as those used „, 

fur i^l^-aiiic batteries) is lixed 
■ by iu«aii8 of a caoutchouc 

cork. Tlie otlier end uftliu 

tube is dran'O oiit to a tine 

point oihI bent round rs sliown 

in Fig. 11. If now a vc&sel 

filled with hydrogen lie held 

ov«r the porous jnr this gns 
I will tsntcr iu more (juickly 
' tlina ihe air cnn issuv, viz. 

in the proiiortion of the 

inveise square rootaof their 

densities or as ^144 to 1. 

or as 38 voluioea to ono 
I volume, sn tliat the preasnre 

iu Oic jiorous cell will in- 
crease and tbo coloured waltT 

plac«cl in the bulb Mill be 

driven out in tlie form of a 

fountain through the niinow 


A aerond experiment ahow- 
ling tl>e mode in which one 

gaa may be separated from 

anolhcr by diffusion (termed 

almdyiis fVom otmo? vapour 

anil Xi>itf I looaen) is rhc 

folloH'iug. A slow current of 

tlic detonating i^aa obtained 

by llie clectmlysia of water, 

and consisting of 2 volumos of hydrogen to 1 volume 

of oxygen, is allowed to pas* through a common long clay 

tobacco-pipe, ttic gus on isf»uing from the pipe being collected 


PlO. 11. 



over weXcT io a piieuniatic troiigti. Oa briugiiig ttie gtts, tbits 
collected, in contact with & Home it no longer detonaUs. 
On tlie contrary, it will mkindlu a glowing chip of vood; thua 
sTiowing that in its possngo thvowyh the porous pipe the grettei 
portion of the tighter hydro{;en haa escaped by diffusion through 
the por«8 of the clay, whilst the heavier oxygen has not passed 

A t/iird experiment to illustrate the law of diffusion is one 
which possesses iuteriMt from another point of view, inasmach 
ss it hiis Itiiun propost'd to ei[ij)Ioy tlie acrangomcnt for giving 
warning of the outbreak of the dau^>eTou3 and explosivo 

gas ternieil fire-damp by the coal-miners. Fire-damp or 
marsh gas is lighter than air, and i:J4 volumes of this 
gns will diffuse through a poious iiiodiiini in the same time 
as 100 volumes of air will do. Ueuce if a quantity of 
fire-damp surround tliu porous plat*, the volunie within the 
vessel will become larger, and this increase of ■volume may be 
made available uitlier to diive out water as io the Brst expeii- 
meot or to alter the level of a column of mercury bo as to 
in.i1fe contttot with a ctiQDPctcd battery and then to ruig a 
warning belL Tlie latter forna of apparattis ia seen in fig. I'i. 






Hnlding a tieaker-glass (a) fillpd with liydrogen or common 
ooat-gas over the plate of porous atucco fft3t«neil into tlio tubn- 
fonnel an increase of volume occurs inside the glass tube Aii'l 
a cdiisecineut depression of tlie mercury Uikcs place in tlie bend of 
tfao tube wIiicL is suilicient to make metallic contact with n 
tH?coud pliitinum win fuaod ltiiY>iit^li tlie <;la.s& nud to bring the 
current to act ou the msgiiet of tba ekctric-bell (b). Tlie other 
tube ia arraugcd for showing that a dense gas, such as 
carbonic ncid, doe» not difTii^c tlirun^ti tlic porous septum bo 
quickly as uir escapes. My inimerKiuy th« porous plate in a 
jar (c) filled with the hcuvy gas, tliu volumu iniiide the tube 
becomes less, tlie level of tbd mercaty in ttie bend in HltoTcd, 
contact is again made with the battery, and the riDging of Ibo 
bdl gives noUoe of the chaoge. 

28 £ffiuii»t of Gattit ia the na>ne given by Ontliitm to Ibu flow 
of gases ander prossuno tJinJush a miiiuio aperture in a iiiL'tnlIic 
plntu. Ttio law whicli regulates dilftisiou is found to liold 
good with ivgunl to thia moltjcnlar motloD of gases, tiie times 
required for cqiuil volumes of diflcrent gnses to flow through 
an apertuie of a diameter of ^ js of on incb having been found 
to b« very nearly proportional to the sc^uare roots of their 
d^ufiitie^. and the veludty uf How being invenicly as the square 
rooi« of their deDsil)e8. 

Tilts 111 M' which Es trtia for the flow of nil fluids through a 
Binallopertui'e in a thia plate has been applied by Buusen > 
for UiG purpose of determinii^ the specific gravity of gaaes, 
tlie method serving admirably when only small quantities of 
the gss cm be obtainod. 

Chemical Xomesclaiukk. 

29 Nomenclature is the flpoken language of clieinisti^, as nota- 
tion is the symbolic written ian-magc of the science. With tlte 
prtv^tre-is uf discw«ry, cheuiicul nwioiickture has naturally 
undcisono great and frequent changes. The ancients were 
acquaiuli'd witli only seven metals, viz. : — gohl, silver, copper. 
tin, iron, lead, and mercury. Of these the first six are inen- 
tiooed by Homer; mercury was not known in his timo, but 
mention ia made of the liquid metal by auUioi-s living one cen- 
tury before Chn«t. These seven nii-tuls wcro oris^iiially supposed 
to T>e in some way connected with the seven heavenly bodies 
llicu known to btlung to our system. Tu bright yellow gold 

* OMmKtrn, p. isi. 

the nntiie of Sol vim given ; whilst whit« silver was tiinnml 
iuna ; copper, which Iiiwl chiefly been obtniiiod frwiu tbu 
ialand of Cypnis and received its oouimon uaint* (cupnuii) 
from this source, was likewise called Veniis, after Ibe pro- 
tectress of the islantl. Tin wiis specially dedicated to 
Jupiter : Iroo lo Mars, tlie god of war ; whilst heavy, dull 
lead wiis couuoctctt with SaCurrt, uud the inabile quioksilvor 
wascniled Merruri/, after the active uiussengerofUic god& Tha 
ulclieniists not only invariiihly iise<l these iiames, but cinploycd 
the signa of the heavenly bodies as symbols for the metals, aitd 
maiiy teinitants of tliis jiruutice are found to this dny in nil 
laii;juii};es Thus we atUl speak of " hiuar-caustic " for silver 
iiiirato,''a&tuTiiiuc poidouiug" for poisoning by lead, wUilat tbo 
name mercury has become the common one of tlic inutol. To 
come to luter times, we lind that the laiigua<;e of the alclie. 
uiets was always Htid desiguedly obscure and enigmatical, 
so that their nume3 for cliemical conipounda were uot buiUMl 
on any principle but even cliosea for the sake of secrecy or 
decepiion, and, tUcrcfoix;, bore no rclution to the subetunces 
tlieiiistdves. From thaie fanciful terms the progress to a better 
state of things has lx?eii slow, and the changes which the itnmes 
have uudergoue have bceu aumerous, whilst the same 9uh«Uiuc6 
has at one time frei|uci>tly boeti designated by many distinct 
names, sevenil of which are atill in use. 

l)o<lies were generally DiimtxL and classed by the alchemists 
by viiluc of cerUiiu real or fancied reaemhiances existiug 
between their physical properties. Thus, bodies whicli can be 
oblaincd by distillation ami arc, therefore, eiwily voUitile, were 
all termed ipiritu, so that alcohol (spirits of wiue) was classed 
to<;ether with hydrochloric acid (spirits of salt), and these agaia 
with epii'its of turpentine, aUboiigb these three substaucea are 
ch(>mi(.-ully As ditTurent as any three substances wvll ciku bu. 
In the aame way, all viscid, thick liquids were termed oih. and 
th\is Gidphuric acid, or oil of vitxcl, came to be placed iu the 
same class as olive oil ; whilst eemi-solid bodies, such as anti- 
mony trichloride were temieil lutUrs, and considered to ba 
analogous to common butter. 

As soon as chemistry became n science, the Domenclaturei'j 
assumed a more scientific character. Some of the teruia whiuh i 
came into uBe during the growth of iho scionce have been 
mentioned in the Historical Introduction. These terms have 
by d^rees been much changed, and, sach revo!iuiou» have 


fiCCompATiied tbe progrose of tlic science, tliat at present tlift sama 
roin{Kiund i& ni>t iti)fnf[)ueutly cWi^iiatE>ii by ditrt>r(9Dt Dame& 
Thns it is clear tliat our nomenclature has not yet attained a 
]ienuanentfonu,lhetiiui]o-4of(;Wniicnl suhstftnccsarenotiilonticnl 
in difliereot languages, aud, even in the sauw lan;rufi);e, diU'erence 
of pmvticc iu uaming ootnpouiuls is fvuod among clwnii^ts. 
Nevi-rthcltfss, wc aic guided by certain specific rules, and the 
stricnc: no louj^r auffera Crum the arbitmrv notnenuUture whicti 
tbe descriptiv« natural sciences liiive to endure. 

30 TliC foundation of tlie modern ftj-stvin of chctuiad names 
was laid by lavoisier and bis colleague!*,' and tlic plan propoiwl 
by them has IxKin uiuintaiut^, with slight muditicalioiis, 
up to tlie present time. Tlie principle npon wliich mir ^-ittem 
(for Inorganic Chemistiy nt host) is founded is. thiU: every 
compound being made up of two or mora elementary liudiiii 
united in different proportions, the name of that compound 
shall signify Use nnlun: of its elemcnlar>- constitiicnts, and as 
ntsrly as possible tbe relative proportionti in which they are 
b^eved to be present. In tlie caso of the Curbon compounds 
(Orgajiic Cliemistry) it waa soon found inipoasible. from tlie 
largo number of clowly nlliud substances, unifornily to apply 
this system, and names sugyested by the oiigin of the bodies 
have been in many cases ailepted. 

Is'o special rule liao been applied to the nomenclnture of tlie 
cU-nientA. Tbe obi common names of Uioso which have long 
been known, have ir. most cases been retained, and when new 
elements hove bwn discovered tbcy have been named according 
to no pre-arranged plan. Some are named from the locality in 
which they liave firat been found ; some from a charactoristio 
property or from the mode of tlieir discover}', hy coumion 
consent ibo names of all recently discoveit'il mctiils end in 
"-itm," as sodium, barium, Taoadium. The names of a gioup 
of allied non-melidlic elements end in " -jW," thus we have 
cihlorine, bromine, iodine, and fluorine ; those of anotber group 
of sonievrhat analogous non-metallic elements end in "-oti," 
OS Inron, CAil>on, silicon, whilst those of two iitliur non-metals, 
more nearly losc-mbliug the mc-tals, end like the latter in 
■ -ivm," Uiiu we have aelenium and tellurium. 
LaT<HHer introduced the teem " axyde " to signify the combina- 

' jmrAarf*<f4.V'nn«HWa<Mrcriki'nig'iifl prmiiD*^ jmf MM. i!>' Mnrrrau. I^voiiltr, 
RcrDiallvl, vt <lv I'linmof . I'urii. I'm. Tnuijlatnl iuio KnytinU Iijr Psataeo. 



The twDipfflind* of 






















tione o( oxy^a vith the other elemeats, and words with the 
flame ending Imve beou Kime employed to deuote the simple 
oombiuatious of two clemcuis or groupa of elemeats, thus : — 


PhiwpboniB h^-dridce. 
Sodium chIorid& 
MBgnesium chloride. 
Lcftd iodide. 
Calcium fluoride. 
Mercury oxido. 
Zinc sulphide. 
Potassium selaoide. 
Calcium phosphide. 

31 Jt not uiifreiuently happens that a metal foims seveml 
distinct oxitlcs or chlorides, in M'liich the constitueata aie pnuent 
in MuiplL' multiple proportigtis uf their combining weighte. In 
tbeso ca«ea it is tuual to give to each compound a uanie indi- 
eating either the nunihcr of atoms of oxygen which we tKiUovo 
to te comWiied with one atom of motftl. or the simplest telntion 
which we ^npiiose it possible to exist between the uuinlier 
of atoms of metal end oxygeu in the molecule: thus the oxido 
btilifvud to conUiiu ono atom of oxyyi'ii is lemied the monoxide : 
ttiatcotitaiiiitigtwoatomshi the dioxide: wliilst oxides containint; 
three, four, or five at«ms of oxyata, aro called trioxidce. t«tTOx- 
and penfoxidea I'espectivi^ly. Sometimes Ihe fir»l oxide is termed 
the protoxide (wparo^, first), the second deutoxide (teineptK, 
second), the (hiid trio.\ide (Tpiro<t, thinl), &c 

W'hi'u the rclntion of iu«tal to oxygen is that of 2 to 3, as 
in red tiiemalite, Ke^O,. the Ljitin pre^x tesfui, moatda^ one and 
a haUfia used, and the oxide is termed a aesquioxida Tim 
same mode of dt'sif^naliou applies to the compounds of metal 
with sulphur, chlorine, &c. : thus we speuk of iron sesqui- 
sulpliide, or, if we please, eesquisulijliide of iron, Fo,S,. of 
antiujony trichloride, or, if we prefer it, the tricldoride of 
antimony, SbCl,. 

In the ciwe of metals, such as iron and mereuiy for iti8tAiiC6,>l 
which form two distinct eeriea of cunipouiids, one corrospondinff^ 
to a lower oxide, and another to a hiyher one, it is customary to 
«9C the ending!* •' -omj " and " -te " to denote the difTerrnce betwocu 
the two sets of compounds. Thua we buve the tuercurou*] 




and the mcnrurtr salts. Amongst others, niercuri»i« oxide, H^O, 
iDorcunww chloride. Hj^Cl, (commonlj- called calomel), iner^ 
curctM uitratc, Hgj(N05)(; aDd, oo the other liuiid, nicrcune 
oxide, HgO, tnorcurie chloiidc. HgClj (oommonly called cor- 
rosive suUinwteX niercurie nitrate, Hg(NOj)^ In tlie same 
'way wo liavo tlie ferroiu salts (from /crmm., inn) conocctcd with 
terrota oxide, F«iO fnlso termed the monoxide), «nd tLc ferric 
ialta connected with ferrjc oxide. Pe,0^ 

Tlie advoDtdges of the use of the cndiogs -ov^ and -ie 
in discrimioatiiig bctnton compounds of the ttame clfnients 
have heen so well I'ccognised tliat tliey nrc applied aot only iu 
the c«se of oxides and chlorides but ul»o iu that of ucids. 
Ttius sulphiir«iu acid, M,SO,.coutAias has oxygon tiian sulphuric 
acid, HjSO^; nitnww acid, HNOj,]eBs than nitric acid. UNO,; 
and canning this distiactioa still further, the names of ttUs of 
acida ending in -om tenuinate in --iU, wliilitt tlioye derived fitim 
acida in -ic end in -aie ; thus for example — 

Nittiwa acid forms salts tcniiod mttiUA. 
SuIphuro«i! ai'id „ „ stdphife*. 
KitriV acid „ „ aitrales. 

Sulpbtim acid ,. „ etii'pbaies. 

With Kspcct to tlic [louieoclatiiro of aci4$ and tails eonm itt- 
(trvncf. of opinion has beeu expressed by chemists, aud hence a 
certain amount of confusion exists in chemical writings. 

l^voisicr, when he devised the present Bchenie of chemical 
nomenclature, K^licved thnt it is oxygen (ofijs •ycvftlw) whicli 
^ves to the bodies lormcd hy runibuNlioii in tlid gas tlu-ir acid 
chumctcis, aad hence the hij^liest oxides of the metals and noa- 
metala were temu-d aeiiis, thus I'.O^ was called phatphorio 
acid, CO, carbonic acid, CrO, chromic acid, 8tc Meanwhile 
other substances poisscssing acid properties became huowii, «ucli 
OS nitric sfriil, HNO^, and sulphiuic acid, UjSO,. and llit'sc w^re 
found to contain hydrogen and they, therefore, differed from tlie 
nuhydrons oxidoa, N,Oj and SO,, from which they may be 
ohtaiiwd by the action of water, lhu<> : — 

N,Oj + H,0 = 211X0, 
aodHO, + H,0 = I!3S04. 

Moreover, acid bodies wore next discovered. such as hydrochloric 
tu:id. HCl, hydrofluoric acid, HF, and liydrocyanic, HCN, which 
contain no oxygen ; atid thus it appears that Lavoisier's notion 
that Lhu presence of oxygen ie alone aeccseary to fonu on acid 

is JDcomplctc, ud a more correct definition of an acid is that 
it Lt A hytlrDgrn campnund, in vrliich ihu \vhal<> or a part of the 
b^drogeii i& cupabia of bolug replaced by a luetal ; in otiier vronU 
nn acid h n hydrogen salt. So that nitric acid is hydrogen 
nitiate or liydric nitrate, HXO;^ and by replacing ilie hydrogen 
by the metal ix>las»ium we obtuin potuKsium nitnitv or nilrut« 
of potassium, KNOj. Sulphuric acid is hydrogen eulpliate or 
bydric sulphate, IlfSd^. ami citiicr oiio or Utlb the atoms of 
hydrogen can be mpUcetl by pot^issium, gixni^ rise, in the first 
instance to a salt termed hydrogen potassium sulphate (or com- ' 
inr>nly biaidplwle of potash) HKSO,. and in Uie second case to 
potassium sulphate (commonly lenocl aulpbat* of pot*sh),KjSO,. 

The anhydrous oxides (such as N^O, and SOJ, from which 
the acids are dcrivcii, may he best termed acid'/wrming orides, 
whilst the lower uxidea, becnuae they have the power of acting 
aa haat* and of forming salts when brought ioto contact with 
acids, arc ttnned bask oxides. 

53 At tlie time when our nomenclature was ini'euted all 
salts wen; sn|>pascd to he compounds of an aeid and a Ma;; 
and uaine^ were f^vcn which iudicat«d the fact itint when 
the ac-id and the hoiw arc brought to^lhcr a ncutml salt is 
produced; thus, if wo add potash (Iho base) to siilphnric acid 
(the ncid} « suit is fnrnKrd to which the name sulphate of potash. 
was given, and this view of the formatinn of suits being st'll 
held, tho nnniG imlicntinf; this view is still commonly used. 
When- the acid is coiuhim^d with a heavy metallic oxide, as for 
instance when oxide of leJiJ is dissolved in nn acid, sucb o" 
nitric acid, the cunimon name nitrate of lead, or more simply 
lead nitrate, does not exhibit the analogy between this salt and 
thiit obtaiiit-d by adding nitrio (icid to potash and called oitratv 
of potash. In order to assimilate these names name ohcraists 
have termed the tirst nitrate of oxide of lead, corrfespomliug to 
oitmtv of potn»h (potfuh being oxide of polassiam); wbiUt 
othera, to avoid tho recurrenoe of the word " of," and to shorten 
the names, prefer to tnention in the name of the salt not the 
base but ihe melal or htmjfont group, so tluit tho similnr names 
of lead nitrate niid pcitnssium nitrate become the deaigaation. of 
iHilh conipouiids. Other cliemL^ts pn:fcr to muilify the termina- 
tion uf the name of the ntetid, making It nn iidjecttve, tlius :— 
potOAsic nitrate, and, lut tlte common word Irad does not lend 
Itself to such adjective forms, we are coinpuUed to use Uic I^tin 
word and term the axil I'lumhie nitrate. 

la this vork no special system of Domenclature will be 
adojitcfl to tbc exclusiou of cvciy otbvr system. As a ink, 
however, the ordmiuy name of the motal wUI be retained fur 
tbe salts, Uius : — Iwiil nitrate, xinc suliphate, jwUissiiim chloride. 
But this will not preclude the OGcaaional uso of tho cotu- 
nion tcniM, u nitrate or CArbonatc of sudii, whilst such naiuc^ 
as fenvus- and ferric-, niemurous- and mercuric- salts will of 
courae be eiuployed. 

We define au aciil to !)e a lijdrogen salt and, therefore, HXOj 
will be, fw a rule, termed nitric acid: the names hydrogen 
nitrate, orhydric nitrate, may sometimes be used. Bodies such 
as NjO^ aOy CiOy will not be termed acids but are referred to 
as acid-fortning uriiles. In some few instances tbe hody CO, may 
be mentioned as uirhooic acid or carbonic acid ga«, owing 
to the fact that it bn.t for a long time been no called i but 
^tlie systematic name by which it will be designated in these 

afjes ia carbon dioxide. 

The following comparison of eomo of the older and common, 
ajid the scientific and more mcxlem names of iuiportant acids 
and salts may prove useful 


Olikr and Cohiidou Nanw- 


Hodrrti nnd Sdentific Ksint. 

XiVrii: iicid 


Hyji-ogeu Jiitratc 

Stitrous acid 


Hydrogen nitrite. 

Sulphuric acid 


Hydrogen sulphate. 

Sulphurous acid 


Hydrogen isulphite. 

Chloric arid 


Hydrogen chlorate. 

Oblorons Kcid 


Hydrogen chlorite. 

Hypochlorous acid 


Hydrogen hypochlorite. 

Otilvr Mid CoDunon Xam*. 


Mmlpm uvi Kri*i>tifli^ Kama. 

Nitrate of potash 


I'olaesiuui uitrale. 

Nitrate of silver 


Silver nitrate; 

Sulphate of lime 


CaJciuiii sulphate. 

Sulphite of lead 


Lead sulphite. 

Chlu»te of potash 


Potassium chlorate. 

ChloritG of »oda 


Sodium chlorit«. 

HyiMichlurite of potash 


Potafiiinm hypuchIorit& 

Protcisulphntc of Iivu 


Ferrous sulpliatc. 

P«rchloride of iron 


Ferric clilorid& 


This new system of nomenclatuie is, however, by no means 
perfect, nor ia it univetsally carried out. Were we to do so, 
long and iQcoaveaient names would have to be used. Tbits 
instead of the common name alum, we should have to use the 
words potassium alumiuium sulphate, and for bitter-spar the 
name calcium magnesium carbonate. Hence we shall often use 
the common instead of the strictly scientific names, as common 
salt for sodium chloride, caustic potash for potassium hydroxide, 
sulphuric acid for hydrogen sulphate, and nitre or saltpetre for 
potassium nitrata 


33 In the list of the Elements already given (para. 9), the non- 
metals are arranged in four distinct groups. This mode of 
division has its origin in a comparison of the volatile com- 
pounds which these elements form with hydrogen; thus we 
lind the following compounds of the members of the above- 
named groups exist : — 

I. Ujdrogen. 












} s} 1} n ^} 






}o g}s 2} 

Hydrogen. ' 







Phosphu retted 


H J-As 


These formnl^ are molecular formulae, and show that the' 
elements of the first group unite with one atom of hydrogen, 
whilst those of the second group require two atoms of hydrogen 
in order to form a molecule of the compound ; and the tliird 
and fourth group combine with three and four atoms of 
hydrogen respectively to foim a molecule. Exactly the same 



relations uo observed v\ku auj of tbeso elements miitv with 
oUifr siiDple IkkUos of tlio first group, such &s chlorioe, iodin« 
and tluoriat! ; thus we have : — 


Phoiiihanu iridilorUv. 

Aiwoit tti-lodiJa. 

Slicon tctinlhiondik 





lu this list the element boron is not menlionetl because we 
are unacquainted witli any compound of boron with hydrogen ; 
but iLs this (Ui'iucnt uuibits with thrvu iitoms of clilariiic to forrn 
liquid bcroQ-tricliloride BCIj, it natumllj falls into the Uiinl 

Hie elements of the first group accordingly poBsess only one 
wmhiniiig nnit, or tboy are vwnad olemeuts. The membera of 
the second are d^nd tUmfntx, titat is, c»ch Atom ha» tvro 
uombiuing units ; whilst those of the third or nitrogen group 
are triad dcmenU, aud the elements of the fourth or oarbon 
group are termed tdrada. 

34 Only theelernenta which belong to one K03up nre of pqunl 
value or are tqitivaltnt one to the oUier, and Uieae, tht-reforc, can 
alone replace one another atom for atom. Un iho other haoil, 
one atom of a dyad is rquivafent to and can ba re]>laced by two 
atoms of a monad, whilst oiiu atom of a triad is equivalent to 
throe of a monad clement and can be replaced by theoi, aa i» 
seen iu the following equations '. — 


CI) 11 L . HI 

^ci|-Hp + ar 





The monad elements unite tunongst tliemseWes to form only 

few and simple compounds ; but if an element posseting more 

tlian one oonibimog power enter itito combitiatiou, tlio niuubL'r 

of possible compounds becoinea larger. Chlorine and hydrogen 

foim only ouii compound; in llic; case of oxygen And hydrogen, 

on the other band, we are acquainted with (wo conipoiiiid». 

In hydrochloric acid the two single combining powers of the 

two atoms are saturated by mutual altachment ; if one atom of 

monad hydrogtn attach itself to one of dyud oxygen, one of the 

combining powers of the o.xygen atom is left unsatumted, and 

J tlii5 may cither combine with hydrogen to form water H — O— II. 

^H or another atom of oxygen may he nttacb&d, and this again may 

^ Batuiate itself with hydrogen, and n-e obtain hydrogen dioxide 

H — — O — H. In a similar mauniT the conatituUon of Qui 


■ till 

CMorine monoxide CI — — CL 
ClJorino irioxidc CI — — 0— — 01. 

As likewise that of sulphur-oxichiorido or thioayl-cbloridd ; 

CI— S — — CI. 

Compounds sre also known of two dynd elements, which are 
mo«t simply n-ptvscutvd as a closed chain of the dyad atoms, 
thaa ; — 


The elements of the nitrogen group possese a. pcctiliatity by 
rbicb they frequently appear as if they were jxntavalent, for the 

jm of tliese bodies not only forms the above-named comiiounds 
with three mouud atoms, but also otliont with five such atoms 
TliuB fluiiDonia and hydroL-hloric acid uiiitc directly to form 
ammonium chloride ; 

NH,+nci = nir,a 

Phosphorus trichloride ahsorU two aloma of chlorine, and is 
conrerted into the pentachloride, thus : — 

PC1, + C1,= R\ 

These oompounds, however, only exist in the solid or liqaid 
state; when they are heated they decompose into the two 



tooleculcit fVom wJiich tliejr liavo been formed. In some casea 
this decom]iosilion can be r<»dily seen ; thus antimDiij penta- 
chloride SbCl^ decompoees into tlie tricliloride SbCl, and fr«e 
cliloriac. Other compounds, Buch na pentacliloride of p1)08]>)ionui 
PCI5, appear to voktilizo without decomposition, but in this caso 
it can bu provLil that the vapour is a mixture and contains the 
tngleciJes of two gfl^es, phosphorus trichloride PClj and firee 
I'lilorine. Tlie vapour densities of these IxKhes accordingly do 
not obey the usual lav ; thus tlie vapour of chloride of am- 
tnomunij if it cotisisiud of siiuilur mok-cules. must pomow tlie 

density of ?5H±Jji^i±i= 26-69. In fact, however, its 

density is only half this TiiimVwr, for four volnines contiln on© 
molecule of ammonia and one of hydrochloric acid ; hence its 
dcaaity (or the weight of one volume) is hiilf the above or 

In the same way iodine fonng huth a inonochloride ICl and a 
trichloride ICljj the fii-st of these hodiea is volatile without 
dtconipoaitiou, the sccoud, however, decomposes ou distillation 
into the molecules It"l and Cl^ 

35 From tlic foregoing it is evident that the Atomic Valu$ 
or Uio Qtinntivatcnce of an element is determined by the number 
of mouad elements comhiniDg with the element in (^ncslion to 
fonn a compound vaporizing without decompoaiUoiL It must 
alao bo remembei-ed tliut ihf onf^ perfedly rrluJAe means icAuJi 
■we poswss /or ascertaining the 7noleai{ar weiglU of a eompotmd 
■it the dctcrnimalion 0/ its vajiour density. 

Hunco Uio molecular weight* of nil compouuda which 
are noii-vohitile or which are volatile only at t^nqx^niturcs 80 
high that we have ar yet been unable to dcteriuiiie their vapour 
density, or of such as undergo decomposition when *hey vola- 
tilize, must at bi'^t be considered as doubtful, although arguing 
from Bnalo;,^ wc may be able to guess at their molecular 
weights with a greater or less degree of probitbility. Th« 
particulars of these doubtful cnscs will be fidly discussed in 
dio introduction to the metab, as well as in Uic thvurutical 
chapters of this work. 


HYDROGEN. H = I, Density = i. 

36 It has already been stated (see Historical Iiitrodnction) 
that vater was loog suppotsed to bo an elementary or siiiiple 
substance, and it was not until the year IVSl that Cavendisb 
praved that wat«r was prodiic«d by the union of (aygea and 
hydrogen gsMe, vbil^C Humboldt and Gay>Lussac &nt showed 
in 1805 tliat these gasea combine by volume iii the simple relation 
of one to iwa Paiacelsoa in the sixteeulh cetiluiy had iudcod 
obtained an influmniablc gaii by the action of dilute acids on 
oerUin raetnls, but tbe true nature of tbia ^ta was (ir»t ascertained 
Iry Cavendish in ITOti.' when he showed that hydiot^n vas a 
peculiar gas to which bo gave tbe name of " intlnmmablo air." 

Hydrogen occurs almost sololy in a state of combination in 
nature, althoii'^h it has been found to exist in the fr«e state 
mixed in small quantiiies with other gases in certain volcanio 
emanations.* It lias aUo )>&cu found by Graham as occluded gas 
in the meteoric iron from Lenarto,' and by Mallet in a meteorite 
from Viii^inia.* It is produced in the decay and decouiposition 
oF various orgauic bodice, Wing found in tbu intestinal gases of 
many anininls, as also by Sadtlcr, iu the gases given olT by the 
oil-wclU of Pennsylvania 

In a fltate of combination hydrogen occurs in water, of nlilch 
it constitutes very n«nrly ono uintli part by weight (exactly 
11-136 jJCTOcnt.), and fmiu tliia it derives its uanie(b&iip, water; 
and "(tvyaa, I give rise to). Hydrogen, likewis* ocwurs in nature, 
tliougli in stnalltir quantities, combined with sulphur, plios* 
pbonis, chlorine, bromine, Iodine, end nitro^n, whilst it forms 
an essential portion of n«arly all organic substances. 

37 PrefMinilion. — (1) Pare hydrogon is beat prepared by the 
electrolysis of acidulateii watvr. For tliis purpose a mixture 
of onu i^Mirt by weight of pure sulphuric acid witb ten parta 
of water ia placed in the gloss decomposing cell (I'ig. 13X 
The positive pole consists of u platiuiun wire (it) melted through 
the glaaa and placed in contact with muicury amulgumated witb 
line ifi), whilst the negative pole («) ia composed of a platinum 


' " Sx]VTimftit( OM FartitiMU Air. " /*i1. Trmu. \7W. y. \U. 

■ Buiuen. Pagg. Ana. luziiL 197. Ch. St. CUtn Dtvills, Omtpt. JUitd. It. 

• Proe. Xog. SiK. x». 502. 

* IMt u. IKS. 




plate- Wlien the current from two or three of Butuien's eU.- 
ments is passed tliroii«h the apparatas a comtaiit stream of 
pure li)-drogoQ is evolved, uiid aft^r being varied bjr tlui hquUI 
quantity of sutpliuric acid coutaiued in the bulbe (d), tlie gas 
may be collficU-d for Rnalytinil piirpo&ra. The oxygen of tlm 
vnt«r is all absorbed by the zinc anoalgam, oxide of zinc and 
ultimately zinc sulphate being formed, whilst tJie whole of tlie 
bydrpgen ia evolved in the pure stute. 

(2) By acting on water wiLli the alkslbe Dietala, or with on 

Kio. 18, 

anuUgom of sodium or potassium. In tliis case the metal re- ' 
places &a equivalent <iuantity of hydrogen in the water, hydrogen 
gas imd tUu soluble hydroxide of the uetol being formed, 

Kj + 2H,0 = 2KHO + H, 

When fl amall piece of potassium is throwD into a basin of 
vater, it swims about on tlie surface, and witli a liisfiing noiso 
bursts iDto flame ; this is duo to (he fact that the metal in 
unitinf; vith the oxygen' of tbe water evolves boat ouough to 
melt the metal and to ignite the liberated hydrogen, which 



then bums with a flame coloured violet by Uie presence of 
the vapours of tho incUiI, SoiUwm, likewise, deooniijoses water, 
but the hydrogen in this caso does not take firt^ spontaneously 
unless the water be hot, or tlic motion of the bead of metal 
be stopped, m when tbe metal is thrown on to a viscid staich- 
putc or on to k iiioinlened Hhc«t of blultitig-[>apt;r, iu wliioli 
cases tb« globule of tuelted melal reinaiiiitig in one plaa« be- 
comes hot enough to cause tho ignition of the bydrogou, which 
tben bums with the yellow flame characteristic of the sodium 
compounds. If the blolting-|wpcr be previously stretched upon 
a wooden tray and moistened with a red solution of litmus, tlie 
tmclc of the molten potiii«j<iuin or nodinm, us it niiii; over the 
pnper, will be seen by a blue line showing tlie furwalion of an 
alkaline product. In order to collect the hydrogen thus evolved, 
tlw amall clciiu glolnilu of sodinti) may \m catijirht and depressed 
below the surface of the water by lueans of a little 8ie\'e of wire- 
gBU7.e under the open end of u cylinder; the bubbles of gaa then 
rise and may be collected, as shown in Fig. 14 


Tio. U. 

(3) By passing st*am over red-hot iron wire or iron borings 
placed in an iron tube and heatoil in a furnace as siiown 
in Fig. 15. (a) being a retort in which water ia boib-J. The 
iron is converted into tlie black or Ferrosofcrric oxide Fe,0^ 
and hydrogen ia evolved, thus: 

3Fc + 4H,0 - Fe,0, + 4H^ 



(4} The itwst convenient mode of prcpariug hydrogen gas fot 
ordinaiy us« when; aliHolute purity is not rw]uisite, is by the 
action of sulphiiric acid, diluted with six to eight times its 
weight of cold water, upon metallic Kinc ; the water must hs 
added because if no water b« present the zinc sulphaW ZuSO^ 
formed in the rraclion eoats tlie tmrfnce of the metal, wliich is 
thus protected from the nctjon of the acid. Uydroohloric acid 
diluted with twice it^ weight of water nuty also he oraployed, 
and poured upon clippings of metallic zioc contained in a gas- 
geiieratin^ botilc. Other nictuls, such as iron, innj be used 
instead of zinc, and magnesium is sometiraes employed where a 
TOiy pure gas is ivi[uired. Tlie acid ia gradually iwumd upon 
the metal by means of Uie tube funnel, and the evolved gaa csd 
be oollccl«d iu cylinders over thv pneumatic trough as ahown 
in Fig. IG. llie above roactiong are represented as follows: 

H,SO, + Zn'= ZiiSO, + Hy 

2lia+Zn = Zaa,+ H, 

Via. 15. 

Care m^ut be taken tluit all the air be expelled from the Baak 
before the g.w is collected, and in order to ensure freedom from 
air the gas is first nllovrcd to fill an inverted teat-tube, which is 
then brought numtli downwards to a flame ; if the hydrogen 
hums qiiietly all air has been expelled, if it bums with a slight 
explosion the evolution must bo allowed to continue before the 
gas is collect^nl. 

Hydrogen thus prepared is apt to contain small (juantities of 

, impurities derived from the materials usf-d ; tliese can be got 

rid of by passing the gas throngli various absorbente, Of these 

inipurities the moirt common arc arseniuretted liydrogeu, when 


^le sine, iron, or acid cootaiiLs ar^uic ; plioejiburetted by<lrogeu, 
when tbey oontaui phosphorus ; nitrous fumes vbeo tho acid 
oootaiia nitric acid cviiiLiates; sulphur dioxide and siUphurett«d 
lijrdroguu wlibQ UiMOgiues are conUinud iu the acid or vi-ht-n 
hot, even dUut«d, sulphuric nctd is allowed to como in contact 
ttith the metal 

In ord«)- to purify thfi gas, the bcaC method is to poas it 
through two U-tubes. each one metre in length, fiUed with 
pounded glass ; in tlic firat tube tlie gUsa is moutcned with an 
B^ueottft solution of It^ oitrate, which absorbs the i-ulpluirvtud 
b^drogon ; the svcoud tube containing an aqueous solution of 

tio. 10. 

silver Bolphate, by which tlie arscniiireUt-d ami pliospIiTircttcd 
bydroj^Q gases ore arre3t«d. After tins the gas is passed 
tbrough a third tubecoDtaining pumice tnoislened with a fitroog 
solution of caustic potash ; tJica through two others, one con- 
taining pumice moistened with strong sulphnric acid, and the 
other phosphorus pentoxide, by means of wliich the gaa is 
thoroughly dried. 

When Iho hydtogen is evolved from metallic iron, or even 
from iupoie zinc, tbe gas po«8Css«s a wry unpleasant smell, 
doc to the iircftcncc of small qufinlilii-^ of vulntile hydnxsaxboos ' 
derived from the carbon contained in lltu metal Tbe best vay 

of removing Hub odour js to pasa the hydrogen through a tul 
filled with small pioccs of chnrconl which absorbs the h^dro-^ 
carbon. Anotlitir imimrily wliich it is mudi motu difBcult to re- 
move from Iiydrog«ii is iituospbcTic air, ThU is partly containe 
dissolv<-(I in tht- liquiiU muA in tlm preparation of tht> gns, bat its' 
presence may also be due to the high diHiiaive power of hydrogen, 
which ciLiLsvH it \i) vitunpc throiijjh tho pon>s of Ihii cork and 
Cfloutclione, whilat sit tlio same time a ttrlain (juatilily of airj 
diffusia into the appiimlus. In order to free the hydrogen ftxw 
tracts of oxyi>eii, the gan must he pn^i^ed through a red-hot 
tube, and then the water, produced by the combination of the 
oxygen ttud hydrugcn, abaorbiid by poaaiiig llio gus over ])hos- 
phonis peiitoxlde. The nitrogen of the air cannot be got rid 
of, SI) that its {ireaence mutit be prevented by a oireful air-tight 
constniction of the apparatus. 

(I>) StMiig itcpmoiis solution of potiish JissulvKs metallic zino 
in preseuce of iron, bydpogen boinf; liberalfid, and a compound 
of zinc oxide and potiwh KjZnO, bciny formed. Tbia proceas 
yields an inodorous gas : 

2KHO+Zn = H, + K^nOy 

(6) Wlien zinc is immersed in an aqueous solution of any 
ammoniacal salt (uxcept the nitrate), sucit as eal-aminontac, at 
40° in conlaut wiUi metallic iron, bydi-ogen is also rapidly 

38 FtvpKTtie&. — Hydrogen ia a colourless, taflteleas, inodorous 
gaa. It is tiiu li^Iit^^t substance known, being lAA'iiy times as 
light as atmosplieiic nir Acconling to the uccumto expcriinenta 
of Rogiiault, one litre of hydrogen at 0° C. ftnd under the pros- 
stire of 700 mm. (*i nieKury weighs at the latitude of 
Paris, 0089578 gmius, or 1 gram of hydrc^en under the 
a.bove-m«nUoaod conditions occupies 1 ri&3t> litres TliP combin- 
ing vcight of hydn)gi>n being less than that of any of the otJier 
elements, it is usual to take this as the unit of comparison and 
tbo atom, of hydrogen is said to weigh 1. Hydrc^ii lias not 
been liquefit'd hy pi-essure, althongh Andrews* exposed this 
gas to a pn-ssure at wliicli it was reduced to xJb of it* original 
volume without any ohaers'ahio change oecuiring, whilst Net- 
iL'rer' brought the pressure up to no less than 2790 atmoapberea 
with u like result. 

I t«ria. Campla Jleruius. tt. 745. 
■ Snt Aae---. JitvffTt for 18(11, p. 78. 
* /"oysr. ^nn. jciv. *S8. 




Hydrogen is an indauima'bte gtia taking (ire wlien bronght 
in contact with a flame, antl combiniiig vitb the oxygea of tlie 
air to form water i it does not support ordinary conil'ustion or 
tLQunal lire ; wlicn pure it nay be breathed without (Janger for 
a short time, but it pi-odtioes & siugiilar effect u[ion tbu voicu. 
wcnkciung it »nd rendering it of liigluT pitcb. On cotnbinitig 
"wilb oxyyeii to form water, otie gram of hydrogtn by weight 
evolves heat suCQcicnt to miae 34,462 grams of water firom 0" 
to 1" centigrade, and this is termed the calanfie. power of 
hydrogeo. aod is, therefore, equal to 'H.4G'Z tkeritml vnits. 

riydivgcn gas dissolves only ftUghtly iii vrutcr, and, unlike 
moat other gases, it js equally soluble for all temperaturea 
between 0" and 20° ; the coelTicient of absorption of hydrogen is 
(hOlSS, or tLia is the volume of hydrogen (measured atO° C. and 
under tbe pressure of 7t>0 inui. of mercury) which it dMSolrcd 
liy one volume of water at all leiuperatures from 0° to 20'* aud 
under the prewuio of 760 nun. of mercury.' Hydrogen is some- 
what mure soluble in alcohol Uian in wat^r, and its aoluhilily 
duninishes with the temperature. The following interpoktion 
fottouU gives the absorptiou cocfScicLt (C) in alcohol for t«m- 
pcmtuies, vit, from 0' to 25" ; — 

C = 0-06925 - 000014876 + OOOOOU* 
39 Abaorpiion. of Hyirogen h/ Mdals. — Grahum * and Dcville 
and Twiost ' haro shown that hydrogen gas posseesca the 
iwculiar capability of diffusiiig tlimugb llic popes of certain 
red-hot metals, such as iron, platinum, or palladium. WTien 
hydrogen gas is passed through a red-hot palladium tube, tlio 
ntte at which the hydrogfn permeates the metal is such that 
through a surface of one square metre, 3'J92'22 cbc. of the gas 
]>ass each minute, -ulicrcas the rato of purmoability through the 
sama surface of plaliumii is 489 2 cbc, and tbut through a 
sheet of caoutchouc of the eamg tliickness and area is repre- 
sented by the passage of 127-2 cbc. of gas in the same time. 
The power of hydrogen to pasa through hot iron, pallndiiim, and 
platinum, whilst it cannot puss through when the metals are cold, 
probably depends on the fact that this gas is absorbed ut a high 
temperatur», and does not require the assumption of aijything 
tike porosity in the structuro of the motiils. This pi-oiicrty. 
which liaa been termed by Graham "oeclvsion," can be 

■ BmiMa'i OMMufry, 145. 
s Gnham. iVw. Av. Sot. sv. 333. xvi. t32. iriL 812 utd 'MO. 

■ DevUle and TtocM, Cumt^a ilmiiu^ Wii. SM. 


examined as foUons : A koown vrcight of the uieUl ])aUa(Uuin 
in foil or wire i» pWod iti a small [nroclain tubi^ gliued insitle 
and out> bii^I connected by oiio «iid to a Sprengel's meicuiy 
pump, wfaicli by tlie flow of mercury don-a tbe long laba 
(Fig. 17) yielcb a perfect vacuum. The tube, having been ex- 
luiusleU, is now lieatud to reduess, and a elrenm of hydrogen 
passed over the red-hot melol for some time, after vhich tbe 
tube ia allowed to cool ; Uie current of g:is is tbea stojtpL-d, 

Fio. 17. 

and the tubo ngnin rendered vncnouft. Xext, the tube is again 
]ieated, and the gas, vttich is thus evolved and driven out by 
meaoa of thu fulling mercury, ia collccled and measured in the 
divided jar placed at the lower end of the bamiuetric tube of tlio 

or all metals palludiiim possesses thia power of absorbiiig 
liydrpgen iu by far tli« highest dej^e. A palladium wire was 
found by Graham Lo at»oi-b at a n>il heal 035 tin>es its volume 



of h;rtlTQgnn and incrooBecI in length from 609i4 mm. to 
618-91 mm., or I'C percent. In another experiojeut the metal 
showed an iucretuc in bulk of 9-827 per ctot. Even at the 
ortlinaiy teiiiiierature palladium ahisoibs 376 volumes of the 
gaa. 1'he appenmnco of tho metal doca iiot uiidi'rgo any change 
a(l«r tlii» nliHorplion of hydrogen, btit ita qwoiRc |;pnvitj- aud its 
conducting power for hoat and t^lectricity as wvll as ita touaclty 
are somewhat diiuiniahed, though to a much less dugrco than 
would probably bu the coeo hy tho siuiiliir admtxtw-o of any 
. noD-metaUio subituiica. For various reasous Gmhiim concluded 
that the hydroj^n ia not chemically (»mbiQc<d with the palla- 
dium, bat nitb«r that the hydro^Q assuiiiml tho solid form 
and acl^ as a quasi-metal, giving rise to a kind of alby, such, 
for instance, aa is obtained vhm sodium and mercury oro 
brought together. The name Hr/dro/jcnium haa been given 
to this absorbed form of hydrogen, and its specific gravity has 
been calculated from tho exiiaiisiuQ of alloys of palladiam 
with plaUimm, gold, and silver, when cbai^'d with hydro- 
gen to be 0733, whorcaa tho number obtained from experi- 
menta vith puio ])alladium (in which tho wire, after heating, 
does not Ktnrn exactly to its original volume) is 0-8fiS. 
Of th€«c two niuiibere. tho former is probably tho most trust, 
worthy, but subsequent determinations by Oewar ' give a siwcific 
gravity of O&iO to hydi'ogouium, wliicli is <*qua] to the ooii- 
denaation of 7 litras of gas into the space of 1 cha Accoid- 
iug to Graham, hydrogenium ia distlDctly magnetic (more bo 
than pulladiuui] ; and haa an electric couduotivity of 6'09, 
that (^ palladium being 8'LU that of c«p[>er being 100. 
Troostand lliiutcrcuUle' liavc rcceutly shown from oliservatioua 
of tJie tension of the hydrogen disengaged at vnrioos tem- 
pcrmtmea from bydrDgcniaod palladium, that this substance in 
all probability contaioa a dctinito comjKiund containing two 
atoms of luctal to one of hydrogen, and, therefore, poaseasing 
the formula iM,U. Similar compounds of hydrogen with the 
alkaline ractals such as ^&^\i and KjII have been pre- 
pared by tho last-moutJoni-d chemists,' and from tho obaervcd 
denaitios of these cuniiKiuuds as compared with those of the 
metals themselves, the density of the combined hydrogen has 
bean to be 0'62, a number exactly agreeing with 
Dewat's obscrvationa. 

^ Dfwar. na. Mm. (41 xIviL to. 824 and 812. 

* Gmipla Seadm.txxritl fp. Vna-aw ; Clutn. Soc /mra. xxvil (M. 

' Co9ifU* JUadiu, Uiviu. p. MS. 

riaLiiiiitn at a red Iteat absorbs 3-8 times, and at 100" 0'7S 
times, iu volume of hydrogeu; nod red-liot irou oaly 0-46 ot 
its voliiiito. 

The meteoric iron of Lonarto,' conutiuing 9088 per cent, of 
irou, yields wlxeu healed in vacuo 285 Uiucs ils volume of a 
gtis coaststing almost entirely (8503 per cent.) of hydrogen. 
This, coupled with the fact that under tlie onlinary pressure 
iron absoiba only about littlf its volume of hydrogeo, woaM 
appear lo sliow tliat ilie Lcniirto mcleoritc hits coiuc from an 
ata)Oiaphere contaiuing hydrugeu luider much greater pressura 
than our own, and tlms we obtain an uiictpevted confimution 
of ttid CDHchiainmi drawn from apfintroscopic (tLi-servations by 
Hu^ins, Loelcycr. and SqccIu respecting the existoncD of dcnte 
oud heulod hyUrugun utmospliurus in the sun and fixed stats. 

The spectrum of hyilrogeu coimsts essentially of four brtglit 
lisea — one in the red, idenlical with Fraunbofer's dark line c, 
and cme in the greenish bine ceincitlcnt with the dark line F. 
Tbe wave-lengths of the^e four line.'<, tiecording to Angstrom's 
nwMurements, are = 6502.1" =4861, Blue = 4340, and Indigo 
= 4101 (in 10 milliontlis nf a millimetre). 

40 Eipfrimitiis with Hydrogen. — The following expcrimeota 
show that hydrogen is a very inflammable gas, burning with 
a nearly coluurless flame, but incapable of supporting ordinary 

(1) Whenalighted taper is brought to the open endof acyhn- 
der filled with hydrogen, the gas will burn nlowly and qnietly 
if the open end be held dowiiwaids ; but quickly ami witli a 
sudden rush of flame if the gas he allowed to escape by 
holding the mouth of the jar upiA-ards. 

(2) That hydrogen does not BU]>port the combustion of a 
candle may be shown by thrustting a burning taper into ajar of 
hydrogen held -with its month downwanis ; the gas inSamea and 
hums round the open end of the cylitiiler, but the taper goesi 
out and may be rekindled on withdrawal at the flame of burn- 
ing hydrogea 

{3) Or the stream of gas issuing from the drawn-out end of 
a tube and furnished with a platinum nozzle attached to (he 
generating flask may be ignited, care bt'ing taken that all Uie 
air has pi'eviously been expelled, when the flame will bum vtith 
a quiet and ahnost colourless flame, 

(4) Owing to the lightness of hydrogen it may be collected by 

* aiiliun, Pm. Ref. Soc xr, Sn. 

(5) Another striking mode of showiBg tlie relative weight of 
air and hydrogen has already been described in Fiij. 3, |>asc *'■'• 
The suspended bcokor-glnss is equipoised by weights placed in 
the pan at Uie otiier end of the beam of the balance, and the air 
is then displaced by pouring upwanla the hydrogen contained 
in a lurgc cylinder. The bmm will no lorgcr be horizontd, 
and weights nuat be placed on the beftlccr-glass to restore the 

(6) Another experiment illustrating the same property of 
hydrogen, is to 611 a cylinder with the gas and to bring its mouth 
downwards, togvtlicr with anotlior cylinder 611i'd with air, also 


moutli downwards ; by gradually lowering the end of the hy<lio- 
gen cyUadiiT uutU the two cylioilers coim: muuLh to mouth, bltu 
hydrogen will be fouDil in the upper cylinder, whilst oa stand- 
ing Tor a moment or two th« lower one will be found to be full 

of BIT. 

(7) Soap bubbles or small collodion balloons ascend when 
filled with hydrogen gns ; tho caoutchouc balloons, now so com- 
nion, ore filled and expanded by forcing hydrogen in with a 
syringe, us 8t*eii in Fig. 19. In conaccjueoco of its low specific 
gravity, hydrogen used to fce frequently employed for in9ating 
balloons, but at present coal f^ is used for this purposes 

Fra 19. 

CHLORINE. CI =3S'37. Density = 35-37. 

41 CuLOltlSB gaa was firat obtaJued and its propei-tica first 
ciamiiied by Scheele ' in 1774 ; he prepared it by tho action 
of hydrocUloric add on manganese oro, and termed it "dvphlo- 
gisticatod marine acid gas." BeitlioIIelv in 1785,' showed thaC. 
•ccoidiug to the then prevniling untipblogiBtic theoij", chlorine 

* Optof.. Toni«> i. 3*7. 

" JKm. it rAMut. df Scimat, P»tx*, 1785. p. 2ja. 



oontd be Tvgnnted as t campoiind of hydrochlorie Bcid gig 
with, oxygen, and ttiis view (d* its oonstitittioD vaa held uutil 
tlie jear 1810, when Davy > satisfactorily proved tbu clementaiy 
n&tuiti of the gaa nud gave it tltc Dame which it nov bears 
(X^i4apAi!, gieenish-jellow), Gny-Lusinc and Thenard* baviug, 
iu the year 1809, tbronn out the siigj^tioa that it might be coa- 
sidorrd to be a simple body. 

Chlorine does not occur in the free state iii nature, but is 
found in large qii».iitities, combined with thu ulkuli metals, 
formiDfT the chloridu of sodium, potassium, and magneaium, 
which constitute tlic Inr^gest solid components of sea^water. 
Sodium chloride, KaC'l, alao occurs in large depouta in the tertiary 
formation in Tarions localities, as rock-salt, whilst tlio cldoride 
of polusaium, althongli occairing less fttquenUy, is found in 
ccrtoiD locaUtics,a8ialhc •salt-beds of Staaiifurt, in Germany, both 
in the pure slate as sylvine KC),and in combination with chlo- 
ride of magnesium and water, as camallite KCl Mg Clg + IJU,0. 
The chlorides and oxycliloridesof seveml other metolaalao occur 
ID naturo. altbongh in small quantities; thus we have le«d 
oxychloridt) FbCl,rbO, known m matlaclcito; ferric cldoride 
FcjClp. found in the crateia of volcanoes ; silver chloride, 
or horn silver, ilgCI ; copper oxycbloride, or aetacamite, 
CajCI(OHV aid many othera. 

The alkaline chlorides occur in tho bodic>9 of plants and 
animals, avd phiy an eascutial ptu-t iu tho economy of the 
tuiiniol and vegetablB world. Chlorine likewise occiira combined 
with hydrogen, forminf; hydrochloric acid, a eubstauoc which 
is fonnd in nature in snmll qiiuntiti^s in certain volcanic gases. 

4a Pnjyaration, — (1) Chlorine ga3 is easily prcpoied by the 
of the black oxii!t> of iiiiuig:iiif.<« or mangBnese dioxide 
, on strong liydrochloric aeitl, UCi, thus : — 

4Ha + MnOj = a^ + MnClj+2H,0. 

kis reaction consists in the removal of two atoms of hydro^n 
in two molecales of hydrochloric add by union with one atom 
of oxygen of the manganese dioxide to form water, tlie two 
atonia of chlorine being set free ; whilst the manganese mou- 
oxide MuO, wtiidi may ba considered aa also being fonaod, 

H < mi. Tm<M. 1311, Y\\ I mnd 33 i Baktriaii Itdurt/or ISIO, read Vot. lOtli, 

■ IMO. 

H * Mtmvinr ^dnwU. TooH IL U7. 


dissolves in the two remiiining molecules of hydrochloric add 
to produce uiODgantjse chloride, MuCl,, and aaother molecule of 

I'W. SL 

water, HjO. When DiaDg&o&aa dioxide and cold conccat 
hydrochloric ucid an: brought tc^;etlier a dark limwuiaU-grecit 
eolutioD ia farmed, and this, ou heating, evolves chlorine gas, 
whilst nianganeso chloride, WnOlj, is formed. There can l» 
little doubt tliat this Aark coloured eolutioa coDtaiD!) a higher 
aud unstablv clilorido of manganese, prohaUy MaCl^ corre- 
sponding to MuO^ which, on heating, decompoaes into 

For this preparation the oxid« of mangiinmo should be used 
iu the form of smitlt lumps five froiu powder, and the hydro- 
chloric acid poured on, so as ahout to cover the aolid ; oa gcjitly 
beating, tiie gaa is l^opiylll^lv evolved, 

(2) It is ot'tt'u more convenient for laboratory vacs to evolve 
the hydrochloric acid in the same vessel iu which it ia acted 
upon by the maaganese dioxide ; and to place a mixture of one 
part of this SQlutaiice and one part of commAn salt in a lai^e 
flask {Fig. 20) containing a cold luiitiire of two parts of strong 
sulphuric acid and two of water ; oa very slightly warming the 
mixture, & ragular evolution of gas takea place. The change 
which hero occurs is represented hy Uie equation :— 

2NaCl + SH^O, + McOj = Clg + 2NanS0, + MnSO, + 2H,0. 



In this cose the su1i>)iui'ic acid acts tipon tlie anlf, fonntng two 
tnolccaIcA of liydmchloric acid, and acid sodium sulpliatc, 
HJJaSO^, whilst the ntati^nci^c dioxido acts upoa the hydro- 
chloric acid, as already described, with forinatiou of chlorine 
and 'wat«r. An exccaa of sulphuric acid is employed, and Uiia 
Ibrnia with tli« metal, manganous sulphate, MitSO^ 


Fio. 21. 
In order to puriiy and dry the gaa prepared by eitlier of the 
above roethodg, it is necpssiiry to pass it, first through a wiutli 
bottle (fr. Fig. 21) contaiiiiiijj water.tofa'cit from any hydrochloric 
scid gaa which Diay b<! oarricd ever, thuu through a sucoikI wash 
bottle (a) contajniaj; Btrou^ sulpiiuric acid, to itue it from tlie 
larger quautiiy of the wiucoua vapour which it tnki'S up tVom 

the water, nnd lastly throiigli ft long inclined tube (c) oontaloitig 
pieces of pumice-stone, moistened with strong and boileil sul. 
phuric acid. Tlic tub« (</) which dips under water serves as a 
safety-tube in case the evolution orgas bftconics too mild, when 
the excess of gas cm thus escnpe. In order to vx\>el tho air 
which tills the apparatus, the evolution of the thloriiio must 
be nllowvd lo go on until the gas ia vholly absorbed by 
a solution of caustic soda. As the cnide black oxuld of 
manganese fi^cijiicntly coiitnina carbounto of lime, the presenco 
of which v'iU cause tho aduiLxturo of small q^iiuiilitics of carbon 
dioxido CO, with the chlorine, it is advisable to moiilen the 
ore \)efore using it with warm dilute nitric acid, which will 
diBsolvc out the earhonate of lime, luaxing the manganese 
dioxide unacted upon ; after well washing, the latter may be 
used without danger of this impurity, 

(3.) By heating a mixture of bichromat* of potash (potassium 
dichroniate) and hydrochloric ai'id, chlorine gas can also be 
obtaiuud, chromium chloride and potasalum chloride being 
formed; thus: — 

14nCl+K,CrgO,=Cla+Crp,+ 7H,0 + 2KCl. 

(4.) Chlorine pfls is evolved when an acid ia added to an 
alkaliiio hypochlorite or to bleachitis-powdor or bleaehing- 
liquor ; tbis pruccsa is employed in bk'achiiig and ahio wlu'o 
•mall quantities of the gas are needed fur disinfecting purpoaea 
The bleaching pnwder is plai'(.>d on a plate or disli, mid a littiOj 
dilute acid (sulphiuiv or byJruchlonc) is poured upon il ; an 
immediate but slow evolution of the gas talccii plncei 

(5.) By passing a mixture of air and hydmchlorio acid overi 
heat«d bricks, a portion of tlic hydrogen of (he hydrochloric * 
acid ia oxidised, water and chlorine ga* being foniicd (Oxland, 
1847). If the niuturc! of gasoa bo allowed to pass over ft heated 
siirfikce impregnated with certain mctalUc guIu^, espcciully sul* 
phate of copper, the oxidation of the hydrogen of the liydro- 
chloric aeid goes on to a gi^ater extent, and by tho absorption of 
the unaltered hydrochloric acid, a mixture of cMoriac and uitmgcn 
gases can be obtained. This process, patented by ^Ir. Henry 
Deacon, of Widnes, is nsed on a large scale for the economic 
production of chlorine and bleachiuy powder. The singular and 
but imperfectly undetalood decomiwaition which takes place 
may be shown on a small scale by tlie following arrangement i- 

The bydnxhlonc acid gas is evolved from the conmtoQ salt and^ 

exiwscd to a f^nLlc heat As tlie hydrochlonc acid enter* 
the tuba containing the eiilphate of copper it mixes with 
RtiriMpheric air which U driven in by the tube e, rrom the 
gaS'lnilder. On passing over tho heated copper flulpiiatc, the 
hydrochloric acid and the oxygen of the air act upon one 
niiothcr, water and chlorine {,'ns being formed acoording to the 

^^^^'°" 4HCH.O,=2H.O + 2CI. 

Durinp the proi^ess the sulphate of copper remaiuB tinclianged 
and may be nsod, for a great length of time. The mixture of 
cliloriiic, uUre^'eii, &t«am, and any unducouipoaetl bydrochlori? 
acid pass by a bent tube into a bottle, f, containing wal«r, by 
which the last-named substance is arrested, together with a 
porlion of the steam which ia condensed ; the mixed gases, still 
coiitniiiiijg ^oiiic aqueous vupour, are then passed tlirottgh a tube, 
d. contaiiiiiig calcium cldoride, by whieU the gases are completely 
dried, after which the clilorine mixed with the nitrogen may 
lie collected by displacement in a cylinder. 

(6.) Chlorine r>aa is prepared for manufacturing purposes on 
a large scale by means of reaction (I) ; the mixture of black 
oxide of nianganeso and hydrochloric acid being placed in large 
6i[uai'[i tanks, made by Yorkshire flags clainj)e(! together by iron 
rode, and the joints made tight by a rope of vulcanised caout- 
chouc. Oiilieatiui; tlie mixture by a steriui-pipe the chlorine gas 
is evolved, l-'or a dcscriplioo of llic details of this mode of 
tiianuf'acture, see the paragraph on Uleaching Powder. 

(7.) Chlorine gas can also be produced by the ignition of the 
iiiih>drou9 chloride of ma^enium. in ^vhich case the metal 
gives up its chlorine, cunibiuiiig with the oxygen of the air to 
I'orm tile oxide ol' itiugni'siu, a soft while powder. TIic equation 
representiug the decomposition 13 as folloM-s : — 

SMgCls + 0, - 2Mt;0 + 2C1, 

43 PrcptrtKi. — Tlieatomic weight of chlorine has been nnually 
taken as 35'5, but the conect number (hydrogen = 1) is 3537 
according to the exact estimations of Uerzelins, Stas, Marignac 
and Penny. 

Ohlonnd at the ordinary atmospheric temperature and pressure 
is a transparent ga'i of a greenish-yellow colour, possessing a 
most disagreeable and powerfully Buffocattng smell, which, when 
the gas is present in small quantities only, re.seniblce tltat of 
eeaveed, hut when it is present in large qtmntities acts as a 



violent irritant, prodacing coughing, inOammation of Lhe mucons 
auiabranes of the throat aod nose, and when inhaled in the pare 
ite even causing death. C'alcuUtiKl from iU alomic weight, 
Isr-t?, chlorine gas is 245012 tiniea heavier than atmospheric 
air. Exact expcrimenta hy Ludwi^* have shown tliat nttem- 
peratoies below- 200' the density of chlorine (tike tlint of many 
other easily condpiLsable gases) is aom»what greater than theory 
reqoires, bnt that at this temperature the experimental and 
theoretical numbers agree exactly. 





Hence 1 litre of the gas under the normal conditions weighs 
S'lT^^M^ grammes. Vilien suhmitttKl to a pressure of 6 atino- 
uphetcs at *)" ot 8 5 atmospheres at llTJi, or, wheu cxpostd to a 
Ittiiilierature of -34** under tlic ordinary alTnosplioric pn-sstiTe, it 
condenses to a yellow liquid,* having a speeifio gravity of 1"33 
which has not been troxei), although exposed to a temperature 
of -90*. liquid chlorine boils at — SS^'G* and is not uiscible 
with water ; iu irlnictive index is lower tlian that of water, and 
it is a Don-condiictor of electricity. 

Chloriue gas diMolves in about half its volume of cold water 

' ft-rtK*. C*f». O'aeO. Ber. L tM. 

• ruwlir CO) * Fluid Clilorbic,* PM. TVaw. ms, p. IM. 

find as the gas instantly attAcks mcn-tiTy, it miub «tth«r be 
coUectec] in tim pnoumatic trough ovvr liot wntcr, or by dlft- 
placinj; the air fcom a dry cylinder, as showit in I'ig. 21, care 
bo'iDf; tAken that the excess of chlorine is nlluwed to escape into 
A draught ciii>buiti(i, m rcpnacuted in the drawing. 

^ Comhtisliotis in Chlorine. — Chlorine i» nut iuflatnniBl>I«, and 
does not directly coaibino with oxygen ; it nnitC8, however, with 
great energy willi hydroytni, furmitig liydrochloric acid HCl, and 
to this propcily it owes ita peculiar and vuJuahlu hlvoclung 
power, lb also coinhines with many metaln, ginng rise to a class 
of conipouuds termed the metallic ckloritlts. 

In each case uf couihinatioti with chIoria« a definite qnantity 
of heat is given out, whilst sometimes light is aUo emitted, so 
that the essential pheaomena of combustion are observed Thns 
It wc ptuu^ a jet from which a icauo of liydrogea bums iiilo 
ft cylinder of cMorine gas (Fig. 33), the hydiogen cantinuM to 
burn, hut instead of water bi-ing piDduoed, hydrochloric acid is 
formed by the combustion. In like manner, if we bring a Ught to 
the mouth (held downwards) of a cyhnder of hydrogen and then 
bring thia over a jet from which chlorine gas is issuing (Fig. 24), 
a lltune of chloruie buruiug in hydi-ogeu will be aeeu. 

If two equal sized cylindcnt, fillbd, one with dry chlorine and 
the other with dry hydrogen, are brought mouili to mouth, and 
the two glasa plates closing them withdrawn and the gasea 
allowed to mix, and if then a flame is brought near the mouths 
of the cylindeTs, the mixed <{aaes combine with a peculiar noise, 
and dense fumes of hydrochloric iwid giis are »ee«. This experi- 
ment must, however, be made in a room partially dorkoDcd, or 
performed by gjw- or candle-light m tlie two gased combine 
with e^ploeiou iu sunlight or strong daylight. 

Tlte following experiments ore cited aa showing tlie power 
with which chlorine unites with hydi-ogen, even whvn the latter 
is combined with some other elemeut. 

(I.) If four volumes of dilorine, CI,, be mixed with two 
volumes of olvtiant gas, C^H,. the chlorine inunediatfaly seizes 
hold of the hydrogen of the latter to form hydrochloric acid 
HCl, while the carbon is set free in the form of a block stooke 
thus: — 

C,H, + 2CIj = 4HCl + C3, 

(2.) If a piece of filtor-papor bo dipped in oil of turpentino, 
C„Hia, and plunged into a jar of cliloniic gas, thu paper bursts 


cosmusnoss in chlorikk. 


into fla.iDe ; the chlorine comliiQiug with the bydrogca of the 
turpentine, while the carbon is deposited. 

(3.) When fiulphuretted hydrogen gas, HjS, is passed into 
chloriiM watur, hydrochloiic acid is fanned by the union of 
the hydrogen of the former with the chlorine of tlie latter, 
and the aulphur Li set free in Uut form of a light yellow 

(4.) When a lighted taper is pinniped into a jar of chlorine, it 
continual to bum with a dull red light, and dense fumea as well 


Fia. 24. 

rio. 2i. 

I a cloud of black sinoka are emitted, arising from the comhin- 
itlion of Uie hydrogen of the wax with the chlorine, and the 
liberation of the caibou. 

In order to exhibit the combination of certain elements ^tith 
chlorine, whereby heat and light are evolved, the following 
experiments may be made : — 

(1) Place sonic leaves of Dutch metal (copper in thin 
iMTes) in a flask provided with a stopcock (Fig. 25), and exhaust 

the flajk -with the air or water pump ; attach the outer end of lie 
stopcock to the neck of aiiiilhpr flask oontiiining chlorine gas. 
On opening the stopcock the cliloiine will niah uitc the vacuous 
(task, and the copper leaf will take fire, dense yellow fumes of 
copper chloride Imiiig foniiwl. 

(2.) Finely powderod metallic antimony thrown into a jar of] 
cliloriue givos rise to « shower of lirilliunt sparks, chloridaj 
of aiitimouy being pnxiuced If the jitr be placed ou the table 
0%-er u powerful duwti-drauglit, all risk oreiicapiag fumes 

(3.) A small piet-e of phosplionis placed in a deflagnUinf; 
spuoii mid phiiiji^d into a yir of chlorine liret melts, and, aSier a 
few minutes, hursts into Biimc with forinntion of the chlorides ol 

(4.) Metallic sodium melted in a spoon also takes fire onj 
immersion in the moist gas, bnming brightly, with the production 
of coiunion xalt — .sodium chlaride ; hut it is a niugular fuel, firat j 
observL-dby Wonklyii,' that sodium may bo melted iudry chlorinoi 
without any coiubiuatiun ui;>curnng. the sui-fiice of tli« molten 
metai remaining bright and lusli-ous; iiataa«ii«ii, im the other] 
liaiiJ, 13 at once attacked Ly both dry and moial chlorine. 

45 Alleged AUotropic CuntHtion of Chtoritie.— It liun been etAted 
by Uraper' tliat cliloriiie which has been exposed to lijiht, com- 
bines with hydrogen vtwrv- easily than that which has been kept in 
the dark, and the coiiclimioii lias been dr&wn that chlorine c.xi:^U£ 
in two allotropic tnodificationik Subsequent careful expprimenls 
made on thia suhjixt by Kuuseii aud Ituscoc," fuile>l lo det«.;cl 
the slightest difl'erence Itetwca iusolated and nun-insolated 
chlorine. It has aleo been stated* that when chlonnc gas ia 
exposed to the chemii;nlly active rays of the sun it increases in 
Tolume, and that this ia not due to any action of the heating 
rays. Further experiment hiis not coiifinnod thest' results, so 
lliat tliLTG does not appi-iir to be sufTieitmt ground for assuming 
tlie existence of an allotropic modification of ordimtry chlorioe. 

46 Bhfiehing I'owrvvf Chlorint. — The characteristic hleAohing 
action which chlorine exerts upon oi-ynnic coloiirm.i; raatters,,j 
and which has become of such enormous importance in 
cotton and paper trades, depends upon its power of combining 

' Ckem. Kern, w. «71. 

» pm. Sfag. for UiS. iitIL 817 : tMo tat 185T, wi iIt. p. Ifll. 

« PhiL Tr-vx 1S17, Fart ii, p. »78. 

* Boiidt. PMt. Mag. nri, xiii. r- mo. 



vn\h hydi 

This Wt-acli 





prvsenc^r of water, th« colouriu^ matter being oxitliiieil and 
destroyed by tlic liberated oxygim of tliu wntcr. irhiUt tliii 
hydrogen and chlorinecomhine together. 

That dry ciilorine does not act upon colouring matters may b« 
readily sbovfn by immersing a piece ot litmus paper, or, better 
stUl, a 8ma1l pioco of lurkfy-rud cloth, prcvioiialy well dmxl, 
ID a jar of dry cMoriinf, when the colour will reiniiin for hotirs 
noaltcred, but the addition of u suall quantity of wat«r causfo 
its immediate disappears nee. 

Clilorine cannot as a rti]c destroy mitieml colours, nor can it 
bitacb black liuts produced by carbon; tliis is well shown by 
THodering illegible Iho ordinarj- pritit (printers' ink is made with 
lamp-black or carbon) on a pieco of emd or paper, by covering 
the whole with common writing ink (which geaerally consiaUi 
of tliv iron solta of orgauic acid»). On imiticniingtlie blackened 
card ill moist chlorine g&s, or iu a solution of cldorine>wat[;r, the 
printed letters will gradually nioku their appearance. 

Chlorine nJao po^seasea powerful disinfcctinif |iro[itirtics, and 
tho gas is largely osed for the desitnictton of bnd odours and of 
the poisonous germs of infectious disease floating either in Ibi; 
air or in water. It ia prolmblc tJiat tlii-s valuable property also 
depcnda upon the oxidation, and conscciuently the ddstrueiiou ol 
tbi'se poisonous viuunatinnts and miiUmalA. 

47 Chlorine ami Water. IhjilraU o/ CA/onV, CI + 5H,0. — 
When chlorine gas i.s pn.sse»i into water a few degrees above 
the freczi tig-point, a solid ciystalline conijioiind of Ihu gas and 
water, termed clitoriae hydrate, is formed. Ily quickly pressing 
the crystals between b]otting-p«iK>r. they may be freed from 
adhering water and analyat-d. Fsraduy found that tlicy con- 
tained 2770 per cent, uf cldcrine, ^bowing that thuy aru 
ooaipowd of one atom of chlorine to five molectdca of water, 
the hydrate having, therefore, the composition Cl+5HjO. This 
liydrat« B|M!cdily deconiposeit, on standing in the air, into an 
aqneoua solution of chlorine and chlorine gas, hut when denied 
op ill n tube it requires to be heated to ^IS" before it decomposes, 
and it Mien foruiH two layers, one of liq^uid dilon'nc, and tJie 
other of tlie aqueous solutioa of tlie gas. AVhen contained in 
a sealed tube it can also be sublimed by heating. Thi.s decom- 
_ position of thv hydmtv inuy be nmdc use of as the most ready way 
■ of preparing liquid chlorine. For this purpose the dried hydrate 
H b pUced in the limb (a h) of a strong bent glass tube (Fig. 26). 





Fia. S8. 

Tbe open limb is then sealed whilst the hydrate is kept cool 
by dipping the other Imib iuto a Jrcexing mixture; after the 
tuba is closed, the limb (a b) is plactad in a vf^ssel of lukewanii 
water aad the crysuU Lh«a rewlve tfaemsel^'es 
into two distinct lajera of yellow liquid, the 
lower of whicli illiquid cliloriuc By pluciug 
tlie limb (be)ia afreeziu;; nilxture the liquid 
cbloritic distih over, leaving thu less volatila 
aqueous eolutioa of olilorine behind, 
Aqutowt solution 0/ CMonne poasessos ft gi'eeuisb-yellow 
colour and smclh) strongly of the gas. Chlorine is most solable 
in water at 10", as below tliis temperature the formation of the 
hydtate commences, and sa tlie t«nip«rature increases above 10* 
the Hohibiiity diminishes, until at 100° no gas diss(^ve4. It ia 
prepared by passing washed chlorine gas through wat^tr as sliowu 
in Ti^ 27, chlorine being evolved in the flask jl, and the 
solution of the gas obtained \a the bottles c, D, and s. 




PlO S7. 

If we wish to absorb the whole of n aroall quantity of the 
ohloriae gas evolved in a gi%'en renction, the appamtiis repre- 
sented in Fig. S8 may be used. Chlorine is led by a gas 
dulivcry-lubu into im inverted retort hariii^ a wide neck and 
fdlcd with waU^ ; the gxi3 dlsplact^ some of the ualer, collects in 



the up|H.<r ])onioQ of the rotott, and may there be absorbed aud 
its qaaxtUty cstimatixL 

Km. 28- 


48 TIm Absorption co-ttfTicicrtt of clilorine in water between 
ICT and 41*''5, is given by the equation 

C = 3-0361-0046196t + 00001i07t» 

from which the following values ani ubtuint-d. 

1 volume of water absorbs the rollowin^' volumea of chlorine 
gaa calculated at 0° and 760 oiui.' 

Cintignde. Corfllcknt. 



10 . . 2-5852 . 


36 . 

1-9099 . 

. 0-04O5 

11 . 

25413 . 

. 0*0439 

27 . 

1-8S95 . 

. 0-0404 

12 . 

2-4»77 . 

. 0-0436 

28 . 

1'8295 . 

. 00400 

13 . 

24543 . 

. 0-M34 

20 . 

17395 . 

. 0-0400 

U . 

2-4111 . 

. 0-0432 

30 . 

17499 . 

. 0OS96 

15 . 

2 3081 . 

. 00430 

31 . 

1-7104 . 

. 0395 

16 . 

232r>3 . 

. 0-(>42S 

32 . 

16712 . 

. 0392 

17 . 

2-2928 . 

. 0-U425 

33 . 

16322 . 

. 00390 

18 . 

2 2405 . 

. W23 

34 . 

15934 . 

. 00388 

19 . 

2-1984 . 

. 0-0421 

35 . 

15550 . 

. 00384 

20 . 

2-156.1 . 

. 0-0419 

36 . 

1-5166 . 

. 0-0384 

21 . 

2-1148 . 

. 00417 

37 . 

1-4785 . 

. 0-0381 

22 . 

2-0734 . 

. 0-0414 

33 . 

1-4406 . 

. 0-0379 

23 . 

2<1322 . 

. 0.O412 

39 . 

1-4029 . 

. 00377 

24 . 

1-W12 , 

. 0-0410 

40 . 

13G55 . 

. 00374 

25 . 

1-9J04 . 

. 00408 

' ScbdnftlJ, A»*. CImi. PSarm. zdil 24, itrL 8. 

It cMonnc tnixecl with another gns, tacit M hydrogen or 
oirboa dioxide CO^ be passed into water at temperatttres 
between 11" and 38*. the volume of absorbed cUlorjae is found 
to be greaU.-r' thun that calculatt-'d front the law- of Daltoa and 
Heniy for paitial pies^ums, aud Ibis excBSN of di$.<o1vod chlorine 
varies la amount with the tcnipeniturn of tlio '^ater, and 
with the nature of the oUier gas jii'escnt 

Saturated chloriiie-wat^r give-s off chlonne freely on BXposurs 
to the air ; it blvitchus organic colouring matters, end, if frve from 
hydrochloric acid, it do^a not redden a piece of blue litmus' 
paper before it bleaches it. Chlorine water undei^goes decom- 
positiou gradually, especially when exposed to daylight, Iiydro- 
chloric acid being formed and oxygon liberated. Indeed, wht-n* 
chlorine water is placed ui direct sunlight, the whoW of tl« 
fioo chlorine may combine with tlie hydrogen of ibu wutvr, and 
its eq^iiix'alent of oxygen be set free, thua : — 

HjO + CI, = 2 HCI + 0, 

It Ima been proposed' to employ this reaction in measuring the [ 
chcnucol action of light, but it i» accouipauiod by nuuy difli< 
culties. Tlie I'ate of the decomposition of the water is iiifliiencedl 
by the quantity of hydrochloric acid which has previously beeiij 
formed, and the preseuce of Ibis eubstance greatly retards Uie] 
reaction according iv a complicaUsd kiw. 


HtdbochIjOKIO Acid, Cfilokhvduic Acid. Hydroges CniompB]] 
OR Muriatic Acid. HCI = 36'37. Density «- 18IS6. 

49 The Arabian Alchemists were acquainted with bydro- 
ohlonc acid in its mixture with nitric acid to form agua rt^, 
which tliey obtained by dislUIing uitre, aal-ammomac, and vitrio) 
together, but 13[i3il Valeatiiie, in the 16th ceiitnrjr', is the Sist 
chemist in whose wiitiiij^ vtv find the moutiou of the pure acid 
under the name of " »piritus salis," prepan-d from " guten 
vitriol" and "sal communi." Glauber fii^t obtained thi^ acid< 
by tlio action of suljthiiric iicid on common salt about the year] 
1648, and Stephen HaIgs. in his work on VeffftaNe Statiet*,} 
puhlifilicd in 1727, observed Uial a liirga q^uantity of a £m 

' SotcM, Jeun. Chfm. Hoe. Tol. viii. jl 14, ISGS. 

» Witlwcf, Ave- 94. 5B7. Aha. Vlum. Pkam. Sv«>. I, <3. 



which was soluble in water was evolved when saUammoni&cand 
oil of vitriol vfcre heated together. It was not, however, until 
Priestley* collected tlie gas thus evolved over mercury, by )isitig 
thid metal instead of wnlcr in n pneumatic trough, that the 
jraseom bydrocliloric ucid was tintl prepared, and to this g&i 
Wiestley gav© the uanie of nmrine-acid air, as calling attention 
to its production from sea-salL Lastly. Pavy in 1810 proved 
that the gas, which had been considered to be an oxygen com- 
pound, was cutii'cly comfinscd of chlorine and hydrogen. 

Ilydrochloiic acid gas, the only known compound of chlorine 
and hydrogen, occura in the exhalations from active volcanoes,' 

» especially in Vesuvius,'' and in the fuiiioroles on Hock,* In 
aqueous solution, the ncid has Iteen found in the w&ters of 
eevemi of the South Americ»u rivers rising iu the volcauic 
districts of thu Andes. 

50 Hydrochloric acid can he fot-nied by the direct union of ita 

cooitittienL elementa. It' efpial volumes of cliluriiic and hydro- 

Kgen be mixed togctlier, no comhinatioa occurs so long as the 

niixtare remains in tlie diirlt and at the ordinary atmospheric 

temperature ; hut if the mixed gaaes be exposed to a. strong 

■ (Mwrnaif Au oo Difftnni Kindt af A <r, I ?71, rol. iii. £09. 

* PmviU-fwtmnie Itunomma of iff UiHf. Oav. Sac. Knn. p. 327. 

■ PkttnWll, TU lale tlrvjiliaH of Vituciua, IBVi, p- V-iS. 

* tiaUMsa, jttm. Ckrm, tAatnt, Ixii. 1. 

ligbt, or if a Qamts be bronglit to llie moutli of (lie jar, or an 
electtie spark passed through the gases, a nnclden GombinatJoii 
takes place, the heat suddenly evolved by the nnioii of the 
chloritio and hydrogen being suffielcnt to produce a violout 
explosion. In order to exhibit this singular action of li<>ht, 
inducing tlic coinhinalion of (.'hlurino and hydrogen, a small thin 
flaak may be filled, in a darkened room, half wilh chlorine gas 
(by di.iplac«ment over hoi; water) and half with liydrogen. Tlic 
flask, corked and covered up, niny the» be exposed either to 
suulight, or to the bright li^ht of buruiiig iungn«sitiiu ribbon, 
when a sharp explosion will instntitly occur, the flask will be 
shattered, and fumes of hydroi'liloric acid will be seen. 

A better inclliod of showing this tombiuatiou is to obtain a 
mixtuTft of exactly equal vohinies of chlorine and hydrogen by 
the electrolysis of aqueous hydrochloric acid itself. For tlila 
pUTposu on apparatus shuwii in Fig. 20 is employed; this con- 
siats of an upright gla.^ tube tilled with about 120 cbc. of pure 
fuming aqueous hydrochloric acid, containing alwut 30 per 
ccnU of IICl. Two poles of dense carbon, as used for the electric 
lamp, pass thrungh tubtilurcs in the sides of the ghus, being 
fastened in their place by means of caoiitcliouc stoppers. Tlie 
apparatus having been brought into a rootu lighti'd only by a ' 
eandtc or small giw flame, the carbon polpa are coimoct«d with 
three or four Hiinsen'H elements, the current from which is 
allowed to yas^ tlnonyli the liquiil At first, gas is evolved from 
the negative pole only, and this consist* of hydrogen, whiltt 
all the chlorine, Mhicli is evolved at tlie positive pule., is ab- 
sorbed by the liquid. After the evolutioo has gone on for two ' 
or three hour» the liquid becomes saturated with chlorine, and 
the gases are given off at each pole in exactly equal voUiinw, 
and consist of hydrogen and chlorine, uncontaiuiualed with oxy- 
gen or oxides of chlorine.* The gaseous mixture thus obtained 
is washed by pius«ng through a few drops of water contained 
in the bulb-tube ground into the neck of the evolutioa vessel, 
and then passes into a thin ghss hulbof aboutthesizeof a hen's 
egg blown on a piece ofreasily fusible tubing. At each eiul t.he 
tube is drawn out so as to be very thin in the glass, and to have 
tlia internal diameter not h&A thnn 1 mm., whilst at the extremi- 
ties the tube is wider, so as to fit ordinary caoutchouc joiuingSL 
lu order to ab-sorb the excess of chlorine the further eiid of tliflr 

■ Kmcm. ChtnK Son. Joura. viti. 16L 



bulb is pUced in conn(>ctii>n with a condenser eontainiiig 
slaked lime aiKl cliarroal {ilaced in alternate layers.. 

When the g»« has |)a8«t;d through the l)nnj-lul)o(at llie rate of 
alxmt two bubblps every second) for about ten minutes, the join- 
ings are looscDetl snd each end stopped by n piece of glass rod. 
In ordorto preserve the gaseous mixture, which is unalterable in 
the dark for any length of time, the bulbs are hertnetieflUy scaled, 
For this purpose Itie thinnest part of the tube is brotijjbt some little 
distance above a very siidiU fliimo from a Butisen's gas^burucr : 
the glass softens below a red heut, and the ends may be drawn 
uut and scaled with safety. It L9, however, advisable to hold the 
bulb in a cloth during the operation of acnting, u not unfre- 
quently the gas explodes. As soon as one bulb a removed a 

* r 


FiQ. 30. 

flecond is introduced, and placed in connection with the evolution 
flsak, and afWr ten minutes scaled as doacribed. The bulbs 
tbna obtained should be nnnibeTed, and the first and last tested 
by ex]tonu'^ them to a strong light, and if theKe explode, all llm 
inlermedialc bulW may be considered Rood. Sixty euch buUe 
may be prepared ■with tlie above qnantity of acid, and may be 
kept in the dark for an anhmitcd time without chan^.' On 
exposing one of these Lnlbs to the light emitted by burning 
magnesiuin ribbon, or to bright daylight, a sharp explosion ocean 
and hydrochlone aeid is formed. 

> Baac4W. Prof. Xtndk. LiL amd nj. £x. Feb. I8«5. 



$1 Ilyclraclilortc acid is also rormcil by Itic KCtion of clilorine 
iiiwiii almost all hydrogen conajwurnds, wliich ar« decompoHe«l liy 
it C'ilUer in tlie dark or in presence of li^jlit ; thus sulphmetled 
hjdnigca, oleliaQt gas, turpentine (see par. 44 (2) }, Bud water 
&re all decompoi^cil by chlorine, liydrochloric ucid being fonneiL 
Wli«D hydrogen is piascd over many iiiGtallic chloride^, sucli as 
silver chloride, bydrocliloric acid is evolved, and the melal 
reduced, thus : 

AgCl + H = Ag + HCl. 

By these and otli^r reactions hydrochloric acid m fi-cqucnlly 
fi>rnied ; but none of tlieni serve for tlie preparation of Uie gas 
on a Iflijje scnle. 

5a Preparation. — For this purpose six ports by weight of com- 
mon salt ere introduced into a capacious flask, and eleven parta nf 
etroiig sulphuric acid slowly poured on it through n bent tube-, 
funnel ; the gua, which ia at once rapidly evolved, is purified 
from any sulphuric acid or salt which may be carried over, by 
passing through n small quantity of wiiter contained in a wash 
bottle, and it may then eitlier bo collrcted by diHplacemeut (tike 
chlorine), or over mercury, or passed into water aa »ha«'n in Fjg. 
36, if a solution of aqueous acid is needed. 

The rcuctiuQ which here occurs is rcprc8ciitod by the cquBtiou : 

NaCl + H^O. = HCl + NaHSO,. 
Hydrochloric acid comes off, and a readily soluble acid sulphate 
of Bodtt, or hydro};ten sodium sulphate, NaHSOj, is left. If two 
molecules of s.ilt ht- taken to one of sulphuric acid,'a leis easily 
eoluble salt, normal sodium sulphnte NjuSO,, is formed, a greater 
heat being needed to complete the decomposition than when an 
excess of ueid is cioployed. thus : 

KaCl + NaHSO, = NajSO, + nCl. 

Tlie pure aqueous acid is best prepured for laboratory use 
from pnre suit and pure sulphuric acid. 

53 jpropcrtizs. — liydracbloric acid is n colourless gas, which, on 
the application of pressure and cold, can be condt-nsod to a 
colourless lici^iiid, but this, according to Faraday, does not freeze 
even when exposed to a temperature of —110*. The gas waa 
fir».t liquefied by Dnvy and Fnratlay,' who estimated tlie tension 
of the gas to be 20 atmospheres at — 16*. 25 atmospherea at 
— 4', and 40 atmospheres at - 10°. The uielliod adopted by Davy 

I Dttvf anil Fandaj-, FkiL Trant. 1&23, pL 161. 



for the Uc]Tiefaction of the gas ia shown in Fig. ,11. Into a tube, 
three times benl. at a right angle aod closed at one end, are placed, 
at a, a few small pii^c«e of sal-ammoaioc (a compound of hydro- 
ehloric acid and ammonia) ; some strong sulphtmc acid U then 


poarcd, hy means of a bent tube-funad (<£). into the second bend 
at b. The open end of the tube ia next carefully (hawu out, 
Uiickened, and closed befoi-e the blow-pipe, and when the tube 
w cold, it is so inclined ns to allow tlie acid to flow on to tho 
•«1-a.mmciotac. Hydrochloric add gus is at once disengaged 
aeeording to the equation :— 

2 NH^a + H^O. = 8 HCl + (NH J,SO,. 
and after & timft th« prvscurc becoinoei sufficiently great to lif^iiefy 
Itie fnrth&r portions of the gas which are evolved, and by 
gontle heat the liqaid may be distilled ovor into the empty limb 
of the tube, lb is found to be a colourless liqoid, having a 
specific gravity of about 1-27. The action of liquid bydro- 
diloric add upon vartoue substances has been lately carefully 
examined by Gore.' The plan he adopted for preparing the acid 
wag the same as that used by Davy, but the tubes were closed 
by pinga of gnua-percha, and placed (for safety) in wooden boxes. 
These exponinciits sliow that the lifjuid acid has but a feeble 
lolveDt power for bodies in general, and. with tlio exception of 
alaminiam, the metals arc not attacked by iu 
Hydrodilorio acid gas ia heavier than air. Its specific 


fVM Bty. S»t. slv. tOi. 



gravity, according to the most accurate expeiimeats of Biot 
am! Gay-Ludsac. is V'J.1S (air = l), or its density is 18'25 
(U = l), the calculat&d density being 1&'1$5. Tbe goa famea 
strongly in the nir, uniting with uttnosplieric moUtum, and it is 
iualantly absorbed by water or iee, yielding the aqueous acid. 
It pussttsses a strouj^ty uvid roactioQ uiid suffocating udour, and 
is not inflaiiimakle. A bunuug candle is extinguished when 
plunged ititn tlie gas, tlic out^r niontte uf Urn Hatne, Ijefore 
extinction, 4^xbibiliii;^ a chamcterJstic green coloration. 

54 Tltc conipnsitioii of hydrochloric acid gas can be hot 
ascertaiiiM as follows : — 

Kfetallic sodiutn decoinpoaes the gas into chlorloe, whicb 
combines with the ntctnl to form sodiura chloride, and into 
liydrof^en. which is liberated. If a small piece of aodium he 
heattid in a dvflagruting Gpoou iiiilil it bcf-iiu to bum, and 
then pluugcd into a jar of hydroclilorie acid gas, the comlim- 
tiou of the metal [union with chlorine) will go in the gas. 
in order to show what volimio of hydrogen is evolvod 
from a giv'on volume of hydrochloric acid gna by this reaction, 
the following experiment, may be made with the eudiometer 
tube, the oooatmction ot which is clearly seen in fig. 32. 1q 


Fio. 3S. 

begin with, botli limbs are filled completely with diy mcrcoi; ; 
then the eud of the tube carry iug the stopcock ia con&ect«d "by 
a piece of caoutcliouc tubing with an evolution flask, fiDm which 
pure hydrochloric acid gas ia Ixiiiig slowly evolved from a mix- 
ture of dry salt and atrong sulphuric acid, care l>cing takcD that 
the airhon been driven ouL On turning the stopcock at the top 



of tli« tttbe, iuid opening the scr^tw-tAp on tlio caoutcUonc in the 
U-tube, the mercury will rim out, and dry liydixiclilorio acid gas 
will cntor tlie one limb, vrhilst air fills the otJier to the soino 
level As soon as the gas reaches a tuarkoii thflttibc iiidicatuig 
that it is two-thirds full of gaa the slopcuck is closed. A 
smuU quantity of sodium aiuolgam is uow prcjiarod by {Missing 
&ix or eight small pit^cut of clcau cut sodimn, one by one 
under the fitirfiux' of a fev outic«>.<i of mercury contained in a 
porcelaiu mortar. The &iual-^iti is then poured into tbo open 
limb of the U-lube so as to fill it, and the end firmly closed with 
ttu! tbuaib ; the hydrochloric acid gas is now trunsforred to the 
limb L'ontainiug the anmlgam, and wt-U shaken so a< to bring 
ihe gas and unalgam into contact, 'i'hu gas is next passed back 
into the cloeed limb, and the pressure equahsed by ^nging the 
ntercuiy in both limbs to the same levct and this is easily done 
by alloving some mercury to flow out by loosening the ecruw-tap 
at the bottom of the U-tiibe. The hydrochloric acid gas will 
be completely decomposed by contact with Imodium amalgun, 
ehlorido of sodium being formed, whibt llio hydrogen is left 
in the gaseous state. This will be found to occupy exactly 
half the volumo of the oiijiinal gas, tho level of the mercury 
ha\'ing risen to a mark previously mode and indicating exactly 
ooe*tliird-of the capacity of the tube. As the closed Umh is 
ptoridi'd with u Ktopcoclc, the ttsidual gas muy be inHamed, 
and thus shown to be hydroj^a 

55 It still however, remains to asceilain the volume of the chlo- 
rine which has disappeared. Thi.s is done as follows : — Two glass 
tubes about 50 cm.Iongoud 1*5 cm. in diameter, drawn out at each 
end to Bne ihreads, are filled with the gaseous mixture evolved 
by the electrolysis of the aiiucoas acid (see par. 48). The process 
ia conducted exactly as if a bulb were being lillod. and tlte tubes 
are tlieu sealed up and kept in tlie dark. When it is desired to 
exhibit the compoeition of the go*, one of the tul>cs thus liUcd 
is brou>;ht into a dimly Iigbt4?d room, and one of the di-awn- 
outeuds broken under mercury. Ho alterntion in the bulk of 
the gas will be noticed. The mercury in which the tube dips is 
nov replaced by a colourless solution of iodide of potoasium, 
and by giving the tube a sUght longitudiual shaking, a little 
of this solution is brgu^-bt in contact with the gas. Xo sooner 
does the liquid enter the tube than it liecomes of a dark brown 
colour, due to the liberation of the iodine, the chlorine uniting 
with the potassium to form the chloride of that metah A 




(2) that these elementary components ootnbine together it-ithout 
chtuigc of vulunie to produce Uie coiniKiuiiil liyiiroclilonc nuid 

This fact may be furllicr illustrated by exposing a second 
seoled-np tube, coDtaiaing the eloclroly tic gas, for a fovr minutes, 
fint In & dim, and tJien to a stiongi-r daylight. The greenish 
colour or the clilorine will soon disappear, a gntdiial combinatioc 
of the gases having occurred. On breaking one end of the tube 
under mercury, no alteration of hulk will he ob«er\'ed, whilst nn 
raising the opeu end iulo some water ptlnred on the top of the 
mercury, an immediate and cotiiplete ahsorptiou will be noticed, 
Bod the tube will become filled vith water. 

In order to itetcnoine with a greater degree of exactitude 
than is possible by the above methods, the relation existing 
bctvrcen the two gases, a quantitative nnnlysis of tbe chlorine 
oontoioed in u given volume of the ckijlrolytii; gas must be 
niiidc. Two experiuieuts thus conducted gave tbe following 
tosults : — 


Chlorine ... 49*85 
EydrogcR ... SO-15 






5000 volumes. 


Showing that the gas obt»in«d \>y decomposiog aqueous hydro- 
chloric acid consiata exactly of equal volumes of chlorine and 
hydrogen, or 


I vol of dilorin* weighing -^ = 17'685 
i „ hydrogen „ 




1 vol. of hydrochloric acid weighing ... 16*185 

^B $6 TTydroolilorio acid gaa is very soluble in water, and tl>e sohi- 
|H tioo u liirgely used for laboratory and for ooiuuiercial purposes, 
and &aquently termed muriatic acid. In order to exhibit the 
solubility of the gas in watur, a large glaaa globe {(^g. 33) placed 
;i on a stand is filled, hy displacement, with the giis; a tube, 
H nacbing to the centtc of the globe and dipping to the bottom of 
H an cqoal-sized globe placed b«noatl). being 6xcd iu a cooutcbouo 



thiough the aid« tabe iuto the sixice iitovti the surfaco of litiuid 
in tlie lower globe. As aonn as the water makes its »ppearanoe 
. at th« top or ihe uib^ a rapid absorption occurs, the liquid rushes 
np in a founluin uud at tfao sonic time bccouiua culuurvd red. 

57 Manufadure of UydrocklorU Aeid, — ^Tliisacid isobtuincdon 
tlie large scale as a byc-pniduct in the niatiiifuclnre nf tuKlii-ash, 
In tiie alkali workii 14) cvrt of salt is iiitTodiiccd into a large 
hemisjilicrical iron pan. 9 feet io diameter, lieiktud by n fireplace 
underui.'atb, and covered by a brickwork dunie ; upon tliia mass of 
ealt ibti a'<tuitiite quantity (10 cvi.) of sulphuriu acid ( l'7j 
is allowed to ran bora a leaden cistern placed above the decom- 
posing pan. Torrents of hydrocbloric acid gas are evolved, which 
collect ill ibe space between the pan and the brickMurk dome, 
whence tbey pass by a brickwork or eartheuwaro flue iuto 
upt%ht Uyyien or condensers, built of bricks soaked in tar, or of 
'YorkabiiQ flags fitted and clamped to>^ther These tow ers, shon-n 
io rertioal section in Fig. 34, and in ground plan in Fig. 35, are 




?io. 3.1. 

filled tt'ith bricks or coke, down which a wnall atream of wattr 
from a reservoir at the top of the lower, is atlowe<l to trickle. 
TIi6 gas, pttssing upwards, as aliovirn in the figures by the arrow, 
neetfi tlte water and is dissolved by it; and as thi< acid-liquor 
^iprcMcbes the bottom of the tower it becomes more and mora 
iMiriy aataraUd with the gaa 
The iqaeoos commercial acul thus obtained from impure 

present in lar;;^ qiiantitii.-s, buiti;- derived &oai tlie pyrites used 
in making tlie sulphuric ncid. 

ThepreeencA of orsonic may Ic detected by Marsh's reaction j 
or by the iidiliiion of Blauuous chloride whidi produces a browl 
precipitate of impure ai'scnic. To remove traces of arsenio^ 
solution of statinoui cli^orido may be addi>-d. the precipitato 

soLDBarTT OF nvDR0cnr.ORic acid. 


allowed tosetUe and the clear liquid re-distilled Chlorine nifty 
be detected by tbc addition to the diluted acid of pure iodide 
of potassium and starch aolution, vhen if chlorine bo present 
the blue iodide of statch vilL be formed. 'Ihe pr^«Dce ol 
sulpliurio acid ciu) be etutly usccrtoined by iddii^ chloride of 
barium solution to th« dilutod acid, whilst that or sulphurous 
acid may lie »hown by adding eiuc to the dilutciL acid, when 
sulpboretled hydrogen will be given o9' and ita presence readily 
ascertained by its blackening action on lead paper. It is. 
however, uot easy lo suparatv these substances so aa to obtain 
a strong pure »cid from one originally iupuro, and by far the 
simplest plan is to exclude the foreign matters by employing 
pure materials to begin with, 

5S Tlie pure sat>aat<»l aqueous ucid is a colourlc^ liquid 
fuming fltronsly in the air, and freezing when oooktl below 
— 40° to a butti-r-like moss liaving the conipoaitiou H('l + 2FIjO. 
It is prepared for laboratory ii»o by means of the apparatus 
shown in Fig. 36. One volume of wntor at if nhsorba 50S 
time* ita voiiinie of liydrochbtric acid nm. ITie weiyht and 
volume of the gas obsoibed unitcr the pressure of 760 mm. by 
one gramme of water at difTerent temperatnres id given in the 
folio wing tabhi.* 


Omw. 1IC1, 



<r . . 

. . 0-825 



4 . . 

. . 0-804 

36 . . . 


8 . . 

. . 0-783 

40 . . . 


12 . . 

. . 07G2 

44 . . . 


la . . 

. . 0-7-ia 

48 . . . 


21) . . 

. , 0-721 

52 . . . 


24 . . 

. . 0-7W 

66 . . . 


28 . . 

. . 0-68a 

SO . . . 


The weight uf gas dissolved uudcr ctianging pressnro (the tompe. 
rature reniHininj; coustaiil) docs not vary proportion;illy to the 
piessoiQ, and, thvrcfoiv, thi^ gim dovs not oU-y Dalton and 
Hcmy's law. Thus, lor instance, under the piessuro of 1 metre 
mercury I grnL of water iHs.soIves OSHG gna. of the gas; 
ccotdiiij; to Dallou and Henry's kw the weight of gas absorbed 
uuder a presaure of 1 decimetre of mercury should be 00856 
gim., whereas it is fotind to he 0*657 gnu. 

* B«MM ind Ditlititf, Ifiiart Aunt CKnt. sU. 1S& 

On beating a satnmled .nolution of tlie gas in water baling a 
specific gravity of 1-22, hydrocbloric acid gas is given off, and tbe 
liquid becomes weaker. On tbe otber baud, a weak acid on being 
boiled, loses water and becomea stronger, so that at last botli 
the strong acid and tlie weak acid reach the same strength, and 
both when W\\&i ilistil ovf,T iiiichangeil, provided the pnissiin: 
does not vary. Tlie aqueous acid, which boils unchanged ai 
110° under tlie nwrmal pivssuru conUiu.'S 20'24 per cent of 
hydrochloric acid IICI' If the distillation proceeds under a 
greater or less pt^ssure than the nnrmal, distillates of coDSUnt 
composition are obtained. l»at each one coatains a different, 
qaantity of Iiydrocliloric acid. This iii cltwrly scvu from 
following table. 

Colnnm I. gives the pressure in metres of merctiry vuii 
whicli Llie distillation wns conducted ; ('(ilniiin IT. the percent 
of Jiydrocblaric acid (HCl) found in the residual acid. 





























































Here th« percentage of the acid and the constant coDipoailioo 
obtained by distillation under a pressure of 1 decimetre \a seen 
to be 23'2 HCl ; whereas when the pressure is incrcasyd to 2'5 
metres the percentage of tbe acid of constant boiling point is 18-0 
HCl. From this it is clear that definite liydratos of hydro- 
chluric acid (i.r, compounds of hydrochloric acid and water in 
simple atomic proportioiiK) are not fonnecl on distillition. al- 
though it happens tliat by chance the liq^uid distilling under a 
prasflure of 760 ram. corresponds to HCl + 8 HjO. In the same 
way if dry air is parsed through aqueous hyilrocbloric acid a 
part of the acid is vaporized and a rusidue is obtained wbiclt 
fur each given temperature remains of constant composition. 
An acid weaker or stronger tlian this ultimately attains tliis 

' Bmocm and Dittmir, Ue. cA 



The followiDg table ehows the composition of tbe constADt 
aqueous hytlrocliloric acids obtained hy leading air at given 
tompeTaturt'S through the liquid. 

Ttmip. P«r Cent of HO. 


Por Cent o( HCL 

0' . . . 


liu* . 

. . 230 

10 . . . 


70 . 

. . 22-6 

20 . . . 


80 . 

. . 22-0 

30 . . . 


90 . 

. . 21-4 

40 . . . 


100 . 

. . 20-7 

50 . . . 


Keaco i( is 6e«D that an aqueous acid which boils noaltered 
under a given pressure, and, therefore, al a coBBtAnt t«inpem- 
ture, roDtaina the same percentage of HCl u the constttot acid 
obtained b)- pasting dry air through the nqaeous acid. Thus tbu 
boiling point of tho acid nnder O'l of pressure, containing 22'8 
jwr ceoL of H CI, is from 61° to 62"; and if dry air he passed 
through on aqucoua acid at 62' the constant point is attained 
when the liquid conlaina 22-9 per cent of HCI. 

59 The followinp: table gives thespccitic gravity of solutions of 
uquTOus hydnjchloric acids of varj-jug streugthu, according to the 
rcooDt «zpetiment8 of Kotb.' 

lOOof A(|u»oiii 

A Mil j^i^vhi H in 

Spec ill c Crftvitj 


a Fill wQiiui'i 

























































From these numbpra Uw percentage of any icid of known 
9p«ci&o ^vit^- van easily bu found by hiteqtolatioa. 

60 The Chloj'ulai. — Tliecompounilsofclilorine with the metals 
RTc formed eillier by the direct union of chlorine with a m«tftl, 
or by tlie rtplaceiiient of Ihc byilroyeii iu hydrochloric acid by 
a metul. Ccrluiii m^ljdi) ciitei vciy readily into coinbination 
witb chloriae, beat beiiig always evolvBil, aiid the phenomena of 
conibufitiou being fretg^ucully obsen'nl. Othi-r met^ti again do 
not combine so easily. Most of tlie melallic chlorides are soluble 
in water; nniong^^t those insoluble are silver chloride AgCl, 
merciirouft chloride (calomel) HgiClj. and Cuprous Cbloride 
CqjCIj, Souiv niulitls cotiibina iu m'jru tlmn ouu pruportioa 
with cliloriiie, tlius wu lind : 

Cuprous Clilorido, Cu,Cl,, 
Murciiruns Chloride. Kg^^V' 
Tin Dichloride, SnClj, 
J'latiLUm IJichlorido, PtClj, 
Furrous Cl)loride, Fe^Cl,, 

Ctiprio CUoridc, CuClt. 
Meronrio Chloride. ilgCI, 
Tin Tctmcliloride, SnCl.. 
I'latinujn Tetrachloride. PtCl^. 
Ferric Chloride, FojCl,, 

The chloridi-s of tlie taetnls arc nsually proparwl by one of 
the following pi-ocesses. (I) By acting un the uwUil with 
chlorine gae, especially when tlio anhydroua chloride is required 
(2) By the action of chlorine upon }it»ta11ic oxides, wheji it 
drives off the oxygen aud unites with Iht! luetal to fonn u 
oMoride. (3) By acting on the metal with hydrocliluric acid. 
(4) By dissolving the o.\iilo, hydntlu, or carbouate of the metal . 
in hydmcliloric VJ'xA. (.j) In ei^rlitin casus, by adding a selubld' 
clitoride to a solution of a salt of the nietnl, when the metallic 
chloride is obtained us an inaoluble precipilnto. 

Chlorine also unites with all the non metallic elfiinenta and 
with ccrtttin groups of atoms tenued radicals to fomt dilorides 
ijf these elements und radicuhi rospcctiviily, &ome examples of 
wliich are as follows: 

Hon- Metallic Clitariilts. 
Hydrochloric Acid .... 
Chloride of Sulphnr 
Trichloride of Boron 
Tetiachiorido of Silicon . 
Pcntacliloride of Phosphorus . 






Cblondca of lotfguiio SadinU. 
Chlorido ol Sulplmtyl .... SO,CI, 
ClilorJd*) of IlwMpboryl .... IXJCl^ 

ChlorUii «f Orfuiio ftoiUcab. 

Chloride of Etliyl C^sCL 

CUloriile (>( Elhene .... C,H^CI, 

Chloride of Acetyl C,1I,0CL 

Chloride of C>-tiuog«a .... CKCl 

6i Dettetion and SdinuUion qf Chlorine. — In the fiee state 
chlorine gaa is recognized by its peculiar colour, it3 suObcating 
emeU, and by its bleaching nction od organic colouring tnattera. 
'^^1lea pTfSL'ut Lu ituialler quautitica; ila prcteace may be de- 
tected by thv blue culour which it causes <mi a paper moistened 
with a soIiitioD of iodide of potassium. KI. aad starch pasta 
owing to the fact that chlorine liberates iodine (torn its com- 
pound with potassium, combining with tlio mctoL to form the 
chloride, KC), whilst the liberated iodine forms a deep blue 
compound with starch. This reaction is very delicate, but it must 
be lemembered that aa excess of cidorine ogftiii removes the blue 
colour, and also that the eaino effect i^ prodacod by broniine, 
nitrom fumes, oh)iic, and other oxidising suUstancca. 

When combined with metals to form chlorides soluble in 
water, the element is usually detected by the formation of the 
cardy white precipitate of silver cliloiidc, AgOl, on addition of 
a solutiou of silver uitiate, AgXO^ to that of a soluble chloride, 
KCl, thiu :— 

KCl + AgNO, - AgCl + KNO, 

One part of chlorine in one million parta of water can thus be 
' : — a faint opalescence occurring. The prticipitated stiver 

L.i becomes violet-coloured on exposure to Ughl, and is iu- 

soluble in witter and dilute acids, ospeciallj nitric acid, but readily 
soluble ill amiitoiiin and is soliitiona of polaasium cyanide, and 
vuliam thioHulphate (the so-called hyposulphite of soda). Mer- 
curoait nitrate: hkcwiseproduces in solutions of a chloride a white 
precipitate of merctiroii.<t dilorido (cnlomcl), which does not 
lUsaolve, but turns black on addition of ammonia. 

lu order to detect a chladde in prest^iice of an iodide and 
bromide, tI>o dried salt is distillod with polossiuin chromote aud 
UTOog eulpliurio acid, when chromiam oxychloride, CrOjCly 


distils over as ii dark red licjuid, dtacompoaed by addition of 
water or animouia. eud yieMinj; a yellow solution wliicli, on 
additiou of bot acetic acid niid a soliiblt: luiul salt, gives a yellow 
precipitate of lead cliromate ; neither bromine nor iodine fonn$ 
ft similar compnutid with clu'omiuin. Cblonoe, when combined 
to form a clilonde, is always eslJmaled as silver chloride, AgCl, 
and according to Stas \4'i-iii of silver chloride contain 30-37 
of ctilorinc. I f the chlorine is present in tlie free state it can 
bg di;tcriuiii*Ml \>y voluiuctric anal^'sis (««!a CMlorimehy, under 
Bleadting Tbwder), or it may be reduced by sidphur dioxide, 
SO, to hydrocliloiiu acid, and tlii-n precipitated as silver 
chloride and weighed. Tho reduction of chlorine to liydro- 
chlonc by means of eulplinr dioxide is represented by tho 
equation . — 

CI, + SO, + 2H,0 = H,SO^ + SilCl. 

Chlorine occuni combined with carbon and other etenmnts to 
certain organic cor.)])ouuds, as in chloroforni, CHCl,. These sub- 
stances, when brought in contact with solution of silver nitrate 
do not yield any piecipiluto of silver chloride, and thu clilorine 
citnnot 1)0 detected or determined by tlic above nicaos. In order 
Lo imcertaiu the quantity of chlorine thus contained in cotiibina- 
■tion, the comptnind must be dveomposcd by possiug its vaponrs 
over red-hot lime, wlicn the chloriue combinoe with the metal 
to form culciuui chloride, and this on being dissolved in water 
or nitric acid yields, on addition of an excess of silver oitnte, 
a precipitate containing the whole of the chlorine. 

BROMINE. Br=7975, Density = 7975. 

62 liBOMlNE docs not occur in thct free state in naltiie, ilwasdia- 
Coveif^d in tho yenr ]82<> by Balard,^ who prepared it from the 
liq.uor called bittern, rcniBiiiinj; after tho common salt has 
crystallised out from con<:L'nt rated sea-water, in whicli it occurs 
oombined with metals to forcu bromides, lie gave it the name 
from ffpSifiov. a bad smell. 

Bromine occurs in couibiuatiuii with silver in certain oree, 
fipom Mexico, Chili, and Brctugne; but is found in larger 
* Atm. Oum. fhyt. Sat. [2] xsxii,, p. ZST. 

qoaDtities (combined vich sadiuni. potassium. niA^'nesiuin, or 
calcium formiog hromida) in tlie iratcr of uiauy tnincntl 
^rii^s, somo of which contain euongli to aerve as a source of 
this dtmeat. It Js also fouml, though in very small quantity, 
in aU sea-water,' and has b«eu detected in sea-'H-eGd fi-oiu many 
localitiviS, an<l even iu c<^rtitiu murine amnula, as well as in 
Engliilt rock-salt, Th« mineral sprin;^^ at Kreutznacb, Kiuiu- 
gen, and Scbi>Debeck, and the polash K-da of Slassfurth, as well 
as certain American epritigs iu Ohio and elsewhere, are some 
of tJiose from which bromine is juvpared on Iho laige scala 

IWparation. — In order tc delect bitJiuiue iu a wiueml water 
or to prcpnre it iu tmall quantities, the following method is 
employed. The motlier-li<iuur remaining after the hrine from 
uiy of the above sovrces has been well crj-etallized is treated 
with a stream of chloriiie gas, so long ns the yi-IIow colour uf 
tba liquid continues to increase iu deptk Chlorine has the 
power of liWraliiig hromiutt from bromidus, itself uniting with 
the metal thus, and the hromine being set free, thus : — 

MgBrj+CI,= MgC'lj + iJry 

The addition of excess of chlorine is to l»e avoided, ns a oom- 
pound of chlorine and bromine is then formed. The yellow 
liquid ifl then well sbsken with chloroform, which diniiolvea the 
bramiiie, forming, on stnndinj;. a bron-n solution below the 
aqueous liquid. On adding caustic potash to tfaia solution the 
colour at once disappears, the brumitic combining to form the 
bromido K I5r, and Iroumtc of potassium, KltrO, thus: — 

3Br,4 tiKHO = KBiO, 4- 5KBr -t- 311,0. 

On concentratiug the eolutiou, a mixture of these suits 
remains, and from these the bromine is again liberated by die- 
tilling the liquid with blnck oxidi! of manganese and sulphuric 
acid in n tubulated retort, The decomposition which here 
occnis is Hiutthir io that which takes placv iu the preparation of 
cliloriite, thus : — 

2KBr + 3H^0, + MnOj = Br, + SK^HSO, + MnSO, -i- 2H,0. 

Darit red fiimes of bromine are liberated, and a black liquid 
condenses in the well cooled receiver. 

If the bromine is required to be anliydrous it must be 

' Tlw vkMt of iIm XitaA Sta i« MJd ta coutuu lAign tuauUtioa, of 09 Imb tim 
0-tS gruB. la tlia hO*. lUnot.) 



redistilled over coQcentnited sulpbnric acid, aad if iodine i* 
present Uiis must b« got rid of previoualy, b; precipitetioD ss 
Bobibdiile of copper. 

For tli« preparation of brooiine on the large 8tiale the motber- 
liqiiom of t'lie tialu contniDing the bromidis, after having been 
mixed with sulphuric or hydrochloric &cid, are treated with sodi 
qaantities of black oidde of manganese as will not evolve more 
chlorine limn u needed to liberate the bromine, which latter 
is then distilled off and preserved This operation is carried on 
in large sqnare stone vessels heated by steam, and the Inomioe 
vhicli conies off is ooUected in a large Wtnilff's hottle. If the 
liquors coiit«in iodides as well as bromidee, the iodine is fint 
liberated by a limited addition of niai^oese dioxide, and tlie 
bromine enenrazds set free. 

In order to eeperate the bromine fVoni the more volatile 
chloride of bromine formed at the B&mo time, the vapours 
coming off from tlie still am not pcrfi-ctly (."Oulttd, the bromine 
collects in the receiver, and the more volatile chlorine compound 
paMea further on into a vessel filled with iron tilings or caustic 
eoda. The impure broiuine contained iii tlic receiver Is then 
purified hy repeated fractional distillations, and thus tlie greater 
portion of the chlorine, as well as the less volatile otig&nic 
bromides, wliicli are always present, may be separated. 

For tliu purpose of freeing the bromine completely Irom 
cblorinQ mere woshin;* with water does not sufQce, and it is 
necessary eithiir to distil it over bromide of potassium, which is 
decomposed by any chlorine present with ronnntion of bromine 
and chloride of potassium, or for exact purposes the following 
mctliod may bn employed The bromine is wholly neutialiied 
by baryta water, whereby bromide nnd bronmte of barium are 
formed (together witli chloride and chlorate). The mixture of 
barium salts is first evaporated to di-yiiL\sa. then healed to redncas, 
and the TCsiJii^ digiitk^l with nicohol, which only dis«olves the 
bromide of bui'ium. The solid salt obtained on evaporation of 
this alcoholic solution is then treated with manganese dioxide 
and aulpliurio acid, when pure bromine is obtained 

TiiD quantity of bromine produced iu Stassrurth in the year 
1873 amuuntc<l to 20,000 kilos, whilst Kngland and Trance 
produced about a like amount,' and AmeriL-a coabibuted in 1870 
no IcsH thim 62,500 1c ilos.^ 

> noftamo, Ktpert tm iXt (^tmital InJtMrTi of Ou rSmiui EAUttloit, pt IS 
* CliHidltir, Chtm. Ktie$, islU. 77. 





_ Properties, — Bromine U a tcary mobile U([uid, so darii 
as to be opaque except ia thin Inycrs. It is tliB only liquid 
elemont at the ordiuary toinpcruture except mercury, lu, 
specific gravity at 0"* ia 31872 : it freezes at - 22" to a reddiali- 

H brown solid, which melts at - 24*5* (Unnmhaiier) ; ' itevapoiato 
quickly in the air. and boils at 03° (Staa), Bromitie possesses a 
very ittiotig uiiplonsant siik-11, the vapours wlicu inlialud pro- 
dnce great irritation, and afffct the eyes ver>* painfully. WTien 
swallowed, it acls as an irritant poison, and when dropped od 
the skin it produces a corrosivu Horo, which is vciy di&icull 

■ to heoL 

" In its general properties, as well as in those of its compouuds, 
broiuine closely resembles chlorine, although tlicy are not so 
strongly marked. Tlius it bleaches organic colouring mattere, bnt 

^ much leHS quickly tlian chlorintt does, and it combines directly 

B with nictala to form hromides, though its action ia less energetic 
tban that of chlorine. It docs not cotnbinc at all at ordinary 
temperatures vith metallic sodium, indeed these two substances 
may be heated together to 200'' before any perceptible action 
oomtncuccs, whereas bromine and potassiuoi c»imot be brought 
together vrithoul eombiualion occurring, aonietinies with almost 
explosive violence.' If brought into contact with free bromino, 
atarch-posie ia coloured orange yellow. 

Uromine nud Wattr. — A dalinite crystalline nonipOHud of 
liTomine and water ia obtained by exposing a mixture of the 

H two substances to a teiiipttmture lu-tir the frce^iug point. This 

™ hydrate consists of Br+5H,0 and it undergoes decomposition 

hydrate consists of Br+i^.j., 
into bromine and water at 15^ 
gave tlifl following results . — 

The analysis of the compound 

Bromine , 
5H,0. . 

^^TTie solnhility of bromine in 
peraturea of 5° and 'i(f,' is shovru 








water between the tem- 
iu the following tible, 100 

I Brr. 7>ruLwA, n«n, Oea. tv. 9t'. 

> htm una Watb. Btr. IktiUfM. ('Ami. Ott. rf. IGI& 

* Iteuni, CAna. Sec. Jotim. ir. K7. 




grama of saturuted aolutiou of bromine voter fiootaining by 
wc^t — 

. 3-60O grams of bnnmii& 

. 3-327 

. 3 2-.'6 

. 3-208 

. 3-167 

. 3126 

The solution of tiromiQe in water Itos ao onui;^ rod colour, it 
soon los&s bromiue in contact \ntJi tJie air. and it blcacliea organic 
colouring lualter. Urotnine wat«r is permanptit in the dark, but 
on exposure to sunlight it becomes acid froiu tlie formatioti 
of hydrobromic acid and «volution of oxygen. 


HroaOBKOMic Aviv. UBr= 80^75. Density = 40-375. 

^4 Bromine like cblorine furmq only ono compound ttith 
hydrogen, containing one atom of Imimiui: luid one of liydnigcii. 
hot, unlike cblorine, tliese two bodies do not unite to fonu 
liydrobromic acid when brought togeih<;r in sunlighL If. 
bovever. hydrogen mid th« vapour of bromine are passed 
tliroagh a rcd-liot tube containing finvly-dividud niclnllic plntt- 
num, a combination occurs of e^iual volom<?s of bromine and 
hydrogen and formation of liydmbromic Hcid gas. The com- 
bination of them two bodies may be easily shown by poaain^ 
hydrogen over bromine vapour and lighting the ewaping gas. 
when dfnse fuuitts of bydnoUic add will be noticed. 

Preparation. — Hydrobromic acid gns cannot well be prepared 
by the action of the ordinary acids on the bromides, ns in the 
case of hydrochloric acid, owiiiy to the facility with which 
hydrobromio acid splits up, with formation of free bromine. If, 
however, phosphoric acid lie lued. free liydrobromic acid is 

By far tbe bost mode of prepariog liydrobromic ncld gas ta 
to bring bromine and pliosphorus together in presence of a litlJo 


vraUr, when it violent action oooars, lijilrubromic acid gas ftnii 
pltmphoric acid being formed : 

P + 5Br + 411,0 = onm + IIJ-O,. 

In order to prepare the gaa a flask provided with n tlnublv 
boredcaoutchonc cork. Fig 37, is made use of; throuj^li one of tin* 
tioJeaagaadelivery-tabeis fixed, whilst Ibrou;,^! tlie other a atop- 
pared funnel tube iii passed. A mixture uf one part by wor^ht 
of uuorphoiu phofiphonia and two parts of water is intniduced 
ioto U»! Ilosk, mill Uii porU of bromine are allowed to fall dmp 
liydrop through the stoppered funnel-tube on to the mixture 

f .li, 3r. 

in the Qask. As eacli drop falls in a sudden evolutioD of gas 
occurs, occoinpuuicd in thu first part of the openitioii \iy a flanli 
of light, and us soon as a certain amount of hydrobronjiutc ncid 
baa been formed the brotniiiu dissolves ((uietly, and on gently 
wanning the flask hjdrobroniic acid gas is given off. This is 
then allowed to pass thnmyh a U-mbt* uonimmuy amorphous 
pbosphoms. to free it from any vapour of hroniino, and it may 
ha eoUcctul in dry »it<)ji]ifred cylinders hy displacement or ovi-r 
metenry. Tbi> samo niipiirntus serves for prnparing a saturated 
aqneooji solution of thu gas ; for this purpose the gas delivery- 
tube ia removed and a short tube substitufud for it. T\ih \>*as*» 
throagh n oork fitting in the tubulus of a i-utort placed in the 
position shown in Fit:. 38; the nock of the retort dips under 
water, and the retort itaelf aerves oa a Rsfetv>e in cane the 

65 iV(>pfrti'«.— Hydrobromic acid U a coloarieBB gas, having a 
strong irritating smell, with ftn aoi<l tast« and reaction. It fnmcs 
strongly in tlie air. and on expoaare to a teuiperature of — 73° 
(oUaiued by the cvapomtton of u ttiixturo of otiicr and solid 
carbonic acid), it condenses to a colourlr.fts li<juid, and atlerwarda 
freeies at 87° to a colourless ice-like solid.* 

■ FsnJav, PhO. Tnmt. lUS, p. 1S& 



Pure n[]iicotis lijdrobroniic acid ia colourless, and rematits so 
even whan exposed to lur; it t'nmcs when Butumtcd &t 0', and 

I then possesses a specific gravily of 178. The weak atmcoiis acid 
becomes sttoti}^, and the toiicontrutud acid wenlcer on dUtilla- 
tion. until (in ncitl containing from 47-38 to 47'8(i per cent, of 
HBr, distils over under pressure valuing from 0753 to 762 
metres. When tlic pressure under wluch the distiUatJon uccufh 
varies, the oouiposition of the coiulaut acid dianges a.s that of 
hydrochloric ncid does, and if a stream of dry air bo passed 
through th« nqaeons acid a point ia niched, difTcrent for OJicli 
t«nipeTatiire, ativhich the acid no longer undergoes change. Thii^ 
the acid which evRporates unchanged in air at 100' contains 
49'3f< per cent HBr, whilst thnt ohtninod at lt>'' ooDtaios 
5l.r>5 per cent, of HBr. 

I The \ariation of tlie specific gravity of the aqneoas acid with 
the percentage of hydrohromic acid dissolved has been determined 
bjr Topeo*,' as also by C. E. A. Wright,* who obtained the 
following numbers : — 
PerCenL HBr. Speo. Gnr. tt IS*. 
_ 10-4 1-080 
m nso II90 
30i) 1-248 
_ 40^ 1-885 
■ 48-5 1-4V5 
49-8 1-515 
The composition of thi."? ga.s is analogous to that of liydro- 
cMoric acid, and con be ascertained io a similar way by bringing 
a given volume of the dry goa in contact witli sodium amalgam, 

Iwboti sodium bromidv is fonncd and hvdrogeu liberated, the 
Tolnmo of which in fuuiid lo be exactly hsdf that of the original 
hydrohromic acid gas. 

$$ Thf Srotaidea. — These compounds are formed in a similar 

■ manner to Iho corresponding chlorides. They potscss an acalogons 
composition witli thujie, and exhibit similar prcipcrties. Dromine 
anit«8 with nearly all the metals, formin-j bromides, which are 
alio prodnccd by the action of inetalii nn liydmbromic acid, or 
B by the action of vapour of bromine on the metallic oxides, 
oxysen being 1i1>crated. 
The metallic bromides are nearly all soluble in water, the 

• JUr. DetOKh. CVm. Oa. liL «4. 

■ Cktm. XMt, KxiiL 24S. 


most iiisoluHle being silver bromide, AgDr,, meTcurous bromide, 
Hg,Br,. and load bromide, PbBr,, which latter is slightly soluble. 
All the brouiiUos are aoUd at the ordinarj- teraperature. but when 
hi'^ted they fuse and voIutUizf, koiuis iiiidurgoiDg dccompositiou, 
others rcmnining tiiichiing«d. They are, Uuvrvver, all decoiupoeed 
by chloriue. either in the cold or upon heating, a metallic chloridfl 
Imin}^ foruicd ntid bromiuv liliemud ; tlw'y «i-e also decomposed 
by Hiilphuric and nitric acids, with cvtiliuioa of hydrobromic 
acid, which again is partly oxir]ij:(!d, brumlnc being set fruc 

67 Dftftlion. tind E^linuitioit of lii'omine.. — Bromine wbou in tJw 
free 8tato may be repognlzed by the red colour of its vapour, and 
by iUt exceedingly disat'fecible odour, and hy imparting to btarcfa 
paste an orange-yellow colour. When present in siimll quanlitiiis 
it may be detected by sliiiking up with chlorufuna or etlier, 
whicli dissolves it. and acquires thereby a red or browuisli 

Bromine in the stale of a eiduble bromide may be delected by 
giving with silver nitrate a yellowish white precipitate of silver 
bromide, ^'Iiicli is insoluble in nitria acid, and» only with 
difticnlty in ammonia, but readily in cyanide of potassiuiit. Also 
by giving with nitrate {but not chloride) of palladium a reddish- 
brown preeijiitnte of the broniific ; by its tinging carbon 
diaulphide yellow in presence of hydrochloric acid and a drop of 
sodium hypocldorite ; and by the liheradnn of bromine on heating 
with aalphuric acid, with aulphiirin acid and manganese dioiudt^ 
or with aulphnrio acid and pi-tfisaium bichromate. 

^\'hen the biomine is piv,-*L-nt «s a solu hie bromide it 19 nsiially 

f-Mimated by precipitution ns bromide of silver, which contains 

42"42 per cent, of bromine. In preaenoe ftf chlorine the two 1 

elements are precipitated together by nitrate of silver, tlie pm- 

oipitate is then fused and weighed. A portion of it is next 

ipfiited in a cnrrent of eliloriuo, wlieij the whole of the bromine 

is expelled, the residue of silver chloride weighi^l, and from th« 

weight thus obtained and ttiat of the mixed silver salts, tlio 

qMfliitilies of chlorine and bromine nns calcnkted. Kor every 

7975 |)aita of bromine expelled, 35-37 parts of chlorine have lieeii 

substituted; or, if a dilTfrcDce of 44 S8 is observed, 79*75 parts 

of hmmiiie must have been present. Hence for any otii 

diflerence the weight of bromine is fouud by multiplying tb 

difference by rpju = 1'797, 




68 When cLlonne gas is passed into liquid bromine it is largely 
abacH'bed, a iwddish yellow volatile mobile uoinppund of tlte two 
I'lctiiL-nU boiiiK ronued. This liquid, wbic^h wus jjinparpd by 
ItaliUil but not aimlyzj-d Uy liiiti. is volublu in water, yieldii^ a 
3rQllow soliitioD, irom wlijch.on iwoliiig to belov 0'. a crystallioo 
hydrate (epantta otit, which melts at + T. 


IODINE. I = ia6-53. Vapour Density = I36'53. 

69 loniXE WM discovered in 181 2 by Courtois,' of Paris, id tbe 
mother liquors of th« soda salta which are prepared from fc«lp «p 
biinit scuwci^d. It was aflerwarda cxaniiDed by Davy,* and 
iDiicli more i:oinpIpte1y by Ciay-Luasac' Iodine derives ita nnme 
frotn iotiStjv, violtit-colourcd. oning to the pet^ulinr colour of ita 
vapour, by nicaus of which it was ftrst discuvL-red. 

Like ehlorioe and broiDine, iodine dues not occur in the free 
8lat« iu uatiin;, but is fnuiid eomliiiied with niKluls to form 
iodidea, which occur in sniiiU Quantities, but widely dlQ'uai-d, 
both in thvorgnnioimd inor^unir kinj.'drjui.'*, having bt'eu detected 
10 8ea-wat«r. iu sea-pUuts ntid aninmle. and iu many miueniL 
springs. Tlw <{uantily of iodine pniKCnt in scu-watcrise^ctrentely 
small, but certain plants and even animals have the power of 
atworhing aud storin>; up the iodine. The ash of the dwp-sea- 
wced (AVcMd jxUmatHi e3|)ecially) contains more iodine than 
that whivh grows in ehullow wiititr, and it is fruiii the wood 
collcctfHl on exposed and rocky t'oiuita, as the Durtli and west 
oooats of Ireland. Scotland, and fVance. that the gn«t«r portion 
of the iodine of comnierc« '\» obtained. Iodine haa recently 
been found iu araall i)uaatitics in Chili soltpotre. Xa NO,, and 
ia commercially obtainfid from the; inothcr-liquorH of litis salt ; it 
is likewise found in combinntiou with tcitvi-r in a ^Ivsican silver 
ore. in tome epf^^imens of South Aineriran lead ore, in certain 
dolomites, and in amall quantities in almost every deposit of 


' Courtoi*. Clmwtit, uiil DpMTmr*. jtun. Ctum. tuxriii. S41, 

* m.t rmu. nu. m 71 «i«i 487. 

* AtM. Chim. IxxKriii. 311, Slfr, aud xti. 6. 



rock salt. Iodine has also boien foand in coal, and it liM bcea 
detected in some few land and fresh-water plauts, and in many 
sea (uiimiib, as in apoiij^cs and oysters, nnd also in cotMiver oil. 
70 Prfparaiion. — luditie is maialy obtained rroni kelp orlmrot 
SGAveod. The stormy months of tJiesprinr; nro thoso in wliich 
tlic dcep-sca tangle is ttirown up on the north coasts of Franco 
and Irelaud and the wfatero coasts of Sf»tland. The inhahitants 
collect the weed, allow it to dry during the sumnier, and tlien 
burn it in large heaps. The a&h thus obtained is termed AW/) in 
Scotlniid and vartc in Nonnan<ly ; it contains frun] O'l to 0*3 
per cent, of iodine. When the seaweed is completidy burnt and 
when the ash is fused, a considcmhle fraction nf the iodine is 
lost from volatili;!atiDii, henc« it ia better Rimply to carboniza 
the weed. On lixiviating systematically cither the kotp or tks 
carbonized weed, a concentrated solution of the alkaline carhon- 
ftC«s, cIiIoi'mIi-'!^ tviid Hiiljdmtcs, t«^idhvr witli the iodtdea and 
bromidfs of the alknli-meulij i^ obtained, and from this solo- 
tioD the carbonates, cbluiidus, and sulphates are allowed to 

Fia. 39. 

crj-statlize, )v«\-ing the bromides and the iodides in tlie mothoi^ 
liquor. This hquor is then treated in several ways in ordor 
to obtain the iodine. 



(1) An excess oT sulpburic acid is added to the liijuor, wlii^ti 
the salpliides and sulphites wliich it cnnlaiiis are d ceo lu posed. 
and tlie iodine and bromiue liberated as hydriodic aud hydro- 
brotnic acid^. In this process tlm liquur, after nny cn-stals of 
sodium «ul|)liato vhieh may have forwed have been taken out, 
ia placrd in iron boHeni. Fig. 33. suiroDnded with brickwork, 
e»ch gently heai«l by a separate fire to a temperature of 60', 
■net fitted witli leaden hoods, whicb can he lifted oBF by means of 
a chain and winch. Each cover in litt«d with a leadca pipe (a), 
and this is conoocled with a series of glass or earthenware coa- 
deosen fitting onu into the oihur. After the introduction of 
the liquor, the covers are luted on wiili cky, tlio pipes (a) are 
fixed in their receptacles and connected with t!ie condeuaeis. 
Mangancie dioxide is thrown little hy little into the still 
through the hole {b), which can be closed by a stopper. The 
iodine tliu? 1ibcrate<l condenses in the retfivcrs,' and tho accom- 
panying water cstapoa iliroiigli a tubulus at the bottom of 
each TGceivcr and runs awny along the channel (r). When no 
more iodine diatiU over, the lenden pipes are dismounted, and the 
Btitlfi nre connected with a. second receiver (n). More tnanganeso 
dioxide is then added, and the bromine, which hitlicrto has not 
been liberated, is now disengaged and collects in (d) and in the 
WoulfTs bottles (E). 

Tlte decompoeitinn occurring during the formation of the 
iodine is represented by the following tx^uatiou : — 

2NaI + 3rr,S0, + JlnO, = I, + 2N'aHS0^ 4 MnSO, + 2H,0. 

Tbe iodine tlius obtained may then be pnKiiitly pnrified by resub* 
linmtioD. but even then invariably contains traces of chloride, 
bromide, and C)'anidc of iodine. 

(2) 11)0 iodine contained in the licinors, after ocjinmtion of 
the crystal I iuible alkaline saJla, may also bo libcrtt^^d by the 
addition of sulphuric at-id containing a considerable (juantity of 
nitric acid- The acidilied lifjuor is tlien itgiUttcd with the most 
voktile portion of petroleum (petroleum-naphtha, heroaiiie). 
which diflaolves the iodine. Tlie peln)]pum solution of iodine 
is next drawn off fr<^ini thu nqiicuiis licpior and ehaken \i\> with 
an aqueous solution uf caustic soda, whereby the iodino is 
withdrawn from tlie hydrocarbon and converted into iodide 

' Out ton of k»lp uanntly vli^ldi lOlbi. of ibiHut. 

and iodatti of poUtssvuni. The iodine ii tlicn Unrated from 
Uiese salts hy the addiliou of liy Jrocliloric acid, thus :— 

5NaI + NalOj + 6HC1 = 6NaCI + 3H,0 + I^. 

In order to purify the commercial iodine it is rnished with a 
stoall quantity of wat^-r. dried ou poraus ]<lntu8, mid irsublimcd. 
Accordiuy to Stas,' the only mode of obtaiuiiiy chemicaliy pure 
iodine (free from every trace of clilorine and biomiiit) is to 
di&Holvo the roiimiercial restdjliiiit<d snWniice in iodide of 
poLftfistuni solution, and then to precipitate tiie iodine by water. 
The precipitabv is well washed vith water aud theu distHlt-d 
witli iftnaiii, llie nolid iodine in ihn diatillate is collected and 
dried in vtuu6. lirst over solid nitrate of calcium, which it 
frequently chuugird. and «(ttrwttid» ovtreolid caustic baryta to 
remove tlie last traces of water and of hydriodic ncid.' 

71 Pt'opertifA— Iodine is a bright, Bhiiiing, crystalline, opaque, 
hliicliisli-grey solid. The crystals when laiRe possess almost a 
roetallio histre ; it crystallizes by sublimation in llie ihomVac 
oystem, in the form of prisms or jiyramids. l-'iuer crysteb are 
obtained from solution, as by i-xposing to tlie air a solatioo 
of iodine in ether, or iu an at^iieous aotuUou of hydriodic acid. 

PiQ. 40. 

The cryst.i]s thus obtained have a ratio of their axes reprejscnted 
liy the numbers 4 : 3 : 'J. The crystal represented in Fig. 40 a 
was obtained by Mariyriac from solution in hydriodic acid. 

lodiiic is a htavy substaaca having a specilic gravity of 
4'948 at 17°, meltin}.' betueen US" and 115° and solidifying at 
liyti (Htas). It bnila above L'00'\ giving rise to a vapour which. 

' JWherehrj, p. lis. 

' ITm I'tviliiatiou *f imlinv in Groat Bribitn amiiiinteii [n 1871 to l14,;pDIIi%, 
whfl*t MChKi liwi Iliin IhU quiiitl ily km nwauriH'tnroEl in rtuii';«. Tbo lUBWIBt 
mule in Clitli from the ni«t)icr-tl(|uan of th« xwta Mll|K!trc *riieftrt nKcutlr to 
htTt cuutldtnLlj UiiTcueO, no lua tliui C0,ui)Olba. romirijc uiniitllj man 



seen by tranfliiiilted white li^ht, possesses, vrhea clivniically 
piire. n $ptent)i(l deep blue colour, but vben mixed with air a 
reddish- viokt colour (Stoe). Tim epcciiic gnivity of iodine 
vapour wfts fouud by Seville and Troost to be 8 72 [air = l), 
wliii:)i i:orn>5j)uiidK lu Lite itcnHily, 1 ibH, provmg tti&t the niolu- 
oitle, or tM'o volumes of iodiue-gas,* wdgbs 12t]'58x2=2£S'06. 
At tbe ordinary temperaturu it voliililixus slowly, sbiningcTystals 
being deposited on llic sides of a botll«, on t]i» bottom of vhjdi a 
little iodiui; lius bwn placed. It ia a bad conductorof electricity, 
and possesses a peculiar smelt les^ penetrating tlmn, tboii(,'li 
bimiUr to that or, chlorine and brouiiiK'. Tlie spccitic huat of 
solid iodiuc 'n, accordiug to tht; cxpcriinciitfi of Ito^iiauU, 0-03412, 
and that of the liqnid 0!0«82. The latent beat of fluidily 
of iodinp is I1'7 thermal units, its lieat of vaporization 2395, 
tlieniiiU uuits. 

■When an electric diacharge is passed throuj^h a heated 
Geissler's vacHuni-tnbe containing a Inice of indine vapour, 
a spectrum of bri;;l)t lines is obtained, characteristic of this 
flemeut.' Tbis uinissioa s]>ui:tnnu ii, Iiowcvlt, not identical with 
the chonicttiristic absorption-spectnim of iodine, so carefully 
mopped by Thalt'ii,' and si;cu wlicn white light is posstd tliiougb 
iodine vapour. Sal^t' has recently shown that when an electric 
enrrcnt of feeble tension h pa.s»ed tJii-oti^'U a (Teissier's tulie 
coutAining iodine, anoUier set of bright bauds is obtained, which 
aroidenlical in position wilh the dark bunde of Tliali!-n's absorp- 
tirni spoo-tmm, each bright band being replaced by a black 
baud when the voponr is ilhimiuated from behind. 

j2 In its chemical propcni«» ioiliiio rt^emblta chlorine and 
broiiiire ; the two latter elements have the fiowep of displacing 
iodine from ita combinatinu with metals (or electro-positive 
elements) thus : — 

Whilst iiscnmbinntioiiswiih oxygen (or with electro-negative 
elements) are uiore stable than those of the other two elements. 
Thus jwline i-xpcls t-hlmine from the chlorates with formation 
of iodate and free cliluriue : — 

2KC10, + T,~2KIOs + ay 

Tbeee diflerences are explained when we examine the amount 

' PlitcVfT »n.l Hitlorf. mi. Tnva., )800. 18. 
> Km Snntin And. /{itadb. lSt!9. 
1 no. Mag. I*] U. ISO. 

of beat QTolved by tbe several deeompoeitiona in qnestico. 
Has hCAt may l)e taken as a mcasui'c of tJic affinity or poT«r of 
combinatiou wliicb the elements exhibit ton-arda one another. 
Tlitis tlio hc4it ovulvcd OD tbe comltinatiou of clilorine, bromine^ 
ftDd iodine with hydrogen, oi the heat modulm of tbe raactioas 
according to Jiiltus Thoinseu'e experiments ' is: — 

II + CI . . . 22001 heat anits 
H + Ilr . . . 8440 
H + I ... -6036 

AVhcD these same elementa unite with oxygen and hydrogen 
to form tbe oxyacids (HCIOj, lllJrO^ UIO3) tbe biiat evolved 
is as follows : — 

C1 + 0,H 
1 +0,H 

23D40 heat nnits 


H«nce vo SCO thitt as regards affinity for oxygen chlorine 
stands nearly midv'ay between hromiue and iodine, for 
43537 + 5384 _^^g„ 

Iodine dissolves but very sparingly iu water, one part being 
soluble ill 5524 parts of wiilur at 10" ; but it dissolves fredy in 
an atjueous solution of potassium iodide, aiid iu alcohol, yielding 
brown sohitions. Tincture of iodine of the pharmacopceia contains 
^02. of ioiliiie, ioz, of iodide of pijlii.'!6iu]ii, rectified spirit 1 
pint. It \» uUu soluble in cbtorofunn, carbon disulphido, uiid 
many li<)uiJ hydroimrbous,imparliii;: to these liiiuida a tine violet 
colour wlieu present in email ipmntilies, and in larger quantitiCB 
forming a black opiique srtbilioii, vbit:h in tbu case of carbon 
dtsulpliide is dintliernious, ollounug tliu iuvisible heating mys of 
low rufiiuii^bility to pass, though it is opaque to the ^nKible mys. . 

lodinedoes not combine directly with hydrogen, bnt unites vriUi I 
many 0!' the nic-LiUs «iul mptiilloids with evolution of light and 
heat. Tims solid phospborna, when brought into contttcl with j 
iodine, first lu^Ils and tlicn bursts iuto flame owing to the heat 
GX'olvod in tlie act of combination ; and powdcreil nntiinony 
lakes lire when thrown into iodine gas, antimony iodide being 
produced, whilst, if tbe vapour of mercury lo ptuwcd over heated 

> ClUm. Soc Joam, xxvl. Uii. 

iodine, iniineiHate action occurs, the ioilides of mercury being 
formed. Whea iodine is brouglit iuto coBtact ^vith water aud 
filings of iron or zinc, a violeut ruiction oi^ciira, colourli>ss goIu- 
tioDs of the respective iodides nsulttiig. The action of iodine 
upon tbe alkali-metals is aaalogous to that of chlorine and 
bromine. >!<ridium aud iodine can be heated togeUier without 
any alteration, whilst if potassium bd employed an explosive 
combiitntioD occurs. 

Potash at once decoloriKeii a Bolution of iodine, iodide and 
iodate of potassiaoi being produced, thus : — 

6I + 6KnO =CKI + KIO,+ 3n,o. 

M'hen acted upon by strong nitric ncitl, iodine is completely 
oxidiz«d to iodic acid 1110^ 

The moet chavactemtic property of free iodine is its power 
of forming a splendid blue colour with starch'pasta. This is 
formed when starch gmnulcs arc brought iuto contact witll the 
vapour of iodine, or, better, wlicn, u sohUion of iodine is added 
to starch-poetc. The blue colour disappears on wurmlag tbe 
solution, but reappeiini on cooling, and its formation eervra 
ae a most delicate te»t for the presence of iodine.' In order 
to exhibit tins property, a. few yniiris of iodide of potassium 
may be dissolved in tlinje or t'uur litres of water placed 
in a lar^c gloss cylinder, and sttriie dear, diluto, wcU b'lilvd 
8tarch-pa9t« addetL As the iodine is here combined with tbe 
metal no coloration will be sern, but if a fnw ilmps of chlorine 
water be added, or, bettor, if a little of Ihc air (containing free 
chlorino)froma bottle of chlorine water bo poinijd ou to the surface 
uf tlie lii^uid, a blue film wilt be formed, which on stirring will 
impart a blue tint to the whole mass. Iodine both free and ia 
combination ia largely used in medicine, 

> CoDfn and (inalttcr de CUatin', Ann. Chim. DO, 67. - 


Hydriodic acid. H I = l:i7'5;t. Density = 63-7i55. 

73 Iodine ninl hydmgen comtune directly togcOtcr wii«n tliey 
ace passed over finely-divided i>tatinuia heated to redjieas, rormtog 
u strongly acid gas, hftving properties very similar to liydrocldoric 
And hydrobromic acid. 

nydriodic auid can nW Im oblaintKl liy heating lodidu of 
potAssiuTu with phosphoric, but not with sulphnric, acid ; for 
when Una latter acid is iLsed, sulphur dioxide SO, and free 
iodiiK; an; formed at thu aauic time, thus : — 

3H, SO, 4- SKI. = 21vH.S0. + T, + SO, + 2H ,0. 

On ttio otiier hand, hydriodic acid is easily prepared by allow- 
ing iodine and phosphorus to act on one another in presence of 
water, thus : — 

P + r)I+4HtO = EHU-H.POj. 

Pnparatiim. — Fortliispiirpose 1 part hy weight of amor])lioiia 
plioaphorus and 15 parta of watei' are broujjht tojietlier ui a 
tuhiilaled n-lorL ur tliusk. provided with a caoutchouc cork and 
gas delivery-tube, and to these 20 parts of iodiiiu aio gradually 
added, the contents nf the Hank iliiritig; tliio npiiratiou heiii}; kepi 
cool by iiunici'aiit]^ tlie llask in cold water. '^Vhen all the iodine 
liaa been added, mid aa vooit iis no furtlier evolution of gas can 
he noticed, the Hask may I>e gently warmed. The gjis tJius 
obtrtineil miiy filht-r be received in dry bottles filled with 
mercury in the mercurial trough, or it may be collectijd by 
displacement, as it is more than four timea ao heavy as air. 

If we possess a concentrated eohition of hydriodic acid, the 
gas may be obtained iu a atill more simple manner. Two parts 
of iodine are di.'i.snlved in a<|uenuj hrdrindic acid of speeific 
(iravity 1*7, and thin fiohitioii is allowed to fall drop by drop, by 
means of a stop-cock fminel-tube, into a fia^\ containing amor- 
phous phosphorus covered with a thin layi nf water. The evo- 
lution of gas occurs at iirst without any application of heat heinj; 
necessary, but aft«r a time the flask may be slightly wanned. 
The apparatus, Fig. 41, is used for the puq>o»e of preparing, 


Kydriwlic acid exist"! at tlie oMinnry tempemturc 
piMmie as a coluurtess gas, having a 9tn)n;;Iy acid reaction 
and suffocating odour, and fumiug strongly in tbc air. It can 
l>e comleiuiCHl 1o a colourless liquid,' by a itrenaure of four 
Qtnioeitlierea at 0', or by exposure, under the ordinar>- atmos- 
Itberiu preasure, to tlie lovr tetnperattire of a bath of ether and 
solid carbonic acid, nnd if cooled to- 55° it freezes to a colour- 
loM ice-like »olJd ma&a. 

Itfl specific gravity (air = 1) has been found to be 4'3737, 
thus ototiely correspoiidiag to its tbeorftii! density, 63*71)5. 

Hydriotlic acid gs,s is easily decomposed by heat into iodine 
and bydrogen, as is M«n by Die violet colour wluob it exhibits 
whoa the gas i$ passed through a heated glass tuba A hot 

FkmJay, Hil. TfHmt. 19IA, i. I'D. 

metallic wire plui^rd into the gas also causes aii iinmodtiite 
ilecom position, violet fiimes of iodine making their appearance. 

74 The juiueous acid is obtained by passing tliogas into voter, 
by which it is JibsorbeJ quickly ami iu large quanlitica, yield- 
ing whcu kept cold by icti a solution which Ia twicd as hcury aa 
water, Iiaving a specific gravity, according to De Luynea. of l-SS. 
A simplt! mode of preparing a dilute aqueous solution of bydii- 
odic acid conaistii in piui.<)iiig a current of sulphuretted hydrogen 
gas through water, iu which finely-divided iodine is saspeodfldi 
the teactiou which occurs being as follows — 

On standing, the clear liijaid may bo poured oS* from the 
precipitated sulphur and tmiltid touxpelanyimce of sulphuretted 
hydrogen. It is found that the strongest acid which can in tliia 
way be prepared Iiu^u spCHiilit' gravity of 1'56. The r«iison that 
a more concentrated acid canuol thus be obtained is explained 
by the fuct thai in the formation of hydriodic acid according to 
the above equation. 12080 heat unita are absorbed, and hence the 
decomposition could not take place at the ordinary teniperataie 
unless by tUo aolutiuu of the ^as iu water 37800 hcat-unita were 
etnitlvd. As. liowt-ver, the more concentrated the eolution, the 
leaa is the amount of lieiit developed, it is dear that at a certain 
point, viz., wlien the quantities of absorbed and emitted beat 
bolaiice each other, the rcactiou must come to au end.' 

On distillation, aqueous hydriodic acid behaves like aqueous 
hydrochloric and hydrobromic acids. Both strong and weak 
aqaeoua acid yielding on diatjllntiou in an atnionphere of hy> 
drogen (to prevent oxidation and liberation of iodine) an acid 
of cousLaut compuaitiou, boiling at 127' (under a prosauro of 
774 mm), and containing 57*0 per cent of liydriodio acid. 
If 4lry hydrogen be led through aqueous acids of varying 
strengths, each ^iU attain the same coastout compoBition at 
the sftue temperature, thus from 15° to 19° the constant acid 
contaiued 603 to 607 per cent of Hf. Wlien the hydrogen 
was passed through the liquid at lOO^.the per-ccntage of hy- 
driodic acid in the coustimt acid was 5K-2.^ and hence it is 
seen that no definite hydrate of the ucid ia obtained by boil- 
ing, 08 was formerly supposed. Aqueous hydriodic acid aleo 

* Naamann, Ber. IktiUth. Chm. Q*t. U. 177. 

* SoKM, Chtm. Jottm. xili. mo. 



!jad\y undeigoeR oxidation with Hbemtion of iodine when cx- 
poeed to the air, the colourless sulutioa becomiDg brown owiuy 
[to Uic uoluhility of iottioB iu the acid. 

75 The Iodides. — Tlie metallic iodides pos&esa great analogy 
with the contapoiiJiiig chlorides and hromides; they are all 
solid hodies, less fusible and volatile than tlie conespoiiding 
chlorides nnd bromides. f>ilvcr iodide. A;; I, morcurous iodide, 
Hg, 1, and mercuric iodide, Hgl,. are iitsoluljic iu water ; load 
iodide. Phi,, sparingly soluble ; whiUl the other metallic ioclides 
dissolve readily in wa.ter. Most of the iodides are decomposed 
ou bttating. either the metal or an oxide being formed aiid 
iodine Mt frvo. 

All the iodides, whether soluhb or in<Lalu1>le in water, nro 
decomposed by chlorine and nitrous acid, the iodine being liber- 
itted. Some of the insoluble iodides posaast a brilliant coloiir. 
Thus, on adding a solution of corrosive tubtimatc (mercuric 
chloride) to a aolnble iodide, a salmon-colonred precipitate is 
thrown down, which rapidly changes to a brilliant ncarlct one of 
tnercoric iodide, Hg[j.which is soluble in excess of either reagent ; 
a solahle lead salt, such its the nitrate or acetate, produces a 
bright yellow precipitate of lead iodide, Pbljj silver nitrate 
gives a light yellow precipitate of silver iodide. Agl, insoluble 
in nitric acid and ammonia. If a mixture of ferrous sulphate, 
FeSOj, and copper sulphate, CuSO^, bo added to that of a soluble 
iodide, alight green precipitate of cuprous iodide Culj. is formed. 
This reaction depcods upon the fact thiit ferrous sulphate is 
oxidi^d to ferric sulphate, Fe,(SO^j, whibt cuproos iodide is 
precipitated, thns : — 

2CuS0^ + 2FeS0. + 2KI = Cu J, + K, SO, + Fc, (SO J, 

Hiis feaciion serves as a means of roughly separating iodine 
from a mixture containing chlorides and bromides. 

The metallic iodides can be prepared by similar processes to 
those which yield the chlorides aud bromides. 

(1) By the direct action of iudiiic on tlio metal, iuj in tlie coses 
' of the iodides of iron and mercury. 

(2) By the action of iodinH on eertain of the metallic oxides, 
hydrates, or carbonates, as those of potassium, sodium, barium, 
caloiniD, and silver. 

(3) By the action of hydriodic acid on certain metals, such 
as sine, hydrogen being liburated. 


(4) By the sctioD of hydriodic acid OD the metaUio oxidn, 
hydrftles, or carbonates. 

(fi) By adding a soluble iodide, such aa potassinm iodide, to 
a solution of tiie salt of the meta], when the metallic iodide U 
thrown down in Uie form of a precipttato ; this method, however, 
can only Ik ased when the iodide required is insoluble. 

76 Jktection and Ettitnation. 0/ loeiinc. — For the detection of 
iodine, the starch reaction, the violet-coloured vepouis, and Lba 
above-mentioned coloured proclpitAtoa arc sufiicieuL 

To estitoato iudlae in tlie free state, a standard solatioo of 
sulphurous acid 13 employed, and the point asoertaincd at which 
auffioient of this solution haa been added to reduce all the iodine 
to bgrdiiodic acid, thus ; — 

I, + 2ir,0 + so, = 2HI + E^g 

lide " 

For till; (luanlitativodet^mEafttEoa of iodine iaa eoluble iodide 
and for tli« exact separation from chlorine or btomiQe, nae may 
be made of tlie fact that the pfdladium nitrate, Pd (NO^^ pio> 
duces vitli solutions of an iodide, an insoluble precipitabo of 
Pdlj. wliidi on ignition yields metallic palladium. Iodine when 
in the form of an alkaline iodide can be weighed alao as iodide 
of silvLT, M-hi'n neither chlorine or bromiuc arc present ; lOO 
partsof silver iodide contain 54'12S parts of iodine. In tliecase 
of the insoluble iodides, it is best either to transform them into 
soluble iodide of sodium by fusiu;; tlipm with carbonate of (oJa, 
or to dijrest them with zinc and dilute sulphuric acid, wImu 
hydriodic acid is liberated thus : — 

2 Agl + Zn + n,SO, = 2ni + Agj + ZnSO.. 

If it is required to determine chlorine, bromine, and iodine, 
when mixed in solution together the following method may be 
employed ; — 

Field has shown ' that chloride of silver is completely de- 
comimsed by diyostbn with bromide of potaasinra, the chlorine 
and bromme chatt'pHi; places ; and tliat both bminide and 
chloride of silver are decani posed in like manner by iodide of 
potafisiam. Hence, if a solution containing chlorine, biomtDi^ 
and iodine, be divided into 3 ei]iml parts, each portion precipi- 
tated by nitrate of silver, the first precipitate dried and weighed. 

) CUa, Soo. (^rt. /t»im. x, SSI. 



rBMond digested with bromide of potassiura, then dried and 
P'veighed, and the third digested with iodide of potassium, then 
dried andwe^hod, the reliitivc quitutities of the three clcmcuts 
^nwy bo determined from the following equations : — 

x-f y -t- z= w 

7975 ^ ^ 

x + y + z = w 



. 126-53 

where w, w', w", arc the weights of tho three precipitatee, 
and x,y,and z,Lbe uukaou-n quautities of chloride, bromide, and 
iodide of silver respectively. Tlie value of x mn.y be found by 
mbtrtctiog the first of th^e eqaations from the second, tbut 
■of y, by aabtrocting the second from the third, and that of z 
finally after substitatiiig the vuluea found for x and y m th« 
fint equation. 


V 77 Two compoumls of elements are known : — 
(1) Iodine zaonochloride, ICI, 
^2) Iodine trichloride-, ICl, 
H They are both obtained by the direct union of chlorine and 
iodine, the higher cUorine beiog formed when the former is in 

looms MONOCBIORIDB. ICI = 1619. 

>I8 prepared (1) by passing dry chlorine gas over dry iodine 
until the latter is completely liquefied ; (2) or, according to 
Berzeliua, by distilling 1 part of iodine with 4 pnrUof pot^isaiuin 
chlorate ; (3) or by boiling iodine with strong aqua regia; after 
dilution with water the lirjuid is shaken up with ether, in which 
the chloride of iodine dissolves and remains behind when the 
ether is evaporated.' 

The product thus obtained is a reddish brown oil, wliicli, on 
standing, eolidiii OS, forming long well-defiiied crystals, which mcdtr 
at S4°'7. It sineUa like a mixture of cblorine aud iodine, 
bleaches indigo iwhition, but does nob colour starch paate blue, 
lie following analyses show the composition of tliis substance : — 

Biunen. An*. Ckem. Harm., hair, 1, 



lodiiie . 

126-53 78-85 
35-87 21-15 

LiqSI Solid. 

77-«5 78-32 * 

161-90 imi>0 




loDiSB Tbictilorioe. ICl, = 23264. 

Ts obtained (I) by adting on ioiline, gonlly Iieatwi with »1 
large excesa of chlorine; (2) by treating iodic acid HIO, withj 
byclrooliloric aciil; (3) by heating ioditto penloxide, 1,0^ vitlij 
pentiichloride of pliosphorus, FCl^. 

I'his compound furiiis luiij; lentoii-coloared crystals, aud very 
readily undergoes diseociation. When heat«d in the air 
2iV it dGcoiiiiiosos. giving off chlorine caa. formini? the me 
chloride ; but when heated in an atmosphere of cblorine it doetj 
not documpuso, except at a much higher tumpomture, whtchj 
riacs as the preasuve of the chloiiua is increased. Tliai, under^^ 
a pressure of one iitmosphcre of chlorine it decomposes iit C7' into 
the nionochloride and free chlorine, and theae again u&it« on 
cooUd<> to form a yellow nublimate of Oie trichloride' The 
composilioa of the corupoiiud ia seen from the foUowu 
analysis : — 

126-53 54-39 
iOO-U 45-61 



232-&4 100-00 


Both these compounda dissolve in water, ether and alcohol 
apparently without ducouiposiliun. When cither of them 
acted upon by potash the decomposition ia as follows:— 

GKHO + 5C1I = 5KC1 + KIO, + 21, + 3H,0. 

They are both very hygroscopic and give off irritating vapouis. 


Iodine unites with bromine to form a solid, volatile, crystalliiiel 
oompound which ia probably tho inonobwmido, and also s datk I 
liquid, possibly the tribroniido. These bodies posBMS properties 
aimilar to tho.<ia of tlie chlorides of iodine. 

BreukMi, Btr. Ikutith. CAm. Ot*. tHL 4S'. 



FLUORINE. F = i9-i, 

78 FlcobikB has up tu the present time resisted the innumer- 
' aWe attempt wliich liave Wea mmlc to isolate it ; it is, moreover, 
the only elcnic-nt whicti has not hmn combiued with oxyt^en. 

Fluorine oocurs not uncommoiily combined will) coJcium, 

fomiing the mineral fluor-sp«r, or culciitm fluoride, CaF,. crys- 

ftftiUzing in cubes and octahedrons, and found in Derbyshire, the 

Han, Bohemia, uiid cWwliere. It is likewise contained in 

other miuerals, such as in crvolite, a fluoride of aluminiam and 

aodium (;^NaP'+AlF,). found in Grconland ; wliil&t in sninller 

qnantities it occurs iu fluor-apatite, yttrocerite, topae, lepido* 

lite, &C. Fluorine has been delected in minute traces in tjca- 

vater and in the watt>r of many mineral springa. Xor ia its 

^nseoce confined to the niineral kin^^tlom, for it hnji been found 

Fin the enamel of the teeth ils wcH n.s in the hone» of manminlia, 

■twth fossil and rcc«nt,a&d it is said to have been detected in the 

hlood, in the hraiii, and in milk. 

The fact that glass can he etched vhcn it ia exposed to t!ie 
fames an.«ing from fluor-spar heated \rith sulphuric scid, was 
known towards the Utter part of the seventeenth century. Scheele 
first Btatcd that fluor-sptir wcs the calcium salt of a peculiar 
acid, which he ohtained in nii impure Btate by diatiUatiag a 
mixture of enlphuric acid and fluor-spar in a tin retort Scheele 
also prepared the gaseous tcimfluoritle of ;<ilicon, SiF^, by the 
action of the acid thus produced upon silica. It is. however, to 
rescRTclies of <«nc, and Tlii^iiard,' that we aits 
^indebted for the firat reliable information concerning hydro- 
fluoric acid. TI1C viewg then held concerning this conipoimd 
were incorrect, inasmuch aa it was supposed to contain oxygen, 
and termed lluoric acid, until Ampere in 1810, and subsequeolly 
Davy, showed that this acid is analogous to hydrochloric acid, 
and tJuit Quor-spar, formerly termed tluate of lime, is, iu fact, 
a compound analogous to calcium chloride, contaiiiing the 
metal calcium comUned with an clement Eiimilar to chlorine, 
termed finorine (fromjfwo, I flow). Even «p to recent years 
I the nature and constitution of the lluoriiie coni|>f)UudR has been 

• Am. CMm. Phft. [1] tiix.. 204. 

discussed ; aud it ia only ktely Uiat Gotv's researches taken 
togctlicr with theprepaRitioQof organic fluorides have dcfioitelv 
proved the true analogy of the hydrogen componnds of fluorine 
and chlorine. 

Ib its power of comltining with hydrogen and the metulg, 
fltiorino surpasses chlorine. Thus, vhen we attempt to lit>crat« it 
from its compounds, it unites at once with phitluum aud sik<;r 
to fonn the fluorides of thoir metals, whilst it decomposes water 
with formation of liydrofluorio acid. Especially remarkabk^ 
however, is its tendency to combine witli ailicon ; it attacks 
glass instantly, replacing the oxygen in silica, SiOg, with 
formation of tho volatile tctTofluorido of silicon SiF,, These 
propertiL-s serve lo explain why fluorine has never been isolated, 
although Diatty chemieta have made the attempt. Thus Davy 
heated dry fluoride of silver with chlorine gas in a glau tube, 
when silver chloride was formed, but the liberated fluorine at- 
taclccd the glusii, liberating oxygen g&s, and when the experiment 
was made in platinum vessels a fluoride of this metal wu 
obtained. Knox tried similar decompositions in vt-ssela made 
of fluor-spitr, but the fluoride* he employed M-ere not dry, and 
yielded on decomposition, hydrofluoric acid, inslead of fluorine. 
Kanimen-r, acting at 80" with iodine ou silver fluoride in a 
glass tube, states that a colourless gas is evolved, which he takes 
to be fluorine, whilst silver iodide is formed. Gore.' however, 
faaviDg most carefully investigated tlie whole subject, finds thai 
perfectly dry silver fluoride ia not decomposed under a red heai 
by either chlorine, biomine, or icxl inc. whilst if n high temperatim 
is employed, a fluoride of the metal [plaLinum. gold, silrer) b 
formed, and when tubes of gmpliite or charcoal an used a 
fluoride of carbon is obtained. Judging from the results of 
t^ese interesting experiucnte, it appears improbable that, for 
the present at least, fluorine can 1)e isolated. 

' PkiL JVa«», 1870. p. «£?. 




HTDBOFLroRio AciD. HF = 20" 1. Density — 1005. 

79 Aubydrous hydrofluoric acid, HF, is a Tolatile coloarless 
liquiil, best obtained. HCcordiug to Frcmy ■ anA Gore," by beating 
to rcdneas in « platinum retort thu dnubic llunrido of bydrogen 
•od potaj^ium UF -(-KF, which has been previously fused. A 
descriptioD of (.fae process employed for preparing pure liydro- 
finoric acid may give an idea of t)ic dif^culty and danger of 
H chemical invcetigations on fluorine and Uuoridcs, as veil aa of 
tlie precautioDH vliich must be taken. 

■ (1) For this purpoae about 200 grammes of the fused anltTraa 

H placed by Gore in a platinum bottle, or KtorC (a Fig. 42). }(o 

VWMla of glass, porcelain, or other aubntance contaiuiu^ silica 

»(un bo u-sed in the preparation of tliia acid, as the silica is at once 
attacked by bydrofluoric acid unless it is absolutely anhydrous, ft 
volatile tetratluoride of silicon and water being formed, thus : — 


4HF + SiO, = 2H,0 + .SiF^. 

The platinum bottle -was then geuUy heated to as to fuse the 
salt, and thus couipletf Jy drive off any traces of water. The long 
platinum tube wns then connected by menns of a lute of fused 
sulphur to tlie neck of the bnttle, the condenser suri'ouudiug 

' j<«ii. Ckim. /HjfjL 131 xlrii. 5. 
• Pkit. Traia. lSi][», i;3. 

this tube being filled with a fn>cziDg tnixtitre poured throogb 
the open tube b, whilst tho iilutinum boltle c, immersed iu t 
freezing mixture, was einployeJ to receive tliis distillate. This 
bottle was provided with an exit-tube of platinum upon the 
Qpper end of which a sltoit- angle tube g of platiuum, tamed 
duwuM'uixIs, WHS fix^d to prevent atlrai'.t«d moisture fiom TunoiDg 
down into the bottle. On gradually raising the temperature, the 
fused salt KcRina to decompose. hydmHiiuric acid hi given off 
OS a. jjiiii, which ctindctises in the platinum tuhe and runs into 
tlic platinum bottle. Great eare must be taken to htve all t[te 
appumlus free from moisture, and the acid must be redisUUed 
in order to remove tmcea of saline matter whi<;h are apt to ba 
carried over. 

Tho ucid thus ohlnined is a highly dangerous sulwrtance. and 
requires the most exti-eme core in its manipuktion, the inluilatiou 
of its vapour h»\'ing produced fatal effect*.' A drop on 
the skin gives rise to blisters aiid sores which only hcul after a 
very long period. From its great volatility the anhydrous acid 
can only be eafely preserved in platinum bottles having a 
Hanged mouth, a platinum plate coated with paraffin being ti<^htly 
secured to thi- Haii^ud mouth by clamp screws. The acid must 
be kept in a cool place not above a temporature of 15^, other- i 
wiae it is very likely to burst the bottlr., and a frecring mixtOMJ 
should always be at hand when expennienting with it (Goio). 

Anhydrous hydrofluoric acid can aUo be obtained by actii^ 
on dry silver tluoiidc; with hydrojjRu. 

(2) If the hydrofluoric acid is not required to be perfectly anhy< 
drous a tnuoh easier process then the foregoing can bo &dopt«d. 
Thia consists in the dpcompoailion of fluor-Bi)ar by strong 
sulphuric ncid, when hydrofluoric acid and calcium eiUpttate an. 
fonned, thus:— 

CaF, + IIjSO, = 2nF + CaSO.. 

For thia preparation vessels of platinum, or, on the hti^ scaH 
vessels of lead, con be employed. On heiiting the niixtuie, the 
nearly aahydmua acid which distils over can either be condensed 
bypassing through a lube placed in a freezing mixture, or into 
a small quantity of water contained la a platinum dish if a 
dilute acid ho needed. The dilute acid may b8 preserved 

' rroCpHor Nti'kK'Jt, of Knticy. di«d in 154D rtnin BccidcDUilIj bnathii^ 
Tkpour of thui avid whilit oEkdcarauruig to UulnU fluuriue. 



gotta-percha l)Ottles. but tliis subetance \a at ouce aut«d upon 
by the anhydtoaa acid. 

One fonn of plaUiium Apparatus nfied for preparing tlie j>as i» 
showa in Kig. 4;i The L'-tube is placed ia a fi'eezing niixturu 
when thegus lias to be condensed If an itqucous solutmu uf 
the acid is nticdud, tlio urrftugfumiit sliown in Fig. 44 may be 
omploycd. It consiitts of a luadeu rulurt. a, on to which a leaden 
head, c, can be cemented at bb'. The neck of tlie retort tits into 
m leaden ivccivcr at e, in which is placed a ])IiiLiiium biisiri con* 
' tainii^ wattip. TTw acid vapoura are Rbsoibed by the wal*r and 
thus ft solution of tltc noid is obtaiuud frc-u from Icud, which 
would not be the case if the water bad been niuiply placed in tbo 
leaden vessel. The tnlio ff nerves to allonr the escape of air and 
x)t excess of hydrofluoric acid gas. 

Fitit i\ 14. 

So Propertiea. — ^The spceifio gravity of liquid anhydrous 
hydroflttoric acid at 15" is 0'9S79 (Gore), or it is a little liglitcr 
than water. It boilsat 19°-4, and does not Holidify at' -34'. If 
it is perfeclly dry it does not act on gloss ; the ali};litc3l tracu 
of moisture, however, renders it capable of doing so. Tlie 
tension of itsvapoiirnt 15" is 390""°. The acid scarcely acts 
upon the metalloids or on the noble metals, and the other mctuU 
do not decompose the acid below 20'. Potassium and sodium 
dissolve in it as in water with evolution of hydrogen and forma* 
tion ufa fluoride; it decomposes tbo carbonatea with efferves- 
cenc« and with formation of fluondes. It conducta electricity 
rather better than pure water, and when it is submitted toclectro- 
lysis with platinom electrodes, hydrogen is evolved at one pole 
and a fluoride of platinum i» fiimicd at tlie other. Its general 
behaviour would lead u$ to place bydrofiuoric acid between 
hydrochloric acid and wuti:r, though it b much moro dotely 
allied to the former than to the latter. 

The composition by volume of the anhydrous acid was s&cer< 






, (ho 

n i« V 

Uined by Gore by measuring ttie volume of bydrogen needed 
to combine with the fluorine contained in a given weight of 
silver fluoride. From tliis and other cxporimcnts he arrived 
at the ooadusioa that oue Tolume of hydiogtMi necessarily 
yields two volumeg of hydrofluoric acid gas, and that this con- 
tains for ev«ry oiio part hy weight of hydrogen 191 partfi 
by weight of fluorine. Tbo density of gaseous anbydrotu 
bydrofluoric acid is t«n limes that of hydrogen. 

Hydroflooric acid is very soluble in tvater, the specific gmvit 
of the solution rising to 1'25. The cODcentrated aqueous acid 
beuoiaua weaker on boiling until boiling at 120" it attains 
a constant composition of froni <iC to 38 per cent of the 
anhydrous acid, but it does not thus form a definite hydrate; 
when allowed to evaporate over caustic lime ia tbu air, tho 
aqueous ucid uttuins a constuut compoaition ooatoioing 326 
cent, of the anhydrous acid.' 

QtialUativt Ddtetwn of Fluorine — In order to test for 
presence of Lydrofluorio acid, its power of etching ou gliiSS 
made use oC Per this purpose a small flat piece of glass is 
covered with n tliin uuil eii'rin film of melted beea*-wax, and after 
cooling, some lines or marks ar» ninde by removing the wax by 
a sliarp but not a hard point. The dry substance to bo tested 
is placed in a platinum cmciblu or small leaden cup, and 
covered witlt strong sulphuric acid, the crucible being gently 
wanned; after the lamp has been removed, the slip of covered 
glass is placet] on the crucible and allowed to remain far tea 
minutes. The wax can then be re-melted and wiped olT with i 
blotting paper, when the etching, indicating the presence of ^| 
fluorine, will be seen. In perromiitig lliis experiment it is wtll ^* 
to remember, on the one huud, that if the (juaiitily of tluoriue 
present be very small, the etching may not at once be visible, 
but may become £0 by breathing on the surface of the glass, 
whilst, on the other hand, if the point employed to remove the 
wax be a hard one. a mark or scratch may sometimes thus be 
seen on the gloss when no fluorine is present. 

The divisions on the s'lAm of endiomutvrs and tbcTmometeis 
are etched by hydrofluoric acid.wliich is evolved from a raixtare 
of fluor-spaj and strong sulphuric acid in a long leaden trough, 
over which are placed the glass tuWs covered witli wnx, and 
having the divisions narked upon them by scratching oS* the 

' RoMoo, Chftn. Sve- J«iim , iIlL, ItS. 


vox. The etching u best eBrect«d iu tbe cold, and vith 
anbydiCHis hydrofluoric acid ; the tube must in this case be 
exposed for eoiRu hours to Llic action ofthv gas, aud tlie trough 
covered with several folds of thick paper. 

8i Fluorides. — The compountLs of fluorine with tlie metals are 
best foroied by acting on the metal or on its oxid«, hydrate, or 
carbonate, with hydrofluoric ncid. The fluorides of the alkalies of 
silver as well as those of most heavy metals dissolve iu water ; 
tbose of th(>alku1iiH!ciirthsftr«iDsolubIe; and those of the earths, 
with the exception of fluoride of yttrinnt, are soluble in water. 
ilost of the fluorides unite with hydrofluoric acid to form crys- 
tallioe cotn[iOuiids, which am termed the acid fluorides. They 
also have a remarkable ftuility of union among tbemselvoa, 
giriog^ rise to double salts, which fniquently are well cry8t&l- 
lized. They are all decompoaed 1^ treatment with .•jnlphviric 
acid, yielding liydrofluuric acid and a sulphate, whilst some, aa 
tbe ailver salt, even uQdergo tbe same decomposition in presence 
of liydrogen alone 

OXYGEN. 0=15-96, Density = 15-96. 

8a Of the clvmvuta which occur on our planet oxygen is the 
most widely diffused, and is found in tbe largest qiiantit]^. 
The old crystalline rocks, which constitute the chief mass of 
tllo earth'a crast, consist of sihcat*^, or compounda of 
silicon and various metals with oxygen. These rocks 
contain from 44 to 48 per cent of oxygen. "Water likewise 
is a compound of oxygen and hydrogen, containing 8S-87 
cent, of the former dement Oxygen exists in the free 
in the atmospliere. wliicii containa about 21 per ccut. 
of ita volume of tliis gas. Although the absolute amount of 
free oxygen contained in the air is very great, yet the pro- 
poilion which tlie free oxygen lieara to that iu a alate of 
combination ia but very small 

It has already been mentioned, in the Historical Introduction, 
that the air was believed to be a simple or elementary eub- 
until the iuvesiijjatioua of I'riestley, Ituthcrford, and 

deele ahowed distinctly that it is a mixture of two different 

Pgaaea, only one of wliicli is capable of supporting combustion 

and leajoratioD. This constituent of tbe atmosphere is oxygen, 

diacovered on the 1st of August, 1774, by PriesUey, who, by 



heating " red precipitate " (mercuric oxide) b^ means of the sun'i 
tftj-s, decotnposfJ it into oxygeu and metallic mercury. The 
discovery of oxygen enabled Lavoisier to put fon*'«rd tlie true 
tlieoiy of combustion, and to tbe body capable of supporting 
tbis combustion lie g«ve tlie nnme "" oxyg^ne " (i^C^ sour, and 
•ftfiau) 1 produce), from tbe fact that the products of com- 
bustion aru frequently of an acid nature. 

83 rrcparation. — (1) The simplest uiclbod of pr«poring oxygen 
ie to beat mercuric oxide, UgO. in a &uiall retort of hard {^asa. 

Fio. «6. 

The oxide dccomposcK al. & red-heat into metallic mercury and 
oxygen; 100 parts by weight yield 74 parts by weight of 

The apparatus in which this decomposition can be sliown is 
Been in Fig. A,). Owing to Ihe comparittivelr high price of 
oxide of mercury, tliis proceas is only need a^ a meana of illos- 
tmting the decomposition. 

(2) The best and most usual mode of pr<-p;trin); oxygen consists 
in heatiiij; potassium chlorate, commonly c»lled chlorate of 
potash. KClOy Tliis salt loees the whole f Syi4 per cent of x\a 
weight) of it« oxygeu, leaving potassium chloride, thus j — 

2KC10, = 2KC1 4- 30,, 

The preparation and collection of the ga^, acconling to this 
method, may b» carried on in th« apparutiu shown in Fig. 46. 

The temperHtare has to lie raised much above the melliog point 
of tUe salt, to about 350°, before the evolutioa of the gtts begins ; 
aud, after a certain time has eUpsed, the fused mass becomes 
Uiick, owing to Uic formation of potassium percblorate, KCIO^ 
a part of the evolved oxj-geo having united witli tho olilorate, 
vbilst potASitiuni ctiloride. KO, aud oxygen are at the same lima 
totmad, thus :— 

2KC10,-KCiO, + KCl+0, 

Whoa inoro strongly heated, the pcrchlorale also dccompoeea 
into potassium chloride and oxygen. 

(3) In order to obtain tlio evolution of oxygen at a lower tom- 
perature.a small q^nantity of manganese dioxide is generally mixed 

Pia. *9. 

with the powdered chlorate ; the gas then comes off at 200' C. 
before the salt fuses, and thus the preparation of the gns is 
greatly facilitated. The manganese dioxide ia found mixed 
with potasitiiini chloride in the residue wlioUy unaltered. 

84 In onit-r to prt^pare oxygen on the large scale this mixture 
of potasainm chlorate and manganese dioxide is heated in a thick 
copper vessel a. Fig. 47, provided with a wide tuhe connected 
with the wash-bottle b. containing caustic soda, for the purpose 
of absorbing traces of chlorine gas. which are generally evolved 
owing to the presence of dust and other organic matter in the 
mixture. It is difficult to give a satisfactory explanation of 
this pccoUar action of the manganese dioxide. It may possibly 
be due to the fact that certain oxides, such as this one, aro 



capsUe of undetgoing a higher degree or oxidation, but tbol 
UmM higher oxifU;* imii very rea<lily with a portion of their 
oxygen, fimning s^'ain the lower oxide. In thiswoy nuch oxides 
would perform tJie part of carrieis of oxygen, first taking it 
up and then setting it free. I'latinum, ia the Qucly-divided 
state known as platinnm sponge, acts in tJie same way as 
msuganese dioxide; aud although it does not nndeigo any 
oxidutioD, it htui the povr«r of condensing oxygen in its porea, 
and its action way, therefore, be explained in a somewhat similar 

It not un^quently happens that the commercial black 
oxide of maagoutise may be aooiiieuLally mixed oi aduUezated 


■with carbon (pounded coal), and this impure material, when 
mixed with chlorate of potaah aud heated, ignites, giving rise to 
even fatal explosions. Ueoce care should be taken to try any 
new or doubtful sample ou u suuill scale beforehand by healit^ 
it with chlorate of potash in a teat-tube. 

The oxygen thus evolved will of coiiise be liable to contain 
carboaic acid, and chlorine ia likewise frequently present ; hence 
if pure oxygen be needed, the gas as evolved must be well 
washed by passing through, or belter, by allowing it to stand, after 
evolution, ovur a solution of caustic soda. 

(4) Many other salts behave like potassium chlorate in 
yieldiog oxygen on heatiug : thus tlie hypochloritee, clilorit«s, 




petcUoiates, bromates and perbromatcs, as well as the todaCes, 
periodatea, nitriit^s, aud nitritus; but tlntse ccinpaunda are not 
OBOally employed for this purpose. 

(5) ScYural oxides, eucb as' maD^uese dioxide, MnO,. lead 
dioxide, PbOj, bartum dioxidu, UaOj, cliromium trioxide, CrO,, 
low a portion of their oxygen when strongly hcntcd. and nil 
tbete may, therefore, be used for preparing oxygen. la order 
U) obtain oxygen hj heating the first-named osidc, the substance 
IB placed in a strong iron bottle which can bs heated in a 
funiace to brijjht rcJuess {Vig. 48), Tlie pure manganese dioxide 
losea oDe-tbird (12*4 per cent.) of ita oxygen, being converted 
into the brown oxide, Uq,0^ thus : — 

3MnO, = Mn^O, + 0, 

FlO. 40. 

(6) By beating mangnucso dioxide in a glusj flask with sul- 
phuric acid one-half of its oxygca id given off, and mangiLnotis 
Bulphatc, MnSO^ is formed. 

2UnO, -J- 2H, SO, = 2MnS0. + SU, O + O^ 

(7) Chromiam trioxide can also be employed for the prepara. 
lion of oxygen, but it is not necessary to obtain this substance 
in the pure state, for if the bichromate of potash, K,Cr,Oj, 
be heated vith sulphuric acid, chromium trioxide is formed, 
thus :— 

KjCrjOj + 2HjS0« = 2KHS04 + 2CrO, + HjO. 

The chromium trioxide is then further decomposed by the 
actioa of t(ul[iliaric acid with the formatiou of chromium 

sulphate, a decomposition vliich is rcndcml visible by the 
change nf colour fiom ttie origiQul n>d to • deep green, tbos : — 

2CrO, +• SHjSO, = Cr, (SO^), + SHjO + O, 

Ss (S) Oxygen can be obtained by tbe decomposition or bleach* 
ingpowder (Mitscberlicli, 1 843 ; Fleitmann, 1865). Fortbispte- 
poratioa a, clear concentrated solution of bl«iching powder — a 
substance containing calciam hypocblorite. CaCljO, — is pinced in 
a Hoak, aud a few diops of cobalt cblorido added. Cobnlt- oxide 
18 prccipital^id on beating the mixture to about SO', and a rapid 
efl'ervescence of oxygen occurs. Tlie cobalt oxid«, which 'a 
formed, is left uDcbanged after the operation, and way be 
employed again ; it probably nets, like the manganese dioxide, by 
the formation of a higher oxide, which is again quickly reduced, 
the oxygen beiag libeiatcd as a gas, thus: — 

CftGIjOj + 4CoO = CaClj + 200^0, 
Co,0, = 2CoO + O. 

Instead of ft clear solution, a thick paste of Meacbiag povder 
may be used, with tlio addition of a little cobalt salt and a 
small quantity of paratbn oil, to prevent the frothing which 
usually occurs. The beat teniperatute for the evolution of gas 
is from 70°- 80° a 

CaCl, + CaCl, 0, - SCaClj 4 O, 

Tbe same decomposition and the replacement of chlorine for 
oxygen may be nhown in a striking manner by pa-i-ting chlorine 
gas. generated in a Haak from laanj^aneso dioxide and t)ydn>- 
chloric acid into a second flask, which contains boiling milk 
of lime, to wliich a little copper nitrate solution has been 
added. Oxygen gas i.i then lib(^ratcd in the second flask, and 
may be collected as usual The following equation explains tbe 
replacement, and we see that two volumes of chlorine yield 
their equivalent, or one volume of oxygen. 

CI, + Ca CTTO), = CaCls 4 11,0 + O. 

86 (9) In order to prepareoxygen cheaply on the large scale 
several other procesaes have been Bugge&tcd. Amongst them 
the following appears to bo the most useful : — 



A tliin fltreaia of Atilphuric add flows into a retort filled wtUi 
broken bricks aod hent«i1 to redness; tlie acid splits up into 
sulpbur dioxide, water, aad oxygon, yittlding 10*68 per cent, of 
its veiglib of Uie gas, or in practice &5 grama, of acid yield 6 
litres of gas, tlius :— 

HjSO^ = SO, + U,0 + 0. 

The resalting sulpbur dioxide and water can be absorbed and 
oondciwed respectively by passiii); ifie gases through a tower 
filled with coke, down whicb water trickles. wlUlst tbe oxygea 

ri be collected iu a gas-holdor. The solution of sulpLur 
xide may be returned to the vitriol chamber for the maiiufiic- 
ture again of sulphotio acid. An appariitus for illustrating 
this deooiQi)Osition on the small seals is described under 
Sut[diuric Acid. 

(10) When baryta, BoO, is gently heated to dork rcdneaa 
in llic air, it takes up an additional atom of oxygen, form- 
ing tlie dioxide, BaO^ but at a bright-red beat litis parts 
with tbc uddilioual atom of oxygen with the reprodiictioa of 
bar}*tii. Ry thns alternately varying the tetiipfKituro, 6rst 
leading air over tlm baryta coutaiued in a porct'lain lube, and 
then placing the tube in connection with a gas-holder aud 
raisuig the tcmpomturc, and again repeating tlic process, a regular 
productioD of gas can be obtained from a small quantity of 

This simple method has not, unfortimately, como into general 
ose, as the baiyta loses its power of Hbsori>tng oxygen, chiefly 
owint! to the fact that it combines with the silica of the tubc<t, 
and tlicn'forc reqair^-s fiuijiKnit rODOWuL 

(11) Potasatnm manganate. K,&IdO^ loses oxygen when boated 
in a current of steam, forming canstic potash and lower oxides 
of manganese, which when again heated absorb oxygen, the 
nai^aDese being reprodnoed. so that the same portion may be 
used over and over again (Tesai^ du Alotay.) 

$7 Pnperties. — Oxygen is a colourlcas, invisible, iustcless^and 
inodoTOOS gas, which does not liquefy when exposed to a pres- 
Bore of 3.000 atmospheres (Natterer). It is a little heavier than 
atmospheric air, having n specific gravity of TIOCGS (air = 1) 
or 15'96 when hydrogen ia t^dfen as the unit. The combining 
weight, according to the rcscorciies of Stas, is not 16, as ia 

' Boasuiif^Dl% AnfL. Ckim. ngi. 13] uxr. 

usually ftssiitncd, but 15-96, and the litre of Uie gas at 0* oDii 
7C0 mm. weighs 1-43028 grams (Rcgnault). 

Oxygen dissolvefi appT«oialiI;y in w«ter; ut 0' C. 1 volume of 
water absorbs 0*04114 volume of oxygftn, measnred uodet the 
Donmil tcuipuruturo aiid prcMHurc. ^Iicii Uie temperattire rises, 
tlio quBiility o( nxjgeu absorbed bwotoea less, aooontiug to a 
ooiu]itic.iLc>il I.ivr. vhich is cxprcftsod bjrthecmpiuoAlfonnulA: — 

c - (KItl 15 - 000108991 + <M)00022SC3t'. 

CerUiD metals also absorb oxygen wlico iu tLo molten state, and 
give ib oIT again on cooling; tliua, multud hUvht absorbs ubout 
tun times its hulk of oxygen, and tbia is emitted wbon thi 
metal cooU, giving risa to tti6 peculiar phoaomenon of tba 
" spitting " of eilver, 

88 Ah oxygon is the constitnrnt nf tlic air which eupporta 
conibiistioD, it naturally follows thnt bodies bum in oxygon wttli 
much greater brilliancy Uiaa ttL«y do in commoa air A glowing 
chip of wood, or the rud tiut wick of a taper, ignites with a 
slight detonation when plungud iuto oxygon gas. and even 
metals such na iron, whicli oxtdizo only slowly in the &ir, burn 
brilliantly in oxygeti. The following experiments serve to 
illustrate this property of oxygon : — 

A buudle of thin iron wire, with tlic enda tipped with sulphur, 
bums whoa plutigi>d into u jar of oxygi-u, rurming tbo blitck 
oxide, FCgO,, which falls down in glowing drops. A piece of 
u-ntvh spring also bums easily nith sploudid sctiitillutions if 
held in ft flame obtained by blowing a jet of oxygen into tlie 
flame of a Hpirit lamp. K%-en a more sLriking luudt* of showing 
the combtistioQ of iron Is to place a heap of cast iron nails on a 
brick, and burn them by means of a b[ovr-pip« fed witli oxygcQ 
and coal-gas contained in sepante gas-bolden. Sabstanoes 
likti sulphur and pliosphorus, which take fin.* rt-adtly in tlKr 
air, bum with much greater brilliancy iu oxygen; combination 
takes place much more rapidly, and, lliereforo, the teuiperuluni 
reached It much higher in oxygen than in the air. Tlie Wat 
method of exhibiting combustion in oxygen is to place the 
eubatance to be burnt in a metal cup, livoled on to an 
upriglil !<tcrii, cnrr^'iiig a round saucer ooutitiiiing wat^r. As 
soon as the body has been ignitod, a large gliLtH gh)1« filled 
with oxygea gas ia placed over it, so that Utc cup oooupica 
a central podtion in the lower halE of the globe, and thcctl 


tlie comljiistion can proceed with great mpiility without fear of 
th« globe being cmcked hy Oieheot pvolveil (Pi}*. 49). In this 
way sulphur bncns with a hripht Tiolet flmno, with formation of 
colourIe» sulphur <)inxi<lc gas, SO,; whilst phasphoruis thns 
burnt, emits a brilliant white light, which vies with sunlight ia 
intensity. In this case the white solid phosphorus pentoxide. 
P,0^ is the product of the combustioQ. 

8g An act of chcuioal tiiiion accompanied bj the erolution 
of light aotl hfMit, is termod a wmhtutian, and henoe oxygen is 
oommonly termed a supporter of combustion, whilst those 
bodies which tha.1 unite with oxygen are called coiubiistible 
sabstanL-es. A UttJe considcrntioa, however, shows that these 

Flo. 401 

termn are only relatively correct, and an oxperiment makes this 
plaia One of the stoppered bell-jars (Figs. &Oand 61) is filled 
with osygcu {{lis, the other with hydrogen ; two gas-holders, oa« 
containing hydi-ogcu. the otlter oxygen, are providwl with flexible 
goa deUverj-tubes, at the end of which is fixed a jrerforated 
caoulcbouc stopper carrying a metal mbe with a nozzle The 
hydrogen gas is allowed to cacape through the nozrfo, then ignit«d, 
and the flamo of hydrogen pluuped into the bell-jar filled with 
oxygen, the caoutchouc stopper fitting tiglitly into the tubulus. 
A flame of hydrogen burning in oxygen is then seeu, the hydro. 

gen being tlie burning body and Uie oxygen the supporter of 
combistion. A stream of oxygen gsa ia next allowed to issue 
{torn tho nozsltt of the second gas-holder, the stopper of the bell- 
jar filled with bydrogcQ, is then removed, and the jet of oiy* 
gun is plunged into th« bell-jar, wliilrt the Qame of a caniJle is 
brought at the same instant Co the tubtilus. On preuing the 
caoutchouc stopper into its place, a dame, not to be d i g tin gui ah ed 
iruin that burning in the other bell- jar, is seen, in which oxygen is 
th(t burning body, and hydrogen ia the supporter of combti 

Most bodies do not combine with oxygen rapidly eno 
at the ordinary attuospberic temperatures to e^'olTe light and 
heat, but n^quire to 1« hfiatc^I befor* combiistioii bogins. Oxidi 
tioa is, however, ofleu slowly going on, as in the case of 


Tta. CO. 

nuting of metaJs, the decay of vood and organio bodies. Tin 
even at the ordinary atTOOspheric I«ui|)ti-ature8. we come to dis 
tinguish between quick and alow combustions, in which not ooly 
is the amount of lient and light evolved very different, but 
different cheniicnl compounds are not uncommonly formed. 
Thi& slow or imperfect combustion frequently occurs in preset 
of certain finely divided metallic particlea, probably owing to fhd' 



iensarion of the gases on the surfnco or in the pores of the 
Thus a siiuill (luantity of epongy tilutinuiii (obtRined l>y 
heatiuj* the double chloride of platinum and ammoDiiim) ulmu 
held over a jet of oonl gas or hydrogan, liist becomes t«d hot, 
owing to the coiubustiou uf the gas occurriu^' on its sarbce, and 
afterwards the t«mper»ture of the inetAl rises so bigh that the 
jet of gas is ignited. A eimilttr ease of slow conibtistioti is seen 
If a coil of line pliitintirD wire be first h(^te<] in a flame and then 
hang whiUt warcii over tlie soiface of some alcohol contained in 
a Bmall beaker glass. The ooil will soon begin to glow, and will 
remain red hot until all the alcohol is burnt, but no flame is 
sevtk. Alcohol has the formula CjH^O, uml wheo it bonis with 
a flamo its constituents unite intli oxypien to form water, HjO, 
andcarbon dioxide, CO}. When burnt slowly, a peculiorsnielliDg 

Pro. Bl. 

body termed a1dehydt< is funned, having the fommla CjH^O ', 
hence only two of the liydrngeii of alcohol are then with- 
dniM-n, water beiu^ formed, whilst the volatile aldehyde vaeupes, 
I giving rise to a peculiar choking smell. 

H 90 Tlic effect of mechanical division on the combnstibiltty of 
V siabstAucea, especially of m«tul», ia well known, and advantage la 



taken of this in tlie prcpftration of the vtrioas fn/n»phori. If 
tartrate of Ictid bo gently heated in a i^liiss tube, the lead is left in 
a Btatc of very fine uiucliauicul dlvisioo, aod mixed with cliorcooL 
After heating, the tulje is hermetically seaUd, aiid on cooling it 
may 1w opened and tho contents shntcen out into the air, when the 
linely divided mcUllic particles vill at once take fire. In the 
same way. If the oxidos uf iron, cobidt, or nickel b« rt^iuoed 
Ijy hydrogen at a moderate temperature, Uie metal j« formed 
in a pulverulent state, in which it tultes fire spontaneously 
on exposure to the air. Tiie explanation of this is, that by 
line division, the ratio of the surface exposed, to the mais 
to be heated becomes so great that the heat generated br 
the oxidation of the surface is suflicicnt to bring the mass to 

The spontaneous ignition of a mass of inHammahle materia]*^ 
like cotton or woollun rugs, wliuti mixed witli n substonoc, sudl^H 
m oil,capable of rapidly absorbiiijf oxygen, and thereby generating 
beat, is one of the most uommoa liourctrs of fiie, both in manufac- 
tories and on board sliip. Siiuilarcasesof spontaneous combustion 
occur in liay-riirks, in wltJeb the hay has been put np damp, for 
moisture greatly assists the jiroccsa of slow combustion. Other 
examples of tbe same thing uro seen in the fires 'vrHch break out 
in ships carrying coal, or in heaps of conl or shale, and these are 
frequently due to the oxidation of the " coal bras&es," or iron py 
rites, FeSj, which the cua! and sliolu generally contain, and which 
on exposure to air atid moisturo is rapidly oxidised to ferrons 
sulphate, FeSO^, thereby evolving heat enough to set the mass o: 
lire. All the supposed cases of spontaneous combustion occurring: 
in the human, body have been clearly proved to be mistakes or 
deceptions, as may be seen by reading Chapter xxv. of Uebig's 
admirable Letters an Chaaiotrif, in which this matter is fully 


Temperature of Ignitum. — In order that a body may take fire 
in air or in oxygen, a certain tempcmturo must ba reached: 
this point is tornied the temperature of ignition. The tem> 
perature at which inllamniatiou occurs varies widely with 
different substances -, thus vhile the vapour of carbon disul- 
phidc is ignited by bringing in contact with it a glass rod lieatiid 
only to 149', a jet of coiU giis camiot be lighted with a a-d-hot 
piece of iron; and, ngoin, certain substances, such as the hquid 
phosph«pplt4»d hydrogen, or zinc etiiyl, only reipiire to 'ha ex- 
posed to the air at the ordinary temp^rntnre in onier to ignite, 





wliiUt nitro);(>a cnii only Iw made to unite with oxygen hy 
hfiitiDg tbe uiixluro to tlie highest knomi temperature by metlis 
of the electric spark, AccoTtUug as tbo combustion is a slow or 
quick one, the temperature of ignitioa varies; thus phosphorua 
ImpQS to cater into eIow combustion in tlie air (phosplioi-escencc) 
ImIow 10* C. ; but wo must heat it up to 60° C^ beforu it begins 
to bum brightly, or to enter into quick combustion. 

91 Tk* iMvy Lamp, — A most slrikiug example of the fact that 
A certaiD temperature niQst be reached before a mixture of in- 
flammable gas can take Bre, is seen id tlie Bsfcty lamp for coal 
mines, iiivunted by Sir Humphry I)avj.> Tbo priuciple upon 
vhicli this dcpunds is ireU illustrated by 
lioliliiig a pi«ce of viie gauze, contalnuig 
about 700 tiiosbes to the sqaara inch, over a 
jet of gas (Fig. 52). If the gas ia lit, it is 
possible to reuiovc tliu gauze several inchtut 
above the jet, aud yet the iiitlanimable gas 
lielow does not take fire, the Hame bnming 
only above the gauze. The metallic wires 
in this case so quickly conduct away the 
beat that the temperature of tJie gas at the 
lovrcr side of the gauni cannot rise to the point of ignition. 
Jn a similar way we may cool down a flame so oiuch that it 

Pio, 61 

of wire be previo«aly Iienteil The "Davy lamp" consists of 
an uil lamp (Figs. 5'6 and 54) the top of wliich ia inclosed in 
a covering of wire giiiisc, bo Umt tlio proilucls of comlMutioo 
of Hid oil con cscA[io, while no flame can pass to tlie outttde 
of tlie gauza Uuuce no if^nitioa ia possible, even if the lamp 
is placed in the most iullaoinuiUtf uiixluw vf Gru-daiiip uod 
air. oltlion^h tlie combuatible gases may take lire and burn 
inside the gauze. It is, liowever. necessarjr, to be careful 
that th» Quiuo thus kiodlL-d iiisido tlic gauM does not bot it 
up to the point of ignition of the inSatoniable gas, and espe- 
cially to avoid placing the lamp in draughts, which might blow 
the Qmno againat a point of the gaiue, and thus heat it above 
the point of safety. Indeed, it was pointed out by I>nvy bimself 
that the lamp It iin longer safe if exposed to a dmughl of air. 
Sevend serious accidents have occuired from Uio neglect of tliosc 
precautions. It has also beoa shown Hint the flarnu burning 
inside a wire gauza may be mechanically blown through the 
gauKti by a current or blast of air passing at the rate of eight 
feet per second,' and this has doubtless given rise to mtiDy 
serious accidents. TIio tiring of shot» in liery pits is, therefore, 
much to be condemned. It id almost unnecessary to say tliat 
the himp ought not to be opened whilst in uae in tlie pit. 

92 The Temperature of Flame, — Piffercnt flames, as well as the 
different parts of the same flame, iwasoss very different tempera- 
tures; tbuy Bunsen^ iindx by expuriment that the temperature 

of the flame of Hydrogen burning in Mie rnr, is 2,0M* 
...» oxygen 2.844» 

„ Carbonic oxide ., air 1, 997" 

„ oxygen 3,003* 


air 3.297*. 

Expftriments made by Bunsen, in which a mixture of carbon 
monoxide, or of hyilrogun, wa,* bunit with the exact proportion of 
oxygon needed for its combustion, gave rbe to very remarkable 
results. These show thnt only onu-third of the total volume of 
carbon monoxide or of hydrogen is burnt, two-thinls having loet 
the power of combination when ruined to the tempcnituru of 
from 2,558' toZfi'-i'-i". If. however, the tempcmtur« of the flame 
be reduced from 2,471" to l.UB" by the addition of soma 

' Gnllowny, Proo. Boy. Soc. xxu. -HI. 
* nU Jfof. [<! ixxiv., y 469 




noD-influatDable j^. then exactly ono'hiiirof the carboo mon- 
oxide or hydiogcu is burut, wliilat Uiu oilier half bus last lU power 
of CKHabimng. These observations show tliat the combustion of 
gases is effected in a mnniicr quite (Iifr<i>reut irom that which is 
usually suppuscil. At tUu hj^he^t ti-iupvratui'C brought about 
by the igmuon, only a small <lcfiuite fntctioo of the gas is 
burnt ; nt a lower tetopernturo a krgor dimple tinctionnl portioD 
of tbegss is oxidised, and the whole of the gas nan only be burnt 
whfiu the temperature of the burning gas siuks below this 
lower limit 

Tlie fact that at high temperatures chemical union does not 
occur betweea subfttooces (say oxygeu and meicury) wlucb caa 
combine at a lower tcmpetaliiro i», of course, well known. This 
fact may assist in explainiii); the above pheuoueiuu ttie com- 
buscioQ of a portion of the mixture causing such au elevation of 
tAai[>ci'atiir<e tliat the nniiainder cannot combine, owing to the 
temperature of decomposition having been readied. TliB new 
and rctiiurkablu rvoult iu tliu oxpuriuieuta juut cited is the 
eimple relntion found to exiat between the burnt and mihomt 
gas, aud the sudden change to another simple relation which 
takes place when the temperature is altered. 

93 J7i£ XeUure of Flame. — It has itlrcudy been stated that flame 
is gas raised by chemical action to incandtwct-nca If flame [lasses 
instODiaiieously or very quickly, through a moss of gaa, as in the 
CttM of a mixtaire of liydn<gen and oxygen, or if n flaiuc is ijuickly 
eeoeiated by the rapid combustion of a solid or litiuid body, as in 
the case of ignition of gunpowder or gun-cotton, tie sudden ex- 
pansion which occuia gives ri-te to an ejcploaion. If, liowt;\er, the 
inflammable gasee come into contact slowly and continuously, as 
in the case of a lighted candle, then u Hleudy fhime i^^ produced. 
Davy wnatliofltst to investigate the nature of flame.' He pointed 
nut that tlio flamo of a oondlc couslnts of three dintinct parts well 
eliowD iu Fi^. 55 — (1) the dork central zone, or aiipply of iniburat 
gas, sonouuding the wick j (2) the luminous zone, ov area 
of mcomplcte combustion ; (3) the non>luminous zone, or area 
of coii>plet« corobuatiun. If one end of a beat glass tube be 
brought into the datk central zotio, tliv unbiimt gusc-s will pose 
itp the tube, nnd may be ignited at the oilier end where Ihey 
eeoapc into the air. 

In ordoT to show that an ordinary flame is hollow, the 
following experiments may be made : — (I) A few gniinB of 

> Pht. Ttami. 181", p^ 45 and 77. 

{^powder are \A&ct^l on a cork ui the middle of s plate and 
some alcoliol poured on to tlie plate ; this maj tLeo be igsiled, 
and ibe gnupowdcr vjll itot fire imtil ihe alcohol is oeari/ 
bimit out (2) The head of a common Incifer match may 
also be (inicUy thnist tlirongh a caudle fi&me and beld in tbe 
dark centnd mne vithout the phospbonis on tlit: tip taking fin, 
whilst the wood will be charred, or may even b^in to bora 
where U comes iu contact with the out«r and beat«d Dantici 


(^) A thin piece of platinum wire beli) horizontally in a candle 
llanie is seen to glow at two points when it comes io contact 
with the out«r zones where the ootuLustion la going on, whilst 
betwevn tliein tlio wire r«inuiiis cool. 

94 Lujiiinoiitij of Flamt, — The luminostity of aflame isgreater 
the higher tlic tfmjwrature ; but this ouiy holds good with Uje 
same kind of fiarae, and the lumiiKisily depends csaeutiidly on 
the i^pecilic cnii-ssive power for ligbt wliich tbe conatitueiita of 
the flame possess. According to KiichtiofTs law, the power of 
a glowing gas to emit light is pi-ojiortionfil to it« power of 
absorbing the same kind of light at the same tempetatura. 
Koiice a flame which is transparent fnr every kind of light 
cannot emit light. Heated to tbe sarae temperature, stdids 
and liquids give off tiiore ligbt than gasos, and den»o gtsw 
more thnn rare gasca. 

According to Duvy, the iuiuinosity of an ordinary llanie of a 
lamp or candle depends u|Hm the presence in that finme of v«iy 
finely divided carbon, which is heated to whiteaesa by the 
oxidation of a portion of the combustible material. 1h/^ 

ic(! lietween the non-ltiminotiii flamo of bviDing marsh 
CH,, and the brightly luminous one of olefiant gas, C^,. 
is explained on Dnvj-'a theoiy hy tJiu fuct that the IuUlt ga« 
uoDtaiua twice as mucb cnrbon m tbe former, and Uiat tJiera is 
nut n auHiciiint supply of oxygvii in the flame to enable ttiifl 
larger qtiontity of carbon to bum at once, aud tliis, therefore, 
separates out. and. vrlii^n heated to whiteness, omits light of 
every degree of reEksagibility. Kumerous facts appear to favour 
tliis view. In tlio lint place, uo know Uiat the light wliicli 
glowing solids emit is inoic intense than that emitted hy glow- 
iog gftses at the same temperature. This bs well seen hy hotdiug 
» coil of platinum vire in the non-lumiuous Same of hydrogen 
gas, vhcD it becomes heated to whitenessL If we hold a sheet 

Fi«. M. 

rir. M. 

of white paper a short time boiuoulally in the flame of a candia 
a black ring of wot is deposited. If air be let into ttie iiitoiior 
of a flame of coal-gas, that flame becomes non-luminous, and 
does not deposit any soot ; this ia clearly st-tru in the Biinscn 
gas-lamp, now univeisally employed in laboratories for hiating 
parposca. In this lamp lh« ctuil-jpis emer^see from a central bum«r. 
(Fig. 57), and passing unbumt up th« tube (f. t, Hg. 56), draws 
air with it through the holes (e, d). and the mixture of air nnd 
gas thus obtained tan be lii;lited at thu lop of the tube, where it 
bums with a faint blue, ptrfectly smokeifss Hume. On closing 
the holes (e, rf) the gaa bums, unmixed with wr. with tbe 
orduiary bright smoky flamt-. These facts aio readily cxphuned 

by assitming that the oxygen thus brought into the intorior t4 
tlie flame enables the carbon to buro St onca Furtlier obserra- 
kioos Ituvti, buwever, sliowu that tliiit expUuintion is at any rale 
incomplete, if cot iudcad incorrect-, for, it insteai] of mixing 
air vritb the coal-gas, other indifTcrcnt gases, such as nitrogen, 
carbomo acid, or even hydi-oclUoric acid gas, bo cmptoynl for 
this purposu, tbe flaiDc likowiee becomes noD-luuinons (Knapp), 
whilst inQiiDunftble gases, such as liydruj^n, carbonic oxide 
(IJIochmnn), and evea steftin (S^indow), produce the iiainc effect, 
ir tlio (fiiscutix mixture be first allowed to pass tbroiigh a i^- 
hot [ilutinum tube, the Jlaiue agiiin tiecom&i lutnitwiLS.' 

Attbougli there is no doubt that the presence of a solid body 
may brJiij^ about t!ie iHuiiiio^ily of « flainu, wc arc certainly 
acijuaioted with cams of Homes whteh emit an intense light, and 
yei do not coutjtiti any solid Iwdy. Thus, for instance; FmnJc 
land' found that oxygen and Iiydrogtin guscs whieli bum witb 
a non-luniinoii8 Ramc under ordinary pressures give riite to a 
luminous flame wlim burning under a. prpssiirt! of 20 atmo- 
Hpherea. On the otliur baud, the flame of a camlle burning on 
the tmniniil uf Muni niiinu emits inueh leas li<;ht than when 
buniiug at Chamounix, although tlie nUe of combustion is tbe 
same in boMi cases. From these experiments Fmnkland OOQ- 
cludee that dense gascis and vapours bt^coma luminous at a 
much lower temperature than the same bndieA when in a more 
rarefied condition. It appears, however, that the alwve nuutts 
may be explained by supposiag that tlie increase of luminosity 
is due to Uie iacreose of temperature of the flame bnnight abont 
by the condonsation of the gas rather than to the increase 
of tlie pratsure itself. This appears to bo borne ont by th« 
observation that it is extremely ditlicult to render a gas flame 
nou-Iumiuom by the addition of oxygen, this effect only 
beiuff pioduded when such nn excess of oxygen is prcseul thai 
the flamo is cooird down (Wibol). 

The vi)[>our of carbon disulpliide biiminc; iu niti-ic oxide givoe 
rise to n flame which ia one of the brighlest we are aequainted 
vith, iind yet no solid substance is prc»eut, nor indeed ia ooe 
formed by the combustion. In tbe same way, in the cose of 
the intensely bright flames produced by the combustion uf 
phosphoms and arsenic in oxygen, the products are gaseous 
at temperatures far below iliat of the combustion. 

* VnM, Ber. ZfeuttA. Chrm. 0*». vlii. S3II. 

■ iiMm. On L^fMma. HmcIi, ISCI ; Fkii. Trmu. 1861, )k <2II. 



95 Heat of Combustion.— It has been shown by numerous ex- 
periments that when the same weight of the same substance bums 
to form the same products of combustion, a constant amount of 
heat is invariably evolved, whether the combustion takes place 
slowly or quickly. 

Thus when two parts by weight of hydrogen combine 
with 15-96 parts by weight of oxygen to form 17"96 parts of 
water, the quantity of heat which is liberated is sufficient 
to heat 68,92-t parts by weight of water from 0° to 1° at what- 
ever rate the combuation occurs. Thus, too, 11-97 parts by 
weight of carbon unite with 31*92 parts of oxygen to form 
43'89 parts of carbon dioxide, and in this act of uiiioa the 
quantity of heat emitted is sutBcieut to raise 96,960 parts of 
water from 0° to 1°. In like manner, the same amount of heat 
is always set free when the same weight of iron is oxidised, 
whether this takes place slowly by rusting in the air, or quickly 
by combustion in oxygen provided, of course, the same oxide 
be formed in both cases. 

Since the time of I^avoisier many chemists have measured 
the amount of heat evolved when different elements combine 
tc^ther. These determinations are surrounded by numerous 
difficulties, and the most accurate measurements have been made 
by Favre and Silbermann,^ Andrews,* and Julius Thomaen.^ 

* Ann, Ckim. ny». [3] ixxiy. 857, xxxvi. 6, xxxtu. 406. 

* PXa. Mag. [3] iKxiL 321, 3»2, and 126. 
■ &r. DetUtch, Chtm. Get. tL 1G58. 



The following table gives the Iieat of combuatiop of different 
elements and conipoimds in thermal aaits for otte gram of 
substance burat :^ 

Combustions m Oxtcex. 


Cbuoooi . . . 

. 7273 . 

. Lavtfi&tcr 

■» • - • 
ti . . . 
„ • • • 

. 7167 . 
. 7912 . 
. 7714 . 

. BnloDg 
. Depretz 
. Onsat 

» . . . 

. 80SO . 

. FavTO And Silbcrmana 

„ ' ■ * 

. 7900 . 

. Audrswa 

Diamond . . . 

. 7770 . 

. Tavre and Silburmaim 

Natural Gmphjl* 
Gail Carbon . 

' . 7811 . 
. 8047 . 

■ » It 

» 4 

. 34462 . 
. 33808 . 

. Andrews 

■• • 

. 34180 . 

. Tlionwen 

Sulphur . . 

. 2220 . 

. Favre and Silbenoana 

rt ' • 

. 2307 . 

. Ajidrbws 

Phosphorus . 
Zinc . . . 

. . 5747 . 
. 1301 . 

• » 

Iron . . . 

. 1576 . 


Tin ... 

. . 1233 . 


Copper . . 
Marsh Gm . 

. 602 . 
. . 13063 . 

. Favre and Silbcrmann 

»» • 

. 13108 . 

. Andrews 

ji - • 

. 13120 . 

. Thotnsra 

01o6ant Gas . 

. . 11858 . 

. Fa^Te and Silbennann 


. . 11942 . 

. Andrews 

M * 

. . 11957 . 

. Tlionist^u 

Carbon Monoxic 

e . 2431 . 

. Andrews 


. 2403 . 

. FiLvrc and Silbermaiui 


. 2385 . 

. Tbomsai]. 

Fmm the above numbers it is seen that the earlier obserrera 
found the beat of combofttion of carbon to he lower than tlie 
later HXiierimi-nters. Tliis is owiui; to the fact, which nt 6rst was 
overlooked, tliat a c«rlain quuiitity of carbon is incompletely 
burnt, carbon monoxide, instead of carbon dioxide, being formed 
and, thorefonj, only a portion of iJie total heal being obtained. 
If^ however, we coDascertein how much of the carbon is bonil 



completely to carbon dioxide, and liow niucli bunit incon]- 
plelely to carbon monoxide, it is pot^gible to calculate tiie exact 
httot of coml)a*tiou of carbon. 

Ail example vill render this plain, [ti n determination bj 
f arre and Sillicrniaiin of the lieat of coiDbuslion of wood char- 
oool, ibe wei^lil of dmrcoul burnt wns 2-4G082 grm. ; tho riao 
of t^mpemtvira caused \>y ttie combustion as indicated by tlie 
thermometer was 8''*74 (the smallest diffcKince of t«niperatiire 
vhich could be read oS* on tb«ir themiometors being 0" 0012 C.)> 

Tbo weight of water in tho calonmctcr wiu . . 201 2*000 grmg. 

The weiftlit of the opper vessel was 684603 
grins. This, multiplied by the apt-ciric heat 
of copper, 0"09515, gives the thermal equiva- 
lent in wntor 65"140 „ 

The Uicrmal equivalent iti water, of theyurpnieters, 
platinum foil, &c., u&ed in the ex[>criiiicDt», 
amounted to 2*270 „ 

Giviug tlic total moss of water to be heated . . 2070410 

Huncc 8-74 X 2079-41 = 18174-9 is tJie total number of 
lal nnila of heat evolved. But cxperimont showed that 
ri78 grma. of carbon oxide ga,s had bt-L-ii pmduceiJ by tlie 
ooinbustion ,- this, if it bad burnt to carbon dioxide, would liavc 
wolved 0-7178 x 24027 = 17'24-7 thennal units ; and hcnco Ihie 
amount must be added to the eiperiiuental number in ordiT to 
obtain the true calorific power or tictit of combustion of the' 

18174-9 + 1724-7 = 19899-ti. Dividing by the weight of 

charcoal taken, we obtain from tins experiment ^.j^osa ^ ^^^^'^ 

as the calorific power of chnrcoaL 

On inspecting the above table, it is fuither Been, that the heat 
of combustion of different sabstances is verj- different If. how- 
ever, instead of calculating the quantity of heat given off by oiie 
jrrara of each substance, we calculate tlie niuuiint given ofT 
when cflch of these substances combines with one gram 
of oxyi^n, we find that the numbera thus obtained are not 
veiy different from one another. Indeed it was formerly 
believed that all bodiea when they nnit« with one and the same 



weight of oxygen evolve the same amount of heat, and this law, 
which is only approximately true for analogoua substances, is 
known as Welter's law. 

The amount of heat evolved when different elementaiy bodies 
combine with the elements of the chlorine group has also been 
ascertained. The following table contains some of the results : — 

Combustions in Chlobine. 

One gram of 




Hydrogen . 

. 23,783 . 

. HCl . 

Favre and Silbermaim. 


. 22,000 . 

. HCl . 


Potassium . 

2,655 . 

. KCl . 


Zinc . . . 

1,529 . 

. ZnCl, . 


Iron . . . 

1,745 . 

. Fe,Cl, . 


Tin . . . 

1,079 . 

. SnCl. . 


Antimony . . 

707 . 

. SbCl, . 


Arsenic . . . 

994 . 

. AsCJg . 


Copper . . . 

961 . 

. CuCl, . 




Hydrogen . 

. 8,440 . 

. HBr . 


Zinc . . . 

. 1,269 . 

. ZnBPj . . 


Iron . . . 

. 1,277 . 

. Fe^Br^. . 


Combustion in Iodd 


Zinc . . , 

. 819 . 

. Znl, . . 





g6 All the oli-ments wiih the singla vzceptioa of fluorine Are 
bund to uoite with oxygen to form an important class of com- 
ids termed osddts. possessing very various properliua Record- 
ing to the nature of the combiiiiDg eknient and the quantity of 
ixygen witli which it unitvs. lu many instances one nictol m 
>uiid to comhiue with oxygen iu sevoml proportions, giving rise 
to distinct o:(i(Ie3. Oxiduj may be divided into thrcu classes, 
.diBtiugiitshed as Banc oxides, Pcroxidce, and Atid-forming 

(1.) JTu basic oxida, etich aa K,0, potassium oxide ; BaO,bariiini 
Dxide; FejOj, ferric oxide, form in combination with water a class 
compounds termed HydraddtA or kydrattd oxida, such ae 
poLush, KOH ; l>ftriuni hydroxide or caustic baryta., 
(OE0«; ffi'Tic hydroxide, F«,(OH)g; thu«: 

K,0 + H,0 = 2K0H. 

BaO + H,0 = Ba(OH),. 

re,0j + ;iitaO = Fc,coir)a. 

lie diaroctcrifitic 7iro]iprty of these oxides as well as of the 
iiTCSpoiHling hydroxides is their power of neutralizing acids 
' and forming compounds which are termed salts. 

(2.) 75l« peroxides contain more oxygen than the basic oxides. 

(A portion of it is loosely comhined mid is giv<,-n off on licatiDf; ; 
thus 3MnC), = Mn,0^ + O^ ; and although they can form 
hydroxides, these peroxides have not the power of neutralizing 
acids und foratiii); ealtx. Tliv following is a list of gome of 

► the mote important ^wronrfes. Barium dioxide llaOj-, pdtoaaium 
t«tioxide K,0,; manganese dioxide MuO,; lead dioxide PhO^ 
(3.) Tht arid-forminij oAdt* also combine with water to form 
j.faydroxides which are termed aeidi; thus — 

Sulphur trioxido SO, yields Sulphuric acid lIjSO,. 
Niiiogen pi;ntoxide N,Oj yicUU Nitric acid H^"Oy 
Phosplwrus pcnloxide TjOj yields Phosphoric acid IljPO,. 

Acids possess a sour taste, turn Hue Htmus red, and neatrallu 
the basic oxides, which when ihey are soluble, Itave the oppoatlc 
^ proper^, and tiutt red litmus blue. 



SalU may be considerod to b« acids in which the hydrogenl 
is replaced by a mctaL Ihey arc obtuiiicd by a variety of reac- 
tions, of which the fuHowing are the most impartaQL 

(1) WheD certain metals are brought in contact wiUi an acid: 

Zu + H^'iO, = ZiiSO^ + H, 

(2) When a basic oiide or a hydroxide acta upon an acid or 
an add-rornuDg oxide, thus : — 

PliO + H^O, = PbSO. + H,0. 
Bfl(OU), + H^SO, = BaSO, + 2HJX 
BaO + SO, = BaSO. 
Ba(OU), + SO, = BaSO, + H,0. 

Thedivision into these Uiree claiwus of oxitle5cannot,hovfeverJ 
be strictly carried out. Tbua vhilat the position of the extrei 
memben or each sones, such as tho strong bases or alkaliei ' 
oil ttit) oue Uaiid, and tlie acids on the otb«r, can be sharply 
deSned, it is often difficult to classify the middle terms aucb 
Afi Alumini), Al.Oj, manganese dioxide, MiiO^. and tin oxide, 
SdU,. which act soniptimt^ as weak bases aad at other time 
weak acitls. 

OzosB ott Active Oxyoes. 0, = 47'88, Density =23-1 

97 So long s;;o as ITt^-'i. Van Mnrum observed that oxygSD 
through which an electric Fpork h»d been passed posaeeaea 
pocidiar smelt, and at once tamiHht» a bright surface of 
cury; but it was not until the year 1840 that the attention 
chvmiats was i-ocallcd to this fact by Scb^^ubein.' Ttiia chejnist'' 
showed that the peciiljnr stro-ngly-smelling substinie, to which 
he gave ttm nnmc of o^rnne. from 5{(M, T sniell. is capobh* of 
liberating iodine from potassinm iodide, and of effecting many 
other oxidising actions. SchSnbein moreover showed that 
is produced in other waya 

(1.) It itt evolved at the positive pole in the electrolysis 
of acidulated water. 

* /ivy. **i»n. IT. »!«. 

many ji 





(3.) It it o1>tainticl ly tlic slow oudoUoa of phosphorus in tho 

(3.) It is fonnoti hy the discharge from an electrical machine 
through air or through oxygen gaa. 

For many y«ais miicti doubt existed respecting the exact 
cbeiuicHl Duture of this oxidisiug principle. WiUiamaoo and 
£«uinL-it caiiiv inilcpmidciitly to lliv cuiicIiisioD that ozone is 
KD oxide o( li3'drD^eu imviii}* the formula H, U,; while Marigoac 
and Dti la Uivc, aa well as TrL^iny uiid Bucquvrul tnunii thai OKOue 
is fonoed when elflctric sparks are passed througli perfectly 
dry oxyyen gas. The explanation of these coiitfadiclory rcsulta 
B lies ID lh« tact that it ifm t'ouud impoasihlc to ohtaiii ozone 

Flc, 5&. 

except in very email qiiantitlL's. and that an exact iuTeeti- 
gation of its coropoeitioD is reQden>d still more difficult by its 
extremely enetjjetic properties. Further researchen, L-oaducled 
*-ilh tho git'iitcfit care, have, however, ehowa that ozone is 
DOthiD^ more thnn condcimcd oxygen, and the steps by 
which Uiifi conclusion has Iwen arrivi?d at constitute an admir- 
able example of the aucceaslul resolution, by the couveryuuce 
of many independent investigations, of an apparently inDoIuhle 

To Andrews' belongs the credit of having first proved tliat 
(uone, &om whatever source derived, is one and the same body. 

• na. Ttaru. im. p. is. 



haTiDg identical properties, tuwl (he same coDstituliou, nnd also 
that it 13 not a compound of tvo or mora elemtiDts, but ox^geu 
in an altered aud allotmpic oonditioo. 

If n $eriL« of ■.■luctric discharges be sent tlirough a tube con- 
taining pure and dry oxygen, only a fimaJl portiou of the f^ is 
converted into o/^ne ; liut if the oxonc is absorbed ua soon as it 
is formed, hy a solution of iodide of potassium, for example, the 
whole of iho oxygen can be gradually coavorted into otooA. In 
order to obtain the maximum production of ozone, pure oxygen 
goa is ulloired to pa^ through on apparatus (Fig. 58), which con- 
sists essentially of aa iron tube (bb) turned very truly on ils 
outside, through which a current of cold water can be passed by 
mcoua of the tubes (cc). OuUide this metal cylinder ia one of 
glass (aa) very slightly larger than the iron one By means of 
the tubes (du) air or oxygen can be passed tbrough the atinoliir 
epaoc between Uie two cylinders. Part of the outer i-yliudcr at 
(g) is covered with tinfoiL Tlie outer tinfoil coating and the inner 
metal cylinder are connected with the poles of an induction coil 
at E and r. By this mcaua the oxygen is subjected to a scries of 
silent discliargcs, by which it is converted partially into OMmei 
The action of this stn^am of ozoniiied oxygen upon n sheet of 
paper covered with a soliition of iodiiie of potassium and starch, 
is strikingly shown when the paper is held in front of the 
current of iBsuing gas. The whiU) surface bacomea instantly of 
a deep blue colour. 

g8 That this ozonizatioD i» aecompaniod by a change of bulk, 
was Bliown by Aridrewg niid Tail,' Those cheiutau filled a 
ginsa tube (Fig. 59) with dry oxygen, one end wiia tlivn sealed 
off, whilst the other ended in a capillaij- tube, bent in fomi 
of a syptioii, aud cuataiithig a li(iuid, such as strong sulphuric 
acid, upon whidi osone does not act. On passing tlimugh tlte 
gas a silent discharge, obtained by attaching one pltttiniun wite 
to one pole of a Ruhnikorff's coil, or to the toudnctor of a 
fi'ictional electrical niachiite. a gruduiil diminution of volume 
occurred, but tlii» nevisr reached more than ^'jth of the whole. 
Alter the ozonized giis was heat«d to about ^OU" C. it was found 
to have returned to its original hulk, and had lost all its active 

This decomposition of ozone into oxygen eau be readily ahown 
by allowing the stream of osoniitod oxygen to poas through a 

PAti. Tntiw. is«o, p. na 



by elie flarao of & Bunscn-latnp. Ewry trace of 
oxidiem<; ocliou -will huvu disappuarcil and the bloe 
io))icle of starch will not be formed ; whilst on removing the 
hot tube an immediate liberation of 
iodiiMS ia observed, if tlie prt-pared pajwr 
is ng-^in 1>rought into coutuct vith th« 
issuing gna. 

In order to gain a knowledge of the 
composition of ozone, Andrews intro- 
duced into bis ozone tube a scaled glass 
bolb containing suliataiicca able to 
destroy the ozone, such as iodide of 
potaasiura solution, or metallic mercuiy. 
After tmmforming into ozone as much as 
pofuible of the oxygen coittaiued in this 
tube, th« bulb filled viih the iodide of 
pocaasium solution was biokcn and the -y 
iodine liberated by the ozoDe. Oiiobattrv- 
ing Ui« column of sulphuric acid in the 
STpfaon (ube, it vaa found to have re- 
mained nnallci'ed after the ozone hod been 
absorbed, ebowing that the absorption of 
the ozone had not been attended with any 
alteration in the volume of the oxy^a, 
whilst on aftcrwftids heating np to 300' C 
DO further increase iu the volume occunvd, 
proving that all the ozone bad bc«n de- 

These facts are explained by the suppo- 
sition that, ill the formation of ozone, 
three volumes of oxygen condense to form 
two volumes ofozone.which, when heated. rm. S9. 

increase in bulk again to form tlio oii^rliial 
tJircc volnmos of osygen. whilst, when acted upon by potas- 
sium iodide, one tliird of the ozone is spent in liberating ilie 
iodine, and tbe other two-thiids go to foini ordinary oxygen, 
thus: — 

Oj + 2KI + H^ = O^ + I + 2K0H. 

This supposition has been proved to be correct by Soret^as foUovrs : 
MsDy essential oils, siicb as turpentine and oil of thyme had 
beca observed by Schonbein to possess the property of absorbing 

oxonc vithout decoRiposing it, and Soret' shoved that tk« 
dimwutuM in volume wliich tiikca place ou the absorption of 
tlie osoiw hy those oils is exactly twice as great «s tlie xncrttui 
of volume obsprved when ozone is decomposed by bMit. A 
aeries of three exprriiriTOts proved tliiit for eTtrj- 193 cbc of 
ozooe aliaorbed by the oil, 947 cbc., iastead of the exact numler 
965 cbo.. of common oxygen woa formed on heating. He»c« 
Diouc possesses tbe molecular formula C>,, three volumea a( 
cotumoD oxygen having bvcii condmsed to two volumes fay tbi, 
formation of OJ:one. 

Soret obtained a confirmation of his resulLi from a totallj 
dificrt?nt poiut of view.' It' the deusity of ozone is one-and-a-j 
half times as preat as that of common oxygen, the i»te of diffusion 
(par. 35) will be invencly u& the bquuru roots of these numben; 
if, therefore, we know the mto at which ozone diffuses, compared ' 
with the rate of diffusion of another gtis whoftc dcnsit}' is al«o 
kuown, we can draw conclusion!* respecting the density of ozouc: 
The gad chusfti for t-xjuTimeiit was chlorine, und it was found 
by e.xperimeut that 237 volumes of chlorine ditfused in the same 
time as 271 volumes of ozoiif, or for one volume of o?:one there 
difliised 0S376 volumes of chlorine, whereas Bcconliiig to tlie 
law of inverse aqnare roots of the densities, this must hare been 
08212 tor 

Brodie,' arrived, by a long series of most exact det«rmiiMt 
at the Muie result, inasmuch as he not only obtained the ratio 
of 1 t-o 2 between tho volume of the oxygon used iu Jibcmtiug 
iodine from potaseiuui iodide and that of the ozone absorbed by' 
turpuultiie, but showed thai the same ratio exists bctwecu Uiis, 
unit and the volume of oxygen liberated by treatment of th4 
ozone with binoxide of sodium and hydriodic acid. 

These experiments prove conclusively that drj' oxygen is 001 
verted by the action of the silcJit electric tUscltarge into an 
tnipie mtHliltcutioii. But Ihey ilo not dwiiJe the question wlietherl 
the strongly-smelling body oUained in Che electrolysis of wat 
baa an analogous constitution, or whether it may not be an oxid 
of hydroyan. Andrews, however, proved that if sHch electrolytic" 
oxygeu is perfectly dried, it does not lose its powerful smell, ant 

> Amu, Chin. Ph^s. [i\ viii. 113 ; Pitil, May. [i] xzii 62, uii uzlr. », 
* Ann. dim. Phy*. Mjslll. 357. 
■ ekiL Tnm. 1873. Pari ii. 48& 

[that if tlie (tried gas lie then pafl^M tbrongh a hot gloss hibc, th« 
fsmell. as well aa tlie osirliziiig power, altogether tiisappcared with- 
out tlic sunllest tttux of moisture heiiig formed, and tlus must 
have been deposited if the electrolytic oxygen had contained 
an oxide of hydmj^eii. 

99 jitmcspheric Oimte. — The difiiciiltf^uesljonasto whether oiwne 
[exists in the stmosphere may now he i«gnnled oa settled in tb« 
I aRirniiitive, although it is present in such extremely small quaati- 
tiv8 thai our knowledge on the amount and on the variation of 
atmospheric ozone is far from satisfactory. The higher oxides of 
nitrogen, amotignk other substances, possess (he same power as 
OKOae of libeniting iodine from potassium iodide, and the^e oxides 
are oertoiiUy formed in the atmosphere hy electrical discbaT^ee, 
M) that if thii oxonc be measured, as is usually tlie case, hy the 
amount of iodine liberated by the variation hi tint of the so-called 
OKone papers, we measure, along with the okoui?, the higher 
oxides of mtrogea. 

The experiment* of Andrews ' have, however, decisiv<dy provwt 

that an oxidizing substance occurs in the otmosphero which nRrees 

in all itfi properties with ozone. Tliua when air at Ute onlinary 

temperature was passed over ozone leat-papers contained in 

a p^m tulje, nn indicJition of ozone was seen in two or three 

minutes. When tlie air before passing over the test-paper waa 

heated to 260° C. not the »li-j;ht4!flt action oecnrred on Uie tcHt- 

pnper, however long the cun-eiit waa allowed lo pass. Similar 

experiments made with an artificial ntmoHpherti of onone, that 

is, with the air of a laijje ohamber containing a little electrolytic 

oxone, gave precisely the samo results. On the other hand. 

when air nuxed with voty aniall quoutitiea of chlorine or the 

higher ojcidc* of nitrogen was drawn over the papers, they were 

I geoerally affected whether tlie air had been proviously heated or 

I not. Boazeau has alion-n tlntt a neutral solution of iodide 

lof potassium on exposure to air becomes alkaline witli the liV^era- 

ttion of iodine, an effect which woidd not he produced by the 

[oxides of nitrogen and which can only be due to ihu prt^cncfl of 

j-oaone hi the air. 

The very small quantity of ozone contained inthe air rendersit 
a mattcrofdiOicultytodetennineits amount. Zenger passed 100 
litresof air tbrongh a dilute solution of hydridiHir acid and obt«inml 
iodine liberatud. which corivspuiided to OOOl or4)-0(i:i milligram 
of ozone; and even here it is doubtful how fur the iodine was 

' Ffot. Jb)}/. Sk. ivi 03. 



really lib«r.ital hy ozonu. Certain obs«ni-«r3 ' slate that the pro- 
portion of ozoDe ill the air staDtU in a direct relation to llw 
amount or atuiosptiertc electricity preacnt, whilst others* contilude 
from their olwen-alioas that under the nomiftl atmosplieric 
conilitions the amount of ozone in tlie air is ahsolu(«1y constant 

The usual method nf estimating the amount of ozone present 
in the air U a verv roii^h cue. It conaistfi in expofting to the 
air piapers which liave been impregnated with a solution of starch 
and iodide of poUutdiiiiu, for a given time (tuul beat in the diuk) 
aud noting the tint which thoy assume eompaied with cettain 
standard tints. Tlie papers prpjiared according to the directions 
of Dr. Mollat nrtt tfiose on which most reliance is placed. It 
has indeed been proposed by Bdttger to ii»c pepcn impr^nated 
with thallioiis oxide &s n test for ozone, as this substance 
not cbangod in tint hy the uitro^eit oxides, hut this suggeetioii' 
has nob been generally adopted, aud donbt haa been thrown by ' 
lamy on the use of thi<i re-agent, as aoythiug more than ■ { 
qualitative test of the presence of oxoue. i 

It M gcarecly necessary to remark that in tliichly-inhabited 
districts, espedally in ton'na where much coal is burnt, oxone , 
is almost always absent, as it is reduced to ordinary oxygen 
by the organic emannCions as well as by tlie sulphurous acid 
con^iUintly present in such air. ^M 

In the air of ihe coutitTy, and especially in scAair, the pnseiK^V 
of ozone can almost always be recognized, often indeed tiy its 
peculiar emelL Rcapectin" the varintions in the amount of 
atmospheric ozonu in difTtireiit locaUties or in difTerent 
we po38es3 nt preaeut uo reliiible information. 

The probable cause of Uie formation of ozone in the air h. 
recently been pointed out by Coru]> v, R«sanez,* inasmuch 
he has shown that OKone is invariably formed when wat«r evA' 
ratt'3, and it is to this source, mlhcr thiin toeler-tncnl discli; 
that till* pioductlon of ozotio must be traced. Tlie prudttction 
ozone by the stow oxidation of phosphorus luis olready been 
mentioned. Sevenil other linbstaiices on oxidntion also f^ve me 
to a f'ortiiation of ozone ; thus turpentine and sevend other essen- 
tial oiU when actml upon by atmospheric o.>cygea transfonn a 
poition of it into ozone. This may he seen by shaking turpen- 
tine in n ttuiili. containing air or oxygen when the liquid M-iU. 

' Kenmiinn, Pom. Jnm. cii. 614, nnd Poi-y, Qmpla Ratdutt, Ixr. 70ft. 
' SniYih, Pnc iitttonl. Set. Jmic td, IStfB. 
* Ann. Ckiai. Pham, elxi. iZi. 



exhibit tlie propeities of ozono. AnotIi«r method by wliich llie 
active variety of oxygen may be obtained is ijy acting with 
strong siilphiiric acid upon dry bitrium dioxide, when oxygen 
is given off which is found to contain considerable quantities of 

loo Praptrtitt. — Ozone prepai«<l by any of Uicse plans is a 
colourless gfts possessing a peculiar odonr, somewhat reHenibliDg 
that of vi-ry diluted chlorina done, when dry, may be preserved 
in flenlcd glass tubes at the ordinary atmospheric temperatiU'C for 
a very long time, but it changes gradually into coiiinion oxygen. 
Kot only is ozone destroyed by heat <at '2ZT the change is in- 
stantaneous), and Ity contact with certain met<illic oxides, such 
as oxide of silver, and manganese dioxide, but also whi'n ngitated 
strongly with glass in fine fragmenta (Andrews). It is one of 
the most powerful oxidizing agents known, it attacks and at 
on<e deati-oys org&nic subfttances sucli aa caoutchouc, paper, &c. 
One of the most cliarncteristic actions of oxone is its effect 
on mercury-. The metal at once loses its mnhility and adhcrus 
to the flurfnce of tlic gltUA in a thin mirror, and eo dclicuto 
is this reaction, that a single bubble of oxytftn containing 
^^th of its hidl: of oxone will alter the physicid characters of 
several pounds of n)crcur>', taking away its lustre and tlie con- 
vexity of ita surface. In its o.iidtKing action the volume of 
ozone d(M9t not \indci;go any aIt«raLioD, two volunti-s of ozone, Oj, 
yielding two volumes of ordinary oxygon, and one atom of oxygen 
being employed for the oxidation. Some non-njclals as well as 
moat metals nr« at once oxidized in presence of moist oxone: 
phosphonis to phoephoric nciiil, sulphides to sulphates, fcrrocyn- 
nides (o fcmoyaQides. whilst blowl is completely decolorized, 
the albumen being entirely, and the other organic niottcrs being 
nearly, all destroyed. Ozone ha-s, however, according to the 
recent expcrimculs of Caiius.' not the power it was formerly 
supposed to possess, of oxidising nitrogen to nitric acid in 
preseDce of water. 

Oiione does not liquefy »t — 110° and under a pressure of 3} 
atmospheres; it it> somewhat soluble in water, imparting to 
water its peculiar odour as well as its oxiiHzirg powers. Accord- 
ing to Curiuft, 1,000 volumes of water dissolve 45 volumes of 
ozone, and it is much more sohihle in certain ethereal oils. 

On account of its oxidising pinperties ozone has beca used to 
bUacb engravings discoloured by age. Jor this purpose tliey arts 

* Liebig, Ann. clixiv. p. 1. 

rolled into Ibe neck of a large balloon in whicb. some vaUn* ia 
placed, and a piece of phosptioras hnng up. Oione prepared hj 
tl>c eleclrio <]isctiat}i:c tins nlao been employed to oxidize alcobol 
CgHflO to nldulij-dc CjlIjO, a body now largely anployod in tb« 
tnaauracture of one of tlie most favouhu* of modem dyes, the 
well-known aniline green. 

Sclitiiilieiii, nnd c<^riaiu ollii^r cItemistA, beliAvod tliat nnotlier 
modification of uxygea besides ozone exists, to wbich th«j gare 
tlie name of ani-otone ; tbc chief peculiarity of thi« body being 
it4 poirer of cotnbiniog with ozone to form ordinary ox^-gea. 
Further experinmnt^ have, however, proved that ant-ozone is 
nothing more than hydrogen dioxide.' 


These elemeats form tn-o conipouuda. 

(1) Hydbogen Monoxide or Water n.O, and 


Water. 11,0 = 17-96. Vnpour Density = 698. 

101 The (luwtion of the discovery of the oomposition of water, 
s substance which up to the end of tlie last century was COBsidiind 
to he a simple body, has been Ailly disciused in the btstoiica] 
introduction. We there luamed that Cavendish finit ascertained 
that by the combustion of two volumes of hydrogen and one 
volume of oxygen, pure water and nothing lilse, is produced. 
Warped, however, as his mind was with the phloyiftlic theoiy, 
he did nut fully tii]dun<tiind thcso K&tdtH, and the true ex- 
planation of the composition of wattjr was first givou by 
Lavoisier in 17S3, when the French cliemist repeated and 
confirmed the experiments of Cnvemli^^h. The apparatus, of 
much historical interest, u^cd by him for proving that hyd^^gen 
gas is really ooutuiiK^d in water, ia seen in faiaimilc in Fig 60. 
The water contained in the vessel « was anow"f(i to drop slowly 
into the tube <rf. from which it flowed into ihogunbarrel df, 
heated to redoeas in the furnace Here part of the water is 
d<;coiiipos«i,l, the oxyprn etit«riiig into uoiubiuiition with the 
uietallic iron, whilst the hydrogen and some undecompoeed 

1 Sm Srodit^ Fkil. Tniu. IBM, p. Uf. 



riteam passed thiough the n-orm s, where tbo steam was cou* 
^deoMd and the bydn^n was coUectetl and measured in tlte 
glass bell jar m. The result of these cxpcriunmLs vraa found 
to be that 1833 parts by weight of hydrogen uaited to 86"87 
parts by weight of oxygen, or li volumes of oxygen with 22"9 
volumes of hydrageo.* 

Cavendish l>y exploding air with hydrogen hy means of the 

electriL' spark had, mi the other hnnd, come ti} the conclitsion 

Uiat the relation hv volume of tlte two gaaes combining to 

[form water wits 1 of uxy<jcu to 2 of liydrogcn, uiid tliis was 

' .*, ti'f 


Flo. fla 



confirmed in 1805 hy the more cxnct exiierimcnts of Gny- 
Lossac and Ilumlxildt.* 

The formation of water hy the combustion of hydrof^n in tlio 
air can h* rcodily observed by means of the arrangement bIiowu iu 
rig. 61. The hydrogen is drit-d by passing tlirough the horizontal 
tube filled with pieces of chloride of calcium, then igniU-d iit the 
end of the tube, and the Bame allowed to bum iinih'r iJie bell- 
jar By degrees drops of waU;r form, tlieae collect on the sides 
of the glft88, and drtq» down into the buhjU basin placed bciieatli 

» Mrmoiw p>r «M. Mcorakr *i Ijivohwr, tftm. dt tAtad. de SeiaUM, 
• Jvnnu de Fttyt. Ix. ISB. 



Auotber apparatus for exhibiting the same fact is seen in Fig. 
62. It conalits of a gla&i gasholder filled with hydrogen, 
which is dried hy passing through the chloride of calcium liibe 
[b), and then burns under the gluss funnel (r). The water 
formed collcwts in tie tube (t), run aspiiatoT (/) drawing the 
steam formed by the coinbustioii through the tube (t^. 

103 Eudiomdric SynthesU of tP'aler. — The method which Caren- 
disli employed for the purpose of ascertaining the compaiition of 
water IB still employed, altlionsh the modem processes are moch 
•upcRor in uc(?unu.-y to iho older ones. It consists in bringing 
known volnmes of the constitnent gases ancccsairely into a endi 
meter iind allowing these gases to combine under the tuflnencC 

Fra. 61 

of the electric spark, carefully observing the cwnaeqnent cliango 
of volume. The eudiometer eraplojtd is a strong glass tube («), 
Fig. 03. one metre in leugtli and 0025 m. in breadth, closed 
at th« top and open at the bottom, having platintira wires 
sealed through the glass nair tba closed end. The tnbe is aua- 
rately divided into divi6ion.s of length by etching a millimetre 
scale on the glass, and tli« capacity of each division of length on 
the scale m ascertained by a process of calibration. coDsisting in 
pouring successively exactly the anrao volume of mercury into 
tJie tube, until the whole is filled with the metal, the licigbl to 
which each Tolume of mercnry reaches being carefully read off 
on the millimetre saik etched ou the gla'ts. 

The eudiometer containing ut the top one drop of water 



' Tender the gases moiat, is Hrat completely filled vith niercciy and 
inverted in the pncornatic tiough {U} oontaiiiing the same metal. 
TTien a certain volume of petfuclly pure oxygen gns, prepared 
from pure potasnum cliloraU?, is introduced, tlio volume is read 
oiT, und the uecassaiy reductions Tor tumpcnilua' uud pressure are 
made. Fur this purpose a thcrmomeler (b) is hung up near the 
endioineler, nnd the temperature as well ns the level of the 
meniBcus of mercury in the tube read off liy means of a tele- 
scope placed in a horixontal position at such a distance that tlie 


Fio 61!. 

mdiulion from tlio observer docs not produce any seDsible effect 
on the rcadiug. The pn^sure to which the gas is subjected is 
then ascertained hy reading off the height of the barometer («), 
also placi'i) ncjir the eiidinniPter, and Kubtmrling from this the 
height of llie colninn of niRrcury in the eiidionieCer uhovc the 
level of thv tiicnrury in the trough ; this height hviiig ohtuined by 
reading the inillimeLre divisions at the upper and lower leveU of 
the tneicuiy. The tcmjtcratute of the mercurial columns in the 
Imrometer and eudiometer must also he observed, 80 that cor- 
rection nitiy be made ftir tliH expunsion of the mercurifil column 
the height of Trbich must be redvced to that of a column at 


'rom these data it is pasty to obtain the volume of tba gas at 
the Doraial tempeiature (0*) and uudertbe normal pressure (cither 
1 ID. or 760 mm. of mercury at 0"). The second part of the 
process ccmaiata ui adding a volume of \mni hydrogen, cam being 
takea aot to allow nny hiihhlcs of gas to reiuaiu attached to the 
sides of the tiil>e. Aiid the voluiiio of hydrogen added must ho 
such that the inflammablu mixture of two voltimea of hydrogen 
and one volume of oxygen sbol] mtilce up not loore tlian from 
30 to 40 per ccut. hy volume of the whole gas, otherwise the 
mercury is apt to be oxidised hy the high tenipeniture of the 
explosioa Thus suppoiiiig we had five volumes of oxygen, we 
must add ten vulumee of hydrogen to combine with this, and 

I ... ' ■ = 28 Toluraes for the purpose of dilution. 
An soon ne the lcmpLT«tuTB equiUliriiim has been estah- 
lished, the volume of the mixed gasea contained in the eudio- 
meter ia again read otf with the same precautions, and the 
leinperatm-fl and pressure again a.*certained an Iwfore. Tlits 

■ having heen ftccomptishcd, the open end of the eudiometer is 
firmly pressed dowa heiow the mercury iu the trough upon a 
plate of caoutchouc, previously moisieaed with comwivo 8ub- 
limate solution, and held tiriuly in thin po.sition hy a stout 

■ clamp. Hy means of an induction coil an electric apark is then 
passed fi-ora one platinum-wire through tlie gas to the other 
wire ; the mixed gases are thereby ignited, and a Same is seun 

B to pnaa down the tube. On allowing the merctiry from the 
trongh again to enter freely at tho bottom of the tube a con- 
aideiabto diminution of hulk is ohstrrvwl. The eudiometer i:) 
then allowed to remain untouched until the temperature of the 
gaa has again attained tliat of the snrrounding air. and the 
volume, pressure, tcn^iou, and tfiii|H^mlurc an: lusct^rtained 
as before. The volume which has disappeared does not, hoW' 
ever, exactly convspond to the true volume of gases which 
have uuited, inasniucli as the water formed, occupies a ecrtaiu 
although a very smnll, spaco. In order to ohtaiu the exact 
volume of the L-omhuied gases, the voluuie of the mixed gases 
hefore the exploaion inusl he multiplietl hy the number W'OO07. 
which represents the fraction of the total hulk of the coiiipnncnl 
gases which is occupied by the liquid water formed, and this 
volume must then he i^uht meted from the observed coDtroctiou. 
For other conections tho article on tlmi subject in Bunaen'a 
Gasomotry must be con.otilted. 



The folloving example of this method may render the above 
explonaiion more dear :'— 

J^fHihms of vxUer hy wlttnu. 

Radorad to M k>< I m. gf I 
Volnnid of oxygen taken .... 9545 
Voluino of oxygen and liytlrogen . . 5.'>7"26 
Volume iiflcr the vxplosioo .... SVliKJ 

- M 

Fio. «t. 

Hence 2862 volumes disappeared, or 05-45 volumes of ox} 
have combiiiKfi with 190'7o of hydrogen. Consequently 10000 
volumes of oxygen combine with IdOdS volumes of tydrugco 
to form water. 

By careful repetition of the above experiments the composi- 
tion of water by volume has been ascertaiuod, witJiiu n limit 
not exceeding j^^ of the totnl volume, to be iu tlie umt 
proportions of one of oxya^n to two of hydrogen. 

A convenient form of voltaoiotur for demouatratiDg the com- 
position of water by volume is ebon^ in Fig. 64. On paaaxagi 


ciimntof electricity through the acidified water wliich fills the 
the TT-ehaped tube, bubbles of oxygen rise from the surface of 
ihd platinuTD plate forming the positive pole, wliiUt bubbles 
of hydrogen are diaeugaged from the negative pole. The gases 
from oacli pole are collected separately, and tbu volume which 
eoUccta in the tube oontAitiing the upgative pole is seen to be 
a liUle more than double that which collects from the positive 
polft On trial the lattw is found to bo oxygen, and the former 


hjrdTogeii. In this experiment the volucio of the oxygen gas is 
found to be rather less than half that of the hydrogen, because. 
ID the first place, it is more solublu in water than hydrogen, and, 
•econdly, because a portion of the oxygen ja converted into 
osone, vbicfa. being coadeosed oxygen, occupies a I<^S3 volume 
tliau oxygon in tlic ordinary form. Tlie fact Uiat ozone is thus 
produced may be shown by bringing sonic iodized starch paper 
in contact with ibc cIcclrolj*tic gaa, when the iodinti will be 
Liberated, and the jxiper will at once be turned blue. By raisiog 
the t^mperatuni of tlic acidulated water to 100°, tbe mlubUity 

c^ tli« oxygen is diniinished. vhUet that of hydrogen raiuim 
UDcliaiigeiJ, aatl at the s&me time the rormatton of ozone ii 
avoidud, eo Umt tiw true volunie relation of 1 to 2 » Uius tuadi 
more closely attained. 

The np]iiiratiu), tht- construction of which is pliitnly shown 
in Tig. C't, in used for collecting; the mixed gaaes e%'otTe(l hj 
the electrolysis of water. The mixed gases, thus prepared, 
oombioe with explosive violence when a flame is bnmgfat 
in contact witli tboui, or when an electric spark ia paasad 
through the mixture. In this act of combination the «bol« 
of the hydrogen and the whole of the oxygen unite to fom 
water : in other words, subject to the correction abon 
referred to respecting the volume of water formed, the total 
volume of the detonating gus disappeats. That tliis is the 
case is scuii from the following experiments made by Bunsen, 
in wbioh air waa mixed with the electrolytic gas, the mixture 
exploded, and then the volume of air detormineil A aecond 
additiou of the explosive gaa waa next made and the volame of 
air Again niad olT, and the operation repeated a tliird timet* 

Origimd volume of air, in which detonating 1 
f;aa had been once exploded J 

After explaiion witli 55'18 vols, detonating i , , „ .„ 
Kaa r^-^* 

Ditto, measured again nftcr 24 houra . . . 11257 

After second explosion with ri'23 vols, deto- | 
Dating gaa | 



Z03 Volumetric Composition of Steam. — Gay-Lnssnc not only 
determined the coinposition of water by volume, but was tha 
first to ascertain that three volumes of the gase9 combine to 
form two volumes of gaseous st^^am ; inaamach as he found tl« 
specific gravity of steam to be 0'6235, the number deduced 
from the ubuve composition being 0-6221. 

This fact can be readily shown by exploding some of th( 
electrolytic detonating gaa evolve»l from the voltameter. Fig. Iw, 
ill the eudiometi:r u Fig. 6{), which is so arranged that tlu 
pressure on the gas can be alttimd at pleosureL Surrounding 
the eudiometer is a glass tube <t), and between the two tubea 
a curceut of ihe vapour of aniyl aJcoboI, which btiils at 182", 
can be pa.s»ed from the flask (f), and the vapoiir, after passing 
through the tube, coadeoses in the tUuk cooled in the trough 

■ OMDiMtry, p. «5. 



and, by means of the induction coil (c), a spark is passed. At 
soon ax ouinbiiintiou has tukeu place, tlie level of mercuiy ia the 
two tubes is brou;^ltt to l]\e same hei<;ht, and the volume of ihe 
water-gas ia accurately ntaU oil', tliu tutapcruturu uf ibe wbole Uioj 
still kept up to 132^ by the corrent of amyl al<M>hol vtipour. IW 
volume is found to be exactly two-thirds of tliat of tbt; origiiul 
mixed gAxcs, and hence we conclude tbat 2 vols, of bydrogea mi 
1 vol of oxygen nuite together to form 2 vols, of water gaa, 

104 GranmHricSyntkaisof Wattr. — Having ibusaacertuned 
tliu volumelric compo^itioa of water, nnd knowing from thu 
exact expcrimcnt« of Rejjiiault that oxygen ia 15'96 times u 
heavy as is easy to calculate the percenUga com- 
position of water by vr«tght ; for, Lakii^j hydrogen as the onit, 3 
volumes weigh '2, aud 1 vol of oxyg>tn weighs I5'96 ; henca we 
have: — 

Pertxntage eumposUion of wattr htf weight 

Oxygen 88*864 

Hydrogen 11136 

lb is, however, desirable In such an important question as that 
of the conipuaition of water tbat Uie«e iiumbens should be ooo- 
troUed by direct experiment This haa, tlierefore, been doneand 
llie principle adopted in this determination is a verj' simple one. 
Many metallic oxides such us copper oxide CuO when heatod 
in a cuiTcnt of hydrogen lose their oxj'gen by comliiiiation with 
the hydrogen to fonn water, the metal being reduced. By 
ascertain ing the loss of wei;:>bt which the oxide thus 8afrers,aDd 
by weif-hhig the water thus produced, we obtain all the duta 
required for (totermiuing the ratio by weight in which the two 
gases ore prcKcut in water, inasmuch as water contiuns no uthcr 
constituent besides oxygen and hydrc^n. 

This method of determining the synthesis of water by weiglil 
was tirst proposed and i-.arTird nut in IS20 by Itcrzeliua aad 
Duloug,' with the following results . — 

Synthesis o/ vsattr bg vt^hi. 


I.OM of wpiRht 
of copper Diiile. 

«at«r fibuiaad. 

I . 

. 8-[l51 . 

. 9 052 

2 . 

. 10832 . 

. 12197 

3 . 

8-246 . 


' A»H. CMm. nf$. XT. SS4. 



IleDce ve have the following numbers as repr«sCDtii^ th« per- 
c«ttUige coiupoeition of vat«r according to Umssc experiments . — 

[Prrctnta^ eompotUion of jcater fcy u>etff!ii (Berstiius and Dulcng.) 

Oxygen . 


88 809 


83 954 


1 1 10 

100-000 lOOClOO lOO-OOO lOOOO 

It is tlius 8««a tbat whilst the mean numbers correspond cloael; 
l-with the calculated results, tlio ao-pnmt« experimcnt« do not 
[agree very closely amongst tUemsiilveg. and do not, tlierefore, 
^ yield us certain infonnation iw to the exact proportions by 
[ weight in which the gasea combine to form water. 

In the year 1843, Dnmas' undertook iu conjunction, with 

Stos, a most car<-ful repetition of tliese expcrimenlA pointing 

out the following prohtble mxocob of error in IlcrEcUus's 

experiments : — 

(1) The wetjtht of water formed onght either to be ascertained 
[ (ft vatvo or reduced to a vacuiiiu ; Uiis reduction would increase 

the quantity of water by about 10 to 12 milligrams. 

(2) The weight of oxygen ought also to borocluced to a vacuum, 

(3) Tlte hydrogen ought to he much more carefully dried than 
[was the case in the older experiments. 

(4j Lastly, even supposing that the weights had thus been 
adjnated, and if the hydrogen had been properly dried, Kerze- 
lins's dtiti'rminatious wen: made upon too auiall u scale to ensure 
the necessary amount of accuracy. 

A factimilo of tlic appaiatus as used by Cumns is shown in 

F 18 the vessel in which the hydrogen is evolved. 

E i» a funnel with stop-cock, containing sulphuric acid. 

A is a cylinder filled with mercury under the suitace of which 
dips a safety tube. 

Tlie first U-tube coutaiu8 pieces of glass moist^jnod with 
nitrate of lead 

The second TT-tuhe contains glass moistened with silver 

The third U-tube containa ia the first limb pumice moist- 
ened with potash, and in the 8C<K>ud limb pieces of solid 
caustic potadL 

1 Jmn. dipt. PMr*.. [3] vIU. ISO. 

The fourtb and fifth U-tu1>cs coDtuin (used solid caustic potash. 
The sixth anil seventh U<tubes contain (iragnifiiils of pumice 
i povdered over with phwphonis potitoxide, and arc immersed 
(in a rrcezins mLTtur& 

Tlie oighlli is «. einall vreighwl lube oontoiniDg phosphorus 

It is a bulb tilown on hurd glass coDtaiDing the dij oxide of 
[copper, furniijhed with a stop-cock (r) nt it« upper end, and 
Idravrn out so as to pass into th« QiLirow neck of the vessel B, 
I ai ilm lover oud. 

The halb B c&o bo heated by tLu BuDfiCQ lamp placed on tho 
Uding holder of the retort-staud. 
B, ia the bulb in vhlch tlie water, formed by the decom- 
position, collects. 

The U-Luhe placed next to the bulb B. cont^ina pieces of 
fus4id cuustic polikstL 

I The next I'-tabe contnitis phosphorus pentoxide and is 
Burronnded by a freezing luiiture. Next to this is placed a 
small we^nbed tube containing phoephotua peutoxidc, whUst at 
the end we £nd another tube like tho lost) but not weighed. A 
cylinder A, filled with sulphuric acid, through which the excess 
of hjrdrogen gas escapvs, completes the arraDgement 

With this apparatus Duroas made no less than 1 9 aeparate 
experiments carried out with evety conceivable precaution. 
The hydrogen, evolved from zinc and dilute aulpliuric acid, 
might contain oxides of nitrogen, sulphur dioxide, arseniuretted 
hydrogen and sulphoretted hydroKcn. These impuritiiis are 
completely elimiiuited, and the gas at the same time completely 
dried by passing over the Bubstances contaiiic<l in tlic U-tubra ; 
the nitrate of lead absorbs the sulphuretted hydrogen ; the sul- 
phate of silvci decomposes any trace of oiwiiiiurcttcd hydrogen, 
and the rest of the tube* sen'C to orreal every trace of carbonic 
acid and moisture, so that the gas pasxin^; tliniiigli thi; stop-cock 
r into the bulb d consists of perfectly dr}' and pure hydrogen. 
I 1q onlcr to render this certain, the small tube uext to the bidb 
is weighed before and after the eixperiment. and if ita weight 
remain constant we have proof that the gas bos been properly 
dried. A similar small weighed tube serves a like purpose »i 
the other end of the apparatus. 

tireat care must t>e taken that the oxide of copper coaUiined 
in the bidb D is perfectly t\ty, for this oxide being a hygroscopic 
substance is liable to absorb water from the atmosphere. The 



weiglilof the bulb contaiuiug the oside is then accurately deter- 
mined, and after all the air has been drivDD out of tlio U-ttibea by 
the dr>' hydrogon, the bulb is fixed iu its place. The bulb destined 
to receive the water is also carefully weighed before tiie experi- 
ment, together with the 3 dryiog^tabes placed beyond it fur the 
purpose of ab-oorbiti}* every trace of aqoeooa vapour carried over 
by the hydrogen. Tlioa the oxide of copper ia bested to doU 
redness; tlie reduction comiDences, and the formatiou of water 
continues for from 10 to 1*2 hoiin^ After this, the bulb B is 
allowed to cool in a ourreot of hydrogen ; theu the spparalui 
is takes to pieces, the bulb rcndcrvd vacuous and tbon weiglted, 
whilst t)ie liydrogen, coutaiued in the bulb and tubes serving to 
collect the water, is displaced by dry air before thb ponioa of 
the oppamtus is weighed. It is clear the weight of hydrogen 
is not directly deLecmined by tliis method but that it is obtained 
aa Uie difference between the weight of water produced and thai 
of tlie oxygen consumed. As, however, tlie weight of the 
hydrogen is only i of that of the water formed, it is evident 
that a percentage error of a given amount ou the weight of 
water will represent a much larger percentage error on the 
smaller weij^hL of hydrogen. The simplest way of reducing such 
errors ia to arrange the experiment so that a large quantity of 
water is olitjiiiivt^l, for the experimental errors leuuio, for tJie 
most ptiTt, constant, and by increasing the quantity of substance 
expcriuicnt<;d u{)on, tlte pcrceutaf^e error is kept down. For 
this purpose I>utaaa took such weights of copper oxide an woold 
produce in general about 50 grams, of water, m that the experi- 
mental enor, on hydrogen takeu as the unit, is rednced to 0-0U5 
of its weight. In the 11) experiments Durnas found that 
840'lGl grams of oxj'gen were consumed in the production of 
945439 grams of water; or the percentage composition 
water by weight is as follows ; — 

Percentagt eompoaition n/ ica/«r Jjr weight (i)Hmi»). 

Oxygen 88-8(>4 

Hydrogen .... 11136 


In other words two parts by weight of hydrogen combine] 
with 159G08 parts by weight of oxygen to form watw, a ' 
number identical with that calculated from the volumetiLo; 



JSxperimaUs with the Ddonaling Mixture of Oxygen and JTt/drcffm. 

105 In oHer to exhibit the explosive force of this detonating 
gas a tJun bulb (b) Fig. 68, of a capacity frum 70 to 100 cubic 
centimctTes is blown on a gloss tiilie. This i& Iillud with the 
gu evolved by the voltameter (a) as shown in the figure, and, 
-when full, it i^ placed over the [vcrforatcil cork (c), tlirougli 
which two insulated copper wires are inserted, and these are 
coDnectcd at the extremity by u lino platinum wire. Tho bulb 
t» then surrounded with the protecting cover of the wire gaaze 
(c), and a carrent of electricity passed through the platinum 
wire, which soon becomes heated to a temperature high enough 
to cftuse an ituttantaneous combination of the oxygen and 
hydrogen to occar ; a sharp exploaion ia beard, and tiiti bulb is 
ahattcred to fine dust. 





kite amount of the energy thus generated can be easily calcu- 
ed when the quniitily of bent developed by tho eombiualion is 
I known. ThuA 1 grrn. of hydrogen on baming to form water 
H evolves 34,402 tliurmni units, or beat Auflicient to raise 34,462 
I gnus, of water from 0* to 1'. But the meelianical equivaleiit 
of heat is 423, that is. a w«iyht of 423 grains falling througli 
the space o( 1 metre is capable of evolving heat enough to raise 
1 gram of wattT from 0* to 1'. H<;nco 1 gram of liydrogwn on 
burning txt form water, sets free an amount of energy represented 
by that reqaircd to raise a weight of 34,462 x 423 grams = 
24.577 kilograms through the space of 1 metre. 

lofi The gasea may. liowever. be nude to ootnUiie not onl; 
npidly. &s we have seen, bat bIsci slovl;^ and qnicUj. 11^ 
teraperatare, the passage of the electric H{iark, &i)d tbc |>refleac« 
of pUtinam and other bottiea effect the ebaoge in the fint 
<^ theae ways. The smallest electric spark suffices to oauae 
the GorabiiiHtion of ibc liu]^>8t masaes of pore detonating gai, 
because tlie beat wliich is erolved by the union of ihoae 
particles io wliotu: neighbourhood tlie epaik paasos is aoffi- 
ctent to cause the combination of the adjacent partideSt 
and so otL In eveiy case a certain <)efinite mmimani tem- 
perature, teriDod the tetnpertUitTt of ignUvm. differing for each 
gas, must be r«uchcd in order that the union xball take plac«; 
Ami the temperature may be so lowered 1^ mixing tjie deto> 
natit% gas in certain proportiooa with inactive gases that the 
pxploflive mixture caimot inflame. Tha!< one volumeof detonat- 
ing g>s explodes when mixed with 282 vols, of carbon dioxide, 
with 3'37 v»)is. of by<Iro{;<:n. or with 9 :t5 vols, of oxygen ; bat 
it does not explodu wbon mixt-tl with 289 vols, of carbon dioxide 
with 3-93 vols, of hydrogen, or with 10-6S vols, of oxygra.' 

From theee expehnieiita the temperatureB at wliicb ttii; 
iiiuntioiiL-d iiiixturee cease to be explosive are found to 
follows : — 

DetonatJi^ gas and carlwn dioxide 17d0'6* 

, „ I.ydrogen . . 2116-8' 

oxygen . . 857-3' 

Itiesc differences in the action of tlie admixed gaaes 
Aocordiog to Dunsen, be nscril>«d ettlicr to tlw differences i 
their specific h(!at« or to tlieir vap'ing conductive or e: 
powera tor lieat, but must beexplaiui^ by thu fact tliat the 
is inHuenced not only by those molecules which take an acti' 
part in tlie mnibination, but iiIho )iy ibosc which are present, but 
wtiich are not immediately engaged in the chemical change. 

107 llie following t'xptfrimvnl strikingly sitows'that a niixtuio 
of hydrogen uiid nir liecome» inftammahle only when a dolinite 
proportion between the two gases bas becui rca<;hcd. Fig, 69 re* 
pru«Bnt« A siutiin^ink-d fjlass bell-jar closed at the top, and covered 
at \\A moutli by a siheot of pnper giimtiiHl on to the glass. 
A glass Hyphon passing through the paper cover is fastened by 
copper wirefl to the bell-jar with lh« longer limb on tlic outside. 



FSyneana oragu-generatiog apparatus the b«ll-jnr is Slhid witli 
hf (Irogvn by diitpUceiuent, a rapid current of the f^ beinfir moilu 
to pass in Uirouyb the syphon, the air finding its wny out through 

>U>e pores of ilie paper. Wheu the bell-jar is fiill of hydrogen, 
die vulcoaizod tube is removed Irom the end of tlie long hmb of 
the syphon, and tho strcAtn of hydrogrn gna which issues from 
the end (hydro^n beiug lighler tlniii the »ir, can be syphoned 
upwnnU) is then lighted and is seen to hum with its uaual quiet 

rio. 63. 

aOD-luminoiuftitne. Aftora short time, howcvcr.this flamo may 
U" M'cn lo flicker, and i.i heard to emit ft musical not* which "begins 
by being shrill, but gradually dcepeus to a \mb* sound, until, oflci 
a Lime, distinct and separate imptdses or beats an? h^ard, and at 
last, when the exact proportions between the hydrogen and the 
atr which cnlcns through the porea of the paper have been 
nacbed, the flame is seen to pass down tlw syphon atid enter the 

bcU-jar, when the whale mass ignites vtth a sudden autl violent 

Tlio nite oEpropogation of the igoitioQ in thft pare detonatiaj; 
gM has tieen estimated by Bunseu ' to be 34 metres per aecood. 

xo8 The Following experiments indicate the slow combination 
oF oxygen and hydrogen. If a spiral of clean platinam wire is ht-ld 
for a few seconds in the flame of a Bunsen burner, and then the 
flftou) extingaished and the gu still nll'>wcd to stxeam out rouDd 
the spiral, it will be seen that tlie spiral soon beeomea rod-hot, 
either continuing to glow as long as the supply of gas is kept nji. 
or rising to a temperature sufficient to ignite the flame (Davy). 
A palladium wire acts in n similar way. but wires of gold, aiiver, 
copper, iron, and zinc produce no actioa of this loud. 

A perfectly clviin gurface of platinum plate also first eflTects a 
slow, hut after a time even an explosive combination nf the 
detonating gas (Faraday). The finely-divided metal (spongy 
platiuutu) wliieli exposes a great surface to tl>e action of the gas, 
al»o induces, at the ordinary temperature, the combination of 
hydrogen mixed with air or oxygen, at first a slow combustion 
tulccs place, but when the metal becomes red hot, a sudden 
explosion occurs (Doberciuor). 

Small traces of certain absorbable gases, such as ammonia, 
destroy the inflaming power of the spongy platinum, but this 
power is regained on ignition. Th'^ most probable explanation 
of tills property of platinum is that this metal posaesaes llie 
power of condensing on to its surface a film of bj'drogen and 
oxygen, which gases, when brought under Ibese circumBtancM 
into intimate contact, are able to combine at the ordinary atmoii- 
plieric temperature, and by the heat which their combination 
evolves, to excite the union of the n'maining gaseous mixture. 

log !7« Oxi/kydrof/en Flame. — By bringing a jet of oxygen gas 
within a llame of hydrogen gaa, bunting from a plotinnm nozzle, 
the flame of the mixed gases is obtained whidi evolves but very 
liitle light, althoufih it possesses a very high temperature, calcu- 
lated by Buuscn * to be 2344'. A watch-spring held in the Same, 
quickly burns with Wight HcintillAtions. Platinum, one of the 
most infnsible of the meUtls. can be readily melted and even 
boiled, whilst silver can thus be distilled williout difficulty. 

The arrangement of such an oxyhydrogen blowpipe is seen in 
Fig. 70, the gases being collected separately in the two gas- 
holders. The uoziile at s ( Fig. 71) is ecrewed on to the tap (rf 

' PMl. J/oy, [*] xxxi*. *n, » Iti4. m. _ 

t»p is thpn gently turned on fio tlial Uie flame bums quietly. No 
IjwcVwanl rush of (^ or e:cplusiuii can livrv ucciir, for the gases 
I ooly mix lit the point wlifre c«mliuatiuu takes place. 
H If auysolid infnsible aud non-vol»tile substance, sucli as a pieoc 
H of quick -lime be held in the Hame, the tempeiature of the sorfaoe 




of the solid h laisod to whiteness, and an intense light is emitted, 
which 13 JVequently used, under ttie name of Uie Prummood 
light for tUumiuating puri^oscs. 

la ceitain metallurgical processes, especially in working tka 
platinum motfils, this high teraperatnTe of the oxyhydrogea 
flftme ia tunied to useful account One of the forms nf ftirnac* 
usfid for this purpose is shovTU in Fig. 72. It is built from « ^ 
block of verv carefully burnt lime A, A. which hss been cut iafl 
half and then each piece hollowed out. so that when hroughl ^ 
togotlier they fonu a chamber into vhich the fliihatnace to 
be melted is placed. The upper block is perforated >ofl 
allow the nozslo (c, q) of the blowpipe to fit iu, and tbe^ 

Fi«. ;a. 

gases pass from the sepamtc gn-sholders. into tvro cob^ 
Oentriu lubis c c nnd b' e', cfich providir<l with a stopcock 
(9 and II), tho hydrogen being delivered by the outer and ihoj 
oxjrgen by the iiiii'cr tube, MM. Deville and Debray' have 
in this way melted 50 kilos, of pUtiuum in one operation, and 
McMK. Johnson. Matthey, & Co. melted, hy this procesa, a masaj 
of pure platinum weit^hing 100 kilos, which was aliown at th« 
Exhibition of lSi>2. Sinc« that lime the same firm has melt«d 
no less than 250 kiloa of an alloy of platinum and iridiuia Cor 
t^ lutcmutionol Metrical Conmti.tsiuu. 

' .^nn. Chim. PKys. [SJ, IvL 2S6. 



no Altrrwaif QridaUon and lUdueticm. — An interesting expcri- 
'xneot exhibiting the incrf-ase and loss of weight od the oxidation 
of metallic copper, «iid the »ab>iiei)uent rflduction of the copper 
oxide is carried out as foUows ! Copper oxide is rubbed up iuto a 
stiff p«sto 'with f,'uiu-water, ami the meusa rolled iDto the form of 
a cylinder about 1 cm. broad, and 3 cm. long, which is then dried 
and ignited in the air, On heating this in a cnrrent of hydrogen, 
the oxide is reduced to theinetal, and a cylinder of porous copper 
is obtained. A platinum wire is tli<.-a wound round it, and the 
cylinder held in tlie Hume of a Buuiien burner, so as to warm it, 
but not bo bring it to a red heat. On now p]un«:iiig it iuto a jot 
of oxygen giw, it is »ci*n to glow from combinAtion with oxygen, 

■ and this coutiuuea until tlie vbole is converted into oxide. 
When removed from the oxygon, the colour of the metallic 
cylinder will be seen to bt changed from a brigljt red to the 
black colour of the oxide. Nisxt let this oxidized cylinder be 
fiuspcndcd from one pun of a balance, and a counterpoise placed 
in th« other pno. The cyliudtT is then rumovud from Iho balance, 
gently heated, and whilst warm pughed up into a wide tuhe, 
placed moutJi downwards, through which a current of hydrogen 
is passing ; ttie copper oxide in at once set:n to glow, wat«r being 
formed, which condenses and drops down from the sides of the 
iabe, whilst the colour of the cylinder changes from black to 
the biilliant red of the rofluccd metal. As soon as the redac- 
tion is comi>lete the cylinder is removed from the hydrogen and 
again hung on to the pan of the balance, when namsidcrabte loss 
^ of weight, due to the loss of the oxygon, will be perceived. 

Pjiopeeties of AVaTER. 

xzx Pure wafer is a clear, tasteless liquid, colourless when 
in moderate q^uniitity, but when viewed in bulk possessing 
a liluidU groiui noloiu-, well seen in the water of curtain 
springs, t-spccially thuse in Ic«land. and in certain lakes, par- 
ticularly those of Swilzi;rlaiid, which are fed by glacier streams. 
This blue colour is also obser^'ed if a briglit white object be 
viewed through a column of distilled wntor about .*ix to eight 
metres in length, contaiued in a tube with blackened sides and 
plate-glass ends. Water is an almost incompressible fluid, one 
million volumes becoming less by fiily volumes when the 
atfflOf^lieric jHessore is doubled ; it is a bad conductor of heat, 
and a worac conductor of electricity, 



Fxpansion and Contraction of WtUer. — ^Wh«D heated frotn 0* to 
A", water is Touiid lo coiUract, thus farmiug % striking exccptioD to 
tlie geueral law. that bodies expand when beftt«d and contract oti 
cooling ; on cooling from 4' to 0* it txpands again. Above 4^ how- 
uvcr, it follo^vs the ordinary Ian', expaRding when heated, and 
coutractiiig wtimi coolud. Tliis peculiarity in the «xpanmou and 
contraction of water may be expressed by saying that tht poiiU 
of mtzximitm density ofwattr m 4°C. ; or according to the exact 
determinations or Joule, y!)4:r>; tliat is, ft given bulk of water will 
at this temperature weigh more than at any other. Altliongh the 
amount of coutraclion ou hetitiD^ from 0' to 4" is bat small, yet it 
exerts a tDOHt inipurtatit influence upon the CCODOtoy 6f uattirv. 
If it vera not for this appareutly unimportant property, our 
climate vrould be perfectly Arctic, and Europe would in oU 
probability be as unitilutbitable as Melville Island. In order 
better to understand what tlie state of things voulti be If water 
obeyed ihu ordinary laws uf expansion by heit, we may perform 
the following experiment, first made by iJr. Hope. Take a jar con- 
taining water at a tenipi^rature above 4", |)laco one lliermometer 
at the top and tmcther at the bottom of the liquid. Now bring 
Uie jar into a place where the tempei'ature is below the freezing 
point, and observe the temperature at the top and bottom of 
the liquid as it cooU. It will bo seen that at first the upper 
thcrmomettit always indicates a higher temperature than the 
lower one; after a short titne butli tltemionieterd mark 4* ; and, 
as the water cools still further, it will be seen that the tliermo- 
meter at the top always indicates a lower tcmponturo than that 
shown by tlie one at the bottom : hence we conclude that water 
above or btlow 4° is lighter than water at 4'. This cooling goes 
on till the temperature of the top layer of water sinks to 0*. 
after which a crust of ice is formed ; and if the mass of the 
water be suflicieiitly large, the t^^inpemture of the water at the 
bottom 18 never reduced below 4\ In Tiatum precisely the same 
phenomenon occms in the freezing of lakes aud livero;' tiie 
surf(iee-wat«r is gradually cooled by cold winds, and thus be- 
coming heavier, sinks, whilst lighter and warmer water n«e« to 
supply its ])1acc : this goes on till the temperature of the whole 
mas* is reduced to 4°, after which the surface-water never sinks, 
however much it be cooled, oa it is always lighter than the 
deeper water at 4°. Hence ice is formed only at the top, lbs 

' Tfiv jHHiit of mtiXiniiim dsnaitjr of KO-valer ii coiudilctmbly lowir tluu) thtt 
«r Tnah) luid u in bet Inlaw CT* C. 



'xoass of water retaining the tomperaturo of 4*. Kad wator 
become heavier aa it oooled dowu to the frec-zing points a ron- 
tiniuJ circulation vrotild bo kept ap, until the whob. mass was 
cooled to 0°, when solitlificatioa of tbe whole would easuo. 
Thus cur lakes and rivers would be ftonvisrtcil into solid nias*5S 
of ice, wliidi the sumnier'a warmth would be quite iusuilicieiit 
thoroughly to uielt ; and hence the climatu of our now ti.'niperate 
zone might approach in severity tlmt of the Arctic regions. 

» Sea- water does not fieujie cm. masst, owing to the great dvptli of 
tjie ocean, which prevents the ivholo from ever being cooled 
down to the freezing |>nint; eimilarly, iu Englnml, vuty deep 
lukfs aeiKt freeze, aa the temperature of the whole moss never 
get* reduced to i" C. 

The following tabic gives the volume, and sjiecirio graviliea of 
water ffir tvriiperatuces varying from 0" to 100°, according to the 
experiments of Desprelx. 


























1 0000083 
















-99729 7 














































1 01205 









X 000870 I 



1022 5S 




















113 Latf.nt Halt of Water. — In the passage from solid ice to 
liquid water, we notice that a very rcmorlcable absorption or 

disappearance of heat occurs. Tliis is rendered plain by the 
following simple exporitneut : — Let us taka a kilogram of wat«r 
ttt llie kiDpemliin) 0*. and another kilogram of water nt 79°. If 
we mix these, the tempei-atare of the mixture will be the n]i«a,or 
SO'^S ; if, however, we tnlco one kito^m of ice at 0° and mix it 
with a kilogram of -water at 79", we shall fiud that Ihe whole of 
tho ice is uitlkd, hut that the temperature of tlie resnlting 2 kili> 
grams of water U exactly 0°. In othor wonts, the whole of the 
heat contained in the liot waler ha3 just sufficed to melt ttieioe, 
but h)is not mi»ed tho tempcnitiiru of the water tlius prudoced. 
Hence we see that in passing ft^am the solid to the hi^uid stit« 
a given wciyht of water takes up or renders latent jiist so much 
heat as would suflice to raise the temperature of the some we^bt 
of water tlirough 79"C.; the latent htitt of imter is, therefore, said to 
be 79 thermal units — n thermal unit meaning the amount i>/ heat 
rtquircii to ntwn a unit wcif/kt of vinter throuijh V C. ^^Tieo 
water freozos, or becomes solid, this amount of heat, whicli is 
necessar)' to kcL-p thu water in the liquid form, and is, therefore, 
well termed the heat of liquidity, is evolved, or rendered scnsthlb 
A Bimilar disappearance of heat on passing from the solid to the 
liquid atttte, and a similar evolution of heat on passing from the 
lit|uid to the solid form, oocuis with all substances; tlie amount 
of heat tlius evcdved or rendered latent varies, lioweter, with 
the uatiire of tlie substance. A simple means of showing that 
heat i» evolved on sulidiftoiilion consists in obtaining a saturated 
hot solution of acetate of soda, and allowinfi it to cool. Whilst it 
remains undisturbed, it rcUuna the linuid form, but if agitated, 
it at once begins to cryataUize, and in a few niomenls bucomes 
a soUd mass. If a dclictitc tliermomcter be now plunged into 
the siUt while solidifying, a sudden riau of Urnipemture will be 

113 Prenmg Point of Watrr ond ^frlting Point of lee. — Although 
water usually freezes at 0° it was observed so long ago as 1714 
by Fahrenheit that under certain circunutances water may 
remain liquid nt tenipemtnres much below this point Thus 
when brought under a diminished atmospheric prbs:suni, water 
maybe coolett to — 12° without freezing; or if water be boiled in 
a ^as3 Hask, and tlie neck of the ttask be plugged whilst it is 
hot with cotton wool, the flask and its contents may he cooled 
to —9' without the water fi-cczing, but when tlie cotton wool ia 
tnken out, particles of dust fall into the wnf^T. and these bring 
about an immediate crysUdlizatioo, the temperature of the mnas 




quickly rising;: to 0*. Sorby * has shown that when eontaimy) in 
thin capillary glass tubes, water niny be cooled to — 15' without 
rre^iiiig, whilst lioussingault ' ba^ exposed water contnini^l iu ii. 
closed 8t«al cyliudcT to a temperature of — 24* for several days in 
MOoeBuoQ without ittt frueeiug. The meltittg poiul of ice utidt- r 
the ordinary atmospheric pivssurc is 0°, but this point is lowcn?d 
by increase of prosaure; thus under a pivssure of S'l atmos- 
phered. ice melts at— t)'O50 and amler 16 8 attnosplieres. nt 
— 0*-129 or the fiwzing point i» lowered by about O'flOTS * for 
every additional atmosph*rft This pwuliarity of a lowering of tlie 
melting point under prftssurc is common to all substoucrit which, 
like water, expand in passing from the liquid to the solid state, 
whilst in ttie cose of bwlies whidi contract under like circum- 
stance*, the melling point ia raised by increase of pressure. 
Thaa in the case of paraffin, Bun^uii * and in the case of sulphur, 
Hopkins, obtained the following results : — 

Under a pressure of 1 atmosphere, paraffin metta at 4G°*3 
85 - ... 48*-9 

lOti ., .. „ 4y-9 

„ 1 atmoaphere.siilphHrniflts at lOT-O 

519 . - ,. I3S--2 

792 . „ . uor-s 



Frum what has 1«en atat«d we should expect tlint by iocreaa- 
jng the pressure upon ice it coidd be melted, and SJouMOn* has 
shown tliat this is the case, (or by uxposinft it to a pressure of 
13,U00 tttraosjihcTcs he has converted ice into water at a tem- 
poniture of — 18°. Thin lowt-rinp of thr iiK^lliiif^ point of ice with 
pressure explains the fuel thtil v, hvw two pii'ci'S of ieo are rubbed 
together the pressure causes the ice to lueU at the portions of 
the surface in contact, the water thus formed running away, and 
the temperature being lowered; then as noon ai the excess of 
pceasure is taken away the two surfaces freeKo together at a 
temperature below 0*, one mass of solid ice iK-ing produced. 
This pbeitomenon, termed r^iaiion,va& first observed b)* Faraday 

> na. M<t9. [4] xviii. im. 

* Ctrmfta Rend, txiiii. 77. 

■ Jini4« TbuiuMti, lUtia. Hey. 'i«e. Twnttt. vol. xri. f. 575, ISfV. 

* Aki. C'Aim. P*ff. [3] x»v. p. SBS. 

* tbff. Amn. cr. 101. 



in 1850, and was uft«rw%rda appU«<I hy Xyudall to explungtscier 

114 The crystalline form of ice is liexsgooal, beu^ that 
of n rhoTnbolioJron. Snow crystals exhibit this bexAgovul fonn 
T«y doarly ; they usnally conaiet of ciyatals which hftvc gMWD 
00 to another crystal in the direction of the three horizont*! 
axes, BO tha-t the snow ciyotal clearly exhibits these three 
directions, as shown iu Figs. 73, 74. 

Ice is clear, and n*hcn seen iu small quantities it appean to 

be colourli'ss, though lar*;o mosHes of ice, such as ioebeiga or 

glaciers, possess a deep blue colour ; tike water it ia alao a 

^'had condnctor of heat and a non-conductor of electiicity, and 

khecomes electrical whuu rubbed. 

Fio. 71. 

Fio. 7t 

Water on frfiezin^ incrcfises nearly ^^ of its bulk, or, acctmling 
to the exact expuriinuita oC Buiiaen,' the specific gravity of m 
at 0° 18 091674, that of water at 0° being taken as the iinit; 
or one volntno of wnter at 0* l>ecome8 109082 volumes of ica at 
the same temperature. This cxpausion, exerting an almoW 
irresistible force, plays an important part in the disinte^tion 
and splitting of rocks during the winter. Water poni-tratea 
into the cracks and crevices of the rock8,und ou freezing widens 
these openings; this proceas being repeated over and over 
again, the rock ie ultimntely Rplit into flfligaienla. Hollow balls 

I 1*0. Hag. [i\ xlU 146. 

of thick cast iron cftn thus eftsily bo split in two by filling tlit-tn 
with u'ater and closing by a liglitly filUug screw, and tljCQ 
exposing them to a temperature below 0^ 

115 When a BAliiie Rolution. sucli «s sea water, freezes, the 
greater part, of the salt remains uofroien, and tlie resulting ice is 
nearly but not ijiiitc frco from saltt for Bucbatuin ' bas recently 
shown that 3«a-n'afei- ice contains common $nlt, not as brine 
mechanicnlly inclosed in the ice, but in the solid form, either as 
[a single cr>'staUinc substance, or as a mixture of ice and suit 
Ciystala. The (Quantity of chlorint; contained in water melted 
firom pack-ice amounted in one case lo 0-1723 Rrms.. and in a 
second to 00520 graia. per liLre. 3ce crystals formed in sua- 
water, wli<>n dhcil nnd analysed, wurg found to contain 1-578 
gnuB. of chlorine per litre luid uulUid iit 1°'3, instead of at 0°. 



Fio. 76. 

P 116 latml Hf'xt 0/ fi/effm.— Under the normal barometric 
pleasure of 7G0"'" water boils in a metal vessel at 1 00* C When 
Lquid wat«r is converted into gaseous steam, a large quantity of 
h(^t becomes latent, the temperature of tlie Bleaiu given oD being 

■ the saiuo as that of the boiling water, as, like all other bodive, 

■ water requires mure lieat for its existence as a gaa tlian aa a 
Uqnid. Tlie amount of hmt ialent in steam is roughly asp^rtained 
by the following experiment. Into I kUograui of water at 0", 
6te«m from boiling water, having the temperature of 100', is 
passed until the water boils : it is then found that the whole 
weighs 1-187 kilos., or 0187 kilo, of water in tlie form of eteam 
at 100^ has raised 1 kilo, of wdtcr from 0" to 100' ; or 1 kilo, of 
Btetn at 100° would raise 5*36 kilos, of ice-cold water through 
100°, or 536 kiloe. through 1^ Henco the latent htat of gttam 
i$ laid to he 536 iJurmat units. 

Whenever water evaporates or passes into the gnseons state, 
■ Proe. Soif. rSte. ixii. 431. 



heat 18 abaorbwl, and so much heat may be tlius abstracted froni 
vaiex that it may he made to freeze by its own evaporation. 
A beautiful illustration of Oih is fournl in an instrnmiMit calleU 
Wollnstoii's CiTrtphoniB, Fig. 75 ; it consists of a beiit tube, 
liavin;; a buib on each end, mtd contAiDing wat«r and vapour uj 
wiitvr, but QO «ir. On placing all tlic water iti one bidb, and 
plunging the rniply bulb into a rree;:ing mixture, a condeiuatioa 
of the vapour of vater ill this empty bulb occuts. and a cotre* 
spouding quantity of wntcr uvuporaicd from the oLlicr bulb 1« 
supply the place of the condensed vapour: this condensation 
and evaporation gn on so rapidly that in a iiliort time the water 
cools down btiluw 0", and u Holid mass of ice is left id the bultk, 

Fio. 76. 

By a very ingenious arrangement tliis plan of freeiing wster 1 
its owu evaporation has teen practically carried out on a 
scab by M. C'urre, by means of whiuli ice call be most easily 
aiid clieaply prepared. Tliis arrangement cotisiats simply of a 
powerful air-pump (A, Fig. 76). and a reservoir (n), of a bygro- 
Bcopic substance, sucli as strong sulphuric iicid On placing a 
bottle of water (c) in connexion with this apparatus, and ou 
piiiJiping for ti few minutes, the water begins to boil rapidly, 
and the temperature of the water ia cooled so low by its own 
evaporation as to freeze to a mass of ice. 

Z17 TtntiQn of ^qutoits Vapmtr. — Water, and even ice. oq< 
stantly give off steam or aqueous vapour nt all lemperatuieSt 
when exposed to the air. Thus we know that if a 


of water be left in a room for some flays, the whole of the 
vrater will gmdiiaUy evapor&te. This powtr of water 1i» Hsr in 
vapour ftt alt tvit)[K-rat'Ures U called the elastic force or tcnsi<m. 
of aqueous vapour ; it may be meamircd, when a muM qimutity 
of water is placed above the mercury in a barouicl«r, by iiier 
dcpniasion wbicli the tou^ion of the vapour thus giviin off is 
eapabt« of exerting upon the mercurial cohinin. If we gradually 
beat the drops of water thus placerl in tlie barometer, we shall 
notice that the column of mercury gTadiially siuks ; and when 
thu wftter is lioated iiji to the huihng ;[H>iDt, thi; mercury in the 
barometer tube is found to stand at ihe .same level an that in tlie 
trough, showing that the elastic force of tlie vapour at that tem- 
perature is equiil to the atmo^pbcric prossurt'. Iltiiice imlcr boils 
ichm the Utision 0/ Us vttpouT is equal to the siipcrincumbcni 
atmo^<rie prtesHn. On the tops of niouatoins, where tbe atmos- 
pheric pressure a less than at the seu's Ifvu), water boil^ at a 
teni}K!rature below lOD" : tJius at KlmXo, at a height of 29 1 4 metres 
above the sea's level, tlie mean height of tliu baromutc-r is 523 
mm., anil the boiling point of wati>r is 9n"'lj that is. the tension 
of aqueous vapour at 90''1 is equal to the pressure exerted hy a 
coluniD of mercury 523 mm. hi^'li. Founded ou tliis piinciple, 
an instrument ha« been coustnictcd for di>t^-rmiiiing heights by 
noticing the temperatures at which watur bulla. A siinplf! 
uxperimeot to illustrate this fact consists in boiling water iu 
a globular Husk, into the iiech of which a stopcock ia fitted : 
as soon as the air is expelled, tbe stopcock is closed, and the 
tlosk removed from the source of beat; the boiling then 
coa»es; but on immersinjj tliu tlaak in cold water, the ebullition 
recommences briskly, owing to the reduction of the pressure con- 
eequcnt upon the coudeuaation of the stemn ; the tension of the 
vnprjur at the tempL-rutura of the wiit«T in the llitsk being 
greater than the ditninislied piewiiire. All other Uquids obey 
a stmikr law respecting ebullition ; but as the tensions 
of their vapours arc very different, their boiling points vary 

When steam is heated alone, it expands according to the 
taw previously ^iven for permanent gasea ; but uhen wat«r is 
preseut, and tho cxi>crinient \s performed in a closed veswl, 
Ute elafitic force of the sluam iucreases iu a far more rapid 
ratio than the increase of temperature. The following table gives 
the tension of aqneoos vapour, as deteiiiuued by experiment, 
at diffcieat tcmpcrnturea measured on the air tbcnnometer. 




TabU tftht Tauioa of l&e Vajmir of WaUr. 


Tension ill luiUiine- 
tresof Dieri'Uiy. 


Tea«{a« b *tnu«|iW, 
1 aimcKjihore -r ISO 












+ 5 



•Z5 _, 




3 ■ 


] 2-699 


^ 1 




S I 




» ■ 




10 ■ 




12 ■ 




1^ I 




1« ■ 




18 ■ 








. 1 

1 18 Waier aa a SoltvtU. — Wntex is the nwsl geDcnJly valoi 
of known Bolveiits. Not only do nioiiy 8olids,9Ucli ns sugar unci salt, 
dissolrc in water, but cerlain liquids, auch as alcohol aitd itcetic 
aci(],inix»')i]t itconipletvly. Ollict liquids agitin,&ucli as etlier, 
dissolve to a certain exteut iu water, although they do not mix 
with it ill all iiioimrlioiis. (iases also dissolve in watoir, soma, 
such as nrainoiiia and hydrochloric acid, iu very l^u^-t quautiliev. 
exceeding marc than one hundred times the bulk of tlie -waUrj 
otliera, again, smli as liviho^en and nitrogen, are hut 
slightly soluhic, while cjirbon ilioxide and someoUief gascai 
as regards solubility, hel-a-cen these extreiuca. 

Concerning the nature of solution, whether of solids, liqc 
or gases, we know nt (>resciit hut little. The phenomena of boIw 
tion differ, however, essentially from those of chemical coiubina 
tion, inasmuch as in the former we have to do with giatlm 
increase up to a given limit, termed the jioint <if saturat^oHt^ 
whereas in the latter wc ob8er\-e the occurrence of constant 
detiuito prD|xirtions iii which, and in no othras^ comlntuitioa 
occurs. Soluliun obeys a Inw of coutinuity, chiuulcal oambii 
one of sudden change or discontinuity. 

TIte sohihility of aolids varies with tlte essential nature 
solid, wiUi that ^f t^ie li<iiui1, and with tlie temperature at ' 






they are Iwonglit together ; the same may be afiid of the solvent 
action of v&t«r upon liquids and upon gases, except tliat tlie 
solaljility of ^vs is ulso iufliioncud liv llie pressure to which th« 
gftfl and the water aro subjected. The quantity of any solid, 
liij^iiid, or giis which dissulvt^us in a solvent, Hueh as wator, must 
be asceflaiued empirically in every case, as we are unac(|iisititfid 
vith any law rogtitatingeuch solvent action, niid ve, therefore, 
cannot calculate the uuouut. The effect of cliange of tempera- 
ture ou the solubility of a aiihstance, whether solid, liijiiid, or 
goiieona miist tilc«wise be determined hy experiment, but the 
elTect of pressure upon the solubility of f^ases is sutgect to a 
simple Invr, known as the luw of Palioii and Honiy. 

iig Frwzing Mixtures. — Tlie solution of a solid in water is 
generally aecompanic-d lij* a lowering of t^mperatnrr, caused by tha 
conversion of sensible into lulcitt licat by tlie liijuefactinn of the 
solid. In th« ca»e, however, of many anhydrous salts, solution is 
accomiianit'd by a rise in tenipemture. Imt this is caused by the 
production of a definit« chemical compound between the solid and 
tlio solvent. By the solution of many salts such a diminution of 
teinpentute is effected that this process may be used for obtain- 
ing ice ; thus when 500 grams, of iJoJassiimi eiilphocyanide are 
dissolved in 400 grams, of cold water, the t«nipcral»UTj of tlio 
solution sinks to — 20°. When common salt is nnxcd with snow 
or pouuded ice a considerable reduction of the tempenttuie of the 
mass occurs, the tvo solid bodies becoming liquid and forming 
a concentrated brine whose freezing-point lies at - 23". Tbb 
solution coDtaiDS 32 parts by weight of salt to 100 parts of 
water, and in order to bring aliout the greatest possible reduc- 
tion in temperature the salt and snow must be mixed in the 
above proportions. Etjunl weights of crystalliKcd calcium 
cliloride and snow when mixed together give a freezing mixture 
whose temperature sinks to from 0' to— 45°. 

Tlie solubility of most chemical compounds increa.se8 with 
the tempemture. a limit in each cose being reached, beyond 
which no ftiithej increase of wjluliility occure. 'Wnicn the tem- 
]jfmUire of such saturated solutions falls, or when the solvent is 
allowed to evoporato, a portion of the dissolved sulwtnnco is 
usually deposited from solution in the form of a solid possessing 
some definite geometrical form, and tenned a cyshil, w}iil»t tbo 
solution is said to crystallite. The subject of the solubility of 
saltA will be Ihrther considered in the chapters introductoiy to 
the metals, 

ISO WaUr of OrytSaJliixdidn. — Many salts owe their crys' 
line cbancter to tbc presence in a solid state of a certain defitii 
□umber of motcciilus of water. Wlicn this clieniically couihiofi 
water is driven off by heat, Uie crysldl fiills to powder, utA 
lience it lias hpien t(;riiied water of crystal) izutioii. Rome salu 
OOittain a kr];;e quantity of water definitely combined in this fonn 
thns the opa^iue white powder of anhydrous iiluio KjAl,4S0, 
unites wiUi no leas tliau twcnty-fuur uiok-cuita of wai«r to 
form tile well-kuown tmnsporent ocLohedral orysUils of coaunon 
almn, K, A1,4.S0,+ 24 J{,0 : in like manner anhydrowi i»n4 
powdery carbonate of soda, Na,COy when dissolved in wa:*r 
dejiosil* large nionocliiiic crystaJs of common wasliing-«0ila, 
hflvinjj tlio composition Xa, CO, + 10 H,(X The temperature of 
the solution frjio wliich such ctystals arc deposited materially 
affect!) the qiumtity of water wiUi which th« siUfc can comhine ; 
thus, in the case of carbonate of soda, whilst monoclinio oryaUb 
of tlie ten-atom hydrate are deposited at the ordinary tempera- 
ture, other crystala, having the corapoaition Na,COj-f 8H,0, or 
agRin others represented by the formuln Na^COj+SHjO, arc 
deposited, when cryatallizatioa is allowed to take place at liigber 

Some cryetalfi, such as those of the washing soda aI)ove men- 
tioned, lose their water on mere exposure to the air, the water 
evaporotiijg, and the suit fuIUu^' to powdt-r, or beconiiuy covered 
with a white powder. Sueh crj-stals are said to tffioretu. Other 
salts again nHjuiR! to bn lu-ati-d up to a li.tmpenttiire conntdejalily 
above the boiliny point of water, in order to part M-ith tbeir 
water of CTystallization ; thus potfish alum loses ton moleeoles of 
water at l()f)^ but it needs to hv heated to 120"' in order t<i drive 
otf a. second lt;ii molecules of water, and it retains tli« la«t 
four molecules until the tetiipcraturu rises to 200^. Other Mlid 
salts, such us cdciuni chloride, and potasaiuiQ acetate, att 
water with Hurh avidity llial wlti:ii left exposed to ihv urr t 
be^n to litpiefy from absorption of the atmospheric moieture ; 
Ba,lU are then said to ddujitesrt.. 

In lliv year 1840 Daltun observed that different wits, wl 
water of crystallization has been driven off by heat, dissolve io 
-Hiiti-r withiHit increaaing the volume of the liquid. Whereat if 
the hydntted ealt is die»oLved, an increase of volume occurs wbich 
lit exactly that due to ttie water which is combined in tho solt 
Playfair and JoiUe^ extended these observations, showing, 

■ Oent. Sk. Xetn. ii. 177 ; lil. H, 18» ; CAen. Sot. QmuU JounL. I 



■for insfiincc. that in the ease of carhonate nf sotla, crystallizing 
with tfii uiolecules of water, ami in t!i»t of the p)iQ.'<pliAtes and 

IBTS^onteii crj-stallizi nj; witli iwvlvii iiiiiluuuU!^, the volmue of the 
whole molecule of hydmted salt is the same as that of its valex 
of crystallisation woiiM be if frozen tt> ice. The i^rticle-s of 
Miltydrous salt woulj hence ap|)ear to occupy tW spaces int«i^ 
iwniiig betwocn those of the water without increasing; its volume. 
Thus the ci^'slals of voiumon washing soila have tlie foUowiu;,' 
compOQitioQ : 








N8, COj + Ifl H, . 

1-4M . 

. \va 

Na, HPO, + 1« H, 0. 

l-b& . 

. 1-537 

NhjPO^ +121130 . 

i-a«i . 

. 1-ES2 

N(i, H .UO, + li H,0 

ITM . 

. irsu 

Nua-WJ, + 12H,0 . 

1-6W . 

. isa4 

^nd, ttierefore, 285'43 grams, uf these crystals occupy exactly the 

^space of 1T9'i> grains, of ice. 

Tbc followiDg table gives the specific gravities of tlie aWve 
montionod iults, first as observed hy expennient. otid secoiicUy 
aa culculutcd upon the above hypothesis, auj shows the close 
agreement of tlie two sets of numbL-rs. 

Bodiiuu CWbctuu . . . 
Ujrdmgto SotUnin Phoiphote 
Homal Sodinni Pliotph-tic . 
HjrdnqtM Bodhiu ArKuate. 
' NouimI SmUubi A»«iut« . 

In the case of certniu other salts the vulumv of the cr^'stal 
was found to ho equal to the sum of the volume of tlie wat«r 
v.i»cn frojcu and (liut uf the anliydrouii salt. 

I3Z Ctyohjnlralfg. — It lia» boon ulrvmly mentJoned tlmt u'lii.'ii 
salt water freezes, the ice which is deposited eoiitiunfi aall. 
tiuthrie,' who has fully investigated this subject, finds that when 
a dilute solution of common .'ialt is cooled down to — ^'o, ice 
begins to Rcpnrntc out, and this formatioD of ice continues until 
tlie teniperature sinks to - 22°. A cunccntrated suit solution, on 
the othLT band, deposits at — T" crystals having the compoBitioii 
KaCl -t- 2HjO, and the separation of this conri|iound, in the form 
of iridescent sailcs. goes on until the liquid has cooled do^in 
10—22*. At a temperature of — SS* another dvfiriit*: hydrate 
Solvates oat - tbia crystalliiit^s iu acicular bundles, )io&se£ses the 

1 Fhd. Mag. [t] xUx. 1, 206. ZMt. 



compofiitjou NaCl + lOH^O, aiid melts at the same teuipentu: 
at which it is tlepoeitcd. 'Many other salts form similar ootii> 
l>ouit(l« with ice, anil to the ntenibers oF lliis tmvr oUm of 
Bubstances Gnthrio gives the namo of Ciyohydrates. Earii 
cn'ohydnite iio8«.-^us a constant coiuposition uid ha« ft deti- 
aite freezing- and tnelttng-point. The existence of 
substances expUios in b satisfactory niatter the low< 
of temperaLum wtiicli uccuis when ice and certain salts 
mixed together, and shows that the maximum freezing eflc 
is obtnined when the two bodies are mixed txigetlicr in the 
[irciiiortiotts netessaiy to form a crj'ohydrate; 

123 AbiiorjAifitt. of Gaten ly U'ater.-~A\l gpses arc 9o1ub1« to 
greater or lesser de{;ree in water, the amount of this salabilitf 
(!fIM-.iuliiig ujwn (I) the imtura uf the ^-us, (2) the U;iiiiM'mtun; uT 
the gas and water, (3) the pressure under which the absorption 
occurs. No simple law is known expressing the relation betn'tca 
the amount of gas absorbed and tlie temperature. Usually the 
solubility of a gas diminisbes as tlio tunipLTulrure increases, but 
the rate of dlmlnutiun varies with each gas, so tbat the amoont 
of gas di9Solvi;d in water at a givun uniipiTatun.' can be nsoer* 
tainotl only by experiment. A simple relation has however been 
found to exist between the (iimntily of gas alsorbed under vniy- 
ing conditions of pressure, llie temperature reiiiaining cuDStant 

III the year 1803 William Htni'y ' proved thai the amount 
gas absorlted by waiter varies directly as the pressure, or, in 
words of the discoverer of the law, " under efjual circumsl 
of tentperature, water takes up in all cuaes the same t'olnrnt 
eoiideuBed gas as of gas under ordioary pressure. But as (lie 
spaces occupied by every giis arc inversely as the compressing 
force, it follows that water take.i up of gaa condensed by on^ 
two, or more additional ntmosp]icres,a quantity which, ordinarily 
comprusaed. \>'ould be eipial to txvice, thrice, and so on, 
volume absorbed under tlio common pressure of the atmosphere,' 
Two years after Henry had enunciated this law, l>aIton' 
extended the law to the case of mixed gases, pro\'iug that wheo 
a mixture of two or more gu^es id giveu prupurtiuns is shaken 
up with water, the volume of the gas having a finito relation 
that of the liquid, the absorptiumotric efiuilibrium occurs w 
the pressure of each gas dissolved in the liijuid is ef|iial to tl: 
of the portion of the gas which remains nnnbsorbed by 
liiiuid ; the amount of each gas absorbed by wat4--r from snci 
' rAii. Tram. U03, xxix. 274. * ifane. Memiiri, ISM, 


in tfefl 



B mixture being solely deiH^nilent on (he prMsure exerted by Uio 
particular gas. This \avf,tfimiG-i Daltvn's law 0/ partial pntsures, 
maybe illiisUoted bythe following exaiople; if two or morcgase* 
which do DOt act cheDucaily upon eacli other be mixed logeUier, 
and thu mixtuns of gues bvougbt into coiitnct nitb vnber uotil 
the alworptionietric equilibrium ia estatiUalieil, tlie quantity of 
h gaa which dissolves is exactly whnt it would have been if 
only the one gas liul becu present in the space. Thus for 
instance the alaorptian ec-e^ient of oxy^n at 0" ia 041 14, 
tbHt of nitrogen at the aame temperature buinj; 002035. Now 
100 volunies of air contain on an averaae 79"04 volumes of 
uitTogftn and 20 9G volame.1 of oxygen, hence th* pftrtial progBure 
OQ the oxygen ia 02096 of an atmosphere, wliilat tbat on the 
nitrogen is 0'7904, and as the aolubility of csch gas is propor- 
tioned to its partial {treasure, 

0-2096 X 004114 = OO08624 

will be the proportion of oxygen disaolvcd, and 

I 0-7904 X 002035 = 0-O16746 

n-ill be the proportion of the nitrogen disfiolved, or the per- 
oentngo composition of the air dissoh'cd in water will ho ; — 





100 00 


Thus the relation between the dissolved ^fisas as found by ex- 
periment agrees exottly with Ihut calculated on the above 
usumptiou, and the law of partial prosaure is verified. 

Every nVsorbed gas whiuh oheyfl the law of pressure will of 
course be driven out of snhiCion when the prtsenre on the gas is 
reduced to 0. This ciui l»e elVtwleil by removing the superin- 
cumbent ppeaaure hy uieana ol au ftir-piimp. by allowing the 
liquid to come in conUirt with an infinitely large volume of 
ftume othor indifferent jf.i3, or, lastly, by boiling tho liiiuid, when 
all the dissolved gas will i>e driven oCf witli tlie issuing steam, 
except where a chemical combiuatiou or attraction exists between 
the gas and the water. 
■ Some gaaes di^ve in waiar in very large quantities, whereas 
I othen are only sUghtlj soluble. Two distinct methods of 

experiineiitalLDii are needed for ascertaining tJie co-efnctt-nu of 
solubility of tlioie two classes. Jn the mae of very solutile 
(;&»(.•» the amount or the abaorbed gas is (letennined cbetuicAlly ; 
in Uiat of the lass soluble Rases a jjeculiar cudiotnetric procen 
haa hccu adopted by Giiiitien ' to whoiu wo are indebted fw 
the firat exact aud extended e\perimeiital iuvealigation rf 
this suliject. Tlie gases wliose solubility liare been deteniiined 
by chemical niethodg are sulplmrcUed liydi-ogen. siL]}^iur 
dioxide, animonia, and chlorine. Tliese gasos, c-volved io a 
state uf purity, were paned for a long time through a laxjia 
volume of water, wliich had been freed frgui air by coutiounl 
boiling, and was kept nt a Cftn-ttanl touiperatiirc during llie, 
experiment. After the gas had passed so long through tl 
wiitvr that the Intter wn« completely aaturatod, the ban>iuet 
prwsure was read off, and a known volume of thp watvr wi 
drawn, special precautions to avoid possible loss of the gas 
obsencd. The gn$ contained in this liquid was then c{uaQtit«- 
tively determined either by means of voluuietric analysis, or bv 
the oRlinarj- processi* of analytical cheraistiy. if tlie volume 
of the liquid does not undergo any appreciable alteration in 
btdk owing to the absorption of llit; gas. wc are uaaily able to 
calculate the, co-eflicieuts of absorption froio the data obtained 
by this process. If, however, the volume of the saturated liquid 
18 considerably larger, as is usually the case, than that of the 
liquid before saluralion, either the specific gravity of tlie satu- 
rated liquid must bo ascertained, or only a email volume of 
water must be saturated, and the absolute quantity ofaljMtrbvd 
gas ascertained by weighing before and after the experimeai. 
123 Buuseu's AhsorptmneUr, as shown iu Fig. 77,* consis! 
essentially of two parts : (I) a eudjometric tube, c, in whii 
a Measured volume of the gas to be experimented upon 
brought in contact wiih a givi-« volume of wutcr j (2) an ou 
vessel, consisting of a glass cylindor, fitting at the lower en 
into a wooden stand, /, and having a water-tight lid at 
upper end. Tlie eudiouicti-r tube, which is divided and accu 
rately calibrated, is partially tilled with the given gas in the 
uautd way over a mercurial trough, and the volume of this gas 
read off with all due precautious ; a measured volume of water 
perfectly free from air is next admitted under the mercury into 

* rTruonMfry, p. 139, oi WfttU** SMicmary, orttelo "Ga«u, Ahsoiptlooi i 
Huvaen't Oaton. 43 wd <i> 


any ilangcr of losing gns or vratcr, nnd plactsl iu Uic gliuw cythl 
der, whicli cnntaioa mercury a iu its lower pail, and wit 
above, in which it cnn be safely shnketi to ensure the cstablitl 
ment of Uie proper abeorptiometric equilibrium bctwixui gas uid 
WBfur. Tht; pressure in th« iulie can be readily a()jiist«d frato 
tiuiti to time by unscrewtug the open ends of the tube ttom the 
caoutchouc plate, and thoa plAcing the inercury inaide iu o»- 
noction witli that oiilRide the tube. Tito lici^lits of the two 
levels of Diorciiry anil tlie love] of the water in the tabe, aa well 
as the t«mpeniturc (indicutod by the thcmtoinetcr k), can then 
be read oGT through the glass cylinder, and Lhua all tlie data 
are obtuincd for aft(!4;rtaitiirig ex»<:tly the vuluiii*' of jjos nlisoibed 
by a given volnme of water under given conditions of tempera- 
ture and pressure. 

134 The tnilh of the law of Dalton for pressures not greatly 
higher than that of tlie atmosphere has Ijccn cxpp.rimenUiUy tested 
by BuD^icn,' who .ihowed that the results of an abeorptioinetrie 
analysis of n gaseous mixture — that is, of au cxpcritncntal deter- 
mittiLtion of its solubility in water, from which the compuaitioii of 
the origioal gaseous mi.xture is cnlculnted, on the supposition tliat 
the law of partial preesurea holds good — agrees exactly with t 
direct eudionietric analysis of the game mixture. Thus it has 
been shown by the saiue chemist that in mixtures of carbon 
dioxide and carbon monoxide, of carbon monoxide aud marsh gas, 
of carbon dioxidi^ aii<l hydrif^cn, thu component gaaea are absorbed 
ill ([tiaiilitics exactly I'egulated by I>altoa's law. 

The limits of pressure beyoiid which gase.s do notobcy the law 
of pressurcjs have not as yet been experiiiietitally ascertained in 
many c:ues ; but, at auy ntte in the cuse of the more soluble 
gases, the limits arc readied within ranges of pressure varying 
j'rom to 2 atmospheres. Tliat under high pressures deviations 
from thti hiw niust i» many cases occur is clear, iDostuuch as 
roost gaaea do nut conform to the law of Boyle under greatly 
increased pressure. So t(W, it is found that certain gases whi(^ 
olxi^y the law of absorption at one temperature do not oouform at 
another; thus, for instance, amnionin dissolves in water at 100" 
under hi^h pressures, iu quantities exactly propOTtiouul to tlie 
prussuiv, although at lowur Iviiipinituivs tliis is not the case.' 

lustancea also occur iu wliich cei-taiu gases, although obeying 

the law of prtissurcs when in the pure state, do not obey the 

law whai mixed together with other gases. Tims mixtures 1 

' Giuometry, p. 131. * ItiMcoa, Ckcta. Soc /tmm. vliL 14. 



vo1iiiiii!S of clilorinfr nn<t 1i)'^rogen, ond mixtures of varv- 
' pTU[Mirtiuiis or clilortne and carbou dioxide, do not dissolve 
vater in quaatitiea proportiooat to the partial pressures of each 
. altJiotigli bulli liy<lrogen ami carbon dioxide obey the law.' 
Amongst the various appliuuccs of the laws of the absorption 
'gtaos in water none is more interesting tlinn tlie procesd piv> 
posed by ifallet for solving theditliciilt prolileitiof scpfimtingtlic 
atmospheric oxygen I'roni tho nitrogen. We have already seen 
that iJic percentft^ti of oxygen contained iu tliu air is 209, 
wbereiw tlie mixture of oxy*;cn and nitrogftii diHsolvt-d in wutt-r 
contains 34*9 per cent, of tlio formor {pis. If tho gas tlius 
disaolvcd be driven olT by boiling, and thiui this a^n sliiiken 
up with wat«r, th(> dissolved gases will possess the following 

teiitage couipasition ; — 
AJter the »cond absorjiiion. 
^1 Oxygen 47'5 

This again set free, and ag&in shaken up with water yields a 
};as«ons mixture, containing 75 per cent, of oxygen. Con- 
tinuing; this process of altcniatcly absorbing and lib(?rntin*^ the 
mixture of gnaes, tlie perceiitiigo of oxyjfen rcguUirly rises, 
until ntter the ftth aljBoqilion the gas contains 97'3 ppr cent., 
^or ia nearly pure oxygen gas. 

1 00-0 


H 135 None of the various forms of water met with in nature 
■ are free from ccrtuin iniinirities. These nmy beef two kinda ; 
(1) Meehauically suspended impurities ; (2) Soluble impurities. 
The first can be scparuted eilliur by aubsjdetice or by luuclianiad 
filtration, the latter cannot be thus got rid of from the water, but 
must be BCparatod by distillntion or by some chemical reaction. 

■ Even ruin- or snow-water collected ia clean, vessels contains 
in addition to the dissolved atmospbcric gases traccj; of foreign 
bodies which are contained in the air either a^ duKt or vapour. 
And DO sooner does rain-water touch the earth thnnital once takes 
Qp into solution certain soluble consiitiicute of tbi' {jnrtion of the 
etrtli's crust through which it ])ercokles, thus gniilually becom- 
ing more and more impure imtil it again reaches the oceaD frora 
which it bad it4 origin. 

* KiiM, Jovm. Chem. Sec siv. 1. 



12& Furificalum of Water. — ^Tlicwpamt ion of suspended matter 
ia effected on the stnsU scale for laboratorv purposes hy fUtration 
tliroux)) ponius paper pliiceH in glasR funnels, and ou llie largSj 
scak l<y«mployiDgfilt«riii{jWda ors&udaQ<l gmvcl. In order to 
Bcpumte iiU8t>eiidiid matter from witter uiwd for (]tiiikiiig|iur[iu8ea 
it is usual to filtE-r it tlirouiili a layer of wmchI cltarunal, whicb not 
ooly holds back the solid uialh'r but also acts lu othur way8,M we 
aliall herealler l^m, in improving tlie character of tlie water. 

Tbe Boluljk c«mtitueiits may be disttnguislied as (I) fixed, and 
(2) votutil<: coiiatiLueuts, outl Mutu- cuubu obtainud frtc ttom tbe 
first of tliese by the process of distillation, wliilat the latter may 
come over with tlte steam and, therefore, require the employment 
of other means. lu order to obtaiu piue distilled water, 8prin{> 

or rain-wftter is boiled in a vessel termod ft still, (b) Fi^. 79, ea 
arranged tJiat the escaping steam is coudensed by paadiiift through 
a cooU-d worm or tube made of block-iin, platinum, or silver, but 
not of f;lii«s, for if this substancG be usod a trace of its manl 
soluble coimtituuiits ttiat is of alkaline aiUcatAs ia nivraya dis*' 
solved. This procvse frc<!8 the wat^r from all iwu-volalite 
impuritips, provided earn liaa been token to prevent any 
nicchaaical spirting of the liquid, but subatAucPS which are 
volatile will still be found in the distillatcL Tlina ordinary 
distilled water invaiiably contains ammonia, as may easily be 
proved by aibling a few drops of Ntatler'a renpcnt. This con- 
stats of an alkaline aolution of nieKurio iodide in potassiuia 
iodida If n few drops of this rengcnt be added tn nl<out 
100 cba of ordinary distilled water contained in a cyUodrical 

puBincATios or watkr. 


tffinTlirg.'m % white pinte, tlio u-aU;r wilt lie seen to 
.S' distiiuit yeDoffifih liut if simill amuunts ur atuinonU 
or AmmoQiucal eaJta be present, -wliilst if larger quHDtiliea of 
ammoaiabe present a bron-ii prncipitate will I>c rovmcd. 

In order completely to fn>e distilled watcir from volatile nitro- 
goDoaa orgiuiit: bodies wliicli it is likewise apt to contain, it ib 
necessary 1o rc-distil it afler it Las been placed iu coiiUict wiLli 
a ttolution of pcitassiuta iiermaiiganatc and caustic potash. These 
substances oxidize the organic matter with foriaatioQof aimnomii. 
aud aft«r about one-twctitiutli of the watur has come over, the 
distillate is usually foiuid to be free from aiamonia, aad to leave 

FlQ. 80, 

no residae on evaporation. If animonia can bo still detected 
the water must again be distilled with the addition of a small 
quautity of acid sulphata of potash which fixes tho ammonia.' 

137 Gasei Dita^vtd in Waler. — All watt-j conliiJnii in soUition 
the gases of the atmosphere, oxygen, nitmgen. and carbon dioxida 
Id Older to obtain wnttr free from tliusc di.ssoIved fpi^m the water 
i* well boiled and the glass vessel in which it is boiled is then 
eeflled hpnii«li<ra]ly. Tlic amuigcment Fig. 80. shows how this may 
\>e conveniently accomplished. After the water lias been quickly 
boiling for half an hour the caoutchouc tube (a) from which the 
* SUu RccAnrJtrt, p, 109. 






stetLm issues Is closed by presaing, the lamp is reEnoved, nnd lh« 
dravirn out neck of the iUsk me1t(->d off before the Mov-pipe nt (A)j 
Kvcn when boiled for many liours a small reaidne of DiUo- 
gen gas is left behind, and on con(l«iLitiig, tli« steam ooiouig 
off from such VAter leaves n minute bubble of nitrogen ao 
thut it appears impossible to obtain water quite free from Ditio- 
gen.' All water which is vxpoj^od to the air dinsolves a certain 
quantity of oxygen and nitrojjen, a tiuantity which is detenoiiud 
hy the laws of gait aUsorptiou. It is indeed upon tliis dissolved 
oxygen thnt the lll'u of wnuir-bi'ciitluijg DiiiniiUs depends. In 
every pure water the proijortion between the dissolved nitrcigMi 
and oxygen is found to be constant, and it is represented by dm 
following numbers : — 1 

PtT'Ceaiage ConvpoaUion of Air Ih»soii>td in WiUfr. J 
Oxygen . . . 34-91 ^d 
Xitro^-ti . . . 65-09 ^M 

lUU 00 V 
1,000 cba of pure water, sntdi as rain-water, when satorated. dis- 
eolvea 1795 chc. "f iiir. If the vra.U:v is rvndoPHl impure by 
the introduction of organic matter undergoing* oxidation. tli« 
proportion iKitwecn the dissolved oxygen and nitrogen become* 
diff«rent owing to the oxyyen having been partly or wholly ustd 
for the oxidation of this material. This is clearly Bho\vn in th*i 
following analyaes. made by Miller, of the dissolved gases con- 
tained in Thames water collected nt various points above and 
below Ii>ndon. 


ThMiu V«ter taken at 

Him- {Sonratst 
mcmnith Hooat, 







Total volume of 
gas [>er litru 

52 7 








Carbon dioxide. 
Oxygen , . . 
Nitrogen . . . 

Ratio of oxy- 
gea to nitrogen 






If, -2 










1 :3-7 







— , , , 



This table 9h«j\v3 ibat wLtTvos the pure water nl Kingslon 
contaim tlie iioriual i^uautity of dissolved osygen, tUe ratio of 
oxjg^a Uj nitrogen increases in a very rapid rate as the mar 
■witer becontes coiitamiiiaieil with Lotiiion sewage, but that this 
ntio again shows signs of s return to the uonnal at Jilrith. 

Hence it IB clear that an analysis of the gases dissolved 
in water may prove of much help in ascertaining whether 
the water is pure, or wlictlior it titut beon cuntaminntfid 
nith putresceDt organic tuntter. Indeed Miller coucludea tli&l 

Km. SI. 

whenever the proportion between dissolved oxygen and nilrogen 
rises to more than 1 to 2 the water is unJit for driukiu-; purpoeos. 
In Older to colWt tlic gnses dissolved in wiitrr it is only 
necessary to boil the water and to collect in a suilahlo measur- 
ing apparatus the fjases which thus 1)6001110 frer. A simple form 
of apparstna used for thia purpose is shown in Fig. SI. ■ It co>i- 
fflfttsof a globnlar flask. ciipnWe of lioldinp from 5(K> to 1,000 
cbc. of water. This flimk. connected with a hulb fljid long tulie 
by s filmng piece of caoutchouc tubing, is 611cd witli the 



water, llie (ulnng botng dosed by a Bcrew-clampi The T>ull>, 
also contAiniii<,' wat<>r, ib wxl heated so im to ma):G tlie vrntcr 
boil briskly, tiad Uiits itie air containe*! in the bulb and hibe 
is drivea out ut tlio <>jK*n f--\n\ of tlie tutte wlueh dipst nmlvr 
nietvur;,'. iVs souii as ulL the air is driveu out. tlit! scn?w-<.-liitiip 
is opCQCil, anil tiMit applied to tlio 6iiiik unlil Ihe wnUir boils, 
wbicb under ilie dimitiislicd pn'ssiin! it will siton da Tli« div 
solved gasrg then bogtii to coino ofT, and are cnllectod and 
measui'ed in lliu cudioiuet^r Slled witli mereury, tlic oimmtion 
bcin}; coutinned for uot leas tlioii an Iionr, until the last trace 
of air has been <}X)>elIed. A Geisslar's mercury pump may 
also be employed for Uiis same purpose. 

Tbc s<-.vcml kinds of natumlly occun-iiig wntGrs may b« classed 
as rain-vr'attir, spring-water, river-watpr, and s»«i-w«t*r. 

128 Rain- Waur. — Althongh this is the purest rnrm of natural 
vat«r inasmu<rb an it has oot come into contact vritli thu solid 
crust of the earth, it still contains certain impuriliea which are 
vaalied out by il from the almo^tphcrL-. Thus raiu-wutcr iuvariidily 
-contains annnoniacal aaltit, cldorido of aodiuni, and or};anic ninttf^r 
'of variong l^inds in the xtate of minute miHpi?ndi>d parlicli^s vhicb 
ive sec when n •■lass full of such water is held up iu the li^hL Tlie 
amount of the constituents thus taken out of the air by the falling 
rain may Hcrvc as a mtians of ascerlaininp; the chemical ctimat« of 
the locality, that is the amount of those varj-ing chemical coosti- 
tuontdi uf the atinoi<pIicTC 'which arc limu^ht in liy load caoscs. 
ITius, for inslanco. the rain colleeled in towns whore much coal ia 
burnt ii geaenUly found to havu an acid inaction, owin;* to the pie- 
ao.nce of free sulpliuric acid derived fi-om tite oxidation of the 
sulphur contained in the pyrites present in inmtcoal. The amount 
of this acid may reach, undtrr curtiuacirciiuistuuix-s,iia much aa 7 
grains per gallon. In towns, the rain- water also conlatus alarif^r 
proportion of aranioniacal salts and nitrates than thai fiiUin;; in the 
countr}', wUilit it is also found to hold in auBpension or solution 
allniminous mutter derived from dcconiposiitg animal auh»taoc«a. 
An elaborate ejcamination of the chemical com|Kisition of a large 
number of snniples of tain-water has Ureii niadis by I>r. Atigna 
S^Diith,' ikud iu this nork uill t)« fottud^ uot only a valuable seriea 
of original determinations of the con8tit»ients of rain-water col- 
!ected in varions parts of tlie country, but a statement of the 
results of the labonrs of other chemists on the same aubject 


< Om Mr owf Bain : rjhr Bt^imtn^ 0/ a CJuitkal CStinaWanr. LDagHum, 


According to tUe ex[ici'tiiiviits of Lnw«a and Gilbert,' the 
average amonnt of nitrogen contained in country rain-water as 
atnmouia, nitronA and iiitrio ftcids is ftbout 9 parts in a Tnillioii 
of rniifwater. Boiissiugault, on the otiier hsmd, foviiid in tlie 
rain of Pftm 4 ]>nrts of niinnonia in one iniUion, and of nitric 
acid O'S in n miJiion. 

Sprint/'Wattr.—tiie water flowing fmm sprJDga. whether they 
are surface- or deep-apriiif^, ia always moro impure tlian rain- 
water owing to Die solmiou of ceitaiii jiortinns of the earth's 
crust, Ihrougli which the water has percolnted. The natnre and 
aiuount of the material taken up hy the water must of course 
change with the nature of the strata through which it passes, 
and we Accordingly find that the noluble constituenLs of npring- 
water var>- most widely, some spring-waters containing only a 
trace of soluhle ingrpdienls, whilst others arc higlily charged witli 
luineta] consiituents. Tlmse waters in which llie soluble iiigre- 
(lteol$ ai'e present only in such proportion as not sensibly to 
nfTect the taste, are termed /rc^fi vntlrra ; whr^rr-as. those in which 
tlic Sdline or gaseous contents are present in quantity snfticient 
to impart to the water a peculiar taste or mcdiciual qualities are 
termed mineral tcaters. Tlie salts which most coninionly occur 
in lolution in spring-water are : (Ij The carlioiiat<^s of calcium, 
magnesium, iron, nud manganese, dissolved in an excess of car- 
bonic acid. (2) The sulphates of calcium and magnesium. (3) 
Alkalino carbonate-s, chIoride.-(, sulphates, nitrates, or .lilinitcs, 
The gaseous constituents consist of oxygen, nitrogen, and carbon 
dioxidi*; the latter giis being present iti varying iinioiiitt though 
always in much larger riitantity than we find il in rain-water. 
The Datnrt! and quantity of the inorganic, as well as of tho 
gueous constituents of a fresh spring, or mineral- water must be 
uccrtaiiied by a complete ehcinicnl nnalyMs, frequently a long 
and complicated operation. 

rag Mintrat- Waters and Tha-nial Sprint}*. — Spiing-wateia 
which issue fmm considerable depths, en* which originate in 
volcanic districts, are always hotter than the mean annual tem- 
perature of tlie I'/cality wlir-re they come to the nurfuce. In many 
of these spring)i the water issuer together with a rnpimis discharge 
of nndiaeolved gas, and in some coses, as in tlie celebrated 
Gvlsiis of Iceland, so carefully investigate<l by Bunson,' steam 

I ftnt. AaiK Htforit. 1851. p. 170. 

* Uii ike i*Intdo-VoIi^aIlk Pbcnonuna «f Iceland, Cav. £«& XtmMrt, lt48i 



accompauies tbe water or rorucs il out at ceiUin iotcn-ala. 
SevenJ rernarkablc hot sjniuys of this kind hav« lately teen 
disoov'etvd tu Xew Zealand, but a still more extensive »«ries 
occur ill tlic district of Uio Tt'Itovratouu vivcr iu lh<i I'nitod 
States. Tlie following is a Hat of the moHt ini|>OTtiint thermal 
^ring$, tlic temjiernture of nil of which is much above that of 
the locaUly where they occur. 

TuBUHAi. Srirmca 

TempL ^mp. 

WUdbad . 

37*5 Haden-Haden . . . 6T-& 


. AV to STo Wiesbaden .... 70^ 

Vichy. . 

45' Karlsbad .... To" 

Bath . . 

47* Trincheras (VenezuelaJ'JT* 

The chief gases found free in thuso springs are carbonic add 
and sulphuretted li^'dtx)geu. 

According to Lliu uialeriaU wlitoh the water oontains in 
BolutioD these springs may be grouped as follows : — 

(1) Carhonattd WeUen vhich are cold, aiut are rich in carbonio 
acid, and conlain small qnantitics of alknlinc carbonates, chloride 
of Bodiiiin, and ollici sult^. Amou<^t the best known of llicac 
aie the waters of 8i-ltxer, A]K>lliiiuri9, and Tuuous. 

(2) Atkalint Watas containing a huyfiv tpinnlit}' of bioar- 
bonute of soda, n3 well as coniiuoii ««lt, and Oluuheraealla. 
These are sometimes wamt. such a.% lite springs at Ema aiul 
Vichy, hut gtrciidly cold. They am often rich in carbonic add. 

(•?) Snlino Waters are tlioae in which the idkahnv btoaibonatit 
is replaced by utlicr saltt, tinis (ilntiler-stUt teaUr, as Marienbad ; 
Maipusian tvaler. such as rrieitrictiHlialt, f>eidschut7 ami Epsom, 
in which the sidphftteand chloride of magnesium occor; CAa%- 
bfote waters in which ferrons carbonate is fouod dissolved in 
carbonic acid, such as that of Pyrniont and S))a ; Sulphnrdted 
tmittr, contuiiiing sulphuretted hydrogen and the sulphidca of tbe 
alkaline inetaU,as the springs at Aachen and Harrogate, Hot- 
springs also occur in which bat very small traces of soluble 
constituents are found, but which from their high temperature 
ate used for the piir|)05C of methcinal bathing : such springs ore 
Uios« of Pfafera 44°, Gastein 35', Biith 4T, and Buxton 2S^. 

(4) Silicious Waten are those in wliich tbe saline coaleuta 
consist chiefly of alkaliue ailicates. such as the liot-spring waters 
of Iceland. 



Tlie following aiirI/svs hy Biiitiieu of Llie minenJ waten of 
rlcheim mid of liaden-Baden may senc as eKamplcs of the 
uty in cliciuiuil ixnupusitioii of curtiuu luiucml watvrs :— 

tlyses of I.OW) paris of tAe Mineral Waters m which Ike ntw 
Alkaline Mdals Ctxsiutn and Ruhidium tcere diieoeertei by 

fiHrUidin. BaJni-Bades. 

Calcium bicarbonate .... 0-28:150 . . 1 473 

MBgnesJiim bicarbonate . . . 001460 . . 0712 

FeiTOUs bicarbonate .... 0-00848 . . 0010 

Manganoiis bicarbonate . . . traces . . traces 

Cftlciuin Mu1|)hate — . . 2'202 

Calcium chloride 3-O310O . . 0463 

Magiicitiiim clilomln .... 0-39870 . . 0-126 

Strontium chloride .... 000818 . . — 

StTontiain sulpbato .... 0-OI9$0 . . 0O23 

Barium aulphate — . . traces 

Sodium chloride 12-71000 . . 20-834 

rotaMiuni chloride .... 09500 . . ISIS 

PotnssiuD) broinitlo .... 002220 . . tmoet 

Lithium chloride 003910 . . 0451 

Kubidium chloride .... 000021 . . 00013 

Ciesium chloride 000017 . . traces 

Alumina 000020 . . — 

SUicft 000040 . . 1-230 

Fi«e catlouio acid .... 1-C4300 . . 0-456 

Nitrogen 000460 . . — 

SulpUuietted hydrogen . . . traoea . . — 

Combined nitric acid ... — . . 0030 

Phosphates traces . . tracer 

Anenicacid — ti&cea 

Ammoniucal suits traces . . O'0U8 

Oxide of coppor — , . tnces 

Organic uiatUfr tracea . . tnces 

Total mIuUc constitnente . .18-2(1028 . .29-6393 

130 Hard and So/i M'uirr. — Wattrs arc familiarly distioguislied 
uliaM and soft, according as they contain ki^c orsmall quantities 
of liinc or magnesia salts in solution. These may exist eithci- as 

carbonates held in solution hj cn.rbouic Kcid, or »» sul 
In lioth caiivs the vnter is hard, that is. it icquuns ntnch soap 
to be used in order to make a lathur, hecause an insoluUe 
ooiiipuiiiiil i» fortTK.-^ hy Llic uuion of the lime or magnesia with 
the fatty iicid of the soap. Itiit in tlie firai inBtance, ^e hardnMi 
ia said tn be temporary because it is removed either by the addi' 
tion of milk of limo or by boiling the water, when the carbonic 
add holding tlie carbonate of time in solution is either precipi 
tattid or drivtsii off, whereas, io the si;i:oiid instaocR, it cauin 
be thus removL-d, and is therefore termed permanent hardtieK 
In order to us(»>rtaiii the iimnimt of this hardness, a simplij 
method was proposed by the tale Dr. CUrk. It coosistd io 
ascertaining liuw iimiiy inoasiiri's of a stAndard soap soluticoi 
are needed by a gallon of water to form a lather. Thus 
this soap lest serves aa a roiij-l! but convenient method of detei^ 
mining the amount of lime or magnesia salts wliich tlie uatcr 

The following is a description uf the method uniploycd f< 
detcrmitiing the bardncss of a water. 10 grams of ^od Castilft 
soap are dissolved in one IttrB of dilute ulvotiol containing about 
So per cent, of alcohol, and the strength is eo proportioned tluit 
1 cba of i\u» solution will precipitate exactly 1 ragrm. of calciam 
carbonate when in Bo]iitiou. lu ordm' to standardise the sonp- 
Bolution 1 gram, uf cuk spar is disnolved in hydrochloric acid, 
the solution evaporated to dryne-ts in order to get rid of the excess 
of hydrochloric acid, and the rcsiduo consisting of chloride of 
calcium disKolved in one litre of diatillud water. Of tliis solution 
12 cbc. are biought into a small stoppered bottle, after being 
diluted up to 7CI cl>e. with di.-^liUed water. The soii[>-solution is 
graduftUy added from a burette, niilil when vigorotusly shaken a 
peroianent lather is formed. If the sohitiun has been made of 
the right strength 13 cba are ueeded fur this purpose, inasmuch 
as 70 cba of distilled water will tliemselves require 1 cbc. of 
soap-solution in order to make a permanent lather. For the 
puqiose uf dotcruiinin<; the hardnoss of a vater, a neasored 
quantity uf thi: water is tiikeu, and the stnndard soap-solution 
run in until a permanent lather is obtained. 70 cba of water 
are uoually employed for Ihi« purpose, becanive every cbc. of the 
soap-sohition will then correspond to one grain of calcium 
carbonate in 70,000, or in a gallon of water. On the Continent,' 
however, the hardness is usually calculated into parts per 100.000 
of water. Ihe hatdntsB of a water is expressed iu d^iees, by 

lie h 



which ia nDderstoocl the number of pnrta of calcium caiLonnte, 
or of the corresponding niagiieHiiim, nr other catuiuni fn\ts, which 
are conlained id 70,000 or in 100,000 parts of the water. Thus 
L Thames walerhas a hardneiis of 15''-U, or containit in solution 
I 15 grains of carboniite of liiim per galloti, whilst in ihe water of 
BaU Luke, only 1'3 giains per gallon nru present, 

131 The Oryanie ConstitutnU 0/ ICittow. — Spring- water not only 
containH inor^'anir, hut aha mhih]e organic consliluents, anil 
these likewise rar}' with the cgustitaeDts of the strata tb^ou^h 
which tlio water p>is*o«. This organic matter may ba dis- 
tiuguialied as (a) that which is derived from a vegetable, and 
(h) th»t derived from nn nnimal soiiivc. If the water has been 

■ collected from moorland it wUl contain some soluble vegutablo 
matter, if it has come in contact with any decomposing animal 
unbetances it will haw t«keu up soluble animal iimttcr. These 

Ptwo forms of impurity are of a very different degree of importance 
as rc^anls the suitability of a water thus impregnnted for drinkiog 

I It ia now generally ndmittcd that n number of epidemic 
diseases, especially cholera and typhoid-fever, are freijnently 
contracted and spread by means of drinking-water containing 
cvi>D the minutest trace of the excreta of penons suffering 
from these diseases. Hence it liecomw very important to 

ibe able to distiQjruisli Lt'tween the hurtful and poisonous 
oninuti oi^^ic impurity, luid tlie coiiipanktivcdy hnrtiiless vcge- 
tabk oiganic impurity. Neither the chemist nor tha 
DOT the physiologist, cau, as yet, HSccrtaiu whether a given water 
is irftpregoated with the cholera or typhoid poison, but we cnn 
k ascertain wtietlier a water eontniiis animal impurity, and if this 
is the case such a water is uiiSl for drinking purposes. 
Nitrogen isone of the char&cteri&ticr-onstituents of animal matter, 
being present in couidderable quantity in a state of combination 
in ever)' part of tlie llesh, nerves, and tissues of tlie body.wliilalit 
is contained in plants in emalhT qtutntity and only in their fruit 
and seedsL Hence if water be inipregiiuted u'ith animal matter 
this will be indicated by the presence of nitrogeu in sohilLon. 
either in the fonu of albumin or albuininoua umlter, if the animal 
matter be contained in the water nnclianged, or if the nnimal 
oiatter has undergone oxiduLiun, in the form of ammonia, or 
^^ nitrous or nitric acid. The amount of the nitrogen which has 
B been oxidized to ammooia can be easily determined by distilling 
H the water with carbonate of soda, when the whole of the ammonia 


is obtained in the distillate aiid CBtimotcd liy Xesalcr'g coloii 
metric test The Nessler's solutiuu h |iKi)an>d as fDUows : — 
35 gmnia of pola-tsinin iixlide, and 13 gmma. of mercuric 
chloride (corrosive sublimate) arc di»»olve<l in «bout 800 cbc. 
of hot wat«r and i\u'.n n galui'ated £olultDU of mercuric cliluridu 
is gradually added until tlio precipitate FortiMid cc&see (o re- 
diswlvc. lOO grams, of cauiitic i>ota.sli are then diAAolved in 
the liquid aiid the cold solution is diluted to one litre, and is 
allowed to deposit aiiy undiwolvcd matter. The wdter under 
examination niu9t be distilled in a glass retort as shown in Fig. 
82, carboaate of soda having twen previounly added, and cam 
must be talLcn Lo free the apponittts from ammoaia by a previous 

Frn. M. 

proceftB of distillation. The liisliUate is collected giiccesaiveJy 
in volumeit of ^0 cbc and the amount of Btninonia in eouh of 
these separate distillates dcWruiined. Tor this purpose the 
distillate is placed in a high cylinder of white glass, 2 cbc. of 
NTeasler's Kolutiuu is added, and the mixture well Ktirred. Tf 
the smallest quantity of ammonia be prewnt, a yellow colour is 
noticed, ond a corrcsponili ng dL-f;rcc of lint ie ohtaincd in n 
second cylinder by pmduidly addinj; a Ktanderd solutioQ of sal- 
ammoniac to 50 c1>c. of wal^r perfectly free from ammonia, 
and containiDf; some of the Kcsslui-'s rougcnt until tlio lint is 
reached. Tliis stendanl solution isprepard by dissolving 3*1$ 
gmms. of ammouiun) chloride in one I'tie of water, anil eacli 
etc, will therefore corrcspoud 10 I tngrra of amnKHiia. 

The nitrates and nitrites present can be estimntf d in another 
portion of the water by reducing Uicsc acids to ammonia hy mcooa 



of tin: h^-(1rogeo evolved from nlumiaiuin in presence of caustic 

In order to estiiaate the quantity of uiialtcrcd albumiDoua 
tier which lunj* possibly lie containe<l in the water, two 
Bses liave been proposud. The lirst of these, proposed by 
AVanklyn and Cliapman, dupcnds upon the foct that tlioac 
iilbuiuinoiis bodiea tire either wholly or in part d(>composcd on 
distUlatioiiwiih an nlkaline solution of potossiuni pormangaoate, 

Khe nitrogen being in this case again evolved aa amiuonia. Xu 
be second process, deacribed by Fraukland and Armstrong, the 
titTogen gas contained oombiaed in nlbaminous matter in the 
water is Ubciatcd aa such by a combustion aualysia performed od 
the dry reaiduoof the water, the vohnna of the free nitrogen being 
Afterwards carefully measured. In Uiis latter process not only 
llie organic nitrogm, bat also the organic cai-hon, that is, the carbon 
derived from aniu&l aud vegetable sources, cau be (jiiantitativvly 
H If. DOW, by means of either of these processes, a water is 
found to contain morc than 015 ]url^ of nlhiiiiiiiioid nitrogen 
to one million ports of water, it may bo considered aa 
untit for drinking pur[>ose^ and many snrraco well*wateni 
occur in large tovriis in wliich the amount of albuminoid 
nitrogen reaches U'3 to 8 parts per lutllion, and such 
waters must be regarded as little better than sew^e, and. 
tlmnifure, aa absolutely poisonous. But water in which no 
nlbuminouB matter has been found mfiy also be larfjoly iiijpreg- 

Inated with sewage or inliltralt^d animal impurity, the greater 
part of which Itai undergone oxidation. Tlius when the amount 
ef free animoiiia exceeds O'US parts per million, it almost 
in^Titiably proceeds (iom the decomposition of urea into airbonQlc 
of ammonia, and shows that the water conaiats of diluted urine. 
In like manner, when the oxidation has proceeded further, the 
Qttragen will be fouud as uitmtea nml nitrites, and should any 
considerable quantity of these substances be found in snrface 
well- or river-water. Uie previous admixture of animal impurity 
may be iuferred. In some iualances, liowever, water from deep 
wells in the cliidk lias been found to contuin nitrates, which 
in such eases caunot as a rule be supposetl to indicate dangerous 
^ 132 The wateranalyst is also assisted ill his attempts to indicate 
■ the limits of wholesomeness in a water by the iktermiuaUim of 
B the UDOujtl of chlorine present 03 cldoride of sodium. &c., wHch 



tho «7it«r coiibiiiis. Not Uiat chloricles we ia themevlves of 
impoTtAuce, but because their presence serves as an indic&ltou 
of sewngR-cotilarniiinlJon. for pure natural waters are almost free 
fniin cliloriile of iioilium, r^liiUt iiriiio ami sewage nrc higlily 
charged with oommoD anlt So that if we niMt irith n vatcr 
almost (ttti from clilorint^ it cannot have couiu into coiiuict with 
sevaga Thiis the water of Olswater aod that of the llinmes 
at Ecvr contain from 0-7 to 0-8 grains of chlorine in the gulloii. 
-whilst many surface wells in large towus Diay be fouiid wliicb 
contain from 10 to above 30 gntius of clilorine per gallon. 
Taken nlone, the chlorine test cannot be relied many pure 
■weU-watcrs occur, euch as those in Cheshire, in the nciglibour- 
liood of the 8attbeil8,ornear Uie sea, which contain ooniinonealL 
If, however, this test be employed in common with those pHs- 
Tiously nieiittonod, the evidence for or agatust a water is nmdered 
iQUcli more cogent As a rule it may be said that water* 
containing more than two gmins of chl6rin« per gallon must 
be looked upon will) xuAj)icioii, uulcss indeod some good reason 
for the presence of commou salt can he assigned. 

Tlie following aiinlyaos serve lo ohow tlte ditfetence between 
a good potable water and one which is totally imlil for driulfiug 
purposw. Ko. 1, tlie watersupplii-d by tho Mundiester Corpora'- 
tion from the Uei-byslure hills ; No. 2 ia a surface-well water, 
recently used for drinking pvirjinses in a manufacturing town, 
althougti little better than ctduent sewage.' 

No.1. OaodWatcr. No. 3. BelWiter. 

Total aolida .... 
Nitrogen as nitrites and 


Free ammonia . . . 
Albuminoid nDunonia . 


Temporary hanluess 
Permanent haixlness 
Tota.1 hariliiess , . . 

I'nrU iirr 





Oralst per PuU pet Gnina fmt 
Gatkiit. UillioD. CdJoo. 


















■ Far Ibe s^kkUI doutb oT the |iraceaH or v«tei ana)^, tite MIciriDg 
v«ti«or itif mom amy beconcnitwl ; — If'airr Axalspi*, by WtDklyn aail OlMponm. 
3nl EiL is; I. TriitiiMT. Lotuloa. Knuikltud and ArnuliODK, Jaunt. CUm. Ae. 
sxl. ^ 77 : pRnltlud, t'Mt. lOVi alto CAmt. Sat. Jmr. Jutu, UTO. jUm 
U«tiorU of tlic Utijml CesuiniMi«ii oa WatarKu^I/. 



133 Birxr- Waters. — Tlie coinpositioa of rivcr-wutcr varies con- 
siderably with the nature of Ite ground over wliicli the -wTit-er 
rnna : tbai T1uiiii<^ tnitcr cnntaiti<i aliuiit 1 1 ^liiiit per gallon 
of carljonnte of lime ; the Trent 21 grains of sulphate of linie, 
or they aru both himl wutcr^, the ilntt tenipornrilv and the sccoikI 
iwrmaiietitly hard. The waters of the Dee and tlifl Don. in 
Abcntociistiire, draining a granite district, are, on the otber hand, 
aoft waters. The composition of tliese wuturs is shown in H(c 
followjug table : — 


Oniimprr riRllon. 

Calcium carbonate . . 
Calcium nulphate . . 
Calcium nitmt* . . , 
Ma!;ncsitiiit curbouiite . 
Smlturu chloride . . . 


Ferric chloride and alii- 

CdciiiTn phoAphalu . . 
Oiganic tnattcr . . . 

3 00 




























8 54 





Unfortunately in England, as ia otlier luanufacturing and 
denftelypopulatedcoiintnes.theninniiigwBter seldom readies the 
sea io its natural or pure stuite, but ia largely contaniiunted with 
tlie aewage of towns, or the rcftiRc from luajitifactures or mines. 
So serious indeed is tlii-<; slntt; of tilings bccuininjj thiit some 
steps arc about to he token to prevent tlie further pollution of 
the livers of tlie country, and a Uoyal Commisaion has alrvtidy 
been engaged fur Home years in examining and reporliag ugKin 
the subject. The following analyses of the couiputiition of 
Lancashire rivers, taken from the First Report of the Commis- 
sioners appoinUsl in ISfiS (p. 15), sljowr clearly the pollution 
wlucli tbe originally pure waters of the Trwcll and Mersey 
tindergo on flowing down to tbe sea. 



Composition of Lakcashihe Eivebs. 
PaHs in 100,000. 

Total soluble solids . . 











Organic carbon . . . 





Organic nitrogeu . . . 




AmmoDia ..... 





NitTogeQ as nitrates and 




Total combined nitrogen 









Hardness temporary . . 


15 04 



Total hardness . , . 





Suspended Matter. — 







From these numbers it is seen that the quantities of free 
ammonia and nitric acid become increased 300 or 400-fold in 
the river below Manchester, whilst the total combined nitrogen 
is increased from 0049 to 1648. 

134 Sea-Water. — The amount of solid matter contained in the 
waters of the ocean is remarkably constant when collected far 
from land. The mean quan^tity being about 35-976 grams in 
1000 grama of sea-water; the average specific gravity of sea- 
water is 102975 at 0". 

•1. The Irwell near its source. 
& Tlte Irwell below Manchester. 

3. The Heney, one of its sources. 

4. The Mersey below StccKporL 


Composition of the Watko ot tbb InisH Sea in thi: Sumuer of 1S70.' 

Ou« thonaand grams of 

■ea-wator contain grams. 

Sodium chloride 2643918 

Potassium chloride 074619 

Magnesium chloride 315083 

Magnesium bromide 07052 

Magnesium sulphate 206608 

Magnesium carbooate tracea 

Magnesium nitrate 000207 

Calcium sulphate 1-33158 

Calcium carbonate 004754 

Lithium chloride traces 

Ammonium chloride 000044 

Ferrous carbonate 000503 

Silicic acid tracea 


For the purpose of controlling the analysis, 1,000 grams of 
water was evaporated to dryness, and the dry residue weighed. 
Its weight was found to be 33'83855 grams. The specific 
gravity of the water at 0° C. was 102721, whilst that at 15° C. 
was 1 02484. 

Forchhammer found that 1,000 parts by weight of the water 
of the mid-Atlantic Ocean contained 3597G parts of dissolved 
salts, whilst Thorpe and Morton proved that tlie total quantity 
of soluble salts contained in the water of tlie Irish Sea in the 
summer is rather larger than in the winter, owing to the greater 
evaporation and diminished influx of" fresh-water in the former 
season. The results of Forchhammer's very numerous analyses 
of sea-water are shown in the following table, giving the amount 
of the chlorine, sulphuric acid, lime, and magnesia, as well as 
that of the total salts contained in 1 ,000 grams of the water. 

' Thorpo and Morton, C/um. Soe. Joum., tiir. 606. 





Valer ftf Iri^ S«^ 










11 -(l» 





193 09 

Witcr of the AtluiUr Otmn. 

AbMltttoamoiiatiR l.OOOgma. 

100 11 99 


2 199 


Htbdogen DroxiDB, OB IItobogen Peboxide. H,0, = 33-92. 

135 This boily was discovered in 1818 by Th(5niid,' whc 
prepared it, by the action of dilute hydrochloric acid od barium' 
dioxide, tlius : — 

BaOj + 2HC1 = H,0, + B«C1, 

The oompoiind is also easily formed by passing a carrent of 
carbon dioxide through w&ter, and gradually addiog barium 
dioxide in very small quantities,' thus : — 

BaO, + CO, + H,0 = H,Oj + BaCO, 

Prtparation. — Hydrogen dioxide is, liowt'ver. most generally 
obtuintid by decomposing puru buriuia dioxide with dtlttto] 
sulphuric acid ;* thus : — 

BaO, + H^O, = H5O, + BiiSO,. 

Tlie pure barinm dioxide needed for these experiniente ia 
prepared sa follows ; — cwutnercial barium dioxide, very finely 
powdered, is brought littic'by Uttlv into dilute hydrochloric acid, 
until the acid it uf^arly neulraliiEtid. Tli« ccwled and filtcrei] 
solution is then treated with baryta- water, in order to precipitate 
the fcn-ic oxide, mnngHnic oxide, iiluniinii, and ailicn which oraj 
always contaiued in the impure barium dioxide. As soon as a' 
white precipitate of the hydrated barium dioxide makes its 
appearance, the solution is liltered, and to the filtrate concen- 
txated baryUi-wnter is added ; a crystalline precipitate tlien £ftU^ 

< Amn. CJirm. Piys. vm. 300. 

' Hiiprer. Con/Af RiitJif*. U: 7M, Rilanl. ihid. \t. JMl. 

* Tttoai»ai,D*r.I>eMMA.Ci,».-w\i.'H. 



'oonaisttfig of hydrated liarinin dioxiile. Tin's is well wmtlivd, 
I and preserved, in the moist Miitp, in slnpi)ered boltlps. In order 
■to prepare hydrogen dioxide 1)y tneans of cbis aubatancc, Clie 
moist precipitate is gradually addvd to a cold niixlureof not leas 
than live piirts of uiit«r to ono part of cutict.'iilmt«d Bulpharic 
acid, until the mixturs Incomes very slightly acid. The preci- 
pitate of barium Hiilphnte is nllotvcd to seltle aial the liquid 
filtered The siuill trace of sulphuric ftcid which the fiUrate 
contains can be precipitated by careful addition of dilute taryta 
HolutiuD. When the aqueous solution of the liydrogcn dioxide 
thus prepared, U brought over suljihuric acid lu vacuo, water 
evaporates, and the solution of tlie dioxide becomes nioro con- 
centrated. If, during tho coiiccntmUon, an evolution of oxygen 
be noticed, a drop or two of sulphuric acid ehuuld he nddcd, as 
the dioxide ia more stable in presence of free acid than when 

(perfectly pure (Thennrd). 
136 Propertus. — After this Blow t^^'apomtion lins hecn carried on 
for some time » colourlesa transparent oily liquid is obtained, 
having a. specitic gravity of I^.'iS. Tliiit liquid evaponit«fl 
slowly ia ranto without the residue undergoing any change 
(Th^ard). Hydrogen dioxide docs not solidify at — SU" ; it 
possesses no smell, has B.n astringeut, bitter tasto, nnd brought 
on to tlie skin produces a white blister, which after a liine 
produces great irritation. It Weaclies organic coloiu-ing matters 
like chloriuc, although acting more slovrly, and is a very unstable 
compound, eaatly decomposing into oxygen and water. One 
rolorae of the liquid at 14* and tniiler a prestsure of 760uini. 
fields, according to Th»?uard. 475 volumes of oxygen, whilst 
the theoreticiil amount is 501*8 volumes. The decumposiition of 
hydroseu dioxide takes place very slowly at a low teniperolure, 
■whilst at 20' the evohition of gas becomes plainly visible, and 
if the ooncentiated solution is heated up to 100* the separa- 
tion of oxygen occurs so rapidly as sometimes to give rifle to au 
t explosion. A dilute uqucous solution of the dioxide is, bow- 
ever, much more stable, and can even he concentrated up to a 
CeitaiiL point by ebullition, a portion of the dioxide passing 
ov(rr undcconiposcd togolher with the vapour of wat*r. Thi« 
explains why in the above decomposition the theoretical quantity 
of oxygen is not obtained. 

Hydrogen dioxide is easily soluble in ether, and if an aqueous 
solution of the compound be shaken up with ether, the 
dioxide dissolves iu iU The ethereal is more stable than 


tlie oqu&oua solutiou, and it can be distilled without decom- 

llydrogpn dioxide undergoes decompoeition in presence o( 
a large [luniber of different solid sa1>«t«noee, und with tbe 
gn»tcr mpidity the more finely divided these aubstaooes tn. 
Souie of the pheiioinenii which thus present themselves may, 
to a cci-Uiin c-xicut, Ue accounted for, but for others we still 
need an explanation. Thus, for ox&tnple. tho anhydrous cora- 
pouml is (lecomposetl with almost uxplo-tivG violence iiitooxygen 
Bud water, iu pi-e&eiict of tinely-divided silver, gold, platiuuin, 
and other mctnU. tho mctoJt themselves, however, remaining 
uuttllei^d. Tlie oxides of these metals also decompose hydrogen 
dioxide easily, being reduwd to tho inctAllic stutu. Thesatne 
dci^ompof^ition also occurs with a dilute aqueous solution of tlie 
dioxide, and the reaction nmy he rcjireseiited by the foUowiii<; 
eqiialioji ; — 

Ag»0 + H.Oj - 2 Ag + H^O + Oj. 

Here we have tlie Teniarkaltlu pl)eiiom(>uon of a, powerful 
oxidizitJK agt?ut exerting a reduciny action upon meialliu oxide 
tlie metal huing formed. Tho explanation of this fact 
liowever, not far to seek. The above-named metals poascasl 
only a weak power of combination for oxygen, and their oxides 
accordingly ducompose easily into their elements. When thes^, 
oxides ai'e brought into contact with hydrogen dioxide, whi 
itHflf ci'iituina one atom of oxyg<-n but ft-ebly iiiiit«d, an analt 
gous reduction takes place, the oiiu aloiTi of oxygen in the dioxide ■ 
combining with one ntom of oxygen in the metallic oxide to 
form a inolfcule of free oxygen. In the same way we explain 
the fact tliat common oxygen is formt-d when uzouixcd oiygCL 
is broujibt in contact with aqueous hydrogen dioxide H« 
too. botli bodica contain a loosely combined atom of oxygen! 
wliicn unite LogcUieMo funu a moli'cule of free oxygen ; tli 

When baryta water (bariiiiii iiioiioxi<leJ is mixed willj hydrcgoT 
dioxide a precipitate of baritim dioxide separAt«3 out; thus: — 

BaO + H.O3 = BaO (OH)j. 

Hjnlrogea dioxide also transforms m&uy other basic oxides, 
especially in presence of an alkali, to peroxides. 'J'hus manganons 
salts become tlius converted into manganese dioxide. On tbtg 






other \\aai. thciie peroxide.! in pi-eaeiitc of an nciil are again 
reduced by hydrogen dioxide to basic oxide. TLus. if liydroj^u 
dioxide be brouglit la coiitact witb dilute sulpliuvic acid ami 
tnangaii^se dioxide, oxygen gas is given oFT, and niangaiioua 
autpliate is formed ; thus : — 

MnO, + H,0, + }r,SO, = MnSO, + 2Up -t- Oj. 

The deconiposiliou here occurring is similar to ilmt wliich takes 
place in the roduction of oxide ofsilrer, and this change is assi&tfld 
by tlie pre!i«nce of the acid, which tlieii combines wilU the faaaic 
oxide to form a salt. 

137 iMtdum and Bttitnnlton of ffy^rogtn Dioxiite. — Tn Opdi-T 
to detect the presence of hydTo;;;eu dioxide iu solution, the 
liquid is rendered auid with stilphuric nctd, somo ctlicr aiid b 
few tlmp9 of pota53ium chTomate are added, and the sohition 
well shaken. If hydrogen dioxide be present, tite solution 
assumes a beautiful blue colour, and oo allowing it to stand 
(he colour is taken up by tho ether and a dtop bluo layer 
separotes out. Tlii» blue cumpouud is percbroiuic acid, and the 
reaction may, ia a similar way, be employed for the detection of 

Wh«n hydrogen dioxide ia added to a solution of iodide 
of potassium and ferrous sulphate, iodine is set fre^ as may 
easily bo proved by the foitinition of (lie blue iodide of stotvli 
(Scbimbein). This reaction is so dtdicat« thai one part of tlie 
dioxide in twenty-live million parl-j) uity thus be delectAtd. Other 
oxidizing; agouti have the power of liberating iodiiipfmm iodide 
of pota.«:sium, but not in presence of fentius sulphate. 

For the purpoK of determiuiug tbc qu&utity of hydrogen 
dioxide present in a solution, tho liquid is acidified with sulphuric 
ncid. and then a standard solution of poLasHium permanganate 
added, luitil the purple tint no longer disappears. The reaction 
Iitn* ooeuiring is thus represented ; — 

2KMnO, + SllaSO^ + H.0, = K,SO, + 2MnS0,+ -Itl^O + 20^ 

Hydrogen dioxide OMurs in small quantities iu the atmosphere, 
nnd has been found in rain and in snow, but the above method 
cannot be used for t^timating its quantity iu this case, as other 
substances contained in the air, sach a.^ the nitrites and oi;ganic 
tuotter, act upon tlie permanganate solution. 

In this case a coloriiuotric method proposed by Sebiine * may 

' Btr. Denttch. Cft«n. Go. vUi, :W5. 



be used. It depends upon the fact that a neutral solution | 
of hydrogen dioxide gradually libemtes iodine from a ueutnl 
solutiuu of potossiuin iodide, thus : — 

H,Oi + 2KI = 2K0H + Ij. 

Snlntiooa contuining small known hut vAryirtg quKnttti<« of 
hyJrogpn dioxide are first prepared, aiid to each of these solu- 
tions, potassium iodide and starch paste are added, the degree 
of lint which the several sohilions attain, owing to the forautioa 
of the hliie iodide of search, is theu compared with that ubtained 
in a siuiiliir way when miti water, kc, is employed. 

An aqueous solution of hydrogien dioxide is an articde of cora- 
mercG aud is used for the purpose of cleaning and bleaching old 
luid sluiuvd uiJ^Tuviugs and oil paiuliiigs. Hie dioxide hus also 
heen emploved as an uuiiuome fur blcuclLing dark -coloured 



138 Although chlorine nnd oxygen do not comhine directly, 
three distinct compounds of these two elements may be obtained 
hy indirect means. We are acftuuiritiid with no loja thnn four 
compounds of chlorine with oxy^uu und hydrogen which are 
known a<i the oxy-acida of chloiine. Of tliejie, the two first 
rnrrespond to lower oxides of chlorine, thiit is. tliey are fonned 
Uy tlie notion of wattr upon tlivm. Tito following are tlie 
eompouurts of chlorine, oxygen, and hydrogen as yet known : 


CI ) 
Chlorine monoxide j-.. t 

Chloride (rioxide ^j^ } 
Chlorine peroxide CIO, 


Hypochlorous acid u r O 

Chlorous acid 

Chloric acid 

Pepohlorio avid 



Chlorine and oxyfjen can only te mnde to comhine tosether in 
the presence of a WIc oxide; thus, if chlorine gas be led over 



dry tuerctinc oxide, chloripe monoxide and mercuric ozy-chloiida 
arc fonaed ; thus :— 

2HgO + 2C1, - HgjOCl, + CljO. 

fHw Bama reactdon tnlces place in presence of water, and in 
this OMO a colourltus solulioa of the corresponding hj'podiloroiu 
acid ia formed. 

Cip+ir,0 = 2C10H. 

WboQ clilorinc is passed iuto a cold dilute solution of an 
altiflli Buch M cnusric potiLsb, instead of the free hy{)Ochlon)ua 
odd tlie ooiTGspondiDg siilL, tenntd a lirpdclilorit^, is fdrmed ; 
thus: — 

3K0n + Gj = KOCl + KG + HjO. 

If tlte Roltition of the alkali be coDocntmtcd, or if it be beatai 
whilst the <ra3 la passed through it. a different reaction lakes 
place, ill which a salt called a chloTutc is funned; thus : — 

6 KOH + 3C1, = KCIO, + 6KC1 + 3HgO. 

From the potassium chlorate thua formed, the chloric acid 
it«(]lf can be obUiincd, aiid by reduction of this acid the oxides 
CljO^ and CIO, may be prepared. Perchloric acid is prepared by 
the further oxidation of chlonc acid. Tlio oxides corresponding 
to thcjip two acida, viz., CUO, iind CI,Oj have not yet bceu 
prepared. The oxides and oxy-acida of chlorine are unstable 
compounds, as indeed mi^hl be expected, owing to the feeble com- 
bining power which chlorine and oxygen exhibit towards one 
nnotlier; in]Ucnce of this thuy net n» powerful oxidizing 
substances, many of tlieni being moat dangerously explosive 
bodies, which suddenly dccoinpoiie into their constituents oa 
rise of temperature, or even on concussiou. It in, however, 
remarkable that perchloric acid, wldch contains the most oxygen, 
U the Que vrtucli ia the most atubtc 


Density = 4335. 

139 So long ago as 1785 Bertbollet noticed that chlorine could 
be combined with an alkali and yet preserve the ptciiliar bleaching 
power which tiad been previously discovered by Scheele.and it is 
to Bertliollct tliat wo owe the practical application of tills 

important property. In his first ex]>eriiiient8 on Uiis substautv 
be employed clilorine water, but afterwards lie absorbed Ibe guf. 
by a solution of cuustic ]N)Ciuh ; aud iLe. liquor tlius obutinvil, 
called Euu do Javt^Ues fmiu the nftioe of a bleacb-worka wlieif 
it waa prepared, was em plo^'iHl for bkiucliiiig puq)osus on tbelar^ 
scal«. Bettliollet ile<icnbed these experiiDenls to Jatues VCa 
who wag at that timfi stnyiag in Pnri^, end he brought the aav 
to Glasgow, whcru Ttruiiii.ut, in 1798, pabcnted an iniprofr 
process for bleaching, in which lime was employed iustead of tbi 
potush. as being a much cheaper subetance.' 

Up to the year 1800-10, when Oay-Lnsaac and Tfi^B 
propouiiiittd thu view that chlorine iiiiylit be consiJtTcd aSl 
element, and when Davy proved that this suppcsilion was oorrecl. 
the bleaching liquors wcreeupposod to contain oxygeoatcd invi 
ales of lite base. Indeed their constitution remained doubiful 
until tho year 18;J4, when Ilalapd* ahowod that the alkaliiw 
bleai'hiu^ compounds may be cousidered to be a mixture 
combination of a chloride and n liyjmchlorite. According to tli 
view Kau de Javellts has the formula KCl 4- KOCI, 
blofiching powder 

CuC]i + Ca(OCl)^ 

Prtjiaralion. — Chlorine monoxide is obtained, as g.ceu 
Kg. 83. by the action of dry chlorine gas Tipon cold dry 
oxidu of mercury, which 13 contained io a tube (a b). The 
crystallizod lucrctirio oxiile can, however, not be used for thti 
puri>Dtu;, as it is not acted ou by diy chlorine, and henco tl 
precipitated oxide must be employed, it having l»eeii prcvitnusl 
carefullj' wn&hed and dried. The reaction which takc» place 
this case has iilrendy been described. Mepciiric chloride, HgCl 
is Dot foriuwi in this reaction, but the oxychlcride. IlgO HgCIj. 

140 Projjfrtifs. — Cblurine tuonoxidc is a slightly yellow colouivi) 
gas (Bnlerd), which has a periuliar penetrating smell, somewhat 
resemblijig, tliouyh diatUict from, that of chlorine Ky exposure 
to a low t«mpcmlun; llic pis can be condensed, as in the tube (u) 
Fig. 83, to an orangti-coloured liquid, which boils at about 
- 10*. If an attempt ii> ntnde ta seal up this liquid in the tube 
in which it has bet-n pivpared, or even if the tube in which it ii 
contained be scratch&d with a tile, it deconipoa«s suddenly wit 

* TcnnBnt't KtM pattnt wu ilecUrvd Invaliil Uirte jrrttn kftcr It LmI 
gruited, u It «M inVTcd t\M ItlvJuhrrK hi Uncaihiro tnil ut Xotliiiglwa I 
«lip]0T«d lins ituteul of potub Urmc the jr.ur XTii. 
' 'Ann. Chim. Pbyt. MI. S15. 

inrpocHLOBous Acia 


a most \-iolent «xplosioa (Koicoo) ; and when poured ont frnm 
one vessel to another a similar explosion takps place (Biilani). 
It likewise esplodeaon lieatiiig. but not so violently, two voliiinea 
dflcomposinji into one volume of oxygen nnd two of clilorinc 
Oo exposure to sunlixlil it rtmniiis witliout npparpnt clian^:*: 
ffjT ftoine minutes an<l tlion luiitlly explodes, wliereas, turcording 
to Cay-Lusiiac it remains uimlleKd in diftuwd dnylight. Many 
easily oxidisbble bodies, euch as sulpliiir, pUosiilioros. or tlie 




Fig. 88. 

metals of iLe nllciiliiit, Inke 6ro in lite gas or produce an explo- 
sion. The gfta is ulso dvcniiipoeod in prcsento of bydiochloric 
acid into free clilorinc iind walcr ; tliu»; — 

2HC1 + C1,0 = 2C1,+ H,0. 

Cidorine monoxide is easily soluble in wattr; according (o 
Ibe experiments of Italard, one voliinie dissolving no less than 
lOl) vuluDics of the goa. 

Hypochlorol's Acti), HCIO- 

141 The aqneouB eolation of chlorine monoxide must be con- 
eidrn-d aa a eolutiou of liypocliluious acid, a compound wliich 
in tbe concentrated state ts unknown. 

PreparaUm.—{\) The solution ia best prepared by shaking 
chlorinc-wstcr with precipitattd mercuric oxide, when the oxido 

quickly dissolves nnd tbe colour of the solution disajipem, 
thus: — 

HgO + 2C1, -J- H,0 = HgCl, + 2aOH. 

The liquid is now distilled in order to roinove the Tat-i 
chloride, and a colourles.^ dislillato in thus ubtAinod. wUictU' 
ulthou;;!) tC coataiDs only half as much chloiine as Ibo origimJ 
chlorine wat«r, possc»8c« an i^qiiol blcticliiiig power.' 

This fact is expiesaeil in the rotlowiuii; equattous, which also 
indicate that tlie hieaciiing effect produced by cblotino is in 
reiLlitj duo to a decomposition of water, the chloriue combining 
with the hydrogen and libcTAtiog the oxygeii. It is. therefore, 
this latter eliunent which is the true bleaching agent, iuosmudi 
OS it oxidizes and destroys the cotonnng ageut. 

(a) Bleaching action of chlorine n-ntcr, 

2C1,+ 2H,0 = -IHCU0, 

(b) Bleaching action of tlta hypouUIoinus acid formed 
the oliloriue water, 

2C10H=2Cm + 0^ 

(fi) An aiiueous solution of hypocbloroos acid ia alsoeasi^ 
obtained l>y adding to a solution of a bleaching coinpoaii 
exactly the ainoimt of a dilute miueral ncid rei)uisi(e (o libetutft 
tlie hypoclilorona aold (Oay-LuBSac). For this purpose a dilute 
nitric. «cid contuiiiiii^ about 5 per c«iit. of lite pure acid is 
allowed to run slowly froDi a tap-burcuc into a Hltered solution 
of coinnioii bh-achiu-;-powder, whilst the liquid is kept well 
stirred in onlei- to prevent a local siiper-Raluration, which wontd 
cause a libcmtion of the Iiydrochloric ncid of the chloride, and 
thus agaiu eOea adecoiaposiliou of the hypocblorous ncid into 
chloririiS and watur. If thia oparation be conducted with caw 
no chlorine in evolved, ov at any mte only a trace if a stigl 
exc^s of nitric acid boa been added, and tlie diatiUate 
perfectly colourless. 

(3) AnoDier method ofnhtiitninj; the aqueous acid i.q to sataiat 
a solution of bleaching-powder with chlorine, then todriveoffth«l 
excess of chlorine by passing a current of air through the liquid, 
and then to distil The foUowiu" equation repmaenta 
reaction which here occurs: — 

Ca(OCl), + 2Clj + 2njO = CaCI, + 4C10I£. 

* OajT'Liunc, Am. Clktm. fAyr. xltii. ]fil. 

In pines of bleachinji-powder baryta water mny be omptoycd, 
uben biirium hyiiocblorih! la ut first forinoci, and this aflerwanis 
deconip09Cil M shown above* 

(4) Hjpochloroos is eo veak ao acid tbat iU salts are decoQi- 
posed by carbonic acid, so riml ir chlorine gas is led into a solntktu 
of n carbon&tti, or pnased tlirouj-b wuter coiitaiiiiiig riiii;]y divided 
calcium eaibonntfl in aiisijonsiou ( I port to 40 of watei). no hypo- 
chlorile is foniicd.but only b)-]K)cliIorons acid (\VilIiam80ii),thu«: — 

CttCOj + 2a, + H,0 - 2C10II + CaCl, + CO^ 

Otber salt) of the alkali-metals act iu a similar wny when a 
stteaiQ of chlorine is passed tbrolt^h their aqueous solutious; 
tilts is the case with stilphate and phosphate of sodium, in these 
cases an acid sail is fortncd ; thus >— 

K»,SO, + nfi + CI, = Kaa + NbHSO. + CIOH. 

Only dibilc solutions of bypocldorous acid can be distilled 
witliODt decou]po«ition; conccutmtod solutioos are readily deconi- 
posedeitlier on healing or on exposure to suiiliglit, part spliltiog 
up iolo chlorine and oxygen, vhilsC another pott undergoes 
uxidation, yielding chloric acid, 

142 Tfit hiq^ocJiloritta, like the acid, are unstable compounds, 
which ill Ihe pure state are almost iiiiknowii. Of these the most 
important is contained in blenching- powder as calcium hypo- 
chlorite, Ca(0C'1)j, and it ia to the presence of this compound 
that the bleacliiD*; propeities of tlie body are due, inasmuch as 
when either hydrochloric or sulphuric acid is added a quantity 
of chlorine etpial to that coctained in the compound is evolved. 
In the firftt ca<e half the chlorine is derived from the hypochlcrlte; 
tl>e other lialf fioui the hydrochloric acid, which lirst liberates 
brpochlomiis acid, and then decomposee it into chlorine and 
water, thus : — 

(1) 2HCl-t-CB(Oa3, = 2HOa-(-CaCl» 

(2) 2HC1 + 2H0a = 2U,0 -^ 2CI^ 

fphuric acid ia used, the result is the snme, as this acid 
decomposes the calcium chloride j thus : — 

CaCl, + Ctt(OCl)s 42 H^O, - 2CaS0, + 2H,0 -|- 2CIy 

• WiUiABMon, Chem. Sot. Uem. U. 2*4, 



CnLonniB Trioxictk. nin [ O- Deiisitj- = 69'21. 

143 Cliloriue trioxido is a grcenisli yellow unsUililc gas, dis- 
covered by Millon iu the year 1843,' o1)Ciiined by the rRtluction 
of i;lilario acid. T\iia citii he olfiictcd in uny of tliw I'olluwin^ 
ways: — 

Prtparalioa. — (I) Four jmiis orpoliusium cblumtu aro [iiixi>tl 
with 'i parls of powdored iiriu'iiic trioxide, A.'»Ji\ iind Wiilur 
added to the mixture so as to fonii a thin paste; tlw paste 
is tben gently healed in a Rask containin;* ditiit^^ nilric acid 
of pp. gr. Vi'll (12 parts) nnd 4 parte of wntor (Millttn). The 
araeuie triuxidc is hereby oxidiixd tooneiiic acid, and tho nitric 
s<id IlNOj, nt (hv somu tiui> rednoed to nitrogen trioxido, this 
in its turn acting as a reducing agent upon tho chloric acid 
(MilloiO; thus:— 

(2) A mixture ornnioiiic troxide, chtomte of potash, nnd «iil- 
phuric ucid which ia dilut(>d wiUi haU its volume of water 
also evolves chlorine trioxlde violently, but without danger, 
(Bramlati); tJius: — 

ASjO, + SKCiOs + 2HjS0, + 2H,0 = 2KHS0^ + 211,^.' ' 
+ 01,03. 

(S) Iu plnce of arsenic trioxidecane-sngarnuiy bo cnipUiy pd, as 
this substance is oxidised in tlie presence of nitric acid, nitrogen 
trioxidc being furmcd. and this again acting as n reducing ogout 
upon the chloric ovid u« ulrefldy described. For tlus purpose a 
mixture is made of 4 parti of polassium clilorato, 1} part of 
cane-sugar. 6 pacts of nitric acid listing a apeciHc gravity of 
I'.t, and 7 parts of watei:. This tnijcturc h placed in u wAU:r 
bath and heated to 73°. when a re^tar stream of cliloHnt^ 
trioxide gus is evolved,' 

<4J Chloric avid ts also easily reduced to chlorine trioxide 
by hydrocarbons gtich as bensolo (Carius), To obtain tho gas 
in this way, 10 |»irta of licuxolo arc gently bested in 100 )iorts of 
extremely concentrated sulpharic acid, the arid mixture diluted 
with lOU parts of water, aiul 12 parts i.l finely powdered 
potassium chlorate aildcd ; Uie action bej; ua spontanoously, but 
it 18 best to heat Oie mixture atoncc to £0*, when tho trioxido 

' .l«u. ChhH. Fkvi. r»lTii. JM. 

> Sctdel, Auit. CUn. rham. elx. S1<. 

is evolvcil in iargu quautitieii (Bruiidau), loatead of benzole, 
uaphthalene may also bo eoiploved (Th. Hermann), 

t44 Fropviits. — Cliloriiw trioxitle is a gpeeniah yellow gns, 
whitli has a ver}' pungent smell, even more irritatiDS thau tliol of 
clilorino, and aUacking the organs of rospiralion very violently. 
Its specific gravity ia AQAf\, and Ii^iice iU exporimeiiUl density 
i» 58'4. whibtthe molecular foi-mulii, CljOj,nMiiiirpfl tlie number 
59*21.^ WUcD exposed to low tempenitures it condenses U> 
a mobile reddisli brown litiuid, having a spcciltc gravity of 
VZZ St 0*, and entering into ebuUitiou Alj^litly above this 
temperature: Evea when preserved in the dark tliia liquid 
undetgoea change after some time, chlorine peroxide being 
ronncd, the prcswaec uf thia eubstauce mising the boiliag* point 
<rf the li<]uid. Liquid chlorine trioxide ia a very dangerous 
sutiiitaiice, the most violent explosions being brou<^lit about by 
most trivial cause* Thus, for inntimt*, Rmuduu olaerved that 
K drup which fell from a height of 20 cm. into a beaker 
sbatu-rt'd llio glass with a t^hitrp detonation. The same docom- 
positioii takes [ikcc when tbia aiibstonce islironghl iu coutact 
with sulphur, phosphorus, arsenic, ajid other easily oxidizablc 
substances. When the moist gas is exposed lo siml^ht it 
decomposes slowly itito irhlorine, oxygen, and perchloric acid. 
Chlorine trioxide diasolvea easily in water, imparting to the 
solution a deep yellow colour. 100 pai-ts of water dissolve 
at Si'-b, and iiiuler a prt^ui-u of 7ri2-3 uiiu. 4-7665 grains of 
the gas, and at SS" and under 760 mm. 6-6580 <Brandau). 
Contmry to the usual law of the solubility of ga-ies, chlorino 
trioxide appears to be more soluble in hot than in cold water; 
hut Oiis exc»)ptioD can b« readily explained, inasmuch as warm 
jrater deeompoaos the trioxide. cotiverting it into bydrocblorio 
" ' chloric acids, thus : — 

3 CI,0, 4 ;iIT,0 = 2HCI + 4HCI0,. 

The hydrochloric acid thus fonned then acts agaia on tli« 
trioxide, and chloriue iii liberotvd, thus : — 

CljO, + 6HCI = 4aj + 3HjO. 

When hrought la coutact with water between 0* and 4°, 
chlorine trioxide forms a solid hydmt^ the composition of vhicb 
bus not as yet been aiiceruined. 

> DrniwlM, Akm. Ck«n. Mann, dl, 3l<li 

Umx>Boi;6 Acid, UCIO,, 

14s Tliis acid, like hypodiloioita acid, is oalj known in 
aqueous solution, and is obtained by difsolWng the trioxide in 
cold wnl«r. It neutmlizes the eanstic alkalies, but does not 
dccoDipofie alkalioo carboimtea. Xbe ohiorites of tlie alkolino 
raetals are soluble in vater, end from tWir solutions the 
insoluble, or diR'tcultly soluble chloriles uf silver and of lead 
may be prepared by double decomposition, as yellow crystal- 
line powders. All tliB chlorit«s aie very ea.sily decomposed. 
Thus if the lead-salt 19 heated for a short tinie to 100*, it 
decoDiposea with dulonntion : and if it is rubbed in a inurtor 
with sulptiiir or certain metallic solpliidcs, ignition occurs. The 
soluble chlorites poasesa a causlic tantc, similar to that of 
the acid, and bleach vegetable colouring raiitteni, evea after 
addition of arseuioua acid. Tliis latter ruitcliou serves to 
distinguish them from the hypochlorite!). AVheu potassium 
clilorite is treated with pliosphoius oxycltloiidc, cUtorino 
monoxide ia given olf, thus : — 

2^^\o + POCI3 = KPOj+ KCl + 2^1 1 O. 

CnLoniHE Pkboxidb. CIO,. Density = 33-ft45, 

146 Tliia gas was first prepared and examined by Da\y in 
1815 ; it was obtained by him by the action of sUvag sulphuric 
acid on poUis^iuin chloi-alc. lu prcpuriug this substance a|tecial 
precautions must be taken, as it ia a highly explosive sod 
dangerous body. 

rrtparatwn. — Pure powdered potassiam chlorate is for this 
purpose thrown little by little intx) concciitreted sulphuric acid 
cotitaint-d in a small retort After the salt is dissolved, the retort 
ii ^vully warmed in warui water. In this rcBction ehlurtc lujid 
is in the first instAUce liberated, and this decompoaed as follows 
into perchloric acid, chlorine peroxide and water, thus : — 

3 HCIO, = IICIO^ + 2 CIO, + H,0. 

Propertia. — The heavy dark yellow gas thus given off piust 
be collected by displacement, oa it decomposes in cootact with 
mercury and is soluble in water; it possesses a peculinr nmell, 
lesembiiog that of cldorinc and burut sugar. ^Vhen exjiosed to 



cold the gas condeuses lo a dark-red liquid, which boiU' at + 9", 
and at — 79*lrec*e8toaQorauge-coIoured cr)'staUine masg. The 
gaseous, and especially the U(|uid oud solid peroxide uiider^ 
eoddea decomijosition, frequently p.xplodtiig moat violently, 
bence their pt^parntiun requires extreme care, la order to 
obtain an aqueous solution of tho gaa, a mixture of ]>otiisaiuin 
chtoi»t« nnd oxalic acid may be lit^iLtcd in a wator h»tli to 70^. 
the mixture of chlorine peroxide and carbou dioxide then evol ved 
Iwing pussixl into water.' The foUowiit;; cqnutioa represents 
the action here occurring : — 

2 KClOj -t 2 II,C,0, = KjC.O, +- 2 HjO + 2 CO, + 2 CIO,. 

Cblorine [Kioxide can Ift presen-ed without cliange in the dark ; 
it is, bovrcvor, slowly docoiuposod into its eleuieiitaty consti- 
tneats wlion uxposed to ll^ht, uiid thiii douomposilion takes 
place quickly aitd with explosion when an eleetde spark h 
passed through the gas, two volutucs of the gas yielding one 
volume of chloriue and two of oxygen. 

Wlwa plioBpliorus, ether, sugar, or oilier easily combuslibla 
anbstances are throM'n into the gaa they take fire ^pontuneously. 
This oxidising action of clilorine peioxide is well illusirated by 
tho following experiment!*. About equal parts of powdcrad 
while sugai- and chlorate of potash in powder are carefully 
mixed together with a feather on s sheet of writing paper, 
the mixture then brought on a plate or stone }ilaced in a. dtauj^ht 
dumber, and a Hiu<;lc drop of strong sulphuric acid ullowetl 
to tall upon tlio>, wlmn a suddeu ignition of tlit-. vrliolu 
innss oocnrs. TItis is caused by the liberation of chluriuo 
peroxide, which sets fire to a particle of sugar, and tlie ignition 
thu^ coinmciiced quicljly uprt-iHi* throughout the moss, and 
the sngar is alt burnt at the cxpouee of the oxygon of the 
chlorate: The combustion of pUosphonis can be br^iught ubnnt 
under water by a sintiliu' react iou : fur this purpose «onie cryfttnU 
of chlorate of potossiam and a few small lumps of yellow 
phosphorus arc thrown into a teat glaas half filled with water, 
and a small quantity of strong sulphuric acid allowed to flow 
iliTough a lube funnel to the lower port of the glass where Uie 
solids lie As soon us the acid touches the chloiale. chlorine per- 
oxide is evolved, uud this gas on coming in contnct^ with tlie 
pbosphorus oxidiKes it, and blight flashes of light are given ofE 

■ Tttei. Ann. CArm. Fkarm. cUxvii 1. 

• fMun and IteViw, Jwm. Ckem. Sot. u. IM. 



Water at 4* dUsoIros abant Iventy times iu volume of 
oliloriiK* peroxide gas, Fonniii!^ ii bri^'lil jt'llow solution, ivliilet at 
lovijr Ifrmiifirfttares n co'^tallinA hjMmttt is formed. If this 
Dqticoud solution is saturated with nn alkali, amixture of chlorite 
and clilorate is romied ; tints : — 

2 KOH + 2 CIO, » KaO, + KCTO, + 11,0. 

When potassium chlorate is ticatccl with hydroclilorio acid a 
yellow gas is evolved, first prepared by Davy, considered by him 
lo he « diatiiict oxide of chloritic, ninl termed Kveklorint, \x 
has, however, recently been shown by I'fibal > tliot this body is 
B mixtura of free chlorine and cldorinc peroxide in ^'aryin^ |n'0- 
portions. This tnixture possesses even more povretful oxidizing 
power thnn chloriuc itself, and is therefore largely used as a 
disinfectant, being not only very effective in removing by 
tixidiitioii putrcscont niuttur in the air, but being at the same 
time very easily prepared. 

Chloric Acid, UCIO,. 

147 Chloric acid is the most important member of tho ceriss 
of chlorine oxy -acids. It was discovered by IJerthoIIet in 1786, 
and ii is obtninod when the low«r acids or rujuvi^us solutions of 
the oxides of chlorine arc exposed to li^ht, 

Priparation. — ('hloric ai:id is heal prepared by decomposing 
liarium chlorate with an equivalent quantity of pure dilute 
sulphuric acid (Gay-Lussoo. 1814); thns:— 

Ba (ClOa), + HfSOj = BoSO, + 2 HCIO, 

The clear solution of oliloiio add must be poured off from Uie 
dcposil.ed pii-cipitiite of barium su1phat«^ and cun.-fully evaporated 
in. tsacuo ovt-r strong sulphuric acid. The residue thus prepnivd 
contains forty per cent, of pure chloric actd correspondinj; to the 
formula HCIOj + 7H,0. When atlviii]its ars made to conccn- 
tral43 the aeid beyond this point, tlie chloric nt-id undergoes 
spontaneous dccompaiitton with rapid ovolution of chlorine and 
oxygeo gases, aud formation of jn-rcldono acid. Chloric acid 
can also bo prepared by docompoain^ potassium chlorato with 
Iiydrofluosilicic acid. If, SiF^ when insoluble potassium flitosi- 
licate, K^SiFq, !» precipitated, and the cblorouB acid retuuns in 
solution together with an excess of hy droll uoHilicJo acid. This 

' jtnn. CAfin. nanii. clszvii. 1, 

"onn \k removed by tbu addition of a little silica and by sobafr. 
queat evaporation when tlie tlaoriao pcisaes sway ns gaseous 
totrafliiorido of silicon, 8iF^ mid tl>u puru chloric acid can b«i 
pouKtl oir from tlie silica, wbicb seiU&i us a pon-der to ttie 
boUotn ol tilt! vessel. 

148 Prcpfflira. — ^Tlie acid obtaini.'d in this way in lliv ■jrontoat 

1 stale of concentration does not rapidly imdei'go cbango at the 
ocdinaiy temperature, but it fonus pcrcliloric acid oa standing for 
some time exposed to light Ot^gaiiic bodies suoh &» wood or pii])er 
decompose tlie acid at once, and arc usually so rapidly oxidized 
as to take fire. d&qu«ou3 cldorio acid ia colourless, possesses a 
powerful acid reaction and a pungout emetl, and bleaches 
vegetable colours iiuickly. It ih a mniio1)asic acid, that is, it 
contains only one atom of hydrogen capable of replacement by 
ft iDCtoI, and a acrios of saUs are thus formed which are termed 
TKi Cfiiorata. — Of these sails potassium chlorate (or clUoral* 
of potasli), KCIO,, is the most imiwrtant. It is vuily formiHl by 
jus-s^iiig clilorino in exco«s into a solution of caustic potash ; 

3 a, + 6 KOH - 5 KCl + KC!0, + 3 11,0. 

' Tlie chlorate is much Ices soluble in water than (he cliloride 
formed at the »anio tioM-, so that by eonccntmting the solution 
the cbloTtite is dppositcd in tabular cryataU. which may bo 
purified trrtm adhering chloride by a second crjHtaJlizatioii. 
Other ehlorat** con be prepared in a eimilar way, thus, for 
instance, calcium clilorate is obtained by passing a cnrrent of 
chlorine into hot milk of Huic vhcQ the fuUowiug reaction 

C.a,+ C Ca (OH), = Ca(aOj),+ 5 C«a,+ 6H/). 

All the chlorates are soluble in water, and many delifinesM 
on expoenre to the air. The potassium salt in one oi the leant 
Bolnble salts, 100 part* by wtiglit of water at 0* dissolving 
about 3-3 paru of this salt, wliilst water at 15" dissolves 
twice ibia amount A chlorate ia recognized by the following 

loitta : — 

(1) Its solntion yieldii no precipitate with eilvcr nitrate, bat 
on ignilioD tho eall gives off oxygen gas, and a fwlation of 
the .vEidual salt (a chloride) gives a white precipiUte on 

aitdition of nilrk add. 

(2) IV the aolution of the cblontLe a few drops of indigo 




solution are adiled, the lic^uid acidnlaled with Bulpliurio aoid, 
anit Aulphurtius aciil (or sodium stJpbite dissulvud in water) 
add&d drop by drop. If a cUloroto bo pnseol tlu bluo oolonr u 
diach&rg«cl, because tlte oblorie add is leduocd to a lowor oxida. 

(3) Dry chlontes tnatad with strong tiulphiuio acid yiokl a 
yellow explosive gu (CIOj). 

The cainpofiitioii of tlio chlorotM hns bvca very cRrufally 
dctenniiied hy Slas' and MarigDac.* T)ip following numbers 
givo tli« [>vn;eDtage ocHiipositioa of silver clduratc according Lo 
tlifi analyses of Stas - — 

Cldoriuo 186257 

Oxygon 25-0795 

Silver 56-3948 


If wqhow divide these numbers by the combiniog weights of 
their respective eleiueuts, wo obtain aa the proportion betweuo 
the atonu of tJto eleniL-nU as followa : — 

Or exactly in the proportion of ono of chlorine, one of silver, 
and three of oxygen ; and bcnce the siiuplcab fonnula for tbe 
compound is AgClO,. 

Perchlobic Acid, HCIO, 

149 This acid was discovered by Stadion in 1816; it is fonnod 
by U18 decomposition of chloric acid on exposure to hest or 
light, thus : — 

3HCI03=HC10^+Clj + 0, + H,0. 

It 18 beet prepared from potassium perchlorate, which can be 
obtained in any qimntity from tlie cldoratc. We have already 
remarked uudto* oxygen, that when potiuwiura ^hlomte ia 
bcated the fused moss slowly gives off oxygen, and a point ia 

■ yiMrrtta irni'rrVT CimljtM mr la Loti tm Pnforlimu, W6, 
• BiU. Vmiv. xlv. »7. 

reached at which the wliole muss becomes nearly solid, owiog 
to the formation of perchlorate, thu3 : — 

' 2 KCIO, » KCIO, + KCl + O, 

The muss is Uicn allowed to coo], powderad, and well washed 
Willi water, to remore th« greater part of tlie chloride formed. 
In ord«fir to get rid of the iiiiftlt^^red chlorate, the cr^'stallina 
powdor is boated with warai tiydrochloric itcid ho loDg as 
cUIuriuc and cldorinu JK^TOxidt! gast^ arc evolved: a mbsuqtietit 
wnsbing with w-ater removes the remainder of the chloride, and 
tlie piiK', 3{)aringly>soluhle perehlurule is left. 

Prqtaraliaa. — In order to prepare perchloric acid, the pure dry 
potassium ult is distilled in a small rvtort with fuiir times its 
weight of ooDcentrated (previously boiled) sulphuric acid. At a 
temperature of 1 10° dense white fumes b^n to be evolved, whilst 
nc«Ionrles3 or slightly yellow li()uid,con8inling of pure perchloric 
acid, HClOj.diaiils over (Uoscoc),' If the distillation be continued, 
this liquid gradually cliATiges intx) it white ci^'stalline nioss. 
liaving the composition IIC'IO^ + HjO. The formation of this 
latter h<idy cau be readily explained ; a porliuu of the pui-e 
perchloric acid splits up durirg the distillation into the lower 
oxides of chloiinf* and water, w!iich latter enitibtnfit with lliv 
purencid ahvady fonued. When the cr>'stalliiie hydrati; i.s again 
heated it decomposes into the pure acid, whicli distils over, and 
into nn ntiueous acid which boils at 203°, aiid therefore remains 
behind in ihe retort. This reuution is employed in the prt>pnra- 
tJoR of the pare acid, HCIO|, as that obtained by the firat pre- 
pttrntiuQ i« guucrally rendered impure by stilpburic aoid carried 
over mechaoically. 

Propertiw. — I*iiro jjcrchlwric acid is a volatile colourless or 
alightly yellow iuoljileli<iuid, which does not solidify at — !{5°, and 
at 15'5 hftsaspecilic gravity of V782. It is strongly hygroscopic, 
quickly oheorbing moisture from the air, and tluTcforL- emitting 
dense white ftuoea of the hydrated acid. When pouatl or 
dropiK^l into walei' it dissolves, combining with the water with 
such force a« to cause a loud hiseing sound and a considerable 
evolution of heat. A few divtps thrown upon paper and wood 
cause an instantaneoiis and almost explosive inilaiuinatioti of 
these luKlics ; and if tlic same quantity be allowed to fall upon 
dry charcoal, the drops decompose with an explosive violence 
which is almost equal to Oiat obeerved in tlte case of chloride 

* Chan. Sit. Javn. XvL 4atie<»). 

of nitrogen. IF the pure aciJ. even in very small quantity, 
come iu contact with tlie skin it pnxluoi-s & serious ^voiint). 
which dufs not heal Tor uivoiKa. Tcrvhloric acid undcrgot,-* 
decomposition on distillaliou; llio originally nearly colourless 
acid bpcomi>.s gnvluiitly darker, until il attains the tint of 
bromine, and nt tost HuUdeuly decomposes with a loud explosion. 
The conipowtiou of the sniiwtimoc vchicli is liene ftirined is un- 
known. The pure acid also undergoes spoatnoeous and explosive 
decomposition when pn'Servcd fur some days oven iti tliu dark. 

T}ie DKlhod.t t^inployoxl in tixiu^ tlm composition of this actil 
may here 1»B referred to as ilhiBimting the mode by which tho 
qiuintitativc analysis of similar hodica is cai-ried out. 

A quantity of the pure acid (HCIO^) is st-tilod up in a 
small glass Inilb (Ki^'. tf-t), whose wei^'hi Itas been praviously^ 

Iaaceituned, and die bulb aiul acid carefully weighed. The 
sealed poutta of tlm tube ans then hmkcn, the acid dilntpil 
with water, and thn aqueous tsolutioTi saliirated with a slight 
excess of solution of potaasiutn carbonate. Acetic aciJ is 
next added in slight excess, and the whole evaporated to 
dtynQsa on a water ballL Tlie potassium acetate lieing 

Pio. it. 

eolnhle, and the potassium perchlorate being in-ioluble in 
absolute abohul, the whole of the hitler wilt fonneil by the 
neutralisation of the acid is obUiined in the pure stute hy 
wa.tliing the dry mass with absolute aloolml and drviii^ t3)o 
residue at 100'. Thus it was found that 07840 j^m of 
the acid thus treated yielded l-08l>0 grum of potassium salt, 
corresponding to 0*7S37 gram of pure perchloric acid, or the 
acid under analysis tontuined 99'8J) per cent, of IICIO,. provided, 
of course, that the suit obtained really had the coiii^'o^ition 
indicated by Uie fonnuk, KCIO,. In order to obtain evidence 
on this point, the quantities of oxygen, chlorine, and potassium 
contained in the salr. were determined as follows : — 

(1) 0-9915 grum of the dry salt was mixed Tfith pure diyi 
oxide of iron, and the mixtun- heated in a long lube of Iiard- 
;*las8, tli« weight of which, when thus Hllcd, was determined. 
Thapreeenoe of the oxide of iron enabled the perchhirale to 
ield up \ts oxygen at a lower temperatarn tlian it would 



if heated alone. Tlie loss of weight wliicli tliu tiil>ft 
experiences on liciiting represents the totnl weight of oxygen 
cosUined in the salt; in this case it amounted to U45T0 gniiu. 

(2) TIjc n-sidu« is next ccunpldely i-xliauafecl witli wano 
vrat«r, antl the chloriue pr(>cipit4)t(>d in the solutioti ns silver 
chloriile; in the alKtve auoiyais UTDl^;! gram of pure silver 
■vfoa nuctled for complete pifoipitatioii, aiid tliis oorrexpuntts to 
0'2024 gmm of chlorine. 

(H) 0'31(>>> gram of the snlt was next carefully heated with 
an excess of pure siil|>huric acid, and the residue strongly 
ignited. In tlus way the potassium pei'chlomle is converted 
into aulphate, which vras found to wei^li 0'2010 grain. 

From thosu nuinbors tJie percuntage composition of the Ball 
can l>e easily obtained, and tlie results, as sliown below, are 
found to correspond, within the unavoidable eixora of experinieut, 
with the uuDihers calcululvd from tlio formula : — 

Analtftis oj Potassium Prrchloruie. 



dJoruie , , 
Oxygen . . 
iVtaAsium . . 

. CI '3537 

. O4 63-84 
. K 3901 





\m 13 

ISO TTt/dratts of Pcrrhloric And. — The monohydrate HCIO^ + 
HsO, whoHe mode of formation has been luciitiuned, is obt^uned 
in tlie pure 8tale by the careful adilitiou of water to the pure 
acid IICIO^, until the crystali make their appeamnca Tins 
suhslancc, diacovered by Scrulhu;, waa furnieily supposed to be 
thu p«n> acid ; it melts at l/if and solidifies ttt this ti:iiiiicratiiTo 
again in colourless iieedle-shaiK-d cryslaU. often several inches 
in leugth. The liquid emits dense white funics on expcsiirc to 
the air, and oxidizes jFiiper. woud, ami other organic bodies with 

As has been stated, the monohydrate decomposes at n higher 
temperature into llic pure acid, and a thick oily liquid, which 
poBsessea a utrikiii^' re-ieinblance Id sulphuric acid, boils at Ifd'A". 
sad baa a specific gravity of 18a. This lifjnid contains 71'6 
per cent of KCIO^, and does not correspond to any definite 
bydrute Au acid of ttm sauie couipositiou, and possessing the 

Botue constant boiling point, ii olAainctl when a weaker acid ia 
dUtillcl. tlte resiiiuv then becomes more and mure coacciitnteii. 
unlil Uiu abtivo comiwsitiou anil boiliug pulut is ivaclicd. 
A(^R«(iu3 pvrclilonc acid, tbeit-fore, exhibits Uic aaiDo relations 
ta this respect ns the other aqueous acids. 

PrrtJUorattS' — I'eichloiic acid is a powerful monoboaic 
acid, foriDing a series uf stilts, U'rined Uic peix:hloi'ut<?s, whiuli 
are all soluble ii] «-at«r, otiil a few of which are dcliquesc«nt. 
Potassium perchKirate. KCIO^, and rubidium {wrubloruto, 
KbCIO^, are the leant ftiilubla oP tlic sulfa, one part of tho fortnerl 
dissolving in 58, nnd the Inrtcr rcKiiiiring 91' part« of \ra.\KV at 
21° (or solutiou. Both \Xwst salts tirv almost iosnlublu ia 
alMoliitc alcohol, nud Uiey may btf. thvivfotf , employed for the 
qtiautitative esttmatioo <if tlie uiutal. 

Till: pcrchlorates aru dietiu^uiGhud from the chloratos by the 
following reactioiiR : — 

(1) They undergo decoinpositioa at a higher temperature than 
the chlorates. 

(2) They are not acted upon by hydrochloric ncid. 
(:i) They do not yield au explosive yi**. ^l^c w''^^ heoted' 

With stronj; sulphuric acid. 



151 No componnd of bromine and oxj^cn has aa yet beon 
obttttnwl, but several oxy-ocids corrospoodijig to thoe« of chlorine 
arc known; vii : — 

Hyimbromous Acid, HBrO. 
Ilromic AciJ, HllrO.^ 
Perbromic Acid, HBrO,. 

Htpobromous Acid, IIBrO. 

This acid together with its Bolts, termed tlie hyiMibromitus, are 
formvd, in a similar muiuicr lo hypochltirous acid, by the action 
of bromine on certain mctnllic oxides (lialard). Thus if bromine 
water be shskuu up with itiercurir nxidt*, and irtlicyeiliMi- liquid. 
thus formed be treated successively with bromiue and the oxide.] 



solution is olitaiQe<l which contains in every 100 clic. 6*2 per 
;Qt. of bromine combtued as bypobronious acid, the rvuclioti 
being as follows . — 

K HgO + 2Brs + H,0 = 2H0Dr + HjfBr, 

^HTbe greater port of thu hypobromous acitl contained is this 
HktroDg solution is decoiuposed ou distillation into brptninc iuid 

oxygen. It mu, huwevcr, be diatilled in vanui at a temperature 

or 40° without unilurgiiiog this eltangi!.' 

A({ucuua hv'iioltrninoua acid is a light aintw yellow coloured 

liquid, vloaely Kaembling in ita properties liypoclilorous acid, 

■ciiog as a powerfal oxidising ayeiit and blenching organic 

colouring inatten. 
^1 When bromiue is added to milk of lioio, tlio compotiud 

CaUr, + Cii (OBr),, a substance similar to bleaching powder is 

formed uud tliis udt is t^rnicd bromide o/ lime. 

Buostic ActD, HBtO,. 

15a When broiaiuo b dissolved iu caustic potash or soda, a 
eolourlesR solution is produced which contains a mixture of a 
; bromide and a broniate ; tlius : — 

SBr, + 6KH0 = aKJlr + KBrOg + 3H,0. 

The difticiiltly soluble potassium bromale may bu vasily separated 
l>y co'stailizutLDU from the very soluble brotnide. Potassium 
l)i-omate is also foniicd when bromine vapour ia pasaed into 
a solution of potassiiuu carl<oii&t« which has been saturated with 
peliloriiie gas. 

Preparation. — Free bromic acid is formed when cLloriue is 
passed into bromine water; thus: — 

Br,-t-5a,+ 611,0 = 2nBrO,+ 10ITCL 

' TIio af id is. however, test obtained by the decompoailiou of 
the slightly soluble silver brumnte. This salt is thrown down 
on the addition of uitratu of silver to a solution of a »oIuIile 
brotnate; tlie precipitate thus prepared is well washed with 
water and then treated nnth bromine; bromic acid remains in 
solution uud the iiuoluLle silver brotuide ia throwu down; 
thus: — • 

SAgBiOj + 3Bri + 311^0 = 5 AgBr 4- GHBrO, 
' DauMT, Clumi. Sa. Jmn. xv. 477. 

properties. — Obtaineil according to the foregoing method^ 
hromio acid is a Htroiigly acid liquid retldt-uing and altimately 
bleodiiug UCmU3 paper. On cODcentraUoo at lOU* the aqueom 
acid decomposes inlo bromim) and oxygou, aad it is at odw 
decomposed by reducing ageuts such as sulphur dioxide ind 
sulphuretted hydrogen, as oIbo by tiydrobromic acid, the rollowiug 
reoctious taking place : — 

<1) 2H BrO, + oSOj + 5H,0 = 2Br, + 5H^, 


(2) ailBiOg + 58115 = Br, -HCnjO + SS. 
(H) H BtO, + SHBr = SBr, + 3 H,0. 

Hydrochloric and hydriodic acids decompose brotnio acid in 
a similar maniii^r witli fomiatioa of the chjorido or iodide o1 

Tliu hromntcs aro as a rule difficultly soluble in water, and 
decompose on heating inlo oxygen and a bromido, but unliko 
the chlomtes uo pcibromutc i% funned in the process. 

Prbbeomic Acid, HBiO,. 


This substance is stated by Kiimtncrer' to be formed by the 
action of bromine on dUutc perclUoiic acid, the btomine 
liberating ciilurine. Other observers liavo, however, failed to 
obtain the sub^auce by this means, and the existence of the 
acid and of its salta is, tltereforo, somewbut uncertain. 


153 Only one oxide of iodine is known with certAinty. Thfe 
i« tlie pentoside ljO„ which iiniii-s with water to fonn iodic 
acid.HlOj. Besides these, liydrated periodic acid, HIO, +2 
is known. 



This acid was discovered by Dsvy in the form of potassinm 
iodate, which he obtained by the action of iodine oa caustic 
potash \ thus : — 

31, + 6K0H = SKI -•- KlOj + 3H,0. 

' Javra, /Vtut CSbtfin. xn. IM. 

PrepttraSim. — (1) Free iodic acid is best obtaiiwd hy dissolving 
iodine in pure boiling conceQlnitcd nitric acid, which oxidizea it 
as folloirs : — 

31, + 10HNO3=6inO,+ 10NO+ 2HjO. 

this puqwse 1 part of iodine is Iieated iu a retort with 10 
of the acid nntil the whole of the iodine is dissolved, and 
DO further evolution of n;d fumes takes place. Tie solution is 
then evaporated and the residue huutvd to S^O" xititil vverj trace 
of nitric iicid is removed. The iodic acid thus los^s wat«r, and 
a white powder of iodic i)«iitc»xide I^O^ is ohtitined. It has a 
specific gravity of 4', aud when heated to SW^ decomposes 
into iodine and oxygen. Tliis .luti^tanee is very soluble in 
water, dissolving with evolution of hcnt and from the thick 
aj'rapy solution tlius ohtaiac^l rhombic cryatuU of Iodic acid, 


UIO,, ore deposited. 


(2) Iwlic acid can also be obtained by the action of dilute sul- 
pbnric acid on banam iodate, which is prepared as follows: the 
requisite quantity of iodine is dissolved in a hot concentrated solu- 
tion of potaMium chlorate an<l a few drops of nitric acid added ; 
immediately n violent evolution of cMonnu j-as coiumonccs, 
and. on cooling, the potussiuui iodate ciyfitaDizes out. This salt is 
then dissolved in water and lo the solution barium -chloride is 
added, when barium iodalc stparutcs out as a. white ponder. 

(S) Iodic acid is likewise fornicd when chlorine is passed into 
water iu which iodine in powder is suspended ; thus: — 

I,+ 5C1,-|. 6H,O = 2UlO,+ 10HCl 

In order to separate the hydrochloric acid which 1» at the 
same time formed, prei'ipittited oxide of silver is added until the 
acid is completely precipitated as the insohilde silver chloride. 

ProptrtU*. — Crj'Stallizcd iodic acid ha.t a specific gravity at 0* 
of 4'629 ; it is insoluble in alcohol, but easily soluble iu water. 
The coucantrated aqueous solution boils at 104",' aud fimt n-dtlcuH, 
and then bleaches litmus paper. Phosphorus, sulphur, and organic 
bodies deflagrate when heated with iodic acid or with the 
pento.\ide. Sulphur dioxide or sulphuretted hydrogen as well 
us h}'driodic acid teduces iodic ncid with sejiaratioo of iodine; 

thus: — 

2HI0, + 5S0, + 4H,0 - Ij + SHjSO,. 
2HI0, + 5H,S = 1, + 5S + UHjO. 
H10a+5HI = 3], + 3H,O. 
' Ditto. Anm. Chcm. Fhyt. {*] uL li. 



S7u laiattSf— Iodic acid ia a moaobaaic acid, and is distio- 
guislied from chloric acid and bromie acid by the fact that it 
Tonus ttdf only tlit; tionual t^lts, but salu vliich are termed acid- 
or hj'dmted-aidt^, wliich must U: regni'ded as molecutar compounds 
of tlie acid with a nonnal salt Thiu the fuUowio^jjxjUtssiuni 
salts are knovn : — 

Ifonnal potasGiuni iodate KIOj. 
Acid potassium iodate KIO,. illO^ 
Di-acid poUift^ium iodute KIO,, SHIO^ 

The normal iodatcn (ik cliicfly insoluble or diffimltly solublo in 
water; tlie more soluble are Uiose of Uie alkaline melals. On 
heating they decompose eitlier juto oxygen and an iodide, or 
oxygen and iodine are given olT whilst eillier an oxide or Uie' 
metal remiiim behind ; thus >- 

Ba(10^, = BaO + l, + 04 

In onlnr to detect iodic ncid the Boliilion acidified with hydro- 
chloric acid is mixed with n small quantity of starch puslu and 
Ihun an alkaline titilpliiu- or n solution of Huljfhiiiotut ucid addud 
drop by drop, tlios liberating; iwline niiich forma with Uie starch 
the blue intliile. 

Sodium ioflatc occurs in nature aasociated with flodium nitrate 
io chili saltpetre, and iodic acid is not uiifrojuently met uitli in 
nitric acid ptvpurud from tliiaaounx. 

Pebiodio Acid, UIO^. 

ZS4 This substance was discovered by Magnus,' and subee- 
qiiwutty inx-estigatod by othet- chemist-s, especially by AiUMor- 
mliller and Itniunivlsborg. Xornial periodio acid, HiO^ is not 
known. The hydrate H^lOa or ElO^ -4- 2HjO is formed eillier 
by tlw action of iodine on aqaeous-perrhloric acid, tlius : — 

HCIO. + 1 + 2H,0 > HjlOo + CI. 

or by the decomposition of silver ptriodflte with bromine. 

rcriodic ttcid is a colourless transparent ctystalline deliquescent 
solid which melts at 133" and at MO' is completely decompoeed 
into iodine pentoxido, water, and osygen. The aqueous solution 
has a strong acid reaction and it acts upon reducing ajjeats in 
a similar way to iodic acid. 

' Poff. Jh*. sxriii, Gil. 

The ptriodaUs fotm a very sin^lar series of compounds 
^possessiiig as a rule a very complicated composition. Tliey may 
be divided into four classes. (1) Tliu iimto-periodatcs ; (2) the 
iues«>-penGdAt«s, (3) tlie para-periudales and (4) tlm di-perio- 
dates. The meta-perioilatcs are derived from ttie nomiBl acid 
IllO^ which as yet has not heuii isolated, thv mcso-|jcriodiitc(i 
from the hj'drat* HjIO^ or HIO, H,0 which has likewise not 
been obtaiued whilst the para sidt« tiiu derived from the ordJnaiy 
acid, HjIO^. The di-periodates form anotlier hydrate, 

2H10,+ n,0 = H.Tj,0,. 

besides theaa salta there are othcTs tlie conetitution of which is 
^ Still more complicated, as for instance, Zn^I,0„ or 4ZnO + I,Oj. 
H llw foUowii^ are some of the best known periodatea. 

I (1) Potassium meta-periodfltd KIO^. 

^^K (3) Silver meso-periodate Ag^lO^ 
^^H Load iiieso.periodato Pb3(I0J,. 

^^H (3) Acid silver poia-penodate Aiij'H^lO, 
^^^^^^ Acid Mudium para-pcrioduti^ KuJf^IO^ 

^^^^^V Xorninl buriuiii p^ra- period ate Ba^(lOg)f. 

^^V (4) Silver di-periodat<> Aj^I^O^ 

M The 

■ chlorin 

■ caustic 


The periodates can be obtaiaed in several ways. Tiius if 
chlorine be allowed to act upon a mixtaro of sodiam iodate and 
caustic soda, sudiuiu periodatG and chloride of sodium ara 
formed; thus: — 

NalO, + CI, + 3N«0H = Na,H,10„ + 2NuCL 

Another means of obtaining tlie periodates is by hcatiog barinm 
iodate ; thus : — 

5BaT,0, = 11a J,0„ + 81 + 1 80. 

Thb barium periodate may be heated lo r«rlui>ss witliout decom- 
positioR, whilst the oth(>r periodates are decomposed at thii 
temperature with evohition of oxygen. Tlie periodates are as a 
role but Rli^htly soluble in wat*r. Their solution eli^litly 
acidified with lutric ncid gives with silver nitrate a dark brown 
precipitate of normal silver para-pcriudalK Ag^lO^ soluble in 
nitric acid, from whidi solulioo on evaporation reddish yellow 
crystaU of silver meta-periodate AglO^ sfiparnte nut. and this 
8ubetani;e on being brought in cont^t vrith water decomposeB 
into the free acid and tlie di-periodatc AgJ,Oy 



SULPHUR. &-si'98« Vapour Density ois'99* 

Xj5 Suu'HVB lutt U-cn knnwa riutu Uio earliest tiuea m il ocuun 
in the free or native stale, iti tho Dcij^-IiliouvhuoJur extinct us well 
u of octivu volcanoui. It wilh I'tiniiiuly li-niii,>il Itiimnliiiie or 
DrtniiflaloiiQ, aoi) wns uiiihiik*!!:!! by Lli« iiluliuiniBtc t» bo llio 
(mooiplo of comlnwtil'ilit.y, ami LeUcvud by tlii-rii t-ii n'prmcnt 
Uio alloniliility of iiidliils liy fin>. Tliv cuiii|i4iut)tlit tif Uiif) 
eJcment occur in nature in mQt;Ii Intver qiiantitiKi, and ara 
much iiiorv widely tliMtriWlvil limn Htiljiluir itself. 11k- com* 
))ouii(l& of 8iil|i|iur witU Dio invtaU, It-rimtl atilphii/e», oud Ibose 
witli tliu ludtal aitJ oxygen termed mlf'katta uv fouml in lugo 
quAntilicfl tii thu iiiiiivml kiiijfduiu. Tliu iiioro iiniiurlttiit com- 
pounds of 8til]ihiir o€L'iirrin;{ in natnro nro tlin rnllovt-iiij; : — 

(1) SutjAidti. Iron pyritwi Ki-K,; coppur pyrilux CuFoA, ; 
^cna I'bS ; cinnnW IlgS ; blDitde j!nS ; yrey aotimooy Sb^S^ ; 
rciilgiir AmjS, ; or[)inii*nt A\\. 

(2) Sulphates, tiypatim L'uSi\ -f 2I[,0 ; }:>-|Mum anliyilrilo 
CaSO^; hditvy xjmr liiiSI),; kiiMi-iitu MgSO, + 11,0; bitter ii|inr 
Mk!*O, + "H,0; ulinibiT (wlt Ni>,SO^ + IHH.O ; gwcu vitriol 

Volciuiio giiitcs almost always contain aulpbur dioxido and 
sulitliurcttod li>'diO};L-ii. »iitl wjion tlicy cuuiv iu voiitucl these 
two gosva mutually (luconipoao with tlio ili'iiuiiiljon v( Muljiliur; 
thus: — 

SO, + 2a^-3Sf 211,0. 

KHd it is very pinhablo tliat native sulphur is Fonned by the 
abovo rtootion. Tliu apiiBratos ahonn in Kiij. 85 wrvu to 
exhibit tluH Hingiitar furiniUiun of n nolid Hul<ntntirit from ivra 
coloiirli'sa fiAMja. Tlio sulphuri^tk'd liy<iru}^n|^t ovulvud in UiB 
boUlo (0) is passed into the Ini^e fliuk (A) into wliJcli is led at 
llie snnie liiut; siil|<1nir dioxide frotn the small flask (K). The 
walls of ihu lar^e tlu<ik iirt; doon seen to become coated irltli a 
yulluw (loposit of sulphur. To avoid the escRpo of llie funiH 
iiidi tlui nMiiii. thu experiment Is made uenr a dovrn-dmught aa 
shown iu thu tli^uro. 

Sulphur compounds nrp aim found widely diatiibiilfid in tlio 
vegetjilitff itnd ftiiiiiinl wai'M, in ocitiiin iir<;ii[iic oom|)ciunds Sttoh 
U tho volatile oils of nuiiJlarJ nnd of pirlic, and in the adds 
on^urriug in llic bile. In aiuall ipuintitieti also »ulphur ocoiin 
in huir, and ttooI, wbilitt it is coulainod to Hid amount of about 


[l per cent, in all the albumioous sulstuuces which fonn an 

[iiaportunt constituent of llie aniiual boftj. 

Aliaost all the stiliibur of miunmrce comes from Ttaly where 

lit is Foimd in the Itonia^iia aud in other parta of the couUaeat, 

[bat espoctally in very birge (jiiantitics in the volcanic districtcof 
tho island of Sicily, whoru it occurs iu vvide-spraad masses 
ruond chiefly on ihc south of the Madonia range stretuhing over 
tbe whole of ilie provinces of Caltonissetta and Oirgt>nti, and over 
a portion of Cstania. No fowor tliao 250 distinct sulphur 
workings exist in Sicily, fmin which the annual production 
ID the jrear 1372 amounted to 93 millions of kilos. Tbe 
dapoaita of Siotliao sulphur oocnr in the tertiary formation 


Fic &a. 

lyii^5 imbedded iu a matrix of marl, limestone, gypsum, and 
cetestine. Tlio sulphur occurs partly in tmnsparent yellow 
OyitaU termed vivtfin mlphttr and partly in opaque cry^Ulline 
masses, to wliich llie ninne of miftmic mlphuT is given. Iloth 
those vnritftica ar« separated from the matrix by a simple pro* 
cesa of fusion. Tlio method dt^scribed in most of the treatises 
on chemistnr', in which the sulpliur ore is n-pre-^iontcd as being 
placed iu carthenwaro pots in a furnace, the sulphur distilling 
out into other jiots pljiccil outaide lijc fuTnace, appears to be 
unknown in Sicily. Iu llie l!on]a{>na an appardlus made of 
-iron and provided wilb u receiver of the »ami3 matcTial is 
aployed, but in Sicily a very simple mettiod of melting out 



the sulphur has long been, and sHU continues to he, in vogue. 
This old pnK:«os consists in placing a hvnp ol' tlitj ore in a. 
round hola dag in the ground avcnq^iug rmin 2 to 3 nwtrM in. 
diamt^ter aiid aWmt onu-hulf niotni in dcjttli. Fire is applii^L 
to thQ heap in the evening, and in the moniing a quftnlJty of 
liquid 8ulp]iui- is found to have uoIlECled in tjie bottom of the 
hole ; thi« is Uien Wiled out, the coinbustion being allowed to 
proceed furtlier until the whole Diass is burnt out. By this 
proceas only about une-Uxird of the aulphiir ooiitaincd in lliu 
ure i» obUttiud whilst the remaining two-thtrda biim^ aw-ay 
evohing elouda or sulphurous acid. 

This rou};h and wasteful process has recently been 
greatly improved by increasing the quantity of ore burnt at a. 


given time, the excavation being made 10 metres in diameter^ 
vitJi B dvpth of 2 j metrus, aiid so arranged (on the side of a 
hill, for tustunce,) that an opoiiin^T cou be made from the lowest 
portion ol' the holu ho that lliu sulphur, us it melts, may flow 
out These holes ere built up with mosses of gypHum and the 
inside covered with a conting of plasterof rarw (see Fig. 8fi). Tlie 
eaicaroni, as these kilutt aix; termed, are then Itlled with the 
sulphur ore which is buiJt tip do tliu top into the fortu of ft cone, 
and air channels (h h b) atv left in the mass by placing large 
tunip» of ihe ore together. Tlie wliolc li«ap is tlten coaled over 
with t»owdcpcd ore. (c o) and this a^ain covei-ed with a layer of 
bumtrout ore, after which the sulphur is lighted at tlie bottom. 

p pcnt'tnite veiy aiowiy m(o the mass, 
sulphur is gradually melted, and ninningftw-ay by theopciiuig (a) 
at the bottom of the heap, 18 cast iiilo motiMe. By thi» process, 
wbicli takes scvural weeks to vrnnpletc, the richest cres, oon- 
taining from 30 to 40 per cent, may Le maile to yield frotn 20 
to 25 per ccnt^ of sulphur, whilst coninion ores, coutuiniiiR from 
20 lo 25 per ccDt, yield from 10 to In ]H:r cent, of siilphur, the 
remainiiig portion of the sulphur bein;; used up for combostiiML 
Otliiir luetiiods of extnu:l.ion liy means of solvents, such 
1 83 disulphide of carboo, or by the use of ordiuary fuel instead 

Fio. 88. 

Flu, 67, 

of sulphur itself, ss a source of heat, have boon proposed, but 
from llie nature of the country oiid its iuhabitanis. these have 
not yet prove^l successful tn Sicily, oiid the mw !:ul|>Iiur still 
reniaioB the cheaix-st fuel for the purpose. 

15G ^fining 0/ Suiphnr. — CouiRiDTcial Siciliuii sulphur 
contains about 3 pvr cent of eitrthy iinjnirities wliich can be 
wmoved by dialillation. the arraiijiemeiit heiui; shown in Fig. 87. 
The sulphur is melt«t1 iu an iron pnt (>f) and runs from this by 
meeot of a tube into the iron n^ioTt (v.) vlicre it i.1 hented 
to the boiling point ; the vnpour of the sulphur then passes into 




the lai;gc cUaoiber (A) wliictt bos a capacity of 200 cubic metres. 
In this chamber tlie xulphur is coaden&cd, to begin witb, in tho 
form of A light yellow dystalliiie powiler iBniiwl Jtoicers of 
ntijjhur, jii3t as aqueous vapour falls as snow wheit the tempera- 
tare suddenly sinks bolow (f. Aflcr a tiuio tlic chnmber bficotoes 
heated above the melting fioiut of sitlpliiir, and thfrn it eoUects 
as a licjuitl which can be drawn off by means «f the opening (o). 
It is Ihi'H cast in tilightly conical wooden moulds, s««ii iu Fig. 88, 
and is knowu as roU sut/thur, or brimslone. It is frequently 
also allowed to cool ui tlic chamber and iben obtained iu largo 
crystalline masses, known ia tho tradu as block sulphur. 

In France, Germany, and Sweden, sulphur is also oblained by 
the distillation of iron pyrites, Fe-S^ Tliis method, which was 
described by AgricoU in his work J)t Re Mtiallica, depends on 
the following decomposilioD of the pyrites : — 

3FeS, = Fe3S.4Sj; 

and tho change which occurs is e3:iictly similar to that by moans 
of vhicb oxygen is obtained from manganese dioxide ; thus : — 

3MnO, = Mn,0^ + O^ 

Thi« decoiapcfiition of the pyrites is sometimes can-iod on in 
retorts, but more generally a kilii similar to a liinc-kiln is 
umi>Joycd for the purpose, having a hole at the aide into which 
a wooden trough is fo^teiiMl. A small ijuiinLtty of fuel is lighted 
un the bun< of the furnace, and theu the kiln is gradually filled 
with pyritvs; a portion of the 8ti1[diur bums away whitsb 
nnotlier portion is volutilizeil ; the burnt pyrites is from lime 
to time removed froin below, and fresh material Uirowu on the 
top so that the operation is carried oii uiunt^ituptudly. In this 
way atxiiit lialf the sulphur which is contained is the pyrites 
can be obtained, whilst only about ono-tlurd the total sulphur 
can be got by diHlilling in iron cylinders. 

Sulphur is likewise obtained iu this country, though in smaller 
quantities, as a by-product in the mnuufacture of coal-gas. 
The impui-e gaa always coiitniiis sidpluirL-ttt'd hydrogen, which 
cnn ho removed by passinj* Uie gas over oxide of iron, when 
imn sulphide is formed. Tliis suljstanoe on exposure to air is 
oxidiMid witli »oivtmtion of fi-c« sulphur, tlius: — 

2FeS * 30 = FejOa + S,. 

The mass can then be again employed for the pm-iflcation of tfa« 
gas, and tliis alternate oxidization and rulpliurizatioD can bd 

fpcated until a product U obtained cont^ning 50 per cent of 
iul|>\iiir, which uiay thru \ie separated from the iron oxide hy 

Another source from which sulphur can be obtained is 
bhu n!&idue or wast« iu the soda itiantil'acture ; this cousists 
v( calcium sulphide mixed wiili chalk, liiiio ttnd alkaJitie 
«i)1phidc«i. The sulphur vhich this mat«ml contmiis wag 
foruierly oHugetJier wasted ; iiuw, howcvftr, the sulphur um lie 
egainvU frum this niutvrinl. Por this purpgs« the waste ts 
B*8t partially oxidized by exposuie to the air, by which calcium 
hiosulphale (hx^iosulphitc of lime) is formed ; on adding hydro- 
chloric neid lu thid oxidized moss, which must still contain a 
jnantity of calcium sulphide, the mixture of salts undergoes a 
jecoRi position with deposition of sulphur, as follows: — 

2CaS + CaSjO, + GHCl = 4S + SCaCl, + 3HjO. 

156 I'mprrties. — Sulphur exists in several allotropic modifica- 

llioiia. Ill nature it occurs iu large yellow tTanaparent octahednk. 

■"tg. 39 ahowfl the fonn of t}ie natural 

srystals of sulphur (<i being the s.iiu. 

[l)ler. and b the more compliciited form) 

[vhich belong to the rhombic system. 

^and have the folIoi,nQg relation of 


Fic. Si. 

tiie ax«s :— o : 6 : r = O'SIOG : 1 : 1-898. 

*]n addition to this primary fonn, no 
K-ss tUnii thirty different cry^tallo- 
grupbic niodltications are known to exi»t in tlic ca^e of 
fiulphur. Cr>'stnls of ihombic sulphur have also been found in 
the sulphur chambers, having b«x-n deposited by slow silblima- 
fttion. The gpecilic gravity of tliin funii ol sulphur at 0'. is 2-05 ; 
■ It is insoluble iu water, very slightly soluble in alcohol and 
H ether, but dissolves rvjidily iu carbon diRulphide. chloride uf 
mlphur, petroleum, benzene, and turpentine, septiratiiig out 
H^n in rhombic crystals when these solutiyus are evaporated, 
I These crystaU are bt-st obt<vineii from solution in carbon 
Hdisulphide, which dinoUes at the ordinary temperature alMut 
Hone-thitd of its weight of sulphur, und this liquid when thu9 
Hfuitnraled on being allowed to evaporate slowly depo8it4 large 
iransiiarcnt octahedml crystals. Sulphur melts at IW'O 
(Brodic), forming a clear yellow liquid, which has a specific 
[gravity of 1-8(I3, and when quickly cooled, it solidifies again 
I ai the same temperature ; },'euerally, however, it remains tiqaid 



at a temperature below its meltiof; point, and then solidifies ■! 
about 111' (Quiiick«}, According to the conditions under wkich 
the passage from the fuaed to the solid state takes plaeo. sulphur 
may separate either la the form of rhombic or of mouodimc 
crystal*. The rhombic crystals are uhtAiiied by placii^ slvoi 
200 grama of sulphur previously ciystallized from snlntiou 
in carbou disulpludc iu a Qask provided with a long iieck. which 
13 a(t«rwarda beub lackwurds aud forwanls several times to 
prevent the entrv of llonting The solpliur is then mell^l 
by placiug the tiask in nn oil bath heated to 130°. and when tbo 
content* are Hipitd tlte flaslc is iininerscd in a vessel fillod with 
water at 95°. Ou standii^ for seme time nt a tempcratnn (/ 
about 90°, crystals are seen to fona, and when a safficient 
quantity have been deposited the flask is ^uicldy inverted ; tic 
portion of sulphur still liquid thon Sows into the ncclc and thetf 
at uiiee s<jltdifie:s, Icitvitig the truuapareut rhumbic erystids i 
the body of the flask. 

If, on the other hand, we wish to obtain the second or moni 
clinic modijiration, melted sulpliur is allowed to cool at tba 
orcliiiory temjtcroture umtl a solid or\ai is formed on the sur&cc. 
The crust is theii broken through, and the portion of sulphur 
still ixmminin^ liquid pourud out; the sides of the vessel wilt 
then be found to be covered with a maaa of long, -vci^ thia 
traDsparotit crystals having tlic form of nionoelinic pi-iants {fig. 
90), the ratio of the fae& ot wliicb &i% ex]jrc3sed by tba 
following numbers :'— a : J : e » 10U4 : 1 : 1004 

When, however, a laige mass of molten gnlphor ia altowed 
cool slowly, rbonibic crystaU cin: formed, and these cannoit be 
tinguished frotn tho niitiiml crystals. Thus Silvestn foond such 
rhombic crj-staU .'i to ti centimctttjs in length in a iuit«a of 
sulphur which had been melted during; a firs 
ill a sulphur mine, M'hcn a transpnreol rfaombio 
crystal of sulphur u heati^d for aome time to 
a tempeiTitiire of 100' to 1 14', appixHtchiug its 
melting-point, it liccomcs opoqu^ owing Co 
being converted into a large number of tnon< 
clinic crystahi; whereas on the other hand a transpar*! 
crj'stal of nionocUoic stdpfaur becomee opaque alW standi: 
tor twenty-four hours »t the Onlinury tenipeisture, havi! 
undergone a spontaneous cliange to the rhombic modifieatioo^ 
the cr^'stal having been converted into a lai^ number of 
' Uiu^erllcH, f^g. A»>i JxW. Mt. 




Kio. yo. 

minute rhombic ciystaU, This converaion is accelerated by 
vibmtiiiii, as, for iiistAiice, wb«a thu erysUiU uio scratched, or 
when tbey are expos(») to sunlight ; and the clunge is always 
accompanied by an elevation of t«mperatare suflicient to 
raise tbe atom or ^1-98 parts by weight ot sulphur tbrouj^b 
72'1>9 themuil unita.' liTottoclinic sulphur luis a s^K-cilic gravity 
of l-yo, and its nielting-poiiit is 120'. Like ibtf ibambic 
modilicatioii, it is also soluble iu carboii dtsulpbide, but whea 
the flolVBOt evaporates thombic crystals are dopnsited. 

Sulphur miik (lac itu{j>hurijt), a tiiKly knows to Gebcr aud now 
aaed as a Diediciue, is sulphur iu a finely dividvd state. It ia 
deposited as a fine whito jiowdcr vliea two parts of jlowera of 
sulphur are boiled with lliirtifen parts of wal«r and uue part 
of Unit; slaked with Uifl-c parts of water, until the whole of the 
sulphur id difLsolved. The re^ldiali-browii soliitioii thus prL-partd 
contains caLcium pentasulphide, which is decutiijjoBL'd ou tliu 
addtttoo of hydrochloric acid with ovoluliuo ol' oulpUurultvd 
iiydrogert and diipositioo of milk of Bulphur, thus : — 

OsSfc + 2Ha = CaCI, + HaS + 4S. 

WTien multed sulphur is ftythLT heated, the pale yellow liquid 
gradually changes to » doik roil colour aad becou)<.'8 more and 
njoro viacid, until at a temperature of from 200* to 2.'»0* it 
becomes almost black and ho thick that it can only with 
difficulty \k poiircd out of the llask. Observed in thin films, tliis 
change of colour froni yollow to red is found to be aseudated 
vitli a distinct change; in the »lMorption-5|iGCtniin, iDasmuch 
as the absorptioD in the red gnultially disappears, wliilut that 
in the bine is gradiially innreAsed (Lockyer). If the tctnperntnre 
be railed still higher, the Itiiuid bccoinea teas viscid, although ita 
dark colour remains, and on cooling down again the above 
di-acribed appearances are repcatetl in iuveree onier. If the riseid 
sulphur is rtpidly cuoU-U, or if the mobile liquid obtained at 
a liigbiT temperature be poured in a thin strvam into cold 
water, the sulphur asaunies the form of a scrat-solid trans- 
parent elastic mass, which can be dnwo out into long tlircada. 
This is known as plastic mtiphur; its condition in au uriittable 
one, and on standing, it gmdually becomes opaque and brittle. 
The plastic vahi-ty of sulphur can be ohtoinetl liy the arroagie* 
nicDt shown in Fig. dl. The sulphur is flrat meltol stod than 
■ Uibckcrlwh, Betlin Aca*. Btr. 1883, «S«. 



liiated to it« boUiug point in the retort. Tlie suljthur vnpour 
condenaea in the neck of the retort, and the liqaid sulphur nitis 
ID a thin ntifaiti into cold vater. 

ir the brittle mass be timtod with carlwu disu]{ihid«, a 
portion dUsulvps ; iinotfaer portioo of the eiUphur rcmaini btbiod 
ill the form of a dark brown powder. 

To{jcthcr with the luodilication soluble in carbon diKolpUide, 
"flowers of sulphur" coutaiiis a light yellow iDWlnble modi- 
fication; and if a solution of sulphur in diKulpliidc of csrboa 
he exposed to tho sunlight, a portion of th? sulphur avpanus 
out in the inaoluble form. These several ^■a^ietie& change alowlj- 
at the ordinaiy temperature, and quickly at 100", into rhombic 



Sulphur boils, accordiug t<i Pegnnult,' under the BOrad^ 
preasuie at ■HH'^-i or at 450° under a pressure of 7"9'9^, giring 
offa deep red vapour, the density «f which, according to Damas, 
is 95-55 at a'li'. whilst according to Deville and TrooBt it remains 
constant betweon 8tJ0' and 1,040", being 3211." Hence it is 
seen that aljove SRft° the molecule of sulphur consists of two 
atoms, aa is the case with most simple gases. At a tempemtnre 
not very far from its boiling-point the vaponrof sidphurconsigte 
however, of six atoms, which dieaociate wlioti the tempcrotiiK 
is raised. 

Whtn sulphur bums in the air or in oxygen, a continnoM 

spectrum is observed, but if a «innU (quantity of siilplmr vapour 

be brought into a hydrogen llamc. a series of bright hands an 

* Xtlatiim da SxptrUaa*, Ao. torn. iL > ClmipL S»mL l*i 8D1 . 



I'beo the bli 



) cone in tb« interior of the OaiDe U cxami 
or when tlie sulphurizwl flnme is brought od any cold surfaoe. 
This bine tint is almost always seen when a pure liydrogea 
flsiiic is brought for urn iustaut against a plecp of jioicelftiu, liiu 
blue oolour being produced, according to Ranvtt,' by the sulphur 
contained in the dust in the air. The absorption aijcctruin of 
sulphur lias been obtiuncd t^ Sitlot,^ and the emis.'ilon spectra. 
of which tlicre ara said to be two, a channeUed^paco nnd a line 
spectrum, have been mapped by PlUcker and Hiltorf," and more 
recently by Salet.' Accortliiig tg Mr. Lockytr two other spectra 
of sulphnr occur, viz., a continuous absorption in the blue, and 
a conlirmoiis nbsoqition in tliu red. The change from the 
cliann«Ued-apnce spectnun to that sliowinp absorption in the 
blue, is obwrved when the vnponr>donnty changes, tho first 
of these spectra being tlmt seen when the vapour pos^cascs 
a numial density. 

157 DittcttMi ami DeterminaUon of Sulphur. — ^Th(i simplest 
mode of detecting sulphur in a compound is to nibc the body 
with pure carbonate of soda, and fuse it before the blowpipe on 
charcoal; sodium sulphide is thus formed niid this may then 
be recognJw?^ by bringing the fused ma&s on to a tiWer coin 
and oddiug water. Tlie smalleat (|«aiitity of sulphur can tlm» 
he recognised by the formation of a brown stain of silver 
salphide. Sulphur is almost always qimntitativcly deter- 
mined 03 barium sulphate, If tho body is a sulphide, as, for 
instanc).-, pjritcs, it is finely powdered, and fused with a mixture 
of carbonate of soda and nitre, the fused ninss dissolved in 
water, and lltt; filtrate, afler acidifying by hydrochloric acid, 
precipitated wilh barium chloride, whereby the insoluble barium 
sulphate is formed, and this, aftpr washing and dr}'iny, 15 ignited 
and weighed. 

» Phn. Mtq. f41 i«t. 821. 

■ Cotnot. lUtd. tlixiv. WS. 

> Fhil. Tntm. ISaS. i. 

* Omjil. lUiid. Ixxiii. SM>, M\, 742, 71^ 


158 These elemenLs anile to fomi ot least two distinct com- 
pounds, viK., hydrogen moiiCHsolphidc or sulpbtirvttcd hydrogen. 
HjS, 8iid liydrogen pcr-sulpliide, H.Sj. 


JIjS. Dcusity = 16-S9. 

Allhougb Geber first dcscribfui the pn^paratton of milk of 
stilpliui' yet wu do not notice either in hiH worlui or in those of 
thfl later alchemists that any mentiw is uitidc of the &ct that a 
fiL>tid smell is given off in the pitKCSS. Not until we come lu 
the writers of the sixtecnlh nnd seventceuth centuries do ve tin<l 
nny description given of gulplnirctted hydrogen, and then it is 
described UDdi-r the general name of sulphurous vii[»ur<. 
Schwlc wiis the Bret to investigatu llii» compound with caie. 
He found that it coidd be formed by heating sulphur in influm- 
nifthlc air, uni] he considered that it nimt l>e made up nf 
sulphur, plilfi^i-^lon and hcat^ 

Siilphwi-etU'd hydrogen is formed when hyiirogfn gi« u passed 
thn)ugh Imiling sulphnr, or when btilpliiir vapour i» burnt in nn 
atmosphere of liYdr%'en. It also is produced in the putrefactive 
decomposition of various OTg»nic bodies (euch as atbunun) which 
ooutaiu sulphur, nnd it is to tlie pT«»Hncc of thiN .«iiti8tance that 
txttten egge owe tlieirdlsa^-reeaUo odour. Sulphurxtt^xl hydrt^a 
occurs, na has been volcanic )^os. whiUtci-rtuitimiuenil 
WBters, such as Ihoscof HatTo>^ate, contain dissolved sidphnrottcd 
hydrogen, aitdil is to tho prcscnc* of tliisgaa that tlte watcns 
owe their peculiar medicinal properties as well 113 tliuir oSensive 

Preparation. — (1) Su]phun.-lt«l hydrt^n b best preparwl by 
acting upon certain metallic sulphides with diJulo acids; 10 
general, ferrous sulphide (sulphide of iron, obtaiuiid by melt- 
ing together iron Mings and sulphur) ia eniploj'ed for this 
purpose, KetTOiis sniphi.lo. FeS. dissolvos rtadily in hydrochloric 
or in dilut« sulphuric acids, sulphuretted liydrogeu gas being 
liberated — thus : — 

FeS + H,SO, = H,S + FeSO,. 
FeS + 2HCI = n^S + TeCl, 




~' Ike appumtus sbown in Fig. 92 maj be used ; the materials 

[aie pliioed in the targe bottle and the gas which is evolved u 

[vasbed by pusiDg through water cooUiiiied in the smallor on& 

BD B regular ovolutioo of gaa for a lung pui-iod 'ui Deoilfid, the 

I apparatus, Vig. 93, is employed. The two gloss globes (a) anil (b) 

am eonnecteil by n nairow neck, whilst the tubuluB of the third 

and uppermost globe (c) paasia air-ti^ht through the uock of (i), 

I The sulphide of iron ifi placed in globe (h) and dilute sulphuric 

I acid poured through the tuhe-fiinnel untU the lowest glube is 


Fin. S3. 

Bllcd and a portion of th« acid has flowed on to the Bulphide 
of iron. 'When it is dofiirod to stop the current of gas, the stop- 
cock at («) is closed, and the acid is forged by the preeaoie 
of the gas Rccumulotiiig in the globe (6) up the lubulus into the 
uppermost globe (c). 

(2) The gaa Urns obtained i», however, never pure, innsrauch as 
the artificial ffrrou.? Bulphiile always contains some particles of 
MCtallio iron, and those coming into contact with the acid evolve 
hydrogCT gas, Hence in order to prepare pum sulphuretted 
bydrugcu, a naturally occurring ptire sulphide, viz.. antimony 
trisulphide is employed, and this Bubstanco, roughly jiowdered, 
on being warmed wiHi hydrochloric acid evolves a i^ular 
current of the pwtv gas. tliua ; — 

Sb^ + GHa = 3H^ + 2SbCl„ 



(3) Sul{>hua*tU-d h}'dty)j;en is also formed wlum 
gas is pa&$eil over certain Uvatcd auJ|}tiidL-s. Thus, if u IitUc 
poirdei-ed anliuioay tmul[tliiile l>e placed in a bulb tubu aa>l 
bested hy a flamo. and if a slov ciirroai of h^drugen be tWn 
passed over ibu huatvd snlphido, thu escajijug gi» when nJlowel 
to bubble tlirough a solution of lead acetate uitl producu bl^k 
prccipitala of Ituid sulphide thus allowing the fonnation 
sulphuretted liydrogcu. Tbu nnctiuii is Ihiu nsprcseDttxl : — 

(4) A continnoua current of sulphuretted hydrogen may 
wise Ihj oUciim^il by beating a mixture of ecjuaJ jiarl* of &ul( 
and purafiiu (a mixture of solid hydrocarbons hnving the 
peneml formula C„ H{„ + ,). By rr^ulalinj; tin; UiuiJi-mlurc to 
wbieh the iiiixtura is bcAtiKl, Ihe evrjUiUou of gna umy W wwily 
controlled. The exact uaturo of the changes which hure oecaA 
remains iis yet uii(l[it<:rinincd.' 

1^9 Properties. — Sulphuretted hydrogen obtained by any of Ibo 
above processes is a colourless, very inamiimablc gas, posscaaing 
a swuetidli tuste and a powerful and very unpleasant anHJl 
lesembling tbut of rotU.-n %'j;^ The gas iiiiiy Ut <;olli!Clt.-d over 
hot water in which it does not disstdve 90 readily as in cold. 
When a light is bnmght to the open mouth of a jar filled 
with the j-as, it bums with a pale blue flitme, the hyi 
uniting with the oxygon of the nir to form water, and 
sulphur partly buruiu^ to i^ulplmr dioxtdo (which can be i 
rt^'n};uixed by its pungent smell) and partly liein^ depoeiti 
a yellow incrustation on the inside of the jar. A nn'xtarc of 
two volumes of sulphuretted hydrogen and lIiriN- vnliunes of 
oxyjien explodes vioU'iitly vrhon an electric sj^ark ia 
through it, (ioniplete eonibnstiyn taking place. 

When inhaled, even when mixed with a conHiilrmMe vi 
of air, tJiO gns acts as a powerful poison, produciuft in!<rriMl 
and asphyxia. Troui the expnriments of ThtJnard it appearo that 
respiration in an atmosphere cnutaininj; j^ jjctrt of its volume 
of this gM, proved fiital to a Ho^j, and smaller animals die when 
only lialf the quantity is pfest^nt Tlte best antidote to poison- 
ing by sulphuretted hydro»en appenrs to he the inhalaCJoa nf 
very dilute ehlorine j.'M ft« olitniiud by wetting n tfiwel with 
dilute acetic acid and sprinkling tho inside with a few grains of 
bleaching powder. It is dissolval to u considerable extent by . 

■ CaUetl)-, Ziit. C^cni.. 1671, 23i. 



sr, ODO volume of water tbsorbing. at 0°, 4*37 volames. aad 

15% 323 roliuiiea of Uic ^'ft& The general cxpressioa for this 

loUltty of siUphuretteel hydrogen in one volume of water at 

nvnt tcnipenitUTos between T aad 43'''3 U 

c = 4 3706 - 0-083687 t + 00005213 t» 

The solution rcildcus blue litmus jiajjcr (n-hunre the name hydro- 
sulphuric acid baa Mtnetimes been j^v'en to the sobstauce) and 
posMSseA the pocnlinr smell and tiLSte of the gus. It, however, 
soon becomes luilky ou exposure to air, owiu;< to the hydrogen 
coDibimc^ with the oxygea of the air, and sulphur separates out. 
ITnder a pressnie of about seventeen ntmotiplieres snlplnirottcd 
hydrogen gas condenses to a colourless mobile lifjuid which 
lioils at — 61^8 audat — 85" freezes to an ice-like solid. Litiuid 
aulpbnietted tydrogen was first prepared in 1823 by Fiiraday, 
by nieaii-s of tbe simple benb4ube apparatus described on page 12^. 
Tr tike closed limb of tliis tube Fnradny brouglit some stroD^ 
aulpharic acid, and above it he placed some smalt lunpe of 
ferrous sulphide, takin<; care Uy Kppanite them from tlie add by 
a piece of platinum foil placed in the tube. The opeu end of 
the bent tube was then clo»e<I liermetic»lly iind the nulpliide 
ahaken down into Ibe acid. Id making experiments of this 
kind OR tlic liquifiable gases, maoy procnutions must be 
taken if ^e would avoid serious acoid(.-nts from explnsiouK 
The tnbe must be chosen of thick wcll-nuncalul ^Ihhk; the 
iDBterials used must be pure, thus if metallic iron l<v cvnlaiaed 
mixed with the sulphide, hydrogen gas will be giveu ofl* and 
the tnbe will probably burst ; and in sealing, Uie sides of the 
glass tube must be ^owed to fall together so as to form a 
strODt* end, otbcnrise tJie tube will girc way at the weakest 
point Prapered with care these ' Faraday's tabes ' will withstand 
an internal pressoio auiountiiig to many tons per square inch 
of surface, and the liquejied ^aaea may be kept in tfaem witlt 
safety for years. Litpu-fietl imlpburetted hydrogen may also be 
ptvpared by pasair''^ tbe gas into a tube cooled to about — TO' 
in a both of aolid c^ul-onk acid oud ether. 

Auotlier mode of pn-paring liriuid sulplmretted hydrogen is to 
seal ap a quantity of liquid hydrogen pcnulphide placed io one 
limb of s Faraday's tube. This body spontaneoosjy decomposes 
into solpbnietted hydrogen and free salphnr, and by degiuis the 
tesaioii at the gas inside tbo tube becomes so great as to exceed 
•evcDteen atnoepheies, under which the gas becomes a liquid. 

i6o Dft^rminaiian of eempo*itu>u. — SulpliiuvU^d hydio^ a 
decomposed when heated by itself, this decotDpasitioa ti^b<l 
nLng at as low a Umiiamturo as 400°.' Upou this tvX i 
method is biisctl for tkfi dDtcrminatioD of the compoaitioa ti 
swlphnrettt^i liydrogeiL Tliis amy be readily accompUsbed ly I 
heating Bonie metaUic tin in a ^ven volume nf the ga& T)i« tin 
docompoMS the %m, combining with the sulphur to form a solid 
sulphide, ftud setting free the hjdro^eu, which is found to occopy A 
the same volume as the ongiiial gae. ^ 

Tho same rMult is obtained wlien e spinJ of platinnm wire 
is }iea.ted to bright redness in the (juji ; aul)>hur is deposited 
in the solid fonn and the hydrogen is left, whilst dq altenttioo 
occuta in the volurne of the gas. Hence ns the specific gravity 
of the gas was found by the experimeuts of Uay-Lussac to lie 
I'l'Jl thu mokculnr wciglit i« 344, or comctin^ this number 
by the more accurate results deduced from analytical data, ira 
have 3:i*'J8. Dfdiuttni; from this the weight of two roliunct 
of liydi'Oji^n we find the weight of the sulphur contained in tbe 
molecule of sulphuretted hydrogen to be 31*98, and hence the 
fomiulft of the gas is SHj. 

i6i Uoih in the form of gm, and as a volution in water sal- 
phuretted hydrogen is largi^Iy uaed in analytical operations la 
the best means of sepiiratiiig tlie metals into various gniopi, 
inasmuch us certain of these metals when in solution as sails, 
sueli as cojipur sulpluttc, uiitimouy tridiloridc, &c.. are pr»- 
cipituted in combinatton with sulphur as insoluble sulpliidas 
when a current of this giis is passed through an acid aolat 
of the salt or mixture of fialts — thus: — ■ 

CuSO, + n^S = C«S + HsSO,. 

2SbCl, + 3H,S = SbjR, + 6HCI 

Other metallic salts are not thus precipitated because 
Bulphidca of this second frroup of uietnls are soluble in acid; 
thn? siilphnn'ttwi hydrnprn gtis deesnot cniisoa priKiipttiitcin an 
aciiiitied solution of furnms sulphate, but if the acid be ncutra-, 
Uzed by soda or ammonia, a black precipitate of iron aulpliide ii 
at once thrown down. 

FsSO^ + H^ ^- 2NaH0 = FeS + Na^O. + 2H,0. 

Again a tliird group of inctslsexists.the members of whicli art' 
* Ujvt, AaTi. Chrm. /Winw., dxit IJit, 




no ctTciiniElaiices precipitated by tbe ^as, their sulphides 
ling soluble in both acid and alkaline solutioiis. 
Many of tlio iiir^oliiUlu siilpbitles aic distinguished by n 
3uliar colour aud ajjpi'aianco so ihat suljiburettetl hydrogen 
used an a qualitativu ix-al for the prcscncB (pf certnin miitals 
as well as a meaua of separating them luto groups. 

The reaction of sulpliureUed hyilnigeji on several motnUie ealt 
soltttions may )» exhibited by means of the apparatus seen in 
JFig. 94. T!ie gas evolved in the two-necked bottle, (A) passes 


Fro. 91. 

tbrougli Uie aevei-al cylindttra, and pn^cipitates the sulphides of 
the metals whose salts have been placed in these cylinders; 
thus, B may contain wpjX-r stitpliate, G aiitiniony chloride, T> 
a solution of »nc sulphate to which acid has been added, And K 
an nmraonincal solution of the same salL 

Both as Q gas or in solution to water sulphuretted hydrogen 
dL-compnsed, as fotlowit, into hydrogen and sulphur by nearly 
I oxidising Bgents, and even by strong sulphuric acid, so that 
this acid caiuiot be used for dryin;^ tlie gaa. 

HyS + H^O, = S + 2H,0 + SO,. 

tt two cylinders, one HUed with clilorine and the other with 
salpburettA.ll bydrogc-n gas. are brought nioulli to nionlh, an 
iniinaliate fonnatJOD of the hydrochloric acid gas and deposition 
of aalphor occura. Faming nitric aoid dropped into a globe 
filled with sulphuietted bydrogtm gas, caunes decompositiou with 
ex^dosire violence. Sulphuretted hydrogen uiimediat«ly tarnishes 
iilvor vith fonnatioa of black silver sulphide ; hence it is usual 



to pH silver eggspoons to pr«v<;ut them from becoming bUck 1 
contact witli ili« sulphupatted hydrogen given off ftwn 
ttlbumin of the egg. Huiicc, t^w, silver coins become blacke 
whea carried iu ike pocket with couitnon lucifvr rautcltut. 

HvDROGES reaartPiiiDK. H^Sy 

l6s Thia substance was disoovered 1>j Sclit4:k>, and alWnrtidf 
mure completely investigated hy BcithoUet It was Gn( 
obtained in the fyrm of a yellow transparent oily liqnid 
pooling a concentrated aquuoiu eohition of penta-suli, 
of potas«imii. KjSj, into dilute hydrochloric iwid, wbm 
l!<|uid. nn Btandins, deposits the substance iu yellow dnipa 
lltncf IkTlhullut K'Uuvud that Uic subetaiico posaeeecd aa 
Biialogous rompoaition to the body from wliich it was fononL 
and ^ve it tin? r«rmula H,S^. TlK-nanl next examined U» 
compoiuid, mid he came to the conclusion that, as in nianr ef 
its propCTtice it resembled the then newly discovered liydropa 
dioxidw, tlie composition of the body would be, most pmbablj-. re- 
presented by the formula IIjS,; althouyh it may be remarked, that 
the analyses of Th<?napd ' showed that it always contiiinod laan 
sulphur than the above formula required. Ilofniaiin has r^rentl^H 
observe;!,* that when yvUow ammonium peisulphide. (XH,J, SjiP^| 
mixed Willi strychnine, a ctTBtnlline conipottnd is fornted having 
the composition C^, H-tN-P.. + I'^. sod this, wJien hi*atc<l wiib 
liydrochloric acid, yiehU oily drofus of llic pcrsulphidc which, 
theTcfore. probably has the formula H^Sy Ilarasdy ' finds tlut tbe 
compound uhtaiued by Bc^rlhollel's process contains snch vnr>'ing 
pToportiona of hydrogen and flnlpbiir as aie repreeented by the 
fonnulje H^S, and HaS„. Still more reccoUy Schmidt* has 
shown tliJit strychnine comhiues with sulphuipttwl hydrogen to 
form a befiiitiful erystalline body, but that it doea ho oulj 
presence of oxygen ; thus : — 


2C„HaNA + eiljS + 0, = (SCflTTaNjO. + SH^j) + 3H,a 

This compound yields hydrogen jwrsulphide on tuL-atiaent 
with an acid, and the substance thus obtained appears to 
identical propeitica with that prepared acconling to other un 

* <4>ia. C%im, Fhyt. xlvtii. p. Tft 
» Btr. DtMtKk Chrm. ««. i. 81. 
» CVw. Six. J"«r»., \i)K\. »7. 

* Btr. I>t*UeA Ckon. Go. riii, 1S97. 


: Tlit^uard's view would be confiiiued that, tliia compound 
:B composition aiulogous to that of kyJrogon dioxide, but 
scorns that owiii;^ lu the vase witli uMch it decomposes 
ito siilphurolU'd Ljdpugfii sn<l 3nli)hiir, it usuiiUj is found to 
tntftin AD excess of the Utter sub«tjiitoo. 
Hyiiroj,'en peraulphide is usually prepared by boiling one part. 
y weight, of slakwd lime with eixtc-eu piirts of wnter and two 
of flowcw of Bulphur, the clear cold solution being potucd 
dilute hydrochloric ucid. A UcAvy yullowish oil scparutia 
tt, sink in-; tu the bottom of the vessel It possesses an odour 
Qtlar to that of 8iilptiurotl4>d hydrogen, but more pungent, and 
vttpoiir attacks the eyes, and its tasle la very acrid and 
unpleusaot ; it« i^pccilic gravity was found to be 17542. It cannot 
be distilled even under reduced pres^ore. and at the ordinnr)' 
|«nit)er.iUire it undei^oes a stow decompoeition yielding snlpbur 
id i-vylviug nulpUuretlcd hydrogen gsa Hydrugcu jK-reulfihide 
howuver more stable in pr«flence of an acid than in that of an 
Ikali : it is easily soluble in carbon disiilphi'li), it in scarcely 
Dluble ill alcohol, and is Insoluble ia chloroform and benzinG. 
blcnchi-s orgtinic colouring nuitturs, and, tike hydrogen dioxide, 
luces the oxides of gold and silver so rapidly that it ignites 
)dliug). Tiie persulphide dissolves pbosphuni* and todiiie, 
gnidiitdly changing thcie bodies into plio«plioni8 sulphide 
and bytlriodic acid. Ou the ottu^r hand, sulphur dioxide bas 
no action on tbe pcnsulpliido, whicli, iu titia r^ftpect, differs 
Gfisentially from sulptiurettod hydrogen. 


163 Tlii-sc- elements combiuu togutlicr to fonn the follon-iag 
coiajmunds : — 

Sulphur nionocMoriUe, Sfi\^ Snlpliur didildride, SCI^ and 
Sulpbnr letracbloride, SCI4. 

SoLTUOR MunochijOKKT. S,C1j. Vapour Density = 67-36. 

Tills compound, the mo*l stable of the chlorides of sulphur, is 
obtainal m a dark yellow oily liquid by passing a cuFreut of dry 
chlorine gas over heated flowers of sulphnr. 



iVgwrafion. — An epparatas unanged for tliis pDrpo«e U 
showD in Fig. 95. T)ie sulplmr is pliiced in a n*Lon imd Uie 
chloride which distilH over is coUoclvd iii Uio cuolcd niC4.>ivur. 
Ity roetificution it cnn be oIiUidimI us b clear amber-<;'ilf)urci] 
liquid posacsaing an uDpleosaut pouclrnting wlour. hnrinf! • 
Bpunific gravity of 17055 (Kopp), and boiling at i;^8'. Tlie 
density of ita vapour is G7'35 so that the molecular wi};ht us 135, 
and thu coRipoutid contains two alorns of sttlphur iu tlie tnotc- 
culc, aud has tliu formula SXIj- When Uirawu iato water sulphur 







V\u 95. 

moDOchloride ^diiiilly di'coiiipuses with the fonuation of hydro- 
ctiloric acid, sulphurous acid aiid free sulphur — thtu :— 

2S,C1, + 2HaO = 4IIC1 -I- SO, + 3a 

Sulphur dissolves ia tbo mouochloridw so rwidity that the soTu- 
tioa fumis, at iho ordiiiftry tempftrature. a thick 8>-rupy liquid 
tumtaiiiiug (16 per cent, of siilpliur. Tliis I'ltipt-rly has betu Iarj:uly 
employed ia the arts for Uic purpose of vukaniring caoutchonc 


Chlorine gns is npidly nbsorlied when passed iiito sulphur 
monochluride at thcordJDarytemjwrutuni.aod theUiiuiduhaiigua 
colour until it finftlly assumes a dark reddish broira tiaL Wheu 
this liquid ts biuited it begins to boil at 04', but tho tliurmotnetot 

soon ri^s us tiie compQund uiiclergoos decomposition into free 
chloriiiv mid t)i« moiiochtoride which remains behind. If, how- 
ever, tho moiiocldoride bo placed in b freeKini; mixture and then 
antumted wilU dry clilorJiic:, uud tho excess of ulilorinc bo subsu- 
i)ueiit1y removed by « cunimt of dry carbonic acid gas, a lii[aid 
rcniflins which annlyfiis shows to be tho tUchlnridf,' In coin- 
biDatioQ, the dictdoride appears to be much more stable. 1* 
fomu distinct compounds with tusouic tricbloridv, thus : — 

SCI, ^VsC%CH- Rose), 
and irith etliy1en« and amylene, thus : — 

C, n, SClj. C,H„ SCI, (F. Gotbrio). 


SUUHDK Tktwchlobide. SCI, 

164 Tho existence of thia compound vras for a long fim« a 
maltor of aiiccruiiiity, but recently Jll ic-haelis • has Bhown 
that when the dichlorido is saturated with chlomie at- 22° 
the t«tTncbloricIc is formed. It forms a light inobilu yt-Uon-ish- 
browu litpUd, which at oiice bc*tiu8 to evolve chlorine wlieii 
talvt'ii onl of tlio freezing niixtnro. The decomposition of 
Iwtii of thcso bodies aei*vc9 as an excellent illuiitMitiofi 
nf diswxiatioij, which doubtlegs all cheiujcal oompounds 
undergo when tlieir tt-mpcnit ure is raist-d sufficiently high, 
although vc ard as yet unable to obtain tempcTattiivid elovated 
eiioiiyh to decompose many chemical compounds. The follow- 
ing table shows tlie composition of the liquid obtained by sntti- 
nitiug (X) tlie dichloride, and (2) tbe nionochloride of sulphur 
with chlorine at tbe given temperatures .-— 

IHs$ociation of Sulphur TetradUoridt. 

H 1 nntintT ■»<! Gai^rODt, ZeiUcAr(/l fkt Chrmi4y 167«>. 155 ; Tliortis ami DtUri, 
■ CAen. Arvx. xiIt. t». * A^%. Clm. tfumn. elxx. I. 




- 29 . . . 

IflO-O . . 

. . o-oo 

- 15 . - . 

4I-9i> . . 

. . B8-l)5 

- 10 . . . 

27-62 . . 

. . 72-38 

- T . . . 

21-97 . . 

. . 7803 

- 2 . . . 

1193 . . 

. . 88-07 

+ 07 . . . 

887 . . 

. . 91-13 

+ 6-2 . . . 

2-43 . . 

. . 07-57 


Dissoeiatwn ^ Sttlj^iur IHttUoridt. 

93-45 . 

87-22 . 
75-41 . 
66-78 . 
5406 . 
20-48 . 
19-45 . 
12-35 . 


000 . 



From tliese tul^lus it is seen Umt wliilnt a diflbreuM of 7*. 
Trout — 22 to — 15, reduces the pci'CCQtnf*e in th« am of 
SCI, from 100 to 41*95. a diftVrpncc of 10° iu the case i.f SCI, 
i-eduoes it oiily frwiu Q'i-15 to 8722, and an elevation of 100* 
does not comiiletely dissocinte tlie dichlorida Telrach bride of 
sulphur forms crj-stallized compounds with certain oielaUk 
chlorides, lUvia ;-A]s C]„ SCI, ; SnCl^ aSCl,. 


BuouncE Hiavtsawe. 


165 Brauiineand siilpliur form only a single compound, whii 
is much more unstable tlian the correspondioK chlorine coni]K>ii 
It is pictpared by diitiolving Hiilpliur iu u alight excess of bromiin-, 
and volatilizing the excess by vif&m *if a current of dry carboa 
dioxide.' BTOmiiie disulplilde is a ruby red litjuid, which 
boils at about 200°, and which hy n'pvfittfd dietillalion can \m 
decomposed completely into stilphnr and bromiufl. 


Sulphur Uoxiodidk 8,1^ 

166 'Unien snlpliur and lodino ore heated together, oven noder 

water, Ihey combine to form a hlackisli grey crystalliDc aoUd, 

* MM. PnttUan Mujr. Chetx. Sat. Jonm. (i)uu., 84S. 



ambling in iu appdarance Uie nutiva sulpliids of antimony, 
nl melting below 00". This sulfstaiice is iodine disulphide, 
The sftme body cau be obtaine<), acconliiig to Gutlmc,' 
tubular crystals by acting upon ctliyl iodide with chloriae 
lonosulphide, when etliyl chloride aud ioiliuu niODosulphidii arc 
thua : — 


A compoond of siilphtir and toiline having the above formula 
depositdd in crystals whiuh nio igomorplious xritli iodine, 
rben a solution ot iodtae aud sulphur iu cu.i'boa disulphide ia 
evaporated (LaiidoU and vom Itath). 


167 Aocordiiijii; to Davy and Dunias,' a compounil of aulphur 
[ fluorine is obtain«d by distilling lead fliioridtj «-ith niilphur ; 
leompodtionof tbe body lias, however, not yet been asceitaiiied. 
! If anlphur is brought into contact vrltb fusod fluoride of silver, 
silver snlphicle 19 formed and a heavy colourless gas ia given off, 
xvhich does not cooilcnse at 0', fHrnts in contact with air, emella 
like the chloridea of sulphur and sulphur dioxide, and etcbea 
glass (Gore). 


Oxides anu Oxyacids of Sdlphuh. 

jfi8 Sulphur fiiniis with oxygen two compounds, which belong 
.Ut tliu class of Bcid-foiiuiog oxidea, and whicb, tbeieforc, when 
ghb into contact with wator. both yield acids ; tlius : — 

Sulphur dioxide, SOj, yields Sulphurous iicid. TT^SO^. 
Ijulphur tiioxide, tiO^. yields Sulphuric acid, JI^SO^. 

In addition to those we are ac([uainted with the oxide SjO« or 

* Cktm. Soc Journ. m». 6*. » Jnn. CUm. Pi^. SI, (37, 


mitpbitr sesiiiiioxi J«, as well as Uie following oxyacub of snlpkni, 
the oorrespomliiig oxides of which aio unknown, 

Hyposiilphiirom acid .... H,SOy 

Tliiosulplniric atid H^SjO,. 

I>ithionic aoid HjSj*)^, 

Trithionic acid H,S^(\ 

Tuimthioiiic ncid h ionic sci<l 

The onincs giwn to the five Inlter acids ant dcnvoJ froai 6tm, 

Slxphur Dcoxipe. so. Density = 31-95. 

The anciuQts were Kwarc tlint whcu sulphur is burnt, puiigeiit 
acid smelling vapours are evolved. Homer mentions that ibt 
fumes i'Tom burning sulphur were pmployed as a ni«ans «t 
fumigation, and Pliny aiaU-'s Itiat they were finploycd for 
purirying ulotli. Tor a loii'^ limv it wiis tlmu|^lit thiit sulphuric 
acid was producod when sulphur was burnt, and it i.s to Stahl 
that we are jiulebted for lirst allowing that the famM of 
buniinj; sulphur are altngether diffftrenc funm sidpliuric aci<J, 
standing tu fact half way between sulphur and sulphnric aciil, 
and, tlicrL'foi'c, tcrmod, accordiiiy to the views of the litne, phlogis- 
ticHltid vitriolic acid. Pricatloy in 1775 first prppared the pair, 
substance in the i^cotis state, to M'hich the nanie of sulphiirou 
acid was afterwards given. 

Sulpimi- i« au <'a.^ily comlmsliUlw liody ; iicoordiiii* to Daltnn 
it ignites at a temperature of 200", bunuii}; in the air with a palo. 
blue flttme, and in oxygen with much greater IfrilHiincy. lu lliis 
act of combustion sulplmr dioxide Li fonimd, and I'aoh atuni of 
sulphur (ivolvfs, according to the eJCperiiiientB of Favre and 
Silbennann, 71,072 thcraiiil units. The volume of tlie sulphur 
dioxide formed is exactly enusd to that of the oxygen, as may bo 
shown by the following esperimenL 

Tlio njipitrutuH i'tii|)loyed, slionti tn Fig. 96. is similar in its 
nnangement to the syphori ^udioniotor previously described 
except that on oiio of thu liinlis a globo-sliaped bulb has 
blown, and this can be closed by a ground-glass stopper. This 
stoppiiF i* hollow, and through it are cemeotod two stout copjwr 
wiii!S; oiiH of these L-uds in a small platinum spoon, wbilet 
to tlie other a small piece of thin platinum wire in attached, ami 
this UoB on the platinum spoon. A fragment of sulphur is dtea 

placed over the thin wire in the s[«>on, ami the tiibt! having 
—^iillvcl with oxygen ^nu, aii<l the Htopiter plnced in posiLion, the 
■eulpliur is iguiled by heatiDg the wire with a cmrcnt. care being 
■token to rciluou tlic pressure wn the gas by allowinj; nitTCury to 
Ptiin out by the sto[>-UL)i, 8i> at to avoid dangur ol' cracking the 
globe. The eudiometer is then allowed to cool ngain, when it 
will be found ihal the level of tlie mercury risi^i* to tlm sAme 
point which it occupied heforo the experimpnl. Hence one 
molecule or sulphur dioxirle contains one iiiol<>cule, or 31*92 
[pans by wcifjht^ of oxytiiMi. and therefore the molecule of the 
[dioxidf, wLii^^li weight G'SdO, coutuiii:; :iI-95 parte, or one atom 
of sulphur, and its molecular formula is SO,. 


169 Preparation. — (1) Sulphur dioxide ia formed not only 
1)y the comboBtion of sulphur, bat aUo by the action of certain 
metals, euch as copper, mercury, or aUver, on concentrated 
salphuric acid ; thus : — 

Cu + 2H^, = CuSO, + 2H,0 + SO^ 

Sulphur dioxide is easily prepared for laboratory ose by 
the above reaction. For this purpose a da^k is half tilled with 
copper turnings or fine copper foil, andsomuch stron<; sulphuric 



acid pourvd iu tlial !liu cojipar is not qaite covered. The itiixtare 
is next heated uiitil the evoliition of gas coinmences ; tlie Umpl 
umt thttu be ntmovotl, as otliorvisc the reaction may usily 
becorao too violent, iiad tttt! llijiiitl frotli over. 

(2) Pure aulpliurdinxirle is also produced wlion stil|>luir an<l 
sulplmrio acid are honttd Ingcther ; thus : — 

S + 2U^0^ = 3S0, + 2H,0. 

(3) It is also formed by tlie decomposition of a sulphite. » 
cuinmercisl sodium salpiiil'C, whicli, viUvn tn:alvd wild 
dilute gulpliuric acid, easily evolves the gas ; thus : — 

jCogSO, + H,SO^ = N*a,SO. + n,0 + SO, 

(4) Sulphui- dioxidc! is ni^e on tliti Inr^ scale for the prepara 
tion of the sulphites, e-ipecially of flotlittin suljiliitc anJ calciuia 
sulphite, which are obtaiocd by pnssing tliu ^hs c-ither into a\ 
solution of caustic sodn or into tnilk of lime. Fur this pur^xwe 
ulmreoal is licatad loiielher with sulphuric acid, when carbon 
dioxide is cvolveil, toavtlicr with .sniphur dioxide; but the 
presence of the former compound for the purpose above tucn tionetl 
is not detrimental ; thus : — 



C + 2UaS0, = 2H3O + COj + 2S0^ 

(5) Sulphur dioxide in used in enonnous qunntitics for tlti 
uuuiufacture of sul^jhuric acid. For this purpase it is chiefly 
obtaiimd by roasting pyrites. Wh«n, liowover, perfectly pure 
sulphuric acid is needed, the dioxide is prepanMl by bumin; 
pure sulphur. 

170 I'ropertifs. — Sulphur dioxide is a colourless ffoa, w 
occurs in nature in certain volcanic emanations, as well u in solu- 
tion in volcanic spriu;,^). It posscsst^s the well-known suflocatins 
smell of burning sulphur. Its specific gravity is 3*2 i\26; and U 
can, therefore, be collected by downward displacement like 
chlorine. If, however, the f^nts is required to be purfwtly free foun 
air, it must be collected over mercury. Sulphur dioxi<le does Dot 
support the combustion of carbon -containing material, and a 
buming candle isexlinguishcd when pluuyt-d into the gas. Cevlaio 
motals, however, take lire when they are healed in the gas; 
tbni), pi>ta.««ium forms the thiosulphate and sulphite, nnd tin and 
finely divided metallic iron are changed partly into sulpliide and 
pnrtly into oxide; Io»d dioxidei, PbO^ ignites when plunged into 
the gas and loses its hruwn colour, with formation of white lead 


Bnllihate. PUSO^ Salpbnr dioxide is easily soluble in vmter, M 
ia seeo frnna tbe follovti^ table:'— 

1 ToL at wiur 

79789 vols 
:ja-37-t . , 
1876ti . 

lT(k). «rilKnhili«B 

eodWitt SO^ 

688fil voU. 


solntion of the gas saturated at O' <lt<i>03its a cTyatalltne 
hvdrate which melU at a temperature of lixini 1° lo 2' without 
evolution of the ^m, and which prolxihly poaseaws the fonaultt 
H>0, + l-tH.O. Tlie solution of the dioxide bus a elrongly 
ucid reaction, and thereToro reddens blue litmus paper, wtiicli the 
pcrfvctlj drr gas does not, as the dioxide only forms sulphurous 
acid, HjSO, by union with water. 

Sulphur dicixidr coiuIl-iisi:^ to n mobile Itt^uid when exposed 
10 pressore or cold. This liquid boila at - 8',* iu vnpour at (►*, 
hn\-iDg ft tension of 1-16506 meteni of mcpciwy. The condcusa- 
tioa of this gnji liy pressure can easily be shown. For this pur- 
pose an c^diDaiy bnt strong glasB tube 2U mm. in diameter amy 
be used; this is drawn out to a point at on6 end, whiUt into the 
other end fits a greased caoutchouc plug', tisten«d on to an iron 
rod. Tbotulx; having bu«n filled with tliodiygnsbydispIacemeDt, 
the p!un;;er is inserted, and the f;as forcibly compressed ; M-lion 
the i»!iiiit;pr has been drivi-n down st» that tlie gas occupies about 
one-fifth of its original hulk, drops of the liquid are seen to form 
nnd to oollect in the ilrawn-out point. At a tempei-ature above 
tiq biiiliug jioint. liquid sul{'1iur dioxide evnpoiales quiddy, 
absorbing vauvli lieut. the tcwvcnitiiro sinkiiiy to — SO* if a 
<{uiclc stream of air he driven throu(jh the liquid. If the liquid 
lie placed uudor the receiver of an aip-pnnip find the air rapidly 
intlidrawn, evaporotiun Uikes place tv quickly lutd so much heat 
it absorbed that a |(Ortion of the li<jiiid freezes to a white snow- 
like miiss. The formation of the solid may also Iw obserwd in 
tbe condeneinj* lube when the phin^n^r is quickly drawn out 
again. According to Pierro its Hjiicitic gmvity at - 20*5* is 
l'49n,nnd it diiLsnlves iodine, sulphur, phosphonis, resins, and 
many other substances which are insoluble in water. 

In order tft prepare liquid s«l|iliHr dioxide in larger quantity, 
the apparatus Fiy. 1'7 is u-tyd. Tlie gaa ev<ilve<l by the action of 

> BnntM uwl ScJiMifcM, Jmn. CSkm. i%irm. xct. 2. 
• PWrw, G)mp(. Jtfd. Ixx. «& 




salpliuric iwid on coppur is purified by passing tUrougli llie vuli 
battle, and adurwanls passes tUroti;j:U Ibu sfiiml ^Isss tiit«. 
sittTounded \>y a freezing miKlurc of ice auil aolt Xbe liijuij 
M-liicli coadeoses and falls into the flask placed beDcatli nu; 
bu prvftcrveii by scaling tlie flask hermetically vbere the itedc 



l''io. 1)7. 

lias been drawn out. It nuy also bo preservod in gllM t&l 
provided with wolL-dosing glass stop])ers, the constraction 
one of which is seen in Fig. 9ft. 

SiUphur dioxide both in the gft.qeoii3 state and io aqneo' 
solution exerli; a bleaching actioaon rcgetobl 
colouring luiiLtors. This fact vas known 
Paracelsus, and it is stiU made UBa of in the 
arts frtr bleacliing ailk, wool, and straw 
lunloi-iiils, which aio destroyed by chlonKP. 
The decoloriiiini; action of sulf^ur dioxide 
depends upon its oxidation in presenro of 
water with fommtion of sml[ihunc acid, the 
hydrogen which is liberated uniting with 
t!i3 colouring nutter to form a colourless body ; thus : — 

SO, + 2H,0 = H,SO. + U, 

Fio. W. 




IDS the Ueactiiag action of this snbstaoce is a ivducing one, 
rhiUt tlmt of oUoctne is an oxidizin); oue. Tlie colouring tuatl«i' 
llbtu destroyed "by ble«chin<j wiUi sulphur tlioxido may often bo 
jlT-sioKd wheu the clcitli ik exposed lo ttie air, as in tim case of 
[liueD marked with Truit stains, or wb«n brouglit in contact with 
alkali, aa ubvii l>K-iii;lii'(l tluniicl t« firet wftj«Iied with so^p 
e reducing ticlioti <>f su){itiur dioxide Is ahu timde use of iii the 
paper tuaDiifftcture, in order to get rid of tliL* vxcvss of chlorinu 
left in the pulp after bleacliinj;, when (he following dccorapoaition 
tjikes place: — 

S0( + c'l, + sHjO = H,so, + 2na 

Sulphur dioxide ia olao a jiuwvrful antiseptic, and hns ht^n 
aoocessfully employed for preveiilinj^ the putrefaction of moat, 
na vt'W aa to sto}^ fermeutation. It is usc<) in the atilphuring of 
vriuc. and serves as a valuable disiuft-cting ageut 

Sulpliur dioxide has buea shown by TyudiUl to undt-rgo a 
remarkable decomposition whtui exi>03e<I bo light. If a beam of 
sunlight be passed through a long tube tilled villi the colour- 
less gas a white cloud is seen to nmke its np^KNmncu, and tins 
coneistfl of finely di^iili'd parlicles of sulphur and siil|'hnr ti-1- 
oxide, which are scpuralcd by the clicinical action uf the tight. 
The gas is also slowly deconipoiied, when a series of electric 
siuirks Aie pasaed through it, into sulphur and sulphur triuxidi;. 
but this decomposition ccosca when u ccHnin (|uaulily uf the 
latt«r compound is fornivd, and cnn only be carried fully out 
when the trioxide is removed by allowing it to dissolve in strong 
sulphuric acid. 

In ord«r to d«t<;ct sulphnr lUoxidu some pnpcr steeped in a 
solution of potassium iodntc and elai-Rh is brought in tlia gas; 
Uiis will at oiico tic turned blue by the formation of the iudidu 
of etarch, if even only traces of the gas he present, iodine buing 
libemted, as is shown by the following reaction: — 

aKiO, + 5S0, + 4U,0 = Ij + 2KnS0^ -r 3irjS0^ 

exce^ of sulphurous acid however will bleach the blue paper 
in with foruiatian of hydriodtc acid ; thu» : — 

I, + SO, + aiijO = 2m + HjSo,. 

This last reaction serves as an excellent means of detcmiiuiag 
the ([uaiitity of sulphur dioxide present in solution. For this 
purpose a stnall quautJly of starch paste ie added to the sohition. 



and tlicn a slundnj-U solutiuu of iodine is added liy nimiu of i 
burette to ttis euluUuii miLil h penuiineut Uue colour from ti» 
fonnntiDD of iodide of stiirch is uljserved. It is, Iiowe^ur, to m 
borne in mind that the above reaction does not take place tutloi 
ihc solutions nri: suflWicntly dUute, for in conceotrated •olutioo 
sul|)buric ucid and bydriodiu acid mutually deoonpCMt^ famii^^ 
frao iiMlini; sulphuroua acid and walur ; thus : — 

2111 + IIjSO, = 1, 4 IIjSOj + H,0. 

Bunsen. wbu has investigated thiJi subject thoronghly, finb, 
that aqueous siilpliitrous acid can only b« completely oxidiioi to 
sulphiirii; ticidby meauaof iodine, w1i«n the proportion of sul{<bui 
dioxide docs not exceed OlM to 005 per c«nt of tlie solutioa 
A sttiii'knl eottittoTi of eiilphurous ncid may, nf course, tiaty be 
iiiied for tb« quantitative detenuinatiOD of iodine, and Bunsai 
baa made use of lliia reaction for the foundation of a guit-ral 
voltimetric method. The principle of this method depends on 
the fact that a quantity of iodine, equivalent to that of tli* 
sulistoitcc under examination, is liberat«d, and the qunntitr o\ 
this iodine is determined voliimotrically by s dilute soIutiuD iif 
gulphnrous acid.* 


ScLpuraous AciP. Il^a 

171 Thia sabstftiicp, liki- many other acids whose coi 
anhydrides are gnseouH, is only known in ni^ucous sohition. 
solution stiidls and tosles like the gas and has a strongly 
reaction. Exposed to the liylit it i:< ilwoni posed with forniatioij 
uf peiitathionic acid. Sulphurous iioid differs from tlio aoi 
wliioh have hithei-lo been deseri1>ed, itiaiimuch as it contains ti 
atoms of hydrogen both of which may l»e rvpluccd by metall 
It is therefore termed a (tUtask ar.iil ; it forma two series of <ialt 
termed sulphites, in one of which only Iialf of the liydrojien 
replaced by 0. motul and which may therefore Iw considered 
being a tuilt and n monobasic acid, another in which tlio whola? 
of the h)-dro|:;eD of tlie acid has b«en rt^placed by a metal. Tbe 
first series of salts are termed aci^.svlphUc* and the latter twmo/ 

1 CAflK, Sac Jtvr.. vUL 210. 

The acid sulpliil«8 of potassium and sodium aro obtained by 
passing sulphur dioxide gas into caustic soda or cnuslic yot»sh 
as long as it is absorbed. If. tlit-n, exactly the saine ijuantity of 
alkali is ailded to this solntion as vas originally ^kt-u for the 
preparaUou, the normul salts nru obliiiuud. All tho sulphites of 
the alkali metals are ensily Holuble in vater, tlte normal sulpliitos 
of the Other metals being' either difticultly soluble or insoluhin 
in wat^r. Thry dwsolve however in atiueoua siUphumns acid 
and exist in such a twiution as acid raIi.'*, buL on eviijionilion Uitty 
decompose with formation of the normal salt and sulphurous 
acid. The satphilcs liave uo odour, and tliose which am »olubl» 
' in wat«r pouoss n shiirp tast«. Thtj are readily detected by tbo 
fact that when they are mixed with diiiit« sulphuric ncUl they Riv« 
off a Hmi-ll nf sulphur dioxide and also tliat their neutral solutiooH 
give a precipitate with barium chluritle which i-t solublu in dilute 
hydrochloric neid, whereas if uitrie acid be added to this soIutioD 
and the mixtui-e wurnicd, a jireoipitiiic of Ixirtuiii sulphate is 
Itirowti down. 

Tmo^•YL CuLORiDK. SOClj. Vapour Density fi03-t 

172 All oxy-acids and many othiT eoiDpoiindB cuutain tlis 
group IJJl, which is a monad radicle, known by thu nnuio of 
hydroxj'L It is thus termed because it ia cai>iibtc of tnkinf; Uio 
place of monad olomnnb such na ohlorine and hmniine, and tit 
ita compounds may be replaced by other monad eli^ments. If 
tho hydroxyl of an acid be rcplaoe<l by chlorine an acid cldoridv 
ia obtained. The chlorideof au]phuroii«)acid.or thionyl chloride, 
has been ubtaiue^l by Uio actiou of phosphorus peiitacliloridt: ou 
sodium sulphite (Canus) ; thus : — 

Tliionyl chloridt* is also obtained by passing sulphur dioiiJe i 
jicntacliloride of phosphorus (Schiffj ; tbns : — 

sOj + PCI, = so { ^' + POClr 

It may likewiioo be prepared by tbe direct union of sulphur tui 
rblorine monoxide (Wutlx). 

It is a cnloiirK-s? bi;;1ily refractive pim^^nt liiiuiil wLtdi fat 
nn exposure In air. Jt boils nt 78" and bfts & specific gravity i 
0° of 1'675. Like all otb«r acid cidoridea. n-licu brought nj 
contact with \ral?r it dpconiposes iuto its corrcspoDding 
and hydrochloric ncid ; thus: — 

§0 { ^[ + 2H,0 - S0| 22 + 2Ha 



173 Tlxis compouud wns discovered by SchiiUenbcpger ' utd 
called by him hydi-osulphurous acid. Jt is obtained l«j* 
action of metallic iron or zinc on .fulphurotij ncid coDtJuii«d t 
closed vossol ; uo evolution uf hydiu^en Uikes place in tJiis 
OS Uie g,as at once combiner iii the nnscent condition with 
oxygen to form wntor, hyposulplnirous (or hydrosulpliurou*) nctd 
being formed ; llius : — 

HjSOj + Ug = HjSO, + H,0. 

A deep yellow-cotonrcd liijuid is thus obtained, pi 
powerful reducing properties. It bleaches organic colonii 
matter more quickly thiin sulpbutoiis (icid, and precipitates t 
uictala silver and mercury from solutions of their soluble tai 
thus: — 

HgCl, 4 H,SO, + K,0 = Hg 4 2HCI + H^SO^ 

TheBodium salt of hyposiilphnroHs acid, or sodium hyposnlphr 
XaHSO,, is obtained by the ncLinn of zinc on a solutiou of bci^ 
sodium sulphite, and the liquid, which is contained in a well- 
clostrii buttle ia kepi ^^uU couk-d by cold water. The foUo%-ing 
is the reaction which tukes placo : — 

SNaHSOj + Zu = NaHSO, + ^X SO, 4 ZnSO, 4 H,( 

T1]e greater portion of the normal sodium sulphite crystal 

> CemfU* B<nJia, Uix. IW. 


It toj^tber with the ziac milpliile os a doablo salt. A smaJl 

quantity, however, rumaiiis rUII ui solution. Iii order LOmmave 

tliL' mutlier liquor cuntaining the hy(>oaiilpLite is poured ofT 

Eioto a lliuk and tlir\,t) ur four UnuM its bulk of strong utcoliol 

I added ; tJi« ulcoliolic solution, ou standiiig well corked, deposits 

la second crop of crystals of zinc-sodium sulphite, snd the supei^ 

[ualaiit li'juid ou ngaiit being poiircti ofT into a well-stoppered 

mask, cvystiiWizeB into a niiiss of colourless crystals of the liypo- 

sulpliilc wtiidi only iiui'ils to he prcss('<I hetweun hloUing jtnjH^r ui 

l>etvs'eeii a cloth and dried in n vacuura. The salt, hovr<:vuT, 

still contains small qnantitics of tho sinc-sodiittn douhio salt 

which must he supanilwl by a frcsli crystallizEtiou. 

Sodium hyposulphite is also formed when a current of 
palvunic electricity is pu^sc-d through a solution of acid goditini 
sulphite, the hydrojieti, which is evolved at tlic uesativo pole, 
simply ahKtractiug froiu tbo salt cue atom of oxygen. Sodium 
bypostilphite is employed by the dyer and oalico-prinler for the 
reduction of indigo, aa it possesses the same retiiicing properties 
as the free acid. In thv moist «tote or lu auliiljuii when exposed 
to the air it absorbs oxygen quickly and changes at once 
into the acid sodium sulphite, 'i'lie aqueous Kolulion dfcomposes 
even when Dot exi>0!«ud to the uir, with the formation of sodium 
thimulphfttc : thus: — 

2NaIIS0, = n,0 -f Ko^.Oy 

In order to prepare hypoaulphurous ncid a clilut« solutiou 

P of oxalic acid its added to n solution of a hypustilphile; a 
yellow liquid ia then ohlained which soon decoinposca, thioaul- 
phuric acid Itfing fortiied. and this h(>ing very unstable decom- 

I poses into sulphur and eidpbur dioAide. 
(1) 2ii,so, = n,s,Oa + n,o. 
<2) H^,0, = so, + S + H,0. 
Tha ease wilh which liyposulphurou* acid undergoes decompo- 
sition accounts for the fact that the existence of this compound 
, has been so lonj; overlooked. lierthollet showed so long ago m 
1769 that iron dissolves ia aqueous sulphurous acid without any 

I evolution of gas. and f oarcroy and Vauqaelin found in 1798 
that zinc and tin also act in a simitar manner. Tliat a lower 
product of oxidation of aiilphiu' is thus formed was even then 
known, but op to tho time of Schutzunberger's discovery it was 
euppused that the piXKluct of the reaction was ItiioBulphuric acid. 



SpU'UUR Thioxidk. so,. A'apoiir Dwisity = 39-91 

174 This body, which is also called sulphuriu atibydri<I«, ua 
ibniierly was terOMMl nnhydmus suljilmric acid, b fyrmwl *l«i 
k nuxturu of sulphur dioxide and oxygen is passed ov»r bealtd 
pUtiiiiuu-itponge. In place of part: pltttitiuiii-i<ponge. plittitiiftd 
ubeetos may he employed ; Ihis is obtained by dipping aoDu 
ignited asbestos iotoatoleiably coiiotut rated »olu(ioo of plt^imun 
chloride and then bringii^ it into fl solution of sul-ammooiac. 
The iusolable double chloride of platimun and auuuooiua. 

VtC\ 2(NH,C!), is deposited on the threads of the asbceU)*, ttifl 
when ia hag been dried and ignited this compound is conv«1«d 
into finoly divided platinum. 

tn order to show the oxidntion of anlphur dioxide to the 
trioxidc the apparatus Fig. 99 mny bo cmployod, .SulphVH 
dioxide ia evolved iu the flask (a) and is nuxcd in tho wash- 
bottle which contains strong sulphuric acid, with the oxygen from 
D giiA-holder coming in through the tube (fr). The mixture n^xl 
passes throiij;]! the cylinder (r) containing pumice-atone soaked 
in strong siilphnric avid iu order to remove I'vpry tmvo of 
moisture, and then passes at (0 over the platinized asbeato& 
As long H3 thin is not heated no change is oliHcn'cd ; so sooi 
however, as it U gently ignited dense white fumes of the 





oxide are formed whicli condense hi a reoeiver {d) oooted by • 
froeziog inixnii-e in the form of loii^ white needles, la ot^er 
to obtniu Uiesc ct^suUs, every portion of tits apiiaratiis must be 
abeotutely dry ; if even » trace of moistiii'e be ]tres«iit tJi« needles 
dj^appeftr at ouw., liijuiti »iilplmric ucid bt-iii-i foniic^d. \V6hler 
hu aIiowh thnt instead of plaiiiiuiu, curtain metallic oxides, suob 
as copper oxiilc, ferric oxide, and chromic oxidp, may be used, 

A much more convenient process for preparing sulphur trioxide 
than the above is by the <Ii»tilIatioa of lumiiig oil of viiriol. 
TIiU sulMtaiice, sometintc« colled KortlbauB(>n sulphuric acid, 
consists of a solution of the trioxide in sulphuriu acid, and is 
obtained by tlic dialilluLion of heated ferroUB eiilpbate. Basil 
Vnleiitine meutioRB that by this process a " philo»ophictil salt " 
can be obtained, but the prfpomtiou of the " sal volatile olei 
vUrioli " from fuming acid waa first described Tjy Biiriihardt in 
th« year 1775. 

In onler to prepare the trioxide, the fnming acid must 
i;ently heated in a retort, and the trioxide ctrllected in a 
-cooled and perfectly dry receiver, when it colktct« in the 
form of \owA trausparent needlee. Sul|ihur trioxide u also 

B obtaiiietl by heating concentiated sulphuric acid with phospfaome 

H pentoxide ; thus : — 

K, + r.Oj = SO3 + 2HP0,. 

B*Tbe siuno sulMtanoc con bo obtained in sevenil other vays, for 

H instance by healing dry antimony sulphate. 

H /VtiprttiM,— Sulphur trioxide forms transparent prisms whioli 

I melt At W and solidify at the same teniperatnre. The melted 

f trioxide often lemains for a considerable length of time in tlie 

liquid state at a temperature btil^w it^ ordinary point of solidi- 

lication, but on i^ttatioii it at once solidities, the temperature 

rising to 16'. The liquid trioxide baa a specific gravity of 1-97 

at 20", and boils at 44)"; it.i (xK-fHcicnt of ozpansion between 

25° and 40" ia 00027, a number whiub is much higher tlian that 

onlioarily obaurved for Itiiuid bodies aud amounting to nearly 

Itbree-fourths of the coefficient of the gases. 
A second inoditication of the trioxide is obliiiucd when the 
melted moss is allowed to stand at a temperature bulow So", 
being then truusformcil into a luiuts of silky needlca which 
do not melt below 5U° When these silky needles are melted 
they nnder,^ a cliange into the first modification^ The 

* ScbultfrSelhdc. Btt. JkuOtA. Cktm. Go. ill. 216. 



second modiftcatioD of the trioxiclc can be kneaded l^etvpeeD 
dDgera, and doeo not redden litmus pnper. 

Sulphur trioxide absorbs iDoi&turo readily from ilie atmrnpl 
and «voIvca dense white fuiaca iu tht- uir. Thrivv-n into maUa 
it diftsnlvea with a hissing Bound, forming sulphuric ticid taA 
Gvnlvinft n large amount of lient, Whon bmught inlii (ontact 
with auliydrous baryta, BaO, a combinalioii with formalion c( 
barium sulphate, BaSO^ occurs with Eucb force that Ihe inasi 
beoome-s red hot. 

If the vapour of sol|)hur trioxide is led tbrougli s red bat 
porculuin tube it is dccotupoNcd into two volumes of salithnr 
dioxide iirid one vulaiue of oxy^ii. This fact indicates that the 
fornnilH of tlie iiubfltaiiCQ is SO,, aiid thus voacludLou is bon^tt 
by the vapour density. 

SQLPiraR SisQtnoxrDP. 8,0, 

i^j So long agu ns the year I80-I: Ituchbolz foiiiii] that wlm 
sulphur is heated with fuming sulphunu acid an inteiiMly hloe- 
colomed solution is fonned. and in the VRnr laia V. C. Vog(l_ 
shi>H*cd that this Iduu body is also protlticwd by the urtioa 
sulphur on eulphiir trioxide. In later ycian this subject 
freiiuc'iitly iittrncLL^d ttic attention of chi^inisls, bat the natiue i 
the blue siiliatanco remained unexplained until R. Weber* quite 
rccL-nlly showed that it consists of a now oxide of Hulphitr. 

In order to pn-pnre this substance, carefully drii^ii flowers i 
sulphur are added, in small r[iinntiti««, to recently prepiircl and 
liijuid sulphur trioxide, n ftvah quantity of sulphur only b*ing 
luldrd when that alreudy pn'-smit has enlcn-d intocombinatioa. In 
order to moderate the reaction, the test-tube in wluch the eolntioa 
is luiule must be plnced in v/nXcr at a temperature of fmni 12' to 
lo". Tbeaulphuron fulling into Ihe trioxide dissolves in the 
form of blue drops which sink down to ihc bottom of die leet- 
tul>e and then solidify. A<t snon as a sulTicient (quantity of tbis 
substance has been foruted, the supernatant siilphnr trioxide is 
poured off and Ibc residue removed fironi the tatt-tube by very 
gently warming it 

Sulphur sesquioxide forms btuLsb-grcea crj'stAlHiw cnista, in_ 
colour closely resombliogmnlacluteL At the ordinary 

< Pvyg. Ann. dvL flSL 



tin/ K't u^M^ m* J 




it slowly decomposer into sulphur dioxide and froe sn][ihur, and 
this decomposition takes place more readily wheu tlic Kubstance 
is wfiirmcil ; thus ; — 

2S,0, = 3S0, + S. 

This compound dissolves in fuming sulphuric acid, giving rise to 
a blue solutiou which ou the atiditJon of cmutnon t^ulphunc acid 
gradually chnugea to a. brovni. Water decoiupi>H(;s thn Bewjui- 
oxide with the separation of sulphur ami tlif funiintioD of 
salphuric acid, sulptmrous acid, snd thiosulphutic acid. 

SfLPiiuBii; Acid. llJiO^. 

176 Sulphuric acid is, without doubt, lh« most important and 
u.-wful acid known, m by its meana nearly all the other acids aro 
prepared, whiUt it^ lonnufacture coDslitutcs one of tlie most 
im{wrt»iit brandica of luocluru iudurttry owin^ to tli« great 
variety of purposes for which it is needed, as there is scarcely 
an ait or a trade in which in some form or other it is not 
employed. It is niAnufactured ou an oiinniioiia scale, uo less 
than 85O.000 tons being at present annually prodnct-d in Oveat 
Britain, and Uiis production is undergoing constant iiicreusc. 

It appeurs prohuhle that Geher \viisac(|unititL'd willi sulphuric, 
or. as it was foimcrly called, vitriolic acid, in iui imjuire Rtat« ; 
buC Basil Valentine -was the first fully to descrilje the pre])ani- 
iion of this aoiJ frtim grwii vitriol or ferrous sulphate, and 
to explain that when sulphur is burnt with saitpettv a peculiar 
acid i» formed. 

Originally, sulpluiric (wid wm obtained exclusively W 
heating RTcen vitriol according to a decoinpositioii which ve 
shall study hereafter. The present method of prcpuriii;^ the 
acid is Baid to liavo been introduced into England from the 
Continent by Cornclina Drobbel. but the first positive infor- 
mation wMcli w(f possess on tlie subject is that & patent for 
Uie maaulacturtt of >^tilphuric acid was grantidto atpiuck doctor 
of Uie name of Wanl.' For this maniifnclure he employed glass 
globes of about 40 to oO gallons in capacity ; a small quantity 
ofwal^r havin;; been poured into tins (jloW, u stoneware pot was 
inti-odiieed, and on to this a rcd-tiot iron ladle was placed. A 
mixture of sulphur aud saltpetre woji then thrown iu to thia 

■ Sa Jfauit't £tiihiiUwy Laid Optn, ITCS, luCro. f. U. 




ladle, and Ihe vessel cloe«J in oid«r to prevent t]ie eacape of tlw 
vapours whicli were (•volved. Tliese va[iotm{ were ahiorbtd bjr 
the Tfttcr, and t-lius sulphuric acid was fonued. This product, tna 
tbe Diode of its tiianufacliiT<<, was tenned oil of ritriol madebjr 
the bell, aseoiitradiistingiiislied from that made from green ritiiol. 
and it cost from Is. Gd. to '^s. (m/, per lb. 

Dr. Fioeliuck of Birmingham -k&s the first to sugigest a gmi 
improTemeut. iu the use, instead of glass globes, of leuten 
chambers, whicli could bo constructed of any wislied-for sist 
Huch leaden chambers were llntt erected in Dtrmiu{;hatn in 1746, 
and iu the year 1749, at I^restonpans iu Scotland. The mode of 
working this chuinbcr wiis bitnJkr to that adopteil with the j^las 
glolies; the ch^irge of sulphur and nitre was placed \rilhiu tb« 
chajnbcr, ignited, and the dnor cloeied. After the lapse of t 
certain time, wlien the (;:reater portion of the ^ases had been 
absorbed by tlie water in the chamber, the door was opened, tli« 
reroftiiiiiig gases allowed to escape, and the cbataber chargctl 

177 The leaden chambers first set up were only six feetsqonre; 
and for mnnyyeani thi^-y d id not exceed ten feet sqnare.but iu ih&sa 
all tbe acid employed iu the country was inanufactumd, whibt 
much was exported to the Coutinont, where the chamber aoid still 
goes by the name of Gujiiish sniphuric acid. The first vitrinl 
works in tlie iieighbmidtnnd of London were erected at Baltcnea 
iu the year 1772, by Messrs. Kin^oteaad Walker, and in 17S3 
A CDUDeotioii of the above tirm established works at Eceles, near 
Manchester. This imuiufucloty, tltu first erected in Lnncashtn, 
contained four chambers, each twelve feeit square^ niid Fuitr otbois, 
each of whiuli was forty-five feet long and ten feot wide. 

In the year 1788 a great stimulus was given to the manufncturrt 
of sulphnrio acid by Eerthollet's applicatJoa of chlorine, dis- 
covered by Seheele in 1774, tolhebloacliini'of cotton Rootla, and. 
from that time to the present, Ibc demand bjis gradually extended 
until it lina become enormous and «lino»t unlimited in extent. 

The ncvt improvement in the maniifiictiirc consisted in making 
the process continuous. The foundations of this mode nf 
manufncturo appear to have 1>een laid by Chaptal, and the 
principle employed hy him is that which is at the present day in 
use. Tlie iwprovemeuts thiw proposed were (I) the introduction 
of steam into tho chanibor instuad of water, (2) tbe continuous 
conibuation of the sulphur in a burner built outside the cbaml>er. 
(3) sending the nitroos fumes from tbe decompositioa of nitre 


in a Bepamt« vessvl, oIoDg with the sulphur dioxide goa 
«r tnui th« chamber. 
17B The theory, so Tar is W6 yet understand it.,' of the 
formattnn i>f sulphuric acid in the Icailcn chamlter may be 
simply expnissed hy Eayiug that although sulphur dioxido hi 
prcs«uc« of water or steam is nnable rapidly to absorb atmo- 
pherio oxy<!i'ti, it is able to laka up ox>^cu from such oxidea 

of nitiogen, as N^O, or NO^ If, therefore, thvae oxidea are 
cnt in the chanibur they give up part of their oxjrgvn to 
lh(f sulphur dioxide, aod are reduced to Ditric oxide, NO. 
This is, howcvvr, able to absorb free oxygeu, mid is at oiioc 

■ reconverted into N^O, or NO^ This couliuuous reacLion may 

■ be represented as follows : — 

r oxT: 

(1) NO, + SO. + n,0 = IlySO, + NO. 

(2) NO + O = NOy 

It is thus clear tiiat nitrous fuutes uci us a carrier between tiia 
oxygen of the air and tbo sulphur dioxide, eo that, theoretically, 
an infinitely ERDall quantity of tliese fumes vill suHice to cauiM> 
t he combination of an infinitely liirge quantity of sulphur dioxide, 
oxygen, mid water to funii siilpIiuHo acid. 

Practically, however, this is not the case, because imtead of 
pure uxj'goQ, air muni be used, and four-finJis of this consists of 
nitrogen, which so dilutes the other giifie» that in order to obtain 
th« neoMsary action h oonsidcnible quantity of these oxides of 
uitro<;f!u must be added. IJesides this uitrogen has to be 
constantly rDmvv<>d from the clianibcrx, and iu its passa^ 
carries much of the Ditnsus fuiues away witli it. altltough must 
of these latter can, aa we shall see, be rcooverud and used 
over oj^D. 

The above decompoisitioii cau be illustrated on the small scale 
by the apparaltis shown in Fig. 100, iu which sulphur oonlaiuetl 
in tho bulb-tube is allowed to burn in a etream of air, 
supplied from the double aspirator ; the sulphur dioxide aod 
Dit puss llirough till! wide (;lius tube iulo the laij^e glass globe, 
but cany iu ou tbi-ir way tin- mtrous fuiiiiui giriieraled in tlio 
small ftask (o), from nitre and sulphuric seid. The flask {b) 
contains boiling vater. from which steam parses into the globe. 
The oaileb tube (e) of the ^lobe communicates with a draft By 

■ 1 P«1)R<«, ISti, Jhh.CJl Phgt. [3] xiL ita. 

E. Welwr. 18fla. Ptn Ann 


tbe foTumla HSO, (KO^, aod ita ronoatlon Is Qxplaiued oa 
foUovg : — 

SSO, + H,0 + y,0, + 0, = 2HS0,(NOj). 


d aa , 

When ftqiieoiis vapour is a^lmittvd, tli« crjstals dissolve with 
formation of sulpliuric aciU aud ruddy fumes; Ujus: — 

179 1^6 Icadea chambers for the munuractnre of snlphoria 

ooKsraucTioN or tus leauen ciuubebs. 


iROW {XSfstracted of a ronch larger siifl than "Wiis formerly 
riUd inri'ttequciitly 30 un^tvn in leiigib, G lo 7 nitttei^ in 
brcuilth, mkI about o mvusn in b«igbt, aixJ having therefore a 
capacity of from 900 to ] ,000 cubic meter* (atout 38.0DI) cubic 
feel). Tlie cbambcrs ore made of Kht-ct lead weighing 35 kilos 
per equaro meter (or 7 Iba. to the square foot], aad Holdered 
together by melting the edges of tlio two «(ljau«nt shcetA by 
means of the oxyhyHmgen blow-pipe. The leaden chamber is 
auppurtvd by a woodea Inimework to wtuvh the l<»idca sheets 

Fw. 101. 

are attached by stiaps of the same metal, and Uje wooden frame- 
work is generally raised iToni the ground on pillare of brick or 
iroQ nnd the whole erection protected from the weather, ^nietiniea 
by a roof, but at any rale by boardiuj* to keep off most of the 
nun. The spiice below the cbftiiiljer ia used either for the sulphur 
banters or for the conceiitrntinp; pans. 

The geneml appearance or biid's*eye view of a sulphuric acid 
chamber in nbowii in Fig. 101, whilst the nn'angeiiiciit and cou- 
stmction of one of the most complete forms of sulphuric acid 
plaut now lu uac in this couutr}' h shown ia Figs. 102, 103, and 



slanting so aj to enable the min to nn off into guUcm pbtMd to 
receive it 

i8o Ite;;innin!^ at the first part of the process wo tiui Hi 
l>vnU-8-kil»s. or burners i^nctd acroas Ihc cnda of the chamber 
lis seen in plan at A, Fi^. 102. in longitudinal sectjou and in elerv 
ttonatA, Fit;, l^- &n<l in cross »ectioa at x. Fig. 103. T!k 
broken pyritt?*, FirSj, is BUed, in moderately air«l lum{«, w 
to the bare ol' the burnere. which have previously been beatei 
to recInt'SJ!. iind -wlit-n tiro burning is onco atartfd the Kit- 
ia kefit itp by placing; a new cliar^'e on the tap of that nearly 
burnt out. The ordiiiaiy charge for each burner of pyritia 


coutaiiui^ libout -tS per cent of sulphur, is 5 to G ewt., which 
is burnt oat iu IweDty-four hours, nnd the kilns are cIiarRwl in 
n"'utar sucarsiiiun, *o thut a constant supply of giu is wolrctl 
liuriiig the whole time, whilst tlie c|Haiitity of air which entent 
the kiln is carefully regulated by a wcll-fiU-ing door placed 

i8i I1i« hot sulphur dioxide. ntti'o*'en. and oxygen gaMs^sre 
liiuwii from the pvTites liunii-rs, llmmgh the whole qrstcni of 
mi-e^, towciD, ami chambers, by hvlp of the powerful draught 
from n Inr^^e cbiumL-y which i« plafcd in connoi-tion with 
\]n- :i]ip(imtiis. Thesn jwses fir*l pass from each kiln into 
.t Tiitral line, built in tin- luiildle «f the kiln, and theuco into 



an upnght brick shaft tlirougb a iiorUoutal earthenware flue, 
< into tb« lowftr part of tlic square dcuitrntiiig tower seen in 
sectiou at ii' ta Fij;. 104. This towt>r, from a Ui 6, is about 45 
fuet, or 14 melertj, in hvight ; it is built up, from a to «, to a 
heijflit of nearly 25 feel, or 8 metera, o( lead liuod with firo 
brick, Qnd of this about 15 feet, or o meters, Crotn ^ to e, are 
fillip up with piwcs uf tliut. 

The object of this Glover's tower, or deititrating tower as tt is 
teniied, is U> impregnate the siilpliur diosidu as it come* from 
the bumera with nitrous fuiuea derived from a lalur stage uf tliu 
opcralioB. This ia effected by allowiug strong nitrated acid to 


tlow down the tower togetlier with a tutrcain of weak chamber- 
■cid. Strong salphuric floid, il8 we shall see, has the power of 
absorbing nitmus fumes, and tlicsc aro given off njiain 
when thtf acid is diluted. Two restTVoirs arc. therefore, placed 
at tho top of the Glover's tower; one containing the strong 
nitrated acid, the other containing weak, or ho called chaniber- 
acid. Roth the strong nitrated and the weak acid arc allowed to 
flitw down together over the coluiiiu of (liiit stones in given 
proportions, aud when they mix. the nitrous fumes diisolved in 
the strong acid are given off and swept away, together with the 
gases from the burners, direct into the chambeta This cvohition 
of nitrous fumes hy mixing dihite acid with some btroug 



Aliotfaer useful end gftined by tlioemploymcat uf iht; mover's 
towen is the coacealrttitoa o( the cliamlwMicicl ; Tor tiut ouly 
itoes the strong acid lose it6 dissolved aitrotis fuuios, but tlie 
weak chfttnber'acid oomitig in contact with tlui liot dry gaaes 
which enter the lower at a Wmperature of 340*. parts witli a Urge 
iliuiutity or its wat^r. which goes into the chamber as steam, 
whilst the concontratcd acid, falling to the bottom of tl-e tower, 
flows into a reservoir, z, Fi}> 102. plac«d to receive it, 

Oo iasaiu;; lV>m lite tower, Uic gas. liiiviii« dow been cooled 
by coDiact with tho atieam of acid to a, t«iuperature of about 


fW-i^Jl P 


Fitt. I4S. 

76", paaaes into the caat-iron pipe, x, Fig. 1 02 (4 foel 6 inches in 
diameter), whence it h delivered nt the liirtiicr end of chtuuber 
No. 1, at a heijjlit of 8 to 9 feet above tht; fliwr. 

iSa llic su]>jily of nitric fnitiuu, which is tiijeded to act as 
uarri^r of the atmospheric oxygeo to the sulphur dioxide, 
ifi fimiisbed \>y Uiu three uitio pnte soeu :a plan and in section 
in Fig. 105. The charpea of 30 Iba. or 135 kilos, of nitrate 
of soda, and 22 lbs., or 15 kilos, of sulphuric acid, of epec. 
PJV.Y. 1-75, are run into the pots from the ouUside, oud after 
lupe of two hours, when each cliarge is exhausted, Ihu fused 



bisulpliato of soda (technicftlly termed sale nixum) is ran off inU 
a pan pkceii uu a platform outside the oven, oiid a new cfau^ 
introdilceil. Thu ilvcom[K.i!<itj(>ii uf Uik uilrn is acoelisntbxt br 
hcnt from llic pyrites buruers, platt'd bolow the brick arch whici 
separates Ihom from thu pots, aud ibti uimiiis fumes are gaibciiKl 
into a cast-iron pipe, z. Fig. 105, wbicti discbar},'OS lis contniU 
into Ui« long borizoiitul iiiuin ciiTrying tbe products from 
pyrit<?s burners into the cliatiiber. 

Tlie mixture of oxygen, nitrogen, aiUphor dioxide, nitric tnt 
and vapour of wntcr no^<r meet willi steain iotmduced lotu 
chamber by the tiib(>s, 8 s, Via. 1 03. and th« reaction as olrrad, 
described eels iu. Haviug iravcUcd through the leogtli of 
ber 2Jo. 1, the gase^ pass by meana of tho connctUog abaft (' 
shown in Fig. 101, into 1b« second chamber, wbere tbtr 
likewise tueel with »teani juts, aud having jiosscd tlirotigti tlna 
oUainlter. luid huviug dt-posited a further amom-.t of Hijuid 
sulpluiric! ttciil which falls on t\w floor of tlie cJianiber, the ga^-s 
are drawn into the ihiid or exhaust cbaaibcr by tlie tlu« (tv)— 
ill Fi^;. lOi. Here, if the prootss is pro[«eriy irorkcd, all t]i«^ 
sulphur dio.\ide b runvi<rted lutu sulpliuric acid, and ml 
aitroufl fumeii must always be visible. For the pui-jctse vt 
determining tho proper working of the proceaa the pcrc^'ntofce ^ 
of stdphur diuxidt! couluined iu tlii> <:as<:6 etit^^nng thi- br-tM 
chambtT, iind tli&t of the oxygen in tbe gases leaving the tbird^ 
cbainber, ia regularly nscertatned in cnreftilly managed works. 

The nitric fumi^'s )ia\'inf; been nddcnl iu excess of tbc (|uatitily 
requircfl lo convert the SO, into H,HO^ atill reuiaiu in chamU-r 
No. 3, and, in ordur to absorb thL-sc, a Guy-Lussae tower (o",' 
Figs. 102 aud 10+) in employed, the ca[Micity nf which onghl in 
be atlcual one huiidn-dth part of that of all the chambers. Tbia 
conaista, like the Glover's tower, of a sriitare tower 50 fei-i 
in height, innde of strong load (10 Ik) aud linMl for 35 fef>t 
with 2 inch thick glazed fire lUea, aud GUed with coke. Tlie 
«xii gaKi>8 from chamber Xo. 3 are drawn in at the bottom 
of tliis coke column, and escnpc to the chimney by tho axit 
tube (i, Fig. lu:^) at tlie toj). Iu their passage tlicy oonic in 
contact wiUi a lintdy divided shower of ittrong acid (sp. gr. l'7o) 
obtaiueil by coiici'iilmliny the chainbt-T-iiciiL TliiJi sinmg sul- 
phuric acid absorbs llie excess of nitrous fumes wluch would 
otherwise pass away up ibo chimney, and Itaving thus becono 
»at.uratt>il with nitrous fumi's. runs away through llw spoilt k 
into n-servoirs for the 8o-«Ulcd nitrated acid, built i. 




cbftni1)er "So. 3, the position of which (mm, Fig. IDS) i» shown 
on the plan. From these reservoirs the nilmted acid is allowed 
to run into ouc of ibo cast-iron air boilers (ittin) ahowii oii tlic 
phin, whence, by air pressure, it is forced up to the cist«rn on 
the top of the Glover's low«r fur eiaploymeiit in th« first part' 
(if the process aa already describpd. 

183 The coiitiiitious procca of acid mitking in the chotiilx-rs 
tan only b« carried on until tho acid has altaiueda specific firavity 
of about 1*55, or contains (54 per ccuL of Ihti pure acid, II^O^, 
inasmuch as an acid stronger tlian this IjegJtis to altsorb tliu 
nitrous fames. In order to obtain a stronger acid, either the 
arrargciuent of the (Jlover'a tower, as dfcscribed. is eniiiloyed, 
or, in worka whtmi the Glover is not used, the chaiubcr-ucid 
13 run into the leailen concentfiiliug pans (00) placed under 
chamber Ho. 2, shonu in plan lu Fig. 102, and in section in 
Fig. loy. Thi! Hume uiid hwilud nir from the fires (y) ph*y 
over the Burfute uf the acid wtnlnined in these pans, the water 
passes away in the form of steata, and tlie strong acid remains. 
Ky this iiKjiiiii* the acid can Vie coiiccntvated until it ntUiiiis a 
speciiic gravity of 1'7I, or contains 78 per cent, of pure acid; 
beyond this dugt-L-e of concentration the hot acid begins rapidly 
to attack the lead of the pans, and it therefore eaitiiot be 
further evnpoisted. It is then run off into the acid cooler 
(p), A leaden trough surrounded by cold water, whonee it 
passes into the strong-acid cisterns {i; Fig. 103), In this form 
the acid is Ivchnicully known iis B. O, V., Iirown oil of vitriol, 
as it ia always shglilly coloured from the presence of tmces of 
organic tuAtt«r. and it is in this condition that it it) very largely 
sold fnr !i great variety of purjKises. 

184 In onlcr to drive off the n.^iDnining portiims of water, the 
acid must beconcentratedorrectified in platinum or glaa^ vessels. 
A common arningenient for conccntratiuff in platinum stills is 
(Oiown in Fig. lOtj, as manufactured by Meesrs. Jolmsun. Mullhcy, 
and Ca, of lx>ndoiL tty means of this appamtns no less than 
200 ctrt. (10,000 kilos) of brown oil of vitriol can lie daily 
concentrated, yielding a product conlfliuing ys per cent, of 
real acid. 

The n-'tort or at ill .(a. Fig. 100) consists of plates of pUtiuuni, 
the joints of which are autogvuoualy soldeivd. Thia rests on 
the iron ring (C). The chnmber-acid runs from the stopcock 
Uiroii^ ft platinum tube on to the heated thick bottom of the 
AOI, where it isi^uickty concentrated, whilst the aqueous vapour 



escapes by the head of the still (l). As sood us llit \i:\iA of the 
concentrated acid reaches the top of the platinum funnel (D), it 
b^us to How olf by means of tlie tube (e) into the plntiaum 
vosacl (F), round which a current of cold water circulates. 
Huving been thud cooled, the acid piisscs into tha stoneware jar 
(h), fiurrouiulod by wjitor, and Ihenoe. by means of the lead or 
stoneware fuuQel (i) into the reaervoir (K). 

Measra Johnsoii, Matthcy. and Co. have quite recently intro- 
dnccd an iiii])rovtid form of platiiium concentrating api>an»tus, 
bymeana of whiuh all evaporation in leaden panaia avoided, 
and thus the operation not only considerahly cheapened, hut 
the acid obtained in a pnrercondition. This new armnj^cment is 
rcprtisent&d iu Pig. 107- aa arc piinamade of p'alJnuui plat«i, 
whicb arc corrugated at the bottom, and heated by a fire placed 


below. In these the eonct'ntratinn proceeds until the acid 
atlains a strengtli of from "8 to 80 per ceni. of H*SO^. It then 
nitia into the retort (h), also having a comij^ated surface, and 
the perfectly couc<>ntratcd acid which is ihiis obtained is cooled 
by passing Uirungli the worm (i>). made of plminum tube. 

In many English works the sulphuriu acid is recliBed in kIaas 
ami not in platinum vessels. TIvsq ghws vesseh np*> large 
retorts made of well-annealed and evenly-blown yliLts (Fig. I OS 
a), of such a size as to contain twenty gallons of the acid. liich 
retort is placed on jui iron saud-bath {h), toihkI which the 
flames from a fire are lUluwod to phiy, but so tliat tUv flame 
doM not touch the retort. A glass head (f) fits 1oo»L-ly into 
the neek of the retort, and through this the aqneona vapour, 
carrying with it a little ncid fume, passes into a condensing 



box. The pluD of s rectifyiug house conCaiiiing tweuty-fuur 
rvluns is shonii in Fi^. 109, The oci'i having been coQCoatrated 
in the lenden pwis (a a a), poMns along the leaden lubes (bub). 
from wliicli the retorte arc filled by meaus of tlie upright leaden 
tubes (d, Rg. 109), which caii be Iwnt so as to diacluirgc the 
acid into the iieck of the retort. Aficr tli« rvctification U com- 
plete the retorts are allowed to cool for twelve hours, mid tlia 
acid ia theu drawn oiil by nteaus of leodea syphons iuto the 
stouewikre coolers (t, Fig. LOS). 

.' (' 

?ta. 1C9. 

In OTder to effect a coutiinmiis rectification in glass vesaels, 
t)ui following arruDgL-niuiit h&a bueu uduplcil in waw works. 
T1ir«e of thti retuTia are placed one above the other, aa is sbown 
ID Fig. 110. Ax t)'">n m tlie acid in retort (it) hat attained a 
specific gravity of 1 si. the tetort is counected witli a system of 
syphon tubes f/Z/jjandchiuubor-acid of tlio specific gravity of 
1'74, and liaving a teinp<'rattire of loO*, Ia alloweil to run into 
the iippenooet retort (D) bj' means of the stopcock. This acid 
gnutuuUy puiset through t]ie tliree nrtort«,n, c, ami n, and when 
it had reached tho last oao it has attained a specific gravity of 


IM, aad is allowed to ruu off dirougb a cooling cliaiiiber (k) 
into the carbo)'. 

185 According to thooiy, lUO part« uf stUpliur burnt ahonld 
yield SOb 9 parts of pure sulphuric acid. In iiractice, however, 
tills theoretical yield is never attained, and for several reasons ; 
in the first pbtcc bccanM* a certnin nmouat of loss taust neces- 
sarily' take place iu working wiih such enormous volumes of 
gaa, and in tho secoud ploco inasmuch as an unavoidable loss 
occurs iu the processea of coucentration ; and thirdly, owing to 


Fis. 110. 

the fact that an amount ofeulphnr varying froni 2 to 5 por cent, 
reninins beliiiid i» the burnt ore, and this amouot cauitot be 
aceuMtely nllowod for. As a f^eneral rule a yiuld of 290 parts of 
pure ncid fniin 100 of sulphur is practically cousidca^d about 
the proper production, so that aliout 5 per cent of sulphur is 
lost on the ax'emiie, of wliieli. bowevor. only a portion pasaee out 
in the (gaseous form into the air. In cust:s where special pre* 
CAutiooa arc taken the yield sometimes reaches from 294 to 297, 
but when th« mflnuTBcturo is not carefully coniluoted mnchmoro 
serious losses occur. Tims in his eighth annufll report (1871) 




Dr. R Acgus Smith gives (p. 17) a table, showing tlie t«tal 
escape of snljiliur scJds (calculated an suljihuric aciil) froui 
tw«Qt}' -throe cbcnitciil works. Kium tJiia it appears that wUlUt 
from some of the works no escape of thcHC acids occuis, thearenifte 
loM of sulphur in the twenty-three works id qtipstion is T'fiOd 
per cent on the total qiituitiiy hurul, and that the loss in the 
case of fonr works actually tiaes to more tlian 20 per cent., in 
one caae amouutiii-! tu an escape of 159 lb& of sulphuric acid 
every hour. *' Fads like these," aays the inspector, " Uispose o( 
the aigument often uned by tlie nioiiufacturoia, th&t thfy ro^iiiro 
the acid, aod that it is to their interest to keep it, aiitl of cuurse 
coudcn.<(e it to the beat of their power. Indeed, certain makere 
are fully aware that they are allowing sulphuric acid to escape 
in large quantitiex, but their reply is that it i.H cheaper to permit 
a large escape and work rapidly rather thoii have liirge chuinbera 
arid condenaa the whole of their gases." 

Tlic amount, again, of aitrate of soda or chili-saltpetre used, 
varjeit considerably even in (he best works, according to the rate 
at which tlie reaction is permitted to proceed, and the complete- 
ness and rapidity with which the nilroits fumes can be recovered 
in the Oay-Lussac tower and agniu brought into the chamber. 
Manufacturers who employ Glover and Oay-Lu.<»ac towers use on 
an avemge 3-5 to Go paits of nitrate for every 100 of sulphur 
burnt, whilst the works where these applianceeare not in use the 
quantity of nitre required may rise to from 12 to Hi parts. The 
largrt the qiianlit y of nitrous huae^ present in the chaniber. the 
quicker will be the formutiou ol' ttulplitiric acid, and tlic proportion 
of furacic which pnys best is a quesUoa for the m&uufacturerin each 
iiistanee to decide. A certain Jom of nilTogpn cannot, of course,. 
be avoided ; tlie fumes are partly not completely condensed, and 
pass oat by the chimney, nad partly, in all probability, reduced 
Xiy the stilphiir dioxide to nitrous oxide or even to nitrogen, 
whidi, OS they cauitot combine again with the atmospheric 
oxygen, mnat escape into the air. 

In onlsr to ctmvert 100 parta of sulphur into sulphuric acid, 
about 310 parts of water in the form of steam arc needed. This 
steam ia costly iu ita production, and Sprengel has recently 
ptojxised to reduce this item of expenditure by employlug a jet 
of water in the form of spmy or In a state of very minute 

None of theflc processes yleM, it must be remembered, chemi- 
cally pure acid, inasmucb aa, in the first place, the w»ter caunot 



thus be ootnpletely removed, and Bccondly, because impurities, 
such OS gnlpliatu of IctuI, arising rtxim the action of the aeid 
uti the li^ulvu coaouDliat-iiig paii», tiud ancaio derived from ttio 
p^-rites, ore not got rid of hy this process of simple coiiooiitrutioa. 

i86 In order 1o |)Te|uire pure sulphuric ncid, the com- 
inercial product must be distilled in a glass retort natil one- 
tliird hits passod over; ihcii thw ri'wjiv'fir is changed and ihc 
acid diBlilled nearly lo dr>ne««. It not unfrequeutly happens 
tb<it in this pruc(.'»» the ucid biiiiips violently oa ehullitioo, 
owing to n small ijvmiitily of solid Iijud Molphate toiiig dejioiiitec) 
on the bottom of the rel^rt ; the additiou of smitll pieces of 
platinum foil or wire stops thin to a certain extent, but a better 
preventive is <-ithtir to heat the retort at the aides mlhcr tlian 
at the bottom ; or when the ebullition becomes percussive, to 
allow tlic li(|uid to cool, ilicn Lo jiour olT the clear acid, leaving 
the deposit belitnd, and to proceed with tlie distillation of tlie 
claiiiied liquid. 

PrapCTlw. — 'I\i& acid tliua purified by distillation still 
contains 2 per cent, of water which cannot be removed by this 
process. If, liowever, the difltillato he coated, the pui« Qcid 
containin*; 100 per cent, of HjSO^, separates out in the form of 
crystals which tiii^It at 10''<^, llietc crystiits when ouce melted 
geiiprally reumiii liquid for a couBiderable time, even when 
cooling Wow their fn'Ozing iwinti the liquid only solidifying 
when it is agitated or when a small crystal of the ncid h added; 
tbo teiiiperatnre then rising to 10 .5°. The sjiecitic gravity of the 
puire liquid acid ia 1-854 at ti' and 1834 »t 24" compared with 
water at the same tcmpemture. Wliou the pur« acid is heated, 
it begins to fuiue nt 30" iuasiuuch as it then purtinlly drcomposcg 
into water and sulphur trigxidc. I'ltis dissociation increases 
with increase of tempeiatnre until at 338°, the b»iliiig>[.'oiiit of 
the liquid, n large quantity of trioxidc is volatilized, hu that the 
residue contiiins from 'JS4 to 98'8 per cent, of the real acid, 
and then this liquid may be diatilled without alttiratioD. The 
vapour of sulphuric acid when it is more stroDgly heat«d 
completely decomposes into water and the trioxida Acconling 
to Seville and Trocitt the vapour density at 440° is 25, wbilat 
for equal volumes of aqueous vapour and sulphur trioxide the 
calculated vapour density ia 

17-96 + 79-86 

= 24 45. 



When heated stiU more strongly, the trioxidu tJius formed ileclf 
splits up into ox/geu and sulphur dioxiJe. This decotnpusition 
may he readily shown hy ullo«'iug sulphuric acid to drop slowly 
into the pktiiium lliulc (a. Fig. 1 1 1), which is filled witii pumice- 
aioiie and heated strongly by tlie lamp ; the niixturo of gnws 
which psciipes consists of one volnmc of oxygen to two volumes 
of sulphur dioxide, which latter goa is aheorlRiJ by juissiiig 
tlirongli vrut«r coiituining cnustic soda, the oxygen escaping in 
tlie fiva nl&\.e, whilst any undecom posed sulphurio Rcid is con- 
densed in the U-tube and collects in tiie flask (d). It has been 


Fiu. in. 

proposed to tifie this proco-w for the preparation of oxygen on 
the lai^ scale, as the material is clicnp and tlio evlphnr 
dioxide can again be used for the manufacture of sulphuric 

187 When sulphuric acid is mixed with water a ooneiderable 
evolmiou of heat liikes place and a contraction ensues. Tlie 
nraomit of heat which is evolved by inixiaj; sulpliuric acid and 
wat#r lias been exactly determined by Thoni*en ; bis results are 
given in the following table : — 



Alb KLfiUK 



H^u, 4 1 ii.a 


B^O, + X Ufi. 


. 0272 


. 16676 


. 9364 


. 16850 


. ino8 


. 17056 


. 13082 


. 173M 


. 14940 


. 17632 


. J 6248 


. 17848 

From the aliove namhera it is seen tbtit the addition of the fiivt 
molecule produces an amount of licat represtfutud by H.ZTi 
thermal uuiUt, or nearly otie-tliir<l of the total posaible, whilst 
the addition of two molecules of water gives off about one-lialf 
the possible quantity. The ht-nt given off by a furtlter addition 
of water iDCi-(!as«s very slowly, and it has been found impossible 
to detormiiiG the point at which no furllmr evolution of bc^t 
is caused by furtlidr dilutioit 

When a mixture of equal molecules of iicid and water is 
cooled down, the mixture solidifiea to a mass of prismatio 
crystals, wliich possess the composition HjSO^ + II^O, and melt, 
according in I'itrro aiid Puchol, nt 7'''5. 

Sulphuric acid is largely used in the laboratory not only for 
the preparation of most of the other acids, hut also for tho 
purpose of drying gasas in consequence of its powerful hygro- 
scopic proportit's. For this purjiose, the gas is best led tlirough 
tubes lliled witli fragments of puniiM-stone which have been 
boil(>d in strong Eulpluiric ttcld. In onlor to dry solid Uodit^a, 
or to concentrate liquids, sulphuric acid ia also employud, not only 
for (ho prepamtion nf luost uf the other acids, but also e^puciaLly 
in caaes where the application of a high temperature is likely 
to produce a decompoaitJoD of theBubstiince, The bodies to be dried 
aro placed over sulphuric acid in a closed space or in a vacuum. 

Sulphuric acid when conocutmtcd does uot act in tlio cold 
Upon many of the mttab, ultlioujih it does so in some caaes when 
healed. Thus copper, nnjrcur)-, antimony, bismuth, tin, lead, and 
ailvez are attacked by the hot acid, with evolution of sulphur 
dioxide; thus: — 

Ag, + 21I,S0. = Ag^SO, + SO, + 2H,0. 

Gold, platinum, iriiliimi, and rhodium are anactod upon. even by 
boiling snlphurLc acid, and this acid is, therefore, employed in 
the seiiaration of silver and gold. Tlie mom easily oxidixable 
metals, Gucb as zinc, iron, cobnlt, miuiganeae, are dissolved by the 
dilute Rcids with evolution of hydix^D and formatiouof a sulpliate. 



Many orgftnic lioilioi are 'loconposoJ by sulptmrio acid, vrlucK 
aljstntcts Tmui tlieiu Ihe Kleiiifuta of wat«r. Thus, fur instance, 
oxalic aciJ, CjHjO^, by healiog witli strong sulphuric add is 
dccompo-^ed into ou-bon dioxide CO,, caibon monoxitie CO, 
and water H.O ; ajid alcohol (.'jH„0 is transl'orraed by means 
of Uiis acid iuto ethylene gas Cjlf, and water BT^O. Wood, 
sugar, and othor suhstauces are blackcntd by eul|)hiiric acid, 
this tiody witbdniwiug fruiu thcni tJie bydrogrMi ami tlio 0):ygcu 
wliich they contain with produ(;tion of water. 

x88 Tht Sulp!taifs.—7hc salts of sulphuric flcid are teniicd 
sulphates, aud as lliis acid U dibasic, like sulphurous add. two 
series of snlphatus exist, viz. — the normal salts, such as Na,SOj 
luid ('rtSO,. and the acid ealts sui^h as JJaHSO^. 

Many Milphates occur native, oxisting as nelbknon-n and 
importttut inincrals ; euch are ; — gypsum, CiiSO, + 2H,0 ; heavy 
Bpar, llaSO,: celestine, SrSO,; Glauber's salts, NOjSO, + lUUgO; 
and lipsom salLi. JfgSO, + 711^0. 

Most of the sulphates are soluble in water, and trystallixe 
well, and tho«o can be readily prepared by di^olving the metal 
in dflat« sulphuric arid, or Ihe oxide or carbonate if the metal 
does not readily diss<ilve. Some few Bulphalcs, viit., calcium 
sulphate and the aulpbatea nf lead and strontium, aix> only 
very sli<;hUy soluble, vliilst liaiium sulphate is iusohible in 
Iwth wuter and dilute acids. Tbis fact in tiuKh* of fur the 
detection of eutphuric acid. A soluble barium salt, usually 
the chloride, is added to the solution supposed to conlain a sul- 
phate ; if sulphuric acid be present, a heavy white precipitate 
of buium sulphate, iiaSO^. falls down, which is insoluble in 
dQute bydmclduric acid. In order tu detect free sulphuric auid, 
together witli Kulplutes, as for ioHtance iu viiM-gar, which is 
sometimes a(Iulterate<l with nil of ntrini, the liquid must be 
evaporated on a vater-bath with a small quantity of sugar. If 
free STd]>hiiric acid is present a bluek rvsidue i.*i obtaincl. 

Free sulphuric acid is foimd in tbc water of certain volcauic 
dislriuta. It hna already been inuntiuni-d thiit sulphur dioxide 
oocura in volcanic guaes, and these when dissolved in water 
gnuhully absorb ojcygcn from tlio air and pass into sulphuric 
add. The Rio Vinagre ia South America, which is fed from 
volcanic springs and riTi-iviy? its name on the account of the 
acid taste of the wat^r, contains free sulphuric acid. A singular 
occurrence has been noticed of free sulphuric acid in the salivary 
ghutda of certain moUusca; thus, according to Biideker and 



Troschel, those of the DoUitnt galea contain about 247 per 

The following tahle by KoW exhibits the percentage of real 
acid, HjSOj, contained in aqueous sulphuric acid of varying 
RpeciGc gravities. 




Baa me. 




gravity at 

of H^O^. 


gravity at 























































































15 2 

































67-0 ; 






























74-7 1 






76-4 1 






78-1 ; 












81-7 ' 






84-1 , 






















• Dingl. Polyt. Joum. ccix. 268. 




189 TTiiH suViataace, which is a aoltttioti of vai^inp <jiinRtilics 
of sulplmr trioxide in sulpliiiric ncid. was known birfoie tlie 
sulphuric acid mauufactiiied from sulplmr. beiiiy termftd iV(»rd- 
hatucn futfifttirlc add, from the fact that it was prepaTed itl 
KordhnuEea in llie Hailz, hy h^aiin^' ivnsled green vitriol. 

Preparation. — (I) "When green vitriol or ferroun sulphal*, 
FeSO, + 7H,0, is roAstvd in tbc nir it loses wutcr and becoinea 
oxidized loa basic ferric eulphate,Fe,S,0^ w)iit:li isUien I'urLher 


Fio. lis. 

heated in clav retoru, as stiown iii Fig. 113, when the following 
deoampoeition takes place : — 

Fe, S, 0, = 2S0, + Fe, 0^ 

The snlpliur trioitidis thus foniied, [larlly comlnm.'s wiUi llic vfater 
which ib still present to form aulplmric acid, wliilst the other 
portion of the trioxidu dissttlvca in Uie sulphuric ucid thus 

Fuming sulphuric acid is now almost entirely prepared in 
Boheinia iu the works of J. D. Stm-ck. The solutioa of grceu 
vitriol obtaiapd W tLe oxidution of tlio pyrites is evaporated 
down, and the re-'<iilu(> ignited, care btiiug taken tlial the " vitriol 
8t<iDe " thus obtained is as free as passible from ferrous sulphate, 
in&HtiQvh AS if this body be present sulphur dioxide is formed 



ia the snbeequcnt diatillativD, und tbiis curries away with il laige ; 
c^uantitiee of the eaaily volatile trioxide ; thos : — ' 

2FeS0. = FcjO, + SO, + SO,. 

The more complet«ly tlie rilriol-atonc ia oxidiicd.tbckrgeris tli« 
yield of Cuming add, whicli on ao averaneamounu to froni ^ to 50 
per ccut> In soiue work;) the gn-cu vitriol is allowed lu crystallite 
out, and the oxidized mother liquors alou« used for the {trodocticoi 
of the fomiiig acid. Futniuj; auliilmriL- acid was formerly chiefly 
used in tbo arts for di^Milving inili^o ; at ]in^ciit, howuvcr, it is 
largely employed in the manufacture of aitificial alizarine. Far 
this pfirpose an iicid is needed uiiich contains more trioxide than 
the ctimnicrcial KuhsUmce, and hence it is prepared pnrposely by 
the mantifactiireni thetnaetves by h«aliiig the fViming acid in cast- 
iron retorts and coltcctinr; the trioxide. which is given ofl*, in 
aiKitlier portion of tlie autd iu well-closed rcceiri-r«. 

(2) This <»>uipoutid, OH has been stated under sulphur tri- 
oxidf), is alKu formed when a mixture of oxygen nnd sulphur 
dioxide is passed orer heated platinum sponge. It faas been 
proposed to employ tltis leaciioQ for the preparation uF coranran 
sulphuric acid on Uie large scale, tlte sulphur dioxide being 
nbtoined tnna the conihuetion uf sulphur, or from the roastinjj 
of pyrites, and this together with air passed over heated platinized ' 
asb^tai, the fumes of the trioxide being collected in water. It 
was found that this process cannot he practi<uilly carried ont, 
iua»much as the platitmm scxin loses ttiia peculiar projierty, 
probably owing to the fact ihiit dirt and particles of duU collect 
un the surface of the meUiL Por the production, huwuver, of a 
stroDgly fuming aeid, the following process, according loi 
Wjnckler/ answers wpll. Common sulplmric acid, aa hns been 
shown, decomposes ou hcuting, into a(|aeouH vapour, sulphur 
diuxidi!, and oxygen. If the mixture of gases be washed by 
sulphuric acid in oi-der to remove the water and particles of 
dust, and then the mixlute of dioxide and oxygen paased over 
heated pliitiiiixed iis)>ustitt, the trioxide is formed and may be 
oollucted in sulphuric acid. 

Propcrtiet. — Fuming sulphuric acid is a colourless, thick, oily 
liquid when pure, but ia generally coloured slightly brown From i 
the presence of organic matter. It has a spt^citic gravity of from 
l'S6 to 1'89, and evoh'cs on exposure to the air dense white 

' Diuitl. f«V' •ToKm. MxriiL 12S. 



fumes, inasiQucb as the voklile trioxida escapes and ccunbiDfes 
with the SHjueoas vapour of the air W form sulpliuric acid. 

^^nten the fuming acid is cooled, white cryateU of th« ccna- 
poand, K^t + SO^ separate oiiu This substAoce melts, accord- 
ing to Miuiguuc, ml 35', fuDii-a strotigly in tho air, and do- 
eomposee euily <>d heating into its I'otutituents. Th« name 
diwiphuru: acid, H^,0., tuu been given to this stibstnnt^ as it 
Harms a series of vety stable salts ; thus sodium disalphate, 
KftjSjOj, is oltainwl by beating the acid sodium sulphate, 
iUiaSOj, so I(H>j< aa wata- i$ given oS; thus : — 

aso.{gi5' = 



"-0 +HjO. 

Wliea etiU mote stxongly b«Ated this sail decompoaes bto the 
Qonnal sulphate and sulphur irioxide, 

Sulphur trioxide and sulphuric acid also unite toother to fonn 
another compound hiiving Uie compositioa SO, + SH^O^, vbich 
consists of a transpareat crystalline mass melting at 20°. 




Vapour Density - 5811. 


igo ^^'i^i1lnt)IDR firxt obliiinod ibi^ !nihBl»iii>e by the direct 
union of hydrochloric acid and sulphur trioxide.* 

It is, however, best prepared by the diRtillatioD of a mixture 
of concentmted sulphuric acid and phosphorus oxychlorido, 

2S0, j2n + I*OC%= 2 SO,|^j" + HPO, + Ha 

Hence it in hwii lliiit chlorosiUpt ionic acid may be couaidcrwl to 
l»e sulphuric acid, in which Ihu gii>np, hydi-uxyl, OH, is replaced 
by chlorine It is a culourluss liquid fuming strongly in the 
air, huving a sitecific gravity of l~Ot; at 18', and boiling al 158', 
lis vapuux decomposes partially on hciUing iuto hydrocbloric 

• Prve. nog. Sot. Tii. 11. 



■cid and siil|ihur tiioxide. and at 21 6* its rapour density is foood 
to be 32*8, or tbe dissociatioD is nearly perfect. 

When thrown into water it decotnpOM* with oxploeive 
violeace, {ormiag hydrochloric and sulpburio acids, and n-hca 
oddod to strong sulphuric acid, disulphuric acid and hjrdrocldoric 
add are formed, ihtu : — 


SO,{oH = 


+ HCL 

( CI 

SuLPauHyLCiiLoitu)E. SOj ^ J^ 

VajKJur Density = GTiJ. 

192 This hody was first prcpoiml by JEegnault in the year 18SS 
by the direct union of equal vuluiucs of chlorine and sulphur 
dioxide iu (he aunligUt.* :Sulphnryl chloride is also fortiit-d wlivu 
a solutioD of the tvu gases iu anhydrous ucetic acid is allowed 
to auttid. Il is, however, most rt-udily obtained by heating chloro- 
eulphonic acid in clo<SL-d tubes at a tvmjK'nituie of 180° for 12 
boar»j^ thus; — 

Sulphuryl chloride is a colourless liquid boiling at 70°, posses- 
sing a stroiijjly ptitigoiil odour, fuiuing slmngly in the air, Iiaving 
a specific gravity of 1659 at 20' and deoomposing in presence of 
a small quantity of water into clilorosulpltouic acid and hydro- 
chloric acid, aud with im excess of n-atecinto sulphuric acid and 
hydrochloric acid ; thus :— 

SO,^ ^ + 2H,0 = SO, I [] J[ + 2HCL 

DlSDLPirtiBTL CnifliiiDE. SjOjCl^ Vaponr Density = 107*25. 

The chloride of disniphnric ndd was first prepared by RoBe> 
by tlic action of chloride of sulphur on sulphur trioxide, thus : — ■ 

SjCl, + 5S0, = SjOjO, + 5S0,. 

> Awl Ckim. Fkw. Ixix. 179. 

s BtliRml, Btr. iktitxK Chan. Ots. nii. 1O04. 

• Pogg. Ann. tiW. »1. 



The same compound hns slso Itecn obuined by Michaelis ' by 
beating sulphur trioxide wiili phosphorus oxycliloridc i thus : — 

GSO3 + SPOCIa = SSjO^Cl, + P,Oj. 

Il IB likewise fomicd wlmn comtuou eall in ticatul with aulphur 
trioxiile, and when tliia latter substance is biougbt in contact 
with aulphurji cbtoride : thus:— 

so,+soJg= Mo. 

It is a colourless fuiuinji li([uid, boiliug at 146*, aud having a 
specific gravity ai 18° of I 819. Water deoooiposea it into 
sulpliuric ai'Kl aud hydiucbluric acid. 


Millou first (ibtuiii«<.I ibis «ul}at.iiic« by tlic nctiou of nioiet 
ohlotiue ujxin suljilnir ur cliloriilo of sulphur. It ia best pre- 
parpd by conling dnwn a mixture of chloride of sulphur and 
ci)Ior-8ulpboiiic acid to —15°, and ihcii saluratiDg tit- liquid 
with chlorine, when tlie follo«'ing decomposition takes place : — 

SOjIICl + SCI, = S,0,C1, + HCL 

Sulphnr oxytctmchloridc fomis a wliilc crysLolUiit! niass, 
which has a very pungent sinull and attacks tliu iiiumus 
mcuibnmc violentiy. It dissolvea in water with a bissiug no)fi«, 
fonoing hydrochloric, Rulpliuric, and «tilphiirrju.s iiciits. Kjtposed 
to moirt uir, it deliquesces with the evolution of cliluriiie, hydro- 
chloric ocid, and sulphur dioxidfi, liraving a rcsidut^ itf thionyl 
chloride and disulphuryl chloride. When the cfiiiipound is 
heated it piirtially snldiitiM in fine white needles, whilst another 
portion decomixisc-s into sulphur dio.xidc, chlorine, thionyl 
chloride, and disulphuryl chlorido. W'lien kept in closed LitW* 
this body li(]uef)fj with the formntion of thionyl and sulphuryl 
chlorides; thus: — 

s,o,a, = SOCl, + S0,C1, 

> AtMcA. <Ur own. {8} vU. l»i 



ScijatniVL Bromide. SO, i ^' 

BroTDiae in tlie pn^scnce of sunlight unites with sulphur 
<lioxide, fonniiig a volatile white solid (!r}'f<UiIliiie mnsH. M-hicIi 
■when acteil upon with silver oxide forms sulphur trioxide ; ' 
thus : — 

SO,Brj + AgjO = SO3 + 2AgBr. 

TnrosuLPHUBTC Acid. HjSjOp 

iga Tlii3 compound is better known under its old uamc of 
"liyposulphuroiiii ncid," with which iittmu, liowt-vcr, wo now desig- 
nate the body obtained by the wdiiction of sulpIniroUB acid. Tliio- 
sulpbtiric acid has not been prepared in the free etale. but it 
fonn» a serifj* of stable salt* which are tiiown ns the thio- 
sulplmtes (hypa'<ulphit<«i). "WTien, dilute sulphuric acid is 
added to a solutiou of a tliioeiilph»te, the solution remains, to 
begin with, ptri'tjclly cl^ar; but sulphur soon bogius to H-pnrute 
out as a white, very finely divided powder, and tlio solution 
ia found to contain sulphurous acid which 13 partly given off as 
SOj; Ihf. iliiu8ul]iliuriR acid, undergoing, on its Ubcrulion, tlio 
foUowiiig decuuipoBition :— 

H,S,0, = HjO + SOj + S. 

The thio9idpliat<?5 are formed in various ways: thus, for 
instance, sodium thiosnlphntu (commonly called hyposulphite of 
soda), which waa first prepared by Chauaaier in 1799, but 
afterwards more carefully examined by Vauquelin, is prepared 
when sulphur dioxide is pti^sed into u solution of sodium 
sulphide ; thus : — 

(a) SO, + H,0 + NftjS = Na^SO, + SH, 
(fr) SOs + 2SH, = 2H,0 + .S^ 
Cc) ifajSOa + a =Na2S30j. 

The aanie salt is also formed according to etjuation (c) wheo a , 
iolutioD of sodium sulphite in boilml with (lowers of sulphur 
(Vauquelin). Sodium thiosulphate is also formed, when iodine 

' CUtiug, Joura. Ctem. £i>r. rii. 3. 



is addei] to a suIuUua of sudium solpluLe aiul sodium sulphide ; 
tlias : ' — 

Na^O, + Na^ + I, = NajS,0, + 2NaL 

Those v»ri()UH metlinds of [ireparaliun ])i)int nut llial thtoflul- 
phuric ^id is tbruied by the addition ol' 8iil]>1)ur to sulpliurous 
acid, jiut OA sulphuric acid is fonned liy tlie lulditiun of oxygeu 
In tbe same subalaiita TIjiosulpliuric aeid may, therefore, be 
r^aixied us ButpUuric acid in wliicU uiiu alum of vxynca is 

replaced by sulphur, and ilsfonnulaisaccordinyly SO,-! c„' 

TliQ decuiu|>osition8 which it« i^alts undergo bear out this iutcr- 
]nvtatiun of its compoulion* Thiis tba ducompusitioti of the 
free Bcid into eulplinr and sulphurous acid has already been 
mentioned; and when R solution of eodium thiosulplmte i» 
treAtod with sodinm amalgam, sndiiim siilphito aad sodium 
sulphide arc formed (Spring) ; thus :— 

Na^Og + Na, - XajSO, + Na,S. 

A^in, when silver thio«idphatc is wanned with water, hlack 
sulphide of silver scpnmtcs ont, and the solution contains free 
sulphuric acid ; tJius : — 



{sa|-^""0 = ^-'^ + sO'1oh 

And, moreover, when a solution of iiodium tfaiOitiilphatH is treated 
with cobalt chloride, black sulphide of cobalt is precipitated; 
thus; — 

SO, 1 2y^ + CoCl, + ffjO = SO, ■[011 + CoS + 2NaCl 

Tbe soluble tbiosnlphates generally ciystalltzo well, and contain 
water of cr3r8taUization, the last molecule of which is very 
dif&cultly D'Diovable by heat^ generally at such a high t«m- 
pemturv that, the decoraposition of the salt has already com- 
mencetl. Hence it was formerly supposed that the thiosulphates 
all coutniticil hydrogen. 

The tliioBulphatos exhibit a great lendoDcy to form double 
salts; those of the thiosulpbutes iuiuluble in water arc found 
to dissolve in an aqueous solution of sodium thiosulphate, 
whicti also haa th« pnwer of distiolviu}; otht^ insoluble salts, 

■ Rpruiff. Btr. lifitt^k. Oltm. 64*. lix. 11S7. 
* SchoilcinBier. Jourtt. Ckrm. Sue. [3] vii. 3M. 



each OS silver chloride, silver biomide, silver iodide, lead 
iodide, lend gulpliiitc. calcium sulphate, Ac ; thus :— 

Sodium- silver thiosulphalc forms dietiiiut urystalj, haviii-r Ihn 
composition AgXai?jO, + H„0, aud tlieeo are distiuguislied 
hy possessing a swe«t taste. The use of sodium tliiosulplintc 
for fixing prints in pliotosrapliy. first sHgfjested by Sir Joha 
Her^cliel, dcpeiul» oii tlic turiuuLiou of this salt. Tho 
silver chloride with wliicli th© photograpliic iiftpor is impieg- 
nntml when exposed to the light Iwcouies blackened, the chloride 
uiKluiijuiii]; a cheiuic&l change, art«r which it is insoluble iu 
sodium tliio!>ulp1mt«. In order, therefore, to fix such a photo- 
urephic print, it is only necessary, after exjiofiure to light, to sonk 
Ihc paper in a bath of the thiosulphale ; the unaltered chloride 
of silver di»!Volve3, and the picture, on washing, is found to be 

Thd thiuaul phiitus atu distiiigimhed from thu sulphites, 
inasmuch as that when dilute hydrochloric acid or sulphuric 
acid is added to their solutioa not only is sulphur dioxide 
(:iviin off as a gas, hul free sulphur is deposited as a white 
powder, hi adding a thiosulphute solution to a silver, lead, or 
mercuric snlt.. a white precipitate of the insolable Ihiosulphate 
ia first thrown down, but this quickly becoinca dark, and 
liiially blauk, from its decomposition into a metallic sulphide 
and eulphurttus ai!id. Sulutioiiii of nicki-l, colwJt, and mercuroug 
salts give with the tliiosalphatee dense black piecipitatcs, and 
w-lien a thiosulphatc is lioi]e<l witli aa uniiaouiacul solution of 
a ruthenium salt, the solution becomes of siieli an intensely 
dark red colour that in tbe couceutrated couditiou it appcai-s 
almoBt black. 

DiTnioNiu Acid. H^SsO. 

193 Tliis acid, formerly called hyposutphuric acid, was dia- 
covered by Welter and Gay-Luasac in IS19. The manganese salt 
of the acid is prepared by paseing sulphur dioxide into water 
oontaimiig manganese dioxide in suspension ; ttius :-~ 

2 SO, + MqO, = MnSjOa- 



At the same time a, portiou of the manganese is converted into 
nuingaaese sulpliAte ; thus : — + MnO, = SilnSO,. 

Id order to obtain Ihe dithionate fccQ from sulpliate, advantage 
is taken of the solnbility of Variiim dilliioiiate in water; baryta 
w«t4.'r. Ua (OII)j, 19 iulded iinlil all the metal 13 prvcii^iuttwl OS 
manganese hydroxide. Mn (UU}j. ftnd oil tlic eulphutic acid is 
thrown down as iiLsoliibli: Lmiuii) sidpliatf;, BuSO^; on cvit|Kiri- 
tiuy uiid ctKdiiijt barium ditbiyiJots. UaS^Oj + 2Hj,0, cryelaUi^tes 
ont, and when thi« i» dccotnpo.'ii'd by titc rc<]uisite (itmntity of 
dilute siilidiuric scid, a soIuHoq of dithioDic acid u obtainefl. 
This solution may be concent rntcd m vafuo ovgr sulphuri* acid 
Until it obtAJni^ ft specific gravity of 1*347, but on attenipLtug to 
concGDtrato it further, the acid is resolved into sulphur dioxide 
and sulphuric acid ; tlius : — - 

la order to obtain the salts of this acid we may add the corre- 
sponding bASe to the aoiti soliitloD, or they mny lie oltaiuvd more 
simply by addiug a soluble sulphate to barium ditbionate. 
Most of tbtMO sails cnstallixe ^dl, and tln-y contain, with the 
exception of the potassium salt, water of crystalliziition. Tlicir 
aqueou>« solutions are not oxidized in the cold either by atmo* 
apberic oxygen, by nitriu acid, or by potassium permanganate; 
t1)ou<;h when they ore heated nith oxididiig agents Ihey 
are dpcouiposed into the sulphates. On heating they decompose 
partially iit 1QU°, and enlirL-Iy at higher tempeiature, into 
Hiilpliiir dioxide, and a sulphate which remiuiis beliiiid; nnd 
when sodium amnlgam is a«ldi*d to a solution of sodium 
ditliioDalc, two molecules of sodium sulphite arc formed (li. 
OUo); thus:— 

Na = 


SO t OJf a 

SO fON-a 

n»o dithionatcs are distinguished from the thiosulpliates 
iitasmuch as (hey evolve sidpburous acid when heated with 
hydroebloric acid without separation of sulphur, whilst the 
solutioD contains a sulphate. 


rai: non-metaliju KLKunNm 

Teuthiomc Acid. H^jOg. i 

194 In 1842, T.anglois obtained the potassium salt of tlie ftcid 
by f;ently licailiig a solution of acid potossitim sulphate n'ith 
sulphur ; tliua : — 

S, + 6KHS0, = 2K^»0g + K^S^. + SHp. 

The same salt is also produced wlicn n solution of potaasiuin 
ttiiosuljiliate is saturated with aulphuc dioxide ; thus : — 

3S0, + aKjSsO, = SK^SaO, + S. 

The ])otassiuni snlt is morco^'cr formed when potaasium silver 
thioBTtlphatc l^ heaiod wiili water; thus : — 




^Mo'^' so. 

S + AgjS. 

When iodine is added to a solution of sodium thiosulphate and 
sodium sulphite, sodium trithionate is likewise formed (Spring) ; 
thus : — 

NajSjCJj + Ni^SOj + Ij = NajSjO^ + 2NaI ; 

whilst n solution of the trith ionat« treated with sodium 
anial^jam decomposes again into 3nlj>hit.; uud thiijsuli>hate. 

Id order to prepare the free trithiotUu aciil, tlunailicic acid is 
added to a solutiua of the potiu^fiiiini salt., when the insoluble 
fluosilicale of potib«:4inia is procipitated. The aqueous acid 
thus obtained has no smell, but has a strong acid and hitter 
tasK; it may be concent rati-d in a vacuum up to a certain point., 
but it is an unstuhle compound, and at the ordinaiy temperature 
easily decomposes into nulplnir, sulphur dioxide, and sulphuric 
acid, 'riie only one of the tiitliionales which is well kuuwn is 
tlic potaH-sium salt. Tliis on heating documposes into sulphur, 
sulphur dioxide, and potnesium sulphite. Its solution ia not 
precipitated by barium c-hloride in the cold, though on heating 
barium sulphate separates out, silver Ditrate gives a yellow 
precipitate which very quickly becomes black on standing. 




Kordos and GC'lis 

313 first prepared lliis avid and its 
, obtatn«ii tho sodium suU hy adding iodine to an 

t'S solution of sodiuDi tliJosulpliatc ; thus : — 

SO f *^^*" 


q OJfa 

+ U = 




n order to prepare the free aci<i, iodine in exoes? is added very 
gnuliialty to Ihiosulpliiite of litinuiii Mi^pondetl in a very small 
quantity of iiFat«r, the iodide of barium and excess of iodine 
being removed by shaking up the semi-solid mass with strcmg 
adoohol, leaving a -wliite crysiaUiue mass of barium k'trathii»umf, 
BaS^Oy Tlii* may then bo dissolved in a small tjuantity of water 
and recryAtAllized, irhilst from this pure salt the ftcid may 
be prepared by adding exactly sufficient sulphuric acid to 
decompose it completely. 

Tetratbiouic acid is a colourless, inodorous, very acid lic^uid, 
whieb, when dilute, may be boiled without undergoing dccoui- 
{Nuition, but in the cuiiccnlratc-d state la easily dccoiupoftud into 
sulpbiiruiia and sulphuric Bciilsandoulpbur. The tetrntluoDate) 
are all soliibh- in wntiT, but their solutions cannot, as a rule, bo 
evaporated williotit decompoeitioa into sulphur and a tiilhionatc. 
Sotllum iiiimlguni dccompuses the CODipciiiid ikIo two luoleculen 
of tbitMulpliatti, and tlie same decompositiuu occurs on addition 
ot potassiam sulphide ; thus . — 

K^40,+ K,S = 2K,S,0, + a 

Pkstathiosic Acid. H^jO^ 

Wackenrodcr first prepared this acid in 1945 by passing 
huTctted hydrogen into a solution of sulphur dioxide, thus:-^ 

oH^+SSO,- H,SjO,+ 5S+-lH,0. 

The milky liquid obtoiaed in this way is digested with metallia 
copier untU it becomes clear, any metallic copper which is dis- 
solved being precipitated by sulphuretted hydrogen. The clear so- 
IntJon can then be concentrated, without decomposition occturrii^. 



tmtil it attains a specific gravity of 1-6, bat if concentrated 
beyoad lliis \>(mt it evulves sulphur dioxide. Fentatliionic acid 
is coluurksa and inudvruua ; iU solta liavti lit-cn uuly sli^jlilly 
investigated; Uiey appear to decomfK>se very ea-sily \iHtli the 
scpamtiou of stiljiliur ntid tlie I'ormatioD of totratliioDato and 
Irittijoiiate. liarium pcutalliiouate is obUiined by dissolving 
barium ciicbouate iu ai:i«eoua pentatbionic acid. On tlie addiuon 
oF aliiubol, a crystalline precipitate of this snlt is thrown down, 
and the sctnte salt ia formed when ohloridu uf sulphur is added 
to barium Lliio3ul|>huU; luid watvi', tbus: — 

2BaSjOj+CljSj = BaSjOa+BaClj+S. 

From tbia reaction it would appear tbat the constitutioa of 
pentatbionic acid is represented hy tlie ft)llowiu({ formula : — 



VHien a solutioo of mercurons nitrate is added t« a pentji- 
thiuni\te a yellow precipitate i» ititinodiatcly fi>i-nied, wliiuti on 
further addition of the morcurous. salt becomes wbit«. titrate 
of silvej" produces a yellow prt;c;ipitat« which very B<M>n beconips 
dark, and when ammouiacal silver soluliciu is ndde<l a dark-bmwn 
precipitate is at once produoed, which gradually hecfimcs black 
from furmatitiu of silver anl}>]iide. The other iiulylliiumc acids 
do not yield a. iirDcipitu.l« with im oiuin oniacal silver salt. 

SELENIUM. Sc = 7g-o, Vapour Density = 79-0. 

197 Wo iiwe the disBovery of Ihis <<Ienieut to IVrzeUus.' He 
6rst found it iii the deposit from the sulphuric acid chambers at 
Gripsholm in Swedon, in tbu year 1817, and it i» to him that 
we arc. indeltt«d for the kiuiwledj^c of its most important com- 
pounds. The name selenium is derived from SeXiii-i), the moon, 
on account uf iL« analogy with the clement tellurium (tcU-us, the 
earth), diacovered shortly before. 

Although selenium is Aomcwhat widely distributod, it ccctiis 
only in small i^uantiliee. It is found ob sulphur SBleiiide in the 
Island of Volcano, and occnrs. chiefly combined with certain 
1 Seiunfiffy J'Mtnt. ixiii. 809, 430 ; /^. vf nn. rii. StS, viii. (S3. 



metflls, Ob Clausilial and Zorgti 'm the Unn, as die mineral 
clauathalite, PbSe ; a selenide of copper aiul k-ad, PbSe+CqSe ; 
lehrbocUile, PbSe + HgSe; sclcnidc or silver, As.Se ; sekiiidc of 
copper, CuSe. We alsu fiud it as oiiofrite, II;{Se+41Ig.S, in 
Mexico; wliilst oucairite, CuSe -|- AgSe, and cntolcrsite, 
(Cii'nAg)Se, oc-cur at Skrikerum in Sweden. Solenium is filsa 
found in veiy small qoanlily in many other miaenils, esitctially 
in c«ti«in iroD-pyrites and coppor-pyrites, and where these are 
used for the nisnuraeture of eulphuric acid, a n>d deposit con- 
UiaingscleuiutQ is fuund in the chambets. 

Prqwrra/ion.— In order to prepare selenium Prom this dfpoett, it 
is mixed with i>f[ual piirLa nf sidphnric acid niid water to a Lliin 
paste and then lioiled ; nittic acid or potassium chlonktc buing 
added until tlio red colour disappears. In this way a solution of 
selenij: acid, H,^SeO^, is ohtiiin>ed, and this ia then heated with half 
its volume of fuming hydwehluric acid until t!iret'-(iunrtt;i-s nf ib« 
liquid has evaporated. My this piucuss chloiine is evolved, 
and Bplpnious acid, ll^SeOj, rnrmed. The cold sohitjun is then 
jMitm^ oir from the solid matter and saturated villi sulphur 
dioxide, when Kelcnium sc{itinit«s out as a red powder. The 
aeleuiuni thus obtained contains lead and other metals, from 
■which it may be separated by either di.-'tiUntion or by fusing it 
wltli a mixture of nitre and carbonate of 6oda, by which 
ineana sodium solenatc ia fomicd, and this is then again treated 
with hydrochloric acid mid sulphur dioxide a^t iihove dt'sciibed 
(Wahler). Selenium may also be easily obtained from the 
chamber deposit hy hciting it on a wnter-bath with a. concen- 
trated dulution of cyauidc ul' potassium until it a^uoics a pure 
groy colonr. On tlie addition of hydrouhluiic acid to the 6]t«i^ 
solution ecleninm is dep^wited in cherry-red Qokea. This also 
contaioB Iwth copper and lend, and these impurities are remuvc^d 
either by the proceas as desciibeit above or by evaporatiug the 
ftleiiium to dryness with nitric aeid and reducing the aqueous 
ilutiou of selenium dioxide by means of sulphur dioxide 

Proptriies. — Seieninm. like sulplmr, exists in two allotropic 
raodificatioHs, one soluble, tbe other insoluble in cndwn di* 
sulphide (BcrzoliuH, Hiltorf). 

Sobihle selenium is obtained as a finely divided brick-red 
uolouied powder, when a cold sulution of seleniomi acid is 
precipitated by a current of sulphur dioxide : and m a black 
crystnUine powder when this gns is passed through a liot 

solation. Other reducing ngenU, sucli rs iron, zinn, stnnnous 
chloride or phosphorotis acid, also precipilate 8ulul>l9 seleniom 
from solutions of .sclfinions iiciil. Sck-uiuin crj-stulli»>s from 
solution in carboa ilisulpbide tu small daik-r«<l iraiisluceut 
ccystah, wfaich aro i«oitiorptious willi tho monoclinic furm of 
8ali>hur, and have a flpecific gta\nty of -lo.' When selenium is 
fo.^ and allowed to cool quickly it solidifiea to a dark brownish- 
black glassy translucent ainoiphoiis briulo mans, which is also 
soluble in carbon disnlphidc, nnd has a specific gravity of -l-'i. 
Soluble selenium tios do deliuit« ineLUDg point, softetiiDg 
gradually on beating. 

The insoluble or metallic selenium is obtained by cooling 
melted sttleuiura quickly to 210° and then kecfpiiig the melted 
mass at this temperature for soma time. The selenium at leagth 
soliJilies tJ) a granular crystnlliiiu mn«8, the- teiiii'emtiire rising 
suddenly in the act of solidilication to 217°. The solid mass 
thus obtained biis a specific gravity of 4'5, and ia insoluble in 
carbon disulphide. This change from the solublf! to the insoluble 
condition also takes place, hut more slowly, at lower tcmpera- 
iiirvs; thus, ifamass of soluble selcuiuiu be placed iu an aii-^-bath 
at lOf*, tho change to the insoluble variety takes place gradually. 
and the teinpfnitun; lisia up to 217*. If a concipntrated solulion 
of potusaium oT sodium selenide be exposed to the air, Uock 
adeuium scparate.i out in microscopic crystals wbioli have a 
specific gravity of 48, and ait likewise insnlublu in carlxin 
disidphide. The insoluble or metallic selenium has a constant 
mcltiii},' point at 21"', and wh.'ii quickly cooli-il it is coiivcrl«cl 
intoanioi'plioussoluble selenium. Both modifications of selenium 
are soluble lu chloride of sclcniuiu and ecparata out from this 
solution in tho form of metHlUc selenium. According to the 
experimeutj* of Mitscherlich, selenium hoils >iomewhat below 700°, 
and forms then a dark-red vapour whicti coodeuses eitber iii 
the form of scitrlet^^i'fr* of selenium, or in dark shining drops 
of the melted substance. Like sulphur, the vapour dHiisity of 
eeleaiam diminishes very rapidly with the temperature ; thus at 
860° thi; vftlK>iir den&ity is 1 10 7, whilst at 1420^ it has a dnn.^ity 
of 815, closely corresponding to the uormal vapour density of 

Metallic selenium conducts electricity, nnd exposure to light 

increases its conJncling jiower.' Tlie peculiar effect of light 

* RanuiulibCM, Bef. CcmImA- CSrtn. tJa. rll. 499. 

■ Salo, Ptw. /toy. Soe. xxi. tSi ; W. Q. Admt, /Mtf. XXuL 133 ; W. SJcBUD^ 
Beriin, At. Xiai. 187S. 



is best exhibited on selonium which lias heen exposed for a 
coDsidenible time to a tcmjicrdtHre of 2H)', nntil it has auaiiied 
a gmnular cnatalline coDdilioa. Xon-luminous heat-rays Oo 
not exert an inflaeuce of this kind, and when selenium is heated 
its etectrical resimanre i» increased. On expo^in<> sel^uium to 
Ibe action uf diffuaed daylight, ilie electriail resistance instantly 
dintini^lies to one-ltalf of what it was Wforu ; thi», howevi-r, is 
only a t«ujporary c)uiti<,'«, for on cutting ofT ttie light, the clrclriiiil 
resistance of the seletiiuiu slowly increases, aud aller a ahurc 
tiiD« reaches the ainouiil exhibited Iwforc tlio exposure. Tliia 
lemaikable property of gcleuium may jirobaLly be inadn ane of 
fen- ptiuloiuctriuil puriKues. 

When seluuium is heated in the air it hums with a bright 
Une flame, fnrniiiig an oxide of selenium to which ia du« the 
eUanictcnstic odour, resi'iubling that of rolteu horae-mdiali. 
nolic«d when selenium burns. The emission spectrum of 
seleiuuin is seen when a Kmall bead of the element is held in 
a aoD-lutnu)OUs gsa Hame ; it is a channelled spectrum highly 
chamcteriatic and beautiful, consisting; (if u veiy laij^ nuuibi-r 
of bright bands, vhich in the f>reen and blue are arran;j;ed at 
t^pilar intervals.' According to Salct,' seleniutn. like sulphur, 
girea two emission spectra, one consisting of lines and the other 
of bands. Tite aljsorptiun spectrum of scltmium has been 
examined by Uemex.' 


Density = 40 7. 

igS Thia gas is formed when selenium va|Kmr and hydmgeu 
are hcaLi-d together, and the amount which is thus produced is 
a function of the lemperrature. The quantity formed increases 
when llic lemperHlure is raised from 250' to 520", hut above 
thia poiut tlie amount gradually dimiuislios. When selenium 
is heateil in a closed tulm filled with hydnk^jt'ti, it sublimes in 
the cool part of the tube in the form of beautiful glittering 
ctj'stals. And these increase in number until the vhole of the 

' W. SL W^h. TxJaro/Spt^ra. p. M. 

I Canpl. And: Ixxiii. BSSudTtS. > Ihd.lsjdr. ll»0; 



selonMiiu has volatilized. TTie formation of tb«90 ciyatals 
dejjeiids upon the decompcwitioD bj heat of the sclent urvttLt] 
hydrogen which is formed ; for when aelenium ia heated in a 
tabe filled with nn indifferent gas, uuly reJ nniorphous selenium 
is found i« Hubliiue, 

Sclciiiiirctted hydrogen is easily ohtained by the action of 
dilute hydrocliloric a<'id on pntaaaium selenide, K.jSe, or on iron 
fieleiiiilt*. Fe8c. It is a colourless, intlaniiiiable gas, possessing 
u sniell which, to begin with, r(.iswiibh« thai of «tilpliurclt«d 
hydrojjcn, but aftevwnrd!* is found to have a much more 
persiHivuL and intolerable oilonr, a small qunnlity affecting 
the mucous uitiiubnniu in u ri^tniirkeblc decree, attacking 
tbfi even, and producing inHamtnfttioD end cougliing which hi£t 
for days. 

Bcrzeliusdcscribesthc effects IIS follows:'— "Id order to bccoino 
acfjuaiiitttd witli the smoll of tliia gaa I allowed & bubble not 
larger than a pea- to pass into ray nostril ; iu consequence of its 
action I so coiii])]etoly lost my scnso of smell for several houni 
that I eoukl not diatiuguiah tha odour of strong ammonia, even 
when held under my ndse. My sense of smuU retumwi alter 
the lapse of five or alx lioui-s, but severe irritation of the mucous 
nienibvaiio set iu and lasted for a fortniglit," 

In onler to ascertaiu Uie comisosition of st'leniurelled hydrogew, 
mctidlic tin is hcntL-d in a nicosurud volume of the gas, when 
tiu sC'lenide in formed, and n volume of liydmgtm ia liberated 
equal to that of the orijiinal 1,118. 

Hydrogi^Di selciiitli; is more soluWe in wut^r than (lie corre- 
sponding sulphur compound, yielding a colourless solution which 
reddeus blue litniUR paper, colonic the skin of a reddish-brown 
lint, and possesaca llic fivlid odour «f thi,' gas. Exposed to tlie 
air, the aqueous solution absorbs oxygen with thu scpamtion of 
led selcDiuiu. When added to Mthitions of Balut of most of tha 
heavy metals, it produces precipitates of tlie insoluble sclcuiduA 
in an analogoua manner to sulphuretU.-<l hydrogeia. 


igg Seleniutn, liko sulphnr, forms several componnds with 

> Lchrtufh, 6 Aud. It. SI 3. 




WliGa acumiil of clilunne is ]iassei1 over BnleiiiitDi. tlia latUr 
melLs aud is cunvotted iuLo u browu ujly liquid, wlik^h iit selenium 
luoQcKhluriUv. Seleoimu is readily dissolved t>y this cotiijK>iiitd, 
nftfiiunting out un cooling in the form of metftUio selenium 
(Katlike). Selenium nionocliloride ia alowly decomi)ys(;d ^>y waier 
accordiu^ to tliu cqnalioa : 

2Se,C% + 3n,0= H^eO, + SSe + 4HC1. 


Tljis lirtily is obtained liy tho further aritlon of cldorine upon 
the mun'iKdilorido, ad well as when eeleniuiu dioxide is lieaUMl 
witli jiliDcsiihoms i>eutacliloride CMicliaelis) ; thus: — 

3SeO, + SPClj = 3SeCl, + PjO, + POCI,. 

Tbe t«trachloride is A wliite snlid body, wliich on heating 
volatilixe« wilhoat ]>reviou8ly meliinj;, suldiming in small 
crystals. It alao crystallizea fruin suLulioii in pliMphorous 
oxycliloridi* in the foiin of bright sliioing culwH. Il disAoh'fS 
in vater with ftinimtioa of liydruclilurio aud sulcmous acids; 

SeCl* + 311,0 = 4UC1 + H^O, 

SKLEiitCM XfosoRlKiiilDE. Se.Br,. 

aoo Equal parts of hroniiDc and st-Ietiiiim combine together 
willi evolution of h«il lo fomi ii black gemi-opflque litinid, having 
II siiecific gravity at 15' of 3G. It has a disagreeable suiell 
reecmbling tbnt of chloride of sulphur, and colours Cho skiti 
of a permanent red-brown tint. On healing it is decomposed, 
und when brought into rootact with water, sclcnious acid and 
hydrobromic acids are formed ; iha* : — 

2Se,Br, + 3H,0 = 3fte + H-SeO, + 4HBr, 



Selesicm Teteabhomide. SeBr,, 

This compouad U formed by tliG further action of bromine on 
the moDobromide. Il is an omnye yellow cri-sUilHne powder, 
best obtaiaed bv adOing bromine to a solution of selenium 
mouobinniiile iu carbon disiiliihidc It is very volatile, vapor- 
izing between 75° and 80° with partial dccompositioii aud 
eubUmiag ia block six-sided scales. It possewca a disagree- 
able Hiiiell siiQklar to tlmt of chloride of sulphur, decomposes 
ia contact with moist air into bromine and the monobromide, 
aud dissolves in an excess of wtUer with foriuatiou of hydro- 
bromic aud soluaious acids. 


Skxenium Se,Tf 

'The compounds of aelBnium and iodine resemble those nf 
selenium with chlorine and broioioe. l^he mono-igdidc ia obtained 
when the two element* are brought together iu the riglit pro- 
portions (.Sclmeider), and forms a black shining crystalline mass, 
melting between 68' and 70° with the evolution of a small 
quantity of iodine. Wlicn more slTOngly heated, it decomposes 
into iodine wliich vulalilizes, and selenium which remains 
behind, and ix decomposed by water iu a similar way to the 
corresponding bromide. 

Selenium Tbtra-iodire. Sel^. 

It ia a granular dark crj-stallinc mass, which melts, nt from 75' 
to 80", to a brownish-lilftck IJfjiiid, translucent iu thin films ; 
when more strongly heated it decomposes into its elements. 


When the vapour of selenium ia passed over melted fluoride 
of lead, a fluoride of selenium sublimes in crystals. These aro 
soluble in hydrofluoric acid, and are decomposed by water 



Oxides and Oxyacidh or Selenium. 

301 Only on* oxide of sclBnium, the dioxide, SeO^ is witli cer- 
taiiity known to exist in tlie free staU*. A lower oxide is stated 
by BerediuH lo be formed when Bclenium burns in the air. and is 
probably t]]e onuxe of ttic peculiar smell then observed, which is 
so pcnetraliiig that if 1 lugrra. of scteniuia be burnt iu a room 
the smull is fierceptible iu every part. 


Pra. lis. 

Selenium niao forms two oxyacids — seleniouB auid, BgSeOg, 
ftod scleuic itcid, H^ScO,. 

SKtj:MUH DioxitfB. SeOj. 

When selcninni ia pkced in a bent lube, as shown inFi<^ 113, 
nnd »tmrigly heated in a current of oxygen, contained in the gas- 
holder and dried by passing over puniice-stonc satumtcd with 
8ul[^aric acid, it takes fire and bums with a bright blue flame, n 
white tiublininte of EoUd g^leaium dioxide being deposited in the 
cool part of the tube Thus obtained it forni.s long, four-sided, 



briglii while. necdle-aililipQd cijrstAU, wliicli do not melt when 
bo&lcd nndpr the ordinary atmmpberic pre^urc, but evaporate, 
when li«ut«(l to about 300^ yielding a greenish ydlon'-colouied 
vapoar possessing a poweTfnl a«id 9iq«1L (Berzelius). 

Selenioi's Acid. D^O, 

202 Seleoious acid U formed -wbea selenium is heated vitb 
nitric acid, or when five parts of ttiti dioxidu nn: dissolved in one 
part of hot water On cooling, ckur, long, colotirli^fs. pnsniatic, 
uitre-shapcil ciVAtals of aelemotis acid separate ont These bare a 
strong aciil taste, and, whvn heated, decompose into 9«leniuni 
dioxide aud water. If sulphur dioxide is allowed to pass into 
a hydroc^hlorlc acid solution of selenious acid, selenium is 
depositcAl as a red powdor. This d«;conipoiiition takti^ pW^; 
but slowly in the cold and in abscncu of light; but vrben the 
licjuid is licutcd or in this sunlight, the change occurs quickly. 
Organic sulistances also bring about tbia reduction, aud the 
colourless solution of the pure acid soon becomes tinged vhcn 
exposed to the air, owing to the presence ot the dust in tlie 
atmosphere, Selcnious acid la dislluguisbcd from sulphurous 
acid by this reaction, for sutphurous acid gradually absorbs 
oxygen from the air. 

Selcuioii.t acid is a dibasic acid, and forma not only acid 
and normal salts, but also salts, containing acid selenit«5 united 
with selcnious ncid; thn?;, IIKSeO^ + HjSeOy 

The normal selenitea of tlie alkaline mctnls are easily soluble 
in water; those of the alkaline earths and Iho heavy niGtals are 
insoluble; whilst all Uio acid salts are soluble compounds. 
When a sek-nitu is hwited on chnrmal in the reducing Bame, a 
characteristic horsi^i-radi.'^h-like smell is emitted, and when 
heated in a gloss tube with sal-amnioniac, selenium sublimes. 
Tlio scleuLtcs azv further distinguishvd by the fact that red 
selenium is precipital^sd when ciulphur dioxide is led into their 
solution ia vatcr or in hjihochloric acid. 


This chloride of sclenimis acid is formed by the action of 
seleuiiiin dioxide on selenium tc^tracbloridc ; thus: — 

eeO, + SeOI,= 2SeOCI» 



It is a yellow lif^uid which futn&i on esiposnre to air, and 
which, wliea cooled helow 10^ (ieposils crystals having a 
specific gravity of 244, It boila at l"9''5 (Micliaelis), and 
deoomposGs vith water in the same way as all acid chloride*. 
VHwit mixed Willi tliiouyl ctiloride, sclcuiutu tetrachloride aud 
«ulphtu dioxide aio foriuoJ ; thus : — 

SeOCl, + SOC!... = SeCI^ + SO^ 


Fonncd by the action of Hcileniimi tetrabromiJc on soleuium 
dioxide The two substauci-s aro m«lted together, and llie 
compound, on cooling, crystftlUzcs iit long needles. 

Seles tc Acin. H-jSeO^ 

303 This acid, discovered In 1827 by Mitsclicrlich, is forraud 
by llio action of cliloritie on scluuiuiu or 011 scleuioua acid in 
presence of water; thus: — 

Se + 3C], H 4H,0 = H.,ScO, + 6HCI. 

By the same reaction selenites may be converted into selo- 
nittca Itromine iimy f<ir Ihin purpose he cnipIoy«() iiislcAd of 
chlorine. Potassium selennte is also ohtained vlicn eek'uiuiu 
ia fused wiih nilpc. 

In onlet to pneparo soleiiic acid, a solation ol" sodium 
selenite in treated with silver nitrate; and to the precipitate 
ohtaincd, isuspcudcd iu water, hroniitii; is added (J. Thonison); 

AgjScOj-j- HjO + Br, - 2AgBr+ JljSeO^. 

The oqneous solution of selenic acid can be concentrated by 
ev&poratinn, but it cannot lie thus coiiiplettfly freed from water, as 
at a temperature of almut^SO" it Itejiins to decompose into oxygen 
nod selonioiis acid By evaporation to 2^3° n liquid is obtained 
having a specific gravity of 2-609. and contfliniiif; 94'9 per cent. 
of selenic acid. When a hut sohillott of the nbovu sttensth is 
pineed under the tet-eiver of an air-puiii]), the sjKK'ifii; gravily 
may be brought up to 2627, and theii it coutaina 97'4 per ceut 
of selenio add (FubiaD)L 



1W eoa emU w t ei ttdd » a aAaodemtTaj aad bqnd. vlach 
ii MwriM* viA water in all pcapactioBa, beat hmg thaAy\ 
cmtvid. Tfct bnlcd aqptoaa add diaalves gald sad eofips ' 
villi ^T****'"* «f ttleaHMi add. wfaibt iraB, bdc, lad otliar' 
SMtaU diMoUc with evolQlioii or bTdnsgen and fnodoctioa 
«ff ariwatea. Tldi add ia not ledtwed cblMs by salpbtir dioxide 
«r bf ndphoreUed bydragen, and diflera ia this reopee _ 
iheteSon, rcmaikalfly frota aelfiuowa acid. Wben boiled witb 
hjdnKbUme aad it deoonposes with the erototkn oC dtlonae 
aadbmiatioBof MloiMtiaddi that: — 

U,SeO« + 2HC1 = HjSeO, + O, + H^. 

Tliia mixtare di^Bolrea gold and pUtionm, these netils com- 
biniDf; with the chlorine thiu set at liberty. 

Ike atUnata exhibit the closest analogy wit]i the sulphates 
•o far lu regards aojonul of water of cryMAllizotioti, ctTsUUine 
form, and Mlnhtlity. Harium selenate. like tlie sulphate, ia con)> 
|)letffl/ iiiwluble ia water.iiid is employed for thb reasoa ia the 
<lHnntitAlivc detcmuoation of sulcsaic acid; it i«, however, 
distingiiintied from barium sulphate inuoiach a; when boiled 
with hydrochloric acid the insoluble selemitc is decompused into 
the tolublewtlcnite, wlierc-as barium sulphate remains uuchaoged. 
All Ihfl other sclenatca aro also reduced to selenitos by means < 
of hydrochloric acid, aud tliia reaction sen'ea aa a means of 
recogDuing these compounds. 


204 Tlieae two dements can be meltad Uijielher in all propor- 
tiooa. When eu]pliur«tt«d hydrogen is passed into a solution of 
uleaiouji acid, a yellow prvcipituto of vjtnutm tfliv/phi<ft, ScS^ 
is Pcmned. Tins Uidy when dried, forms a red solid mass melting 
at a little above 1(X)', and allenranlB eoUdifyiiig to a translucent 
ortwige-red mtaa. 

U on Uie other hand Hpleniumtled hydro^n be passed into a 
eolution of aul|ihui'ou8 acid, a yellow predpitate is formed, 
which appL-nn chiefly to con»i»t of suiphnr diseJeHuU, SSe,. 

When fiidphur and aeleuium are dissolved together in bisul- 
phidc of uarbon, an iitomorphoua mixture of the two clcmontg 
cryflt^dlixt^a out on, cooling. This mixture if it contain not more 
than four atoms of sulphur to ono atom of selenium aiummea 



the moiiocluiic form of the seleuium ciystals ; when, however, 
the amount of salpbur is increased, the rliomljic form of the 
Latter element is assunoil (Beltcndorf, and vom Itath). 



It has long bccu ksoivu that when selenium is dissolved in 
fuming; sulphuric ftcid, a heautiful green colour is produced, and 
it has recently heen )>roved that this colour is due Co the fonna- 
tioD of the above voiupuuiid. Thi^ suUst&uce is best prepared 
by di&solviiig sf^lenium in freshly distilled well-cooled 8ul]>hur 
trioxidf. The r.onipound then separates out in the form of 
tdrry dn>ps which soon sohdify to priemalic crj'stuls, having a 
dirty green colour, and yielding wlicu broken up a yellow 
powder. The compouml (UsBoIvea in sulphuric acid with a 
green colour, and is decomposed on addition of water with 
Mpamtion of selenium and formation of sulphuric, sulphurous, 
snd aeleuious aciil«. On heating, the body does not melt but 
decompones into selcuiaui, selenium dioxide, and sulphur dioxido 

$ELE.vo8n.piiunrc Acid. 


This compound, which con-esponds to thiosulphnric acid, was 
diacovered by Cloez,' and like this latter acid ia not known iu 
the free atat«. Its potasaium salt in obtained when a aolulion of 
aulphurowB acid is mixed with one of potassium selenidc. or 
when selenium ia dissolved in a solution of uurmal potussiuni 
aulphitc The stlenmui plaits are isoniorphoua with tho thio- 
snlpbates, and are decomposed by all acids, even by sulphurous 
acid, with the separation of red »eleiiium. 

SELKNOTniTitromc Actd. H,SeS,Og, 

The potassium salt of this acid ia formed when a solution of 
pofusiuin seleno^ulphate is niived with oii excess of norrual 
potassium sulphite, and a coDCcutrated solution of selecioiu 
acid, thus: — 


Butt. Sot, Chim. lUMll 



yk« tritliiouic acitt, tliU suhsttance ia not koovm in the firee 
state. Ita reactions correspond to those of its sulphur represen- 
tative except that the prccii>itiitca coutuiu Helenium as well as 

TELLURIUM. Te = ia8, Density = laS. 

ao5 Telhiniitii occurs iii amall quantitte3 in the free atnte in 
nature, mid by early miiiemlogists was termed aarum poradoxiaa 
or metaUam proUematum, in cousirijuciicu of its luftallic limu-c. 
In 1782 native telluriiimwas more carefully examined l>y MilUer 
von Ileichenstein. lie came to the conclusion that it cotLtaincd 
a peculiar uictal, auil at bis suggcstiou, Klaprulli' iu 1793 
madean investigation of tlie telluriuDi ores coiilirming llic views 
of the former exporimeuter ihnt it contaiued a new metal, to 
which he pwe the name of irlliirium fruiu tdhtji, tbo earth. 
Berzeliua' iu 1832, made a mom exhaustive investigation on 
tellurium; ho likewise considered the substance itself to be a 
nuilal, but jta coiiiiiouuds were tbiiud to coiiespond so closely with 
tho><e of BidphuT and selenium, that tellurium was placed in the 
aulplmr j,Toup. 

Telhiriiiiii bflongs to the rarer elements. It occurs in 
Transylvania, Umigaryj California, Virginia, Brazil, and Bolivia, 
IB small (^uniititiea in the native state, hut it is generally 
found in combination with metals as graphic tellurium, or 
sylvaiiitc (A^Aii) To,^; black ti'lliuinin, or Nugyagito (AuPb)j 
(TeSSbJj,; white tellurimn, or silver lellnride, AgjTe ; tetra- 
dymite. or bismuth telluride, lU-Te^ &c~ 

PrejHiriitiini.—ln order to jirtjiaiti jnire ti'Ibiriiim, •cllnriutu- 
bismuth eoiitaiuing about 60 per cent, of ti'llurium, 36 per 
cr-iit. of hisimilh, and ahuut 4 \h:t cent, of sulphur, is mi:(ed 
with an equal weight of pure carbonate of soda, and then tlte 
mixture rubhed up with oil to a lliick paste, and heat^xl 
strongly in a well-closed crncible. The mass is then lixiviated 
with water, and the liltvrod suhUiou, which conlnius sodium 
tclluride and sodium sulphide, is exposed to the air, when the 
tellurium gradually scpaintcs out iw a grey ptmdpr, which after 
washing and drying may be purilied by distillation in a current 
of hydrogen (Berzeliu-t). 

1 Cftlt. ^mn. i. 01. 

' J^. Ann, xxriii. SH ; xxxii. 1 auA &77> 



In order to obloin the Icllurium from graphic- or fi-om black- 
tellurium, the ore u treaud with liydtxicUluric acid iu order 
to free it from ftntiiiiouy, nrec-iiic, and otb«r bodies. Tliii 
residue is tlicn boiled with af[ua regi&, and the liltnit« eva- 
porated to drive uff the excess of nitric acid ; ferraus siiliiluitH 
is tbeu added, wliicb )ti'vcipit(tt«» the ;;old, niid the tdluriuDi 
%» thrown duwii in the hltrate by means of Bulphur dioxide 
(v. Schrbuer). 

Pr<fperli<a.—l'\ais tvUurium is a Wuish-wbitcbody [)os»o»siDgft 
tnetallic Instre, ami ci^stalUEiiig iu rbombobcdra. Tellurium ia a 
very brittle substance, and am tlii>n<rore be eaHily powderttd. Its 
specific yravity is 6'24 : it melta at about SOO", and boils at a 
still higher teiiipeniture. and may accordingly he uasily piiriGcd 
by distillatiou in a sLrcaiii of hydmgen gas. 

Tellurium bums when healed in the air with a blue tlaute 
«volviug whiti- vapours of tcUuriutu dioxide. It is insoluble in 
water and carbon disulphide, but di^olves in cold fuming sul- 
phuric acid, itDpariinj; to the solution a. deep-red colour, -whicb ia 
lirobttbly due to the formatiDH of acomjiouiid nnalogous to sulphur 
sesquioxide. uamcly, STt-O^, tlio tellurium being pfccipitflted 
oo Uiv addition of walur. On hi-utiug the sulphuric acid solution 
the tellurium is oxidized, Bulphur dioxide being given off. In 
the same vay it rapidly undergoes oxidation in the presence of 
nitric acid. 

When heated ucarly to the nielting-point of gloss, IcUurinm 
emila a gnldi^ii-yi^llow vapour, whic:h givt-s an absurpliun spuc- 
tnuD, L-onsisting of tine lines stretching from the yellow to the 
Tiolet.* The emtitsion spectrum of telluiiuiu lins bcr.n uupped 
by SaJet » and l>itte.' 

According to Dovillc and Troost the vapour of telluriuiD 
poseesses a speciSc gravity of 9*08 at 1390°, which number 
agrees well witli the theoretical density of 1 28.* 


TELLtTBiUM lIviniinE, on Telllketted Hvdsogkn. H,Te. 
Density ^C;. 

3o6 This comiwund, discoveiwl hy I»iivy in 1810, is a coloar- 
le^ gas poe6e«sing a fwtid siuoll similar to that of aulphurett«Ki 

I Oomu. Camj*a AniTiui Ixxi*. 1190. ■ lUd. hxlii. Stf2. 

> Ctm/M Htndw, Uxiu. »»-7<l * Ibid. Ivi. $71. 


hydn>g<Ml. Ic is formed in small quantities vhea tclluriiun is 
befttcd in hydrngon gas. If tiiis is allowed to tsike plucu io a. 
soared tube, the same pheDomcnon presents itself as is obaen'ed 
vrith 8e1«nium, antl tJie tellurium sublimes in luug gUtleriiig 

In order to prepare tellurelted nj-cliogen, tellurium is heated 
with iinc, Rud tlic zitic telluride tlius turmed, dc*;ompo*;d by 
hydrochloric acid ; thus : — 

ZnTi: + 2HC1 = ZaCl, + HjTa 

Tellurium hydride is easily combustible, bnming with a blue 
flame. It is sohible in wukT, and this solution al)aorhs oxygen 
from the flir, tellurium being deposit«(L Like sulphuretted 
hydrogen, tolhiretted hydrogen pTecipitat«'3 many of the metals 
frnm their solutions i:i the form of telhirides. The soluble 
tellurides, bucIi &s i]\o%o of the alkaltiiv niclab, form brownish 
red Bohitions frnm whi(;h Udlurium is deposited oo exposure to 
tlic air. 

The density of tellurium hydride, as that of selcniureltcd 
hydrogen, has not been as yet directly determined, but Bineau 
has shown that both gnscs, when they arc heated witli certain 
inetnis, give up all their seleuium or tellurium, thu« leaving 
a residue of hydrogen which occupies tlic same volume as 
tlio original gas. Henee each molecule of both of these gases 
contains one molecule of hydrogen combined, as analysis shows, 
with one atom of each of thfiais elemcnls. Conseqncntly one 
volume of tellurium hydride contains oue part by wciuhL of 
hydmgen and sixty-four parts by weight of tellurium. 


207 This compound is fonned togptUer with the tetrachloride 
when chlorine is parsed over melted tellurium. It nuiy be 
sepamtvd from the less volntite tctnichloride by distillation, and 
thus obtained, it forms an amorphou.'i almost black mnss which 
gives a greenish yellow powder and w easily fusible, yielding 
a deep red-coloured vapour. 

Water decomposes the compound with separation of tollimum 
and formation of tellurous acid ; thus : — 

2TcCl, + 3H,0 = Te + HjTeO , + 4Ha 



TELLonniM Tbthacoloridb. TeCI^, 

Is fonned by ilie furtlicr nction of clilorinft on the preceding 
oolDpDund. It is a vliite cr^'^talline Wly whicli easily melte, 
forming a ycUow liquid, which when more stronfily hoatwl 
becomes at last of n (lark rod colour and begins t« boil. It 
is extremely hygroscopic, and is decoinpoatd wlien thrown 
into cold wator, an insohihle oxychloride b«in^' formed together 
with telluroii3 acid. Uot water, oo the other hand, gives 
rise only to the formation of the ktter compound. Like the 
coireepondiug tetrachlorides of sulphur nud seleninm tt forms 
ciystalline c<;mpoumts with s tarj^u number of metallic chlorides. 


Telltjkium DiBEosiroE. TeUr,, 

Is best obtained by heating the tetrsibraniido nith tellurium. 
On healing it volatilises in tlie form of a violet vapnur, which 
CDiiden^s to black needles, readily lueltiiig, aud ajjaiu solidify- 
ing to a crystalliuQ mass, 

TEixtrniUM Tetbabbohidb. TeBr^ 

In order to prepare this compound^ finely divided tellurinm 
is added to hroniine which has been cooled down to 0°. It is 
a dark yellow solid body wluch can be sublimed without de- 
cotoposilion. It ilis*o!vi'8 in a small qimntity of -water with a 
vellow colour, but when added to a larj^e (jiiantity of water the 
lutioQ biwotncs colourless from the formation of hydrobromjo 
^md tcllurous acids. 


Obtained as a dark block crystalline mass by heating iodine 
and tellurium together in the propter proportions. 

TKLLCttltlSJ Tetea-iodide. TcI„ 

Is formcfl by the action of hydriodic acid on telloroua add ; 


H,TcO, + 4ni = Tel, + 3H,0. 

It fonns an iron-grey crj-staUine mass which melt* when Kcntly 
bent«d. and when hcnlod more strongly decomposes with supftm- 
Lian or iodine. It is but sUglitly solahle in cold water, and is . 
docomposed by loiliag w&ter. 



In prepared by heating the dioxide mtb hydrofluoric acid in n 
pktinum retort. It dietils over as a colonrlesa, transparent, very 
deliquescent mass. 

0.\lt>E8 ASn 0.tTACtnS OF TM-LUBimt. 

208 LilcR sulphur nud »clotuuiii, tellurium ^-ields two acid- 
foriuing oxides, TcUj, and TeO,. 


Occurs ill the impure state in nature as lelhirit* or tellnriunij 
ocltTC, from FuccWy in Trausylvauia. It i» formed by the ■ 
combustion of tellurium in the air, and separate out in small 
octahcdra when tellurium is dis.solveil in n-arin nitric acid. It 
is only very sliylitly eoluble in walvr, «ud the soluliou docs uut 
redden blue litmus paper. On beftting it melts to a lemon- 
yellow Ii(]ui(I which boils on further henting without decora- 
position, whilst on cooliug it sylidifiea to a white cryslidline 
mass. Although Ihia is an, acid -forming oxide, it also exhibits 
basic properties, inanmucli hs it combines wilh certain acida 
forming an uiistal^le clase of salts xvhich are decomposed by 

TELLUitopa Aciix HjToOj. 

I8 obtained by pouriiiy a solution of tcllurinm in dilute nitric 
ft':id into water. It separates out iu the form of a veiy 
voluminous precipitate, which when placed over sulphuric aci<l 
driaf to a litjht white powder. It is but slightly soluble iii 
water, aud Uie solutioa poseeases a bitter tast*. Tellurous acid. 



like sulpliuroiui acid, is dibasic, and therefore fornu tvo series of 
salts : thus we have, normal potassium tellurite, KjTeOg, aad acid 
potassium tfillurit*;, KHTeO,. Tetm-tellurites also cxiat. and 
these are obtained by the combimtiou of noi-mal Lelluritt^a with 
the dioxide ; thua ; — 

K^TeOg. 3TeOj. 

Tbv tellurites of the alkali metals arc soluble in water, and bic 
fonned by the solution of the acid in au alkali, or also by fusing 
Iha dioxide with an alkali. Tlie tellurites of the alkaline earth* 
ore ouly slightly Bolubte, and tliose of the otlier metaU are 
insoluble in nrater, but soluble in hydrochloric acid. 

Tkllurii'm Trioxide. TeO,. 

This oxide is prepared by beating crystaUiied telluricacid to 
Bsarly a red hcut. If it is he«i«d too strongly, a small ({uantity 
at dioxide is formed with evolution of oxygen, but Ibis can be 
separated by treatment with tiydrurtilaric acid, in which it di^ 
aoires, whilst thelrioxide is insolubla Tellurium trioxide ia an 
orange yellow crystalline mass, which, when stroiiyly heated 
decomposes into oxygen and the dioxide. 

TEU,uitic Acid. H^TeO^. 

209 \VIien tellurium or the dioxide is fused with caxbonate cf 
[M}ta»b and saltpetre, potassium tellnrate is formed ; thus : — 

Te, + KjOO, -t- ^iKNOs = 2K2TeO^ + N, + CO. 

The same salt is produced when chlorine is passed througla 
au alkaline solution of a tellurite ; thus : — 

KjTeO, + 2K01I + a, = K,TeO, + 2KC1 + Hfi. 

Oo dissolving the fused mass in water, and adding a solution of 
barium chloride, the insolublo hurium tcllurat« is precipitated; 
tliis is ptuified by washing with water, and afterwiudH decom- 
posed by the exact amount of sulphuric neid necessaiy. The 
clear acid solution, filtered from the sulpliatc of barium, gives on 
evaporation crystals oTthe hydrated acid liaWng the composition 
HjTeO^ + 2HaO. Tha^e are dilYicultly soluUe iu cold, but 
readily soluble in hot water. Vr*hen the crystals are heated to 
ltiO°tl)cy lose their water of crj-stollization, and the telluric acid 



romains as a white powd«r nearly inaoluble in cold, but readily 
dis-wlving ia Lu>c wutcr, with formation of tlie crj^stnlline 

Tlu Ttllmratts. — Amoiifist llio tcllurau^ only thoMu of tliu 
ulkali'liietals nro tiiorc f>t li^'i^ readily eolublti in water, those of titu 
remdltiiii<^ metiiU lieing eitln^r ftparingly soliiltlii or insoluble in 
TaltT, aUlioiiyh yeiierally tlissulviiij; readily in Uydrochloric acid. 

CcrLiiiii 1)1* the lellttratcii are found to exisi in two modifica- 
tions, viz. : — 

{a) As coluurless salts, eoluble in water ov in acids. 
(&j As yuUow salts, insoluble in vriitci and iu acids. 

Besides these modilicatiaiis we are acquainted not only with 
uortuol aud ticid tellurates, but wltli sewml otlier series of 
acid salts ; thus we have : — 

(1) Normal potassium tellunUe, K.TeO, + 511^0, obtained 
upoD evaporadon of a Mlution, either in tlic form of crystalline 
crusts, or as tt gum-like residue, both bfing soluble ia water. 

(2) KjTeO, 4- TeO, + 4I[siO, a salt spariuijly soluble in cold, 
but dissolving freely in hot wat«r, aud CTyetallizins to n woolly 


(3) It^TeO^ + 3TeO, + 4H,0 (or :i KHTt-O^ + 2 H^TeO. + U/J). 
a Bait spatingly soluble iu wiilvr, obtained by adding nitric acid 
to salt Na 2. 

Theyellowmoililication of this salt is obtained when salt Xo. 2 
is heated to redneas. On adding natei f>> the tvsidue, aonnal 
potn-^sium tellnrate dissolves out, and a tetrftlellurate remains 
beliind, being iusulublc iu U(iU>r and in dilute aci<l-'«. 

Barium tellurata, BaTeO, -v 311,0, is a wliiit (lowdor uul pre- 
cipitated in dilute snlutions as it is not quilL> insuluUf iu watL-r. 
The di- and tetm-tellurate of barium, as ivell aa ths cjilciuiu 
aud strontium lellurates, are similar white precipitates, whilst 
the magnesium tellurate is rather more soluble. All the other 
telluratea are insoluble iu water. 

■Wlien a telluratc j» heated to redness, oxygen, is evolved and 
a toUurito formed, and tins reduction also occun*. with the 
evolution of chlorine, when a tellurate is heated with hydro- 
chloric acid ; thus : — 

K,TcO, + 2Ha == K,TeO, + H,0 + CV 





3IO Is obtained as a dark brown procipilata vrhen sulpliuretttd 
liydrogea is passed tliruugh aa aUiidine solutioD oi a tellurite, 
until it is fiatomted, and then hydrochloric acid adilei). Tlie 
dry compound, wlieu rulibed. exhibits a nietaUic lustre, aud on 
bcAtiog it tutiltSr but is decomposed at a high tCQipcrature iutu 
sulphur ftud t^'iluriutu. 

TEU-URirM Trisclfhide. TeSj. 

In order to obtain this autaunce, a dilute solution of telluric 
acid must be saturated with sulphurfUed lijilragen in a dos'-d 
vessel, and the solution allowed lo stand. Tlie irii-nlpljule is 
deposited gradually as a gnienisli-black pawdiT. 

Both fiutphides combine witli metallic sulpludos to form tliio 
salts; tbuti— 

Potassium tliiotellurite, Kj^ToSj. and 
Polasaium tliiotelluiutt, KjTefi^. 

NITROGEN. N = 14-01, Density = 14-01. 

ail Dr. Kulht'iToiU, Professor of Bolaiiy iu the ITuiversily of 
KdinboTgh, showed in the year 1772 that when animals breathe 
iu a closed volnme of air, it not only becomes laden witli impurv 
air from the respiration, but contains, iu addition, n constituent 
which ia incapable of supitudin^' cunibustiou and rcspiratiuu 
He prepared this constituent by trcatiag air in whiub iiiiiinals 
bad breathed with canstic potash, by means of which Uie fixed 
air (carbonic acid) cau be removed. Tbe residual air was found 
to extinguish a bnrniug caQdlc, und did not sujiiKtrl tliu life of 
animals which were brou);bc into it.' 

Iu the same year I'hestley lound that when coibou is burnt 
ia a closed hell-jar over wnt^-r, miti-fiflh of the common nir is 
converted into fix^d air which can ba ab^orlied by milk of lime ; 
a residual (phlogistioutcd) air incapable of supporting cither 
cwmboition or vespiration bt-iiig MX. I'ritstley, however, did not 
cumiider that this air was a contstituent of the aliuoapliere, and 
it U lo Scbeele that we owe the first statement* contained in the 

' Kulhrrfonl. Dt an MrpMtito, JEdiiti. 1172. 



tutmductjoa to bis trratise on Air mid Fin. tli&t the ' air must 
be coiaposcd of twu dilTvrcut kinds of elastic fiuids." The cou* 
stituent known a.i mephitic or phlogisticiited air wns fint 
coBsideted to be a simple Ijorly by Ijivoisicr. wlio gave to this 
giLS the namm asott (rrom a, privaiivc, Hud ^aiij, life). Chtptal 
Krst suggested tlit- iininu nitrofjen, wbiuU it now generally bears 
(from nitr-jim, siltpetre, and livvata, 1 give rise to), because it is 
contained in saltpetre. 

Nitrogen is found in tliu free slate in the atmosphere, of 
which it forms four-fifths by bulk, and occurs also in coinbi- 
□atiou ill many bodies such as amnioaia, in Uiu nitrates, and iu 

Kio. 114. 

many organic sub«tanoo8 wbicA form an ewential part of the 
bodies tif vegetables and aoimaU. 

aia PrcjiaratiorL, — The simplest niotliocl for preparing nitrogen 
is to remove tlie oxygen from Uie air. This can be done iu a 
varied of ways :— 

(1) A sniaU light porcclaid basin is allowed to swim on the 
water of a pneumatic trough. A small piece of phosphorus is 
brought into the biuiin and ignited. The basin is then covcreil by 
a largo tubulatwl 1x!U-jiir(9ee Fig. 114). The phosphorus burns 
with the dejiositioij of a white cloud of phospbonts pentoxide, 
which, however, soon (li.'wolves, whilst on cooling, one-fifth of 
the contcnta of the bell-jar ia found to be filled with water, 
llie colourless resiJiifd giis is iiitroyeti ; this may l>e t!»i]ly 
proved by first allowiug tha btrll-jnr to sink so far iu the Irougli 
that the level of the water in tlte luside and outside ia equa], after 
which, on opening tlie stopper and plunging a burning taper 



into tiie bell-jar. the Hame U seen to bg instantj}' extio- 
gnished. Thu uitrogen thns obtained is never perfectly puri;, m 
it always cuiitaius small quaotititis uf oxygeu whieli have nut 
bceu removal by the combustion of the phosphorus. In pre- 
tence of aqueous vapoiti, pbuspliorus alowly iLbaorbs tbe oxygva 
of the air, eveu al the oiilinnry temperature, whilst tbo sulpbides 
of the alkali metals a» wvU us moiac sulpbido of iron (obtained 
by healiug flowers of aulphur, with iroQ filings and a little 
water) act in a similar way. 

(2) lu order to oblaiu pure nitrogen, air contained in a gas- 
holder i^ allowed to ftasa through tubes, t mid t'. Fig. 115, 
containing caustic potash and sulphuric acid for the pnqwse of 
piintyiug tlio air fi'uui carbon dioxide and drying it. The air 
thus punned is passed over turnings of pure metallic copper 
contained in a long glass tube (e f ) which ia heated to rcdiiess 

Pti^ lU. 

in a oharcoal furnace ; copper oxide U thiu formed, and pore 
nitrvgcn pniwes orer and is collected in the pnoumatJc trougK 

(S) Pnre nitrogen can nliw> be obtainod hy heating a concen- 
trated aoluiiou of ammonium nitrite ; thns : — 

(4) By Uie action of chlorine upon ammonin, pure nitrogen is 
sUo formed ; thus : — 

sy H, + 3 Cij = N, + 6 NTI.CL 



Tho chloiiac evolred io a Urge flask passes iaio a three- 
necked-bottlA flask containing a sttoug aujucous buIuUod of 
ammonia. Tlit; tiitn>K«a fi&A wlitch is tiere liberated ia collected 
in tlie oiUiusry wajf over water, aa sliowTi in Fig. 116. Care 
must, liowovor, bo lakvu in this pivparaliou tliat the amniouia 
is alvrays preeent in excess, otlierwise chloride of nilmgen may 
be formed, aatd tbia ia a higtdy dangeroas body, which vzplodea 
most violently. 

(5) Amtnouiuta iutnit« aud atuuiouium obluriJe, when heated 

Fio. 11& 

together in solntion, yield a taixture of iiilrogein and chlorine 
guacs ; thu9 ; —, + 2NH.CI = 5N, + CI,+ 12HA 

The gases tlius evolved may he separated by passinj; tliem 
throu(^h milk of limfl or enustic soda Bolation. when the 
chlorini! ia absorbed and ifie nitroyen passes over. 

(G) On heating ammonium dichromate, nitro^n gas, chromium 
eesqaioxide and water, are formed ; thus : — 

(NHJi,Cr,0. = N, + CrjO, + 4HjO. 

Xitrn^en mny he ohtainvd by this rcnction nt a cheaper rate 
hv heating a mixturi^ of potassium dichromate and sal-ammoniac 



instead of the ammonium dichiomate, wliicli ia a somevhst 
expensive salt ; tbus :^ — 

KjCrA + 2 NH,C1 = N, -f CtjO, + 2 KCl + 4 H,0. 

fti3 I^vperitM. — Pare nitrogen is acolourless, tast«1es», inodor- 
ous gas, which is distinrpmhed by Ma inactive prapertiee ; hence it 
is SQincwhitt diOiciUt to i^ccrtHiu iU pn'senc-c iu small qiiatilities. 
As has beeD said, it does not support combu&tion. nor do«s 
it hum nor remU-r hiiit;-w»tt;r tiirhJtl. It combines directly 
with but \&y few eleuients, although indirectly it con easily hu' 
made to fomi rniiipramiU with n large number of the eleniftiitary 
btNlies. (iiid ninny of its conipoundg. such as nitric acid, am- 
in^iiia, chloride of nitrogen, &c^ possess chtmictwrislic and 
rematkable jiropertiea. Tlje specific gravity of nitrogen is 
0'97i:i. and one litre at 0", ami undur the nonnal pnasure, 
weiyhs l'25C167gnii. (ReitiHtult). 

Xitrogeu is but slightly soluble in water, one volume of 
water absorbing only 0*01607 of the put at 10°, and a smaller 
qoautity at higher temperatures.* The co-efiicleut of tlio 
solubility of nilrogeu (•:) may be found by the following inter- 
polalton formula : — 

<:=002l>346 - 0-00053887(+ O-OOOOllSfirt 

The gas is mlber more soluble in alcohol than in "uratcr. 

Thcro UK two dinmcteristic spectra of nitrogen both obtained 
by passing the spark from an induction coil through a GeisAler's 
tube containing a small quantity of hij^Lly rarelied nitrogen gas. 
Th« nitrogen spectrtitu coininonly ohliiincd in this way is a 
chonnellod one. exhibiting a large number of bright bands, 
oepeciolly numerous in the violet. If tlic spark ia produced 
by high tenRion, as wlu^n a T.«yden jar is used, a spectrum of 
ottmerous tino lines dislributcd thraugltout the length of the 
^Gctrom will bv obtaiuud (I'lUckur). 


Ammonia. tiU^ Density = 8'505, 

314 Ammonia is found in th(> ntnia^pbcrc in tlie form of the 

carbonate fomiing a sinnJI but essential comtituent of the air. It 

likewise occurs in contbiiiiition with aitrio and nitrous acids 

iu rain-water, and, csi<ecially as Gal-ommoniac, NH^G, and as 

1 Bnnwu'a Onomttrit, p. 144. 



sulpljate of ammonia, (NHiJ^SO,, deposited on the «id«, Uw 
craters, and ia the crcvines of tlie lava streams of activfi volcanoes, 
oi well as mixed with boric acid in llie fiiniaToles of Tuscan;. 
Miuiy samples of ruck-salt also coutuiii tmces of nuuuoiuaviil 
oompounda. and all fertile eoil coctains this subetance, which 
is likewi3e found, althoiigh in small qiiaiititieii. widely distributed 
iu raiu mid in niiiiking water, as well a^ in sea-vater, in claj'e, 
mttrla, and ochres. Ammoniacat suits nrc also found in the 
juices of plauU ittid in most ouinuil fluids, especially m tbe 

Ammonia was known to the early alchemiatft in the form of 

the Cai'boiiate under tlie name of spiritui solis urijia:. In the 

fifteenlli c«nt»ry liiisil Valentine showed that tliv Siune body 

may be obtained by the action of an sUcali upon Bal-ammoniM; 

aiid Olauber, in consctiuciim!, tenimd this iKidr spiritnn lythtUis 

iKdia armoii-iaci. Snl-ammouiac, vliich was known to Oeber, 

appears to have bocn brought in tlic seventh contury from 

Asia to £uTOpc, and was known tiudur the name of mt-arvto- 

niaeum. It is possihlc that this sal-aniiitoniac was derived 

from tlie volcanoes of Centml Asia, tlelier, however, describes 

the artiiicial production of the salt by hettling urine and common 

ealt to};uthtir. In lutor tiinoi), sul-auitnonioc was brouglit into 

Enrope from Eg>"pt, where it was prepared from the soot 

obtained by buniing camel's dung. Its original name waa 

altered to eal-arnt»niacuni, and then ogain changed to aal- 

ammoniacum, Thia last name served originally to describe tbe 

common salt (cldoride of sodium). whii:h wils found in the 

Libyan doscrt in the neighhourliood of the rnina of the temple 

of Jupiter Ammon. Bm-le says in his •' ilenioir* for the Nnlurnl 

History of Huniau Ulood;"' — "Though the ml-armoniac ibaiM 

made in the Bust inuy i-onsist In great i)art of camel's urine, yet 

tbat which is made in Europe, and commonly sold in our ahopa, 

is made of luan's mine." Later on, sal-ntumoniac was obtained 

l^ the dry dlslillatiou of animal refuse, such as hoofs, bones, and 

horns ; tbe carbonate of ammonia thu.4 obtained being neutralized 

with hydrochloric acid. I'rnm this mode of preparation auimonia 

was fonnerly termed spiritt ofharUhorn. 

Up to the time of Frieatley, ammonia was hnown only in the 

state of a^queous solutioD, termed spirits of hartshorn, or 

a^irUnt volatilis talis ammoniaci : and Stephen Hales, in 172", 

mentions that when sal-ammoniac is heated witli lime in a 

1 Boyle, op. W. £»7, 1BS4. 



bI cIoBed by watiT, no air is given out, but, on the coalmiy, 
fvKta 19 drawa iuto tlie apparatus. 

I'riestle}", in 1 77-4, repeated tliis experjmeul, with tlie differ- 
ence, however, that he u£t>d uicrcur)' to clom liis apparatus. He 
tlius discovcrvd aiiiuionla gas, to wtiiuh lit; pivt- tliu name of 
aikttUne air. IIu also round, that, wbcn electriu sparks arc 
allowed to pass tlirough tlii.'i alkaline air, iu voltimo undei|;oes 
ft rexoarkable cliaiige, and iJl« rp.sidual air is Tuund tolmcom- 
bnstible. ULTtboUct, following up tbJs discovery in 178S, 
slutwuU that tbe ittcreaije of \'iiluiiie wtiioti atiinioitia giis thua 
undeifjoes is due to tbe fact tli»t it la decomposed by the electric 
ifjnrk into hydrogen and iiitroyoii. This discovery was conlirmed, 
atid the couipositiuu oX the ^ne more accurately det«ruiiu4>d by 
Austin (I788X H. Davy (1800). and Henry (18(19). It was 
shown by thom that, in tlie reaction above desoribcd, two vohimus 
of ammoDia arc resolved iiito throe volumes of hydrogeu and one 
of nitrogen. 

315 It baa recently been proved by Donlciu tliat ammoniii 
cnn l>c synthetically prepared by the direct combination of its 
clemente,' the silent electric diachorge beiug, for this purpose, 
pat^sod thnnigli a niixtum of nitrogen and hydrogen. 

Ammonia is also formed : — 

(1) Hy the pHlrefaclion or decay of the nitrogeuous con- 
ittitnents of plaiit.'^ and aniinak 

(2) By tbe dry distillatiou of the same bodies; tbat 13, by 
healing tliese substances strongly out of conluct with air. 

(3) By the action ofhydrngeu on the salts of nitric or nitrous 

It is to the tint of these proctsscs tlinb wc o^vc the existence 
of ummoDia in the atmusphcre, nhiht the second serves for tbe 
production of nmniouia and its compounds, especially of saU 
ammoniac, on the large scale. 

At the present day almost all (he sal-anmioniac and other 
ammoniacal stdts arc prepared from the ammomocal hquor vrhich 
is obtained as a byc-])roduct iu the manufacture of coal-gaa. 
Coal consists of tliu rt-nininfi of ai] iincicnt vegetable world, and 
contain? about 2 per cent of nitmg:pn, the (freater part of whiuli, 
in the process of the dry distillatiou of the coal carried on in the 
iDi&nufMlure of the ^'tt?, \i obtiiiiu'il in tlie fomi of ammonia 
dissolved in ttie water and other products formed nt the same 

■ W. r. DoaUn, Pnc. Scf. SK. xxi. »L 

In order to prepare saUammoniuo Dtim this liquor, which 
contains not oiily Tree untmonio, but the salpliidc, cuibonate, 
enlphitc and thiosulphato of ammonia, it is hoiliad witli milk of 
lime to liberate the wliulu of the ammonia. This ammoni;i 
diatihi over, and tlio dintillato is ueatrali2«<] with bjrdrochlori<; 
acid, and tlie sul-ammomac formod as follows :— 

NH, + HCl = NH^CL 

TMs salt is then evaporated to diyneas aJid purified bj? subli- 
mation. Prequently, however, itulplmte of amtnonia is first 
pr«pnred, and as thiA ia uiure cosUy purilicd, it is much tised 
as the nw materia.) from which the oUier aDUUoniooal oom- 
pouods are maiiufocturvd. 

Prtpartdum. — If any one of these ammoniacol salts be 
heat«d with an alkali, «uvh as potash or sodit, or with ilii alkaline 
enrth, such aa lime, tha aminouitt is set free as gas. In order to 
propare the giis it i» only neceasary, therefore, to heat together 
sal-amraouiac and slaked lime; thus: — 

2 NIT,CI + Ca(OH)a = 2 NH, + CaCl, -i- 2 H,0. 

In order to ensure the decomposition of all tlio sal-ommoniac, a 
l»r^ excess ofUjiio is usually employed. One part by weight 
of powdered siU-ammoiiiiu; is for this purpose mixed with two 
pnrt.s of caustic lime slaked to a line dry powder; these are veil 
mixc«1 tc^ether, and then introduced into a capacious Qaak, placed 
oil a piece of wire gauze and heated by a Bunaen-hunp. The 
ammonia gas, which comes off when Ihv mixture is Heiil)y heated, 
is then dried by allowing it to pass through » cylinder tilled with 
smull hiiups of f]^uick-liine, ami Uic g^d thus dried may be col- 
lected eitherover mercury, or, like hydrogen, by upward displace- 
ment in an inverted dry cylinder as shown in Fig. 117. inasmuch 

8 '50 5 
ta this gfls is -TFrr^ = 0-586 times as light aa air, one litre 

woighin-; at 0° and under 760 mm. pressure, 0'76193 grams. 

3i6 Properties. — Puru ammonia is a gas, possessing, 
tike its aqueous solution, a peculinr pungent alkaline odonr and 
caustic taste. In the solid state, liowcvcr. it ]>o$seBSes but a 
very fuiut smell. AninioDift gus turns ivd titmus-papor blue, 
like the alkalies, neutralizes scids. and forms with them a series 
of stable compounds, termed the ammoniacal aaita. 

Amiuoaia gas was first liqueti(;d by Fnradny, in 1823, 
by heating a compound of silver chloride with ammonia, 

placed in one lirab of a sCroug bunt tube hermetically sealed, 
whtUt tliB ulbur limb was placed in b freezing mixUire; The 
.compomid of Rilvt^i- chloride nnd ammonia is obtained by 
-fiattuatin^ dry pre<;i[jitah:d silver chloride with antuionia gu : it 
has the furuula Ag€l(Xlfj)jand fueea at 33*, whilst at about 
1 15° it begin.t to part with its. animnnia. Tho gnu thus collects 
ill the tube until iLe piesaure is reached under which it beglna to 
CODdeoM u a cluar, liighty refrocliu;^ liquid. Whuu tho silver 
chloride cools, the ammonia is aijttiii ulworbcd, the original com- 
potind being ic-fomivd. Uiiuid aiuntouiu is hko easily obtained 

Vm 117. 

hj- leading the gns into « tube plunK«'.il in a freezing raixture 
composed of crystallized ciilcitini chloride and ice, and having a 

' tempeinturf of —40°. Liiiiiid atiimonia is a colourless highly 
refracting liquid, boiling n.t — 39*7 (Bunsen). When Mic tcm- 
perntnre of the liii>id i« lowered to below — T5' in a bath of 
solid carbonic acid and ether ])laced in vactio, a mass of whil« 

' tmoBluceut crystals of solid ammonia le obtained (famday). 

The co-efficient of expansion of liquid ammonia is 0'00204, and. 
iherefon;, largw than tliat of most littuids having a higher boiling 

'point; its apecific gravity comjiared witli water at 0* is 06234.' 

* Jnlljr, ^OH. Ck*m. tiuirm cirl{. 181. 


m 4^ 


afetiid lif to enpontiaa CM CM^ >e AvwB hr the I 
AzpnoMoL 7\te »pfaata» rep ai red lor tbis fmr^mm ooaHO 
iMiiiiilly of two lUiMi; glHi tabM (« n4 A. F^ US). w^A 
KB doMd bdor nd aie uma a jb ei togclka by ike tabs |c c) 



Pig. lis. 

and id d). Tlio tube {d d) «nds at (/) in a narrojver tulie 
(m in),\rtiirli la at thU point melted intotlie tube (a). The tabe 
(a) U Llireo-roiirtlu filled with rd aleoliolic solution of amtnoiiiu 
ftatumtnd nt S°, nnri Ww.n placed in the cylimloT (a). The 
syphon tuho (//) anA tlie t«te {//), which reach to tb« 
Iwttom of the cylindpr. arv fixed in pfisilion through the cork. 
In order tiaw to perform the expcTiment, the cylinder (A) is 
neorljr fiUvd with warm water ; the glass stopcock (k) is 



opened, and the tube (b) placed in ice-cold vfater. The water 
coDtsined in the fUak is now quickly boiled, and thus t)io 
water io (a) is rapidly lit'ated to 100°, and tlie Binmoiiia saa 
drivtjn out of solution uDtil I'y ita owu pressure it liqHelies in {!>). 
As soon aa the condensation of liquid antiiioaia ceases, the 
ebullition is stopped and a. portion of the hot waler is witli- 
drawn from tlie cylinder by tiieans of tbe syphou (</), cold w&ter is 
allowed to enter the cylinder, and after a while this is Teplavcd 
hy ieo>cold -wat^r. The cylinder (b) is now removed, wl»^n the 
Uqoetled ammonia begins to eviiporate and is again absorbed by 
the alcohol, though only slowly. But., on dosing the stopcock (h), 
the gaa above the alcohol is quickly absorbed, and thus tbe 
eqnilibiium is dislorbed. The ammouia now passes rapidly 

Fio. iiii. 

through the tube (m ni). and is abnorbed 90 ^aiekly that the 
liquid amtuouiii iu (b) begins to boil, by vliicli the tumpKratuiv 
19 sODiDch lowered, that if n tittt-tuhe contuinin^ water is placed 
outside (/') it is sdou hlled with ioe. 

Ammonia may be used for the artificial production of ice. 
For this purpose an appamtus (Fig. U!)) 1ia« bevn iuvenU'd by 
M. Cunt^. It coiifiiets of two strong iron vessele connected by a 
vent-pipe of tlie same metal. The cylinder (a) contains water 
saturated with amuioiiia gas at 0°. Wlipn it is de-iired to procure 
ice, the vessel (A) coulainingthcnmniODiASolution, which we may 
term tlie retort, is jEridually h<^ated over a lar}je gas-burner. The 
ammoma gaa is thus driven out of solution, and as soon ils tlic 
pressure in the interior of llie veswel eswed-i that of sevi'ii 
nbnospberes, it condeuses iu the double-walled receiver (b; 



When the greater portion of tlie gas has thus been drivea out ur 
the water, the apparatus » revearstfd, tlie retort (a) heing cooled 
ia a stream of cold irut«r, vhilst the liquid wbicli it is desired 
to boost is place<l in the cj'liiider (v), placed in the interior 
poitioa (z) of tlis hollow rvlinder. A re-«bsorptioQ of the 
ammonia by the witur now takes place, and a oonseqnent 
eraparatioQ nf the liqii^iied animonia in the receiver. Tliis 
evaporation la aoc»m[iianivd by the absorption of heat which 
becomes latent in the gas. lias the receiver is soon cooled 

fio, 120. 

down far below ihu frrcxing point, and the L'quid conlained 
in the vessel (rt) ia frozen. Por the fTOdnclion of larger 
quantities of ice, a contitmouii iunnmnia freezing machine of more 
cotnpHcattid coDatnictioQ, but arranf^ed on the same principle, 
has been devised by M. Ciitt6, in wliich 10 Mtos. of ice ca& 
be prepnrcd by the combustion of 1 kilo, of coaL' 

Ammonia is not oombiistiblo at the ordinary tenipemturc, 
and u flaiQC is «x(iu}>:uislied if pltni^c-d into tliv gas. Kut if am- 
laonia be mixed wilh oxygen by passing through a tube, the 

' lor-mikklnft machinca deptixliiig on the mmtpnnciplctin'iioviniiMlD which 
liqiu£ed ialjihiir dioxide, or ctbcr, aro eiaplojcd lusUoit of ■qneouii anaiDoniK 



escajiing gas may be ignited, and burns villi a pole yellow Siunc. 
witb fotToation of water, nitrogen gas, and nitric acid, H NO^. 
Another metbotl of stliowing the combnslitiilily of nmmonia is 
to pal a jet of tbis gas iuto the bottom of an ordinary Jiimsen- 
burner, in vrbich a Rama of voat-gas IB already I)urnij]<; ; tbc 
flame becomes at once coloarad yoUov, and increases greutJy in 
diraeosioDa A third experiment of this nature is, to allow a 
strR&m of oxygen gas to bubble throagb a small quantity of 
Btro:^ aqueous ammonia plaoi^d in a fla^k and wanued as shown 
in 1;^. 120; ou brining a tight iu contact with the mixed 
gasoB issuing from tbtt uvck of the ttiii*k thoy will be seen to 
bnm with a large yellow flame. 

217 Aminoniagaa is vei)- soluble in water; one gram, of water 
absorbs at 0" and under normal pressure, 0'87S gnua or 1 143 cba 
of the gas. Tbe solubility at different tcmperanires i.'* given in 
Ui© following tablt! (Rosfioe and Diumar) : — ' 


































































Tbe same observers have found that the absorption of ammonia 
in wnl#r does not obey the law of Dalton and Honry nt the 
ordinary atmoapheric temperature, iuasmnch as llio quantity 
absorbed dues not vary directly as the prossure. Sims' has 
shown that at higher temperatures the deviations from the 
law b«uome less niitil at 100° the gas obeys the law. tlie quantity 
absorbed being directly proportioual to the pressure, taken o 
coujM uad«r pressures hij^her than the ordinary atmospberio 
in«e8ur«, inasmuch as boiling water does not dissolve any of the 
gas ondor the pressure of one atmosphere. 

In order to show the great solubility of ammonia gas in water 
the same apparatus may b« eiii])loyed which was ustsd for 


> Oitin. Soe. Xftarn. m. 116. 

• Quart. Joum. CSnt. Soc. (xlr. 1). 


directly from the amiuoDiacul liquor of the gas-works inHteiid of 
from sal-aDHDOQiac. For this pui^iose the liquor ia heatetl 
logethvi with milk of lime in an irou builut having u capuvity 
of 1,000 gallons. The gas vhicli is evolvml is first patmNl 
tluougfa a long ejratem of ooulin); tuhes boforo ib cnlcrs tin: 
wushing mid condensing apparatus. The condenser consists nf 
n seriuti of tubos tUk'd with chiu'ooal. l>y means of which aay 

Fin, 121 

Tomftinii^ fimp^Teumatic imporitiee are reii)nv<Hl. Bj this method. 
if th« ^^tem of tubes be gnfftciently loni^, and by the uae of 
a sufBdcnt minaber of waeh-bottl«s, a perfectly pure liquor 
funmouifi! can be obtained. 

Tlie fact that great hcjit Ia evolved in the procIuctioD of the 
saturated Bolation of ammoiiia is rendered ovideut by the 
folloiriDg experiment. If a rapid (ftirrent of air be passed 


through a coM conoentratetl solution of otnmonui. the gns vill 
be driven out ofeolutioi], aad an amount of h«at wUl be absorlwci 
esactly efjuai to tliat whicli was fii%'en off when the eolation of 
the gas vas nuule. in con3H|uci)ce of vhich Ihc ti^mptmturQ 
of the liciuid will bv tuxu to full below -40*. A stoall (jiuuitlty 
of mercury may thus bo traxt^n. AmmonJA is very soluble 
in alcohol, and this solution, vrhich i» frcquetilly used in the 
lalioratorj- , is moat conveniently prepared by gently vamiii^ a 
concCDtrotcd tqueoiu solattou of nmmonia and passing the gas 
thus evolved iuto alcohol. Tiiis itietUud may oiso be vuiployed 
for preparing tile gu in place of limtingMil-nnimanittc withUmoL 
3i8 C'omjKuiticit of Ammonia. — In order to deteraitne tlie 
compositioD of ammonia the arrangement sbowo in Fig. 123 is 
omployfd. The amnionin gtw w placed in the closed limb of 
the syphon eudiometer, after vhich the mercurial column in both 

limbs is brought lo the saow height, the volume accurately 
read off, and n geri(>s of electric sparks from Ihe induction coil 
allowed to piuf:t thmugh the gim until iui volume undergoes no 
fiii-ther altcrutioa. The tube and gaa are next oJlovred to cool, 
and the prensuro in Iwth limlw ngaiii ndjiistoil. On tbo volumo 
bting agiiin measured it is seen to have doubled. Oxygen is 
next added iu such proportion thnt the miKturo shall contain 
no more than 35 per cent, of the explosive niixtnre of oxygen 
and hydrogen (2 volumes of hyiirogen to 1 of oxygen), and 
an electric spark \a pnsseid tli rough tlio mixture. J'rum UiO 
alteration of volume which takes plac<>, the proportion of 
faydrogim to nitrogen can reudily be deduced, \)a is 8e«n from 
the following example : — 

Volume of ammonia 2(H) 

,. iiilntgeii and hydrogen . . . 40-0 

Alli^r Llie addition of oxygen 1575 

AAer tliu explosion 112*6 



Honce 45 voluuieg have disappeared, of which 30 consisted of 
hydrogen ; conscqueutty two voLumu^ of auimonia conUiii 3 
volumes of hydrt^n and 1 volume of nitro-jpn. 

That Uie relation between bydrogeti niid uilrogen in atnmonia 
gas is in tlio }>ropoTtiou of Uirvc vvlumeH of the fonncr to one 
of tlie latter can bo sLown by the following axporiment thus 
dearly described by Prof, riofmann : — ' 

A gloss tube for holding chlorine, havin^ a HOiall S 

stoppered portion sepantted from ilie rest of the [| 

tube bjr a glass stopcock used for receiving solutioa 


Fm. Hi. 

of miimonia, and ndtnittiiig it. drop by drop, to the chloriDe, 
constitute the requisite apparatus (Fij^ 124). The glass tube is 

.fttmi 1 to I 5 metre long, jtval<-d itt One und, open at tho other, 
and nwrkoil off. by elastic eaoiitt-himi! rings slipped over it and 
clippinR it fimily, into thin^! cquiil portions. 

The npparatiia is tlmn employed, T)ie long chlorine* tuljo hiiving 

' been filled with lukewnmi water and inverted over a pneumatic 
trough, with its mouth immcrst^d below tlio watcr-Iovel, i:i iillcd 

t-with chlorine in tlipusim] way (see Fig. 125). When fuU, it is still 

Fslloired to stand for altout fifteen niinulc.9 over the dilorine 
delivery-tube, that its interior sarfoce may be quite freed from 
the clilorine^iLtuniled water thnt would else n-mnin adherent 
to it The stopcock is now closed and the chlorine thus shut 
in the tube, lliis is then removed from tbe trough, and tamed 
■ rnlnduaion M tftdtm Chfmtglrg. 



round 80 tliat tlie stoppered end is uppermoab, I'he Biaall epacfi 
beCvrecn tbe stopcock ami ttie end is next twu-tliirds filled witli 
a fttong Rolution of ammonia, (tod a flin!>le drop of the anunonu- 
solulion is sufTered to fall into thu cUorinc tulK, tha stopcock 
boiag opuuid for n moment for this purpose (Pig, 126). TLe 
entrance of tliis drop into tho atmoephere of chlorino it nuu'k«d 
by a small, lamlicDt, 3'elIowiBh-green flame at the point where 
the drop entera tbe gas. Drop by drop, at intervals of s few 
aeconds, the ammonia solution is allowed to full into the 

Fjci. ns. 

chlorine- tube, the ammonia of each drop being converted, at the 
infttent of ita contact with the clilorine^ into hydrochloric acid 
and niti'Ogcn with a flash of light and the formation of o dense 
white clouil. Tho adtlitioa of ammonia must bo cuntinund till 
the whole of the chlorine present ia Bupplied -with bydropen 
nt tho cxponae of ammonia. To insure the lunmoniat-al solu- 
tion being added in exceas, a column of three or four centimetres 
U abundantly sufficient, The result is tluit tlio hydrochloric 
acid formed combines with tho excesA of ammonia to fonn a 
compound, utiicb makes its ap^H^iirance as a white deposit lining 



the interior of the chlorine tiibe. TIiU deposit^ being 8olu1)Ie. 
is readily -washed down end dissolved by ^itating the liquor in 
the tnbe, which now contains the whole ot" the nitrogen separated, 
except a. tittle whicb remains dissolved in the liquor. Thin amall 
quuDtit]' of diesolved uitrogeu is easily expellvd ftom Iho liquor 
by hoat^ 

We are now sure of t«'o jwiuts, viz., that the whole of the 
clilotiue has been converted into hydrochloric acid at the 
expense of the ammonia ; &ud, that we possess witlua our tube 
the whole of the uitro^-eu llitis set free. 

Fir. 1S4. 

It becomes oar nest object to withdraw the extxn of the 
aia. Pur this purpose dilute sulphuric acid, wbiDb fixes 
^^ ifl introduced by means of the portiou of the tube 

previously employed to admit ainmonia. 

The nitrogen, K-iiiy U«ia freed from all intermixed gaseom 
bodies, hns only now to be brought to mean atmosphcrio 
temperatHru and preasurc ia order that it may bo ready for 


The tomperature, which bad been rawed by the application 
of heat to the liquor to expel the dissolved nitrogen tlierefrom. 



is readily brought back to tlie ntean hy pluoguig tl]« tube into 
cold vraier. To equalize the pressQTe within and without U>« 
lutie. the lieut syphon tiilic (Fig. 127) is eniplojed. Oiieeiid of 
tlib c'uimuiuiK'iiU-s wilL tlic iutehur uf the tul>«, wbilo the uLbcr 
]i1uiigi» Ixjiimlb tbu sarfttce of w-atur Kulijoct to atuionjibciie 
pressure. Tbal tbJK ]ui>sKiire (>xceedft that of tba gw in tbe tube 
U at 0DC« sccD by the tlow of water through the syphuii into ' 

Fio. 187. 

the tnbe. A.<i tli« water-level in tbe tube rises, the nitro^n. 
pievioufily expanded, gradually apjiroaclius its nonual volunn*. 
which it exactly attains wbm tb** flow coasw, sbowiiiu tlw 
pTOSSUK within and without to be in cquihhrium. I^oth t^rn- 
peratuie and prwiHure being now at the ntean. all the requisite 
conditions are fulfiUi-d for oliLaining rui rxnct kiia%rledge of tho 
true voltuiie of nitrogen; and this, on inspootion, is found to 



exactly fill ooe uf Uie three divisions marked olT al the oulset 
OD oar tabe. 

Now, bearing in mind that wc siartwl with the three 
dJvisiuiiA full or cliloriiif, aud ttmt va have saturated Lhid 
chluriiie with hydrtigen supplied by the aiiintonta ; bearing in 
mind. luoreovor. thai hydropon combines with chlorine, bulk for 
bulk, it is evident tliut the one measure of uiLtxjgen which 
remains in the tabe has resulted from tlie decomposition of a 
qnantity of ammonia containing thr(>e measures of hydrogen. 

It is, tlierefore, clearly proved by this experinieut that 
ammonia is formed by tlte 'union of throe volumes of hydrogen 
with one volume of nitrogen (Hofmanu). 

219 Dfifftion and Eatimation 0/ Ammonia. — The method 
adopte<l for the detection and estimation of small traces of am- 
monift with Ncssler's reagent hog alrendy boon described uujer 
Natural Waters (ste ]>. 252). If the quunlity of ummuiiia iir of 
ammonincal salt be larger, it may bo detected by the peculiar 
smell of the gas, by ita alkaline reaction, and by the fonun- 
tion of white fumes in presence of strong hydrochlonc acid. 
When au animoniocal salt is present, the animouia must be 
libemte'l by heating the solid salt, or its solution, witli a caustic 
alkali For the estinmtiou of ammonia in qtianlities larger tlian 
tiiose for which Keasler'a metliod is applicable, it is uauol to 
distil the ammonia either into hydrochloric acid of known 
streiigUi, and (hen to ascertain, by volumetric analysis with a 
atandard solution of alkali, the amonnt of hydrochloric acid 
remaininj! free, or into hydrochloric acid of unknown strength 
to which a sohuion of phitinic cMoricJe, I't'l,. is added. On 
evapotnttng tlicrentilting solution to drj'uessou a water bnth, and 
exhausting with alcohol, an iosolnble yellow precipitate of 
the double chloride of platinum and ammonium, -NII^CW 
rtCl|, ia left, and this can either l>e collected on a weighed 
filter, or it may be ignited and the quantity of the metallic 
platinum reuiaiuing weighed, from which tlie weight uf ammonia 
is calculated. 

In addition to its u»e in the laboratory and as a means of 
obtaining artificial cold, ammonia is also largely employed for 
the preparation of airbouate of soda, for the productioiiof aniline 
colours, and in tlie manufacture of indigo. 

The sails of ammonia will be described under the Compounds 
of the Alkaline Kctals. 




320 This hi\ais, wliicli i« somctiiucs termed oxy-aiiinioiiia, wu^ 
di»coYored in 1865 by Losscu ; it is ouly known in aqueoufl' 
solniiou and In combinatioD with acids.' It is fonned t^ tbe 
action of nascent hydrogen on nitric oxide gas, thus: — 

2NO + 3H,= 2^•OII,. 

For the purpose of preparing hydi-osylamine, nitric oxide, 
evolved from its solution in ferrous auIplmlH, in led through a 
scries of fhuks contaimag granulated tin and hydrochloric acid.* i 
As hydrogen in only slowly evolved from ttiis niixturo in the 
cold, a small iiuantity of plaiiDiim letracldoride is added to 
tlie contents of each flask ; utL-tallic plattuiun is thus precipi- 
tutcd on to the tin, and a. galvanic action is set up, by which 
meaiu the solution of gas becomes more rapid. j\ft«r the action 
has contiuu[>d for two hours, the liquid is poured off, and the tin 
in solution precipitated by sulphurotLed hydrogen, the sulphide 
filtered off, and the solution evaporated. The residue ia Uieu 
treated with nh»oluta alcohol, whi(;h leaves tuiiUftsoIved the 
greater part of the sal-ammoniac formed in the reaction, vhilat 
it dissolves the hydrochlorides of hydraxylamine. In order to 
free the alcoholic solution tVoiii tlie small quantity of sal* 
ammoniac winch it contains, n few drops of plntinam chlorid« ' 
lire ftdded. the precipitate of the double chloride of platinum 
and aiuutoniiiin being littered ofT, and the filtmt« Rgiiin cvapo- , 
rated to dryness. Th9 residuf, consistiiiH of hydrocldoride of'' 
hydroxylaminc, or oxy-snimonium chloride, NOH^CI, is then 
treated with the i-ecjnidite quantity of dilute sidphuric acid, and 
tlie solution. cvaponitetL To the sulphate of hydioxylamine 
thos prepared, baryta-water is added until the whole of the 
flulphurie acid h^ been precipitated, when an aqueous solation 
of hydroxylamine is obtained. 

Prepared in this way hydrorylamine forms a colo«rless,i 
odourleas sotutioa, pns-sessing a strong alkaline reaction. 
When distilled, no residuo is left., and the distillate contains 
aranionia. together with undccomjiosed hydroxylamJna Tlie 
sohitioii of liydroxyTamine possesses strongly reducing properties, , 
precipitating the metals mercury, silver, and gold from their' 

I AmL Cfum. Ftiarm. Siippl M. r\. 330. 

* Ladwlgaad ncin, Btr. Oetcuidt. C/iem. Oa. IL 181. 


solutions, and Uirowing donn cuprous oxide from a hut solution 
of cuprio Bulphate. This last reaction serves as a most delicate 
test for tbe presence of part in 100,000 parts 
of «-ater being tbna recogDisable. 

The eattfl of iiydroxylamine vriU bv described hcrvafler. 
On lieattng Uiey all decompose witli elTi>tTGaccnco, tho oitrato 
yielding nitric oxide gns, aaid water, thus : — 

NO,n, KOHg = 2 NO + 211,0. 

He constitution of bydroxj'lamine is represented by the for- 
inula, K < H, it is, tlicr«forc, ouuuonia in wbich one atom of 


hydrcgeD is replaced by the monad radical bydroiyL 



an Tltia dangerous Wly woa discovered \>y Duloog' in 
1811, who, DOtwitbstimdint; the JacL tbat be lost une eye and 
ibnso fingiTs in the pi-cparation of this body, yet contioued 
the investigation of the fliiKttaiice. A siniiliir nccidfut bap- 
[teiied in 1S13 to Faraday and Davy, who had, (mwever, 
beeu made aware of the cxph-tsivo propoitica of this sub- 
Stanca. " Knowiu-; tlmt the liquid would gu off on the slighleat 
provocation, the experiinenterH wore musks of ghiss, but this 
did not save tbem from injury. In one case Faraday was 
holding a small lubo containing a few graiiiti of it between bis 
Gager aud thumb, and brought a piece of watin couieut tiear it, 
when ho was suddenly stunned, and on luturning to con- 
eciousnesa found hirii.4i.dr KtrnMliitg with hin hand in the name 
position, but torn by the shatti^rod tube ami the glass of his mask 
even cut by tbo projected fragments, Nor was it easy to 
say when the compound rould he relied on, for it seemed very 
capricious ; for instance, one day it rose quickly in vapour in 
n tube extiausted by tlie aii-pump, but ou the next day, when 

• St^welgj 7oun. Tiii. 802. 



subjected to the same tituitmeDt, it cxpludcii villi a fearful 
iioi»c and ii^'uriii^; Sir H. Davjr."' 

The composition iif Uie rliloride of nitrogen }im not yet b«cD 
detennioed with accuracy. It is formed wbeii cblohuo is led 
into a warm solution of $iiI-ainiuoiiittr, or wlieii a soInticHi of 
hypochloroiig ncitl is liroiij^lit iuto contact with amnioma (Balard). 
If a galvanic current be [tasaed through a coaoentnited solution 
of aftl-ammoniac, chloridtt of niti-ogiMi is deposited on the positive 
pole (Boltger, KoUie). Those methods of fonniitidn appear 
to show that cliloride of nitrogen is formed by the hydrogen of 
aninonia being replaced hy chlorine. Whother this replaoemeat 
is perfect or only partial remains for the present undecided 


Fm. 12A. 

Chloride of nitrogen is a thin, yellowish oil, liaving a specific 
gravity of 1*053. It evaporateii quickly on exposure to the njr, 
and po68e6B«s a peculiar puugont stik^U, tho vapour attacking 
the eyea. "When cliloiidii of uitrnjien is quiddy heated, or 
when it is brought in contact with certain bodies, euch as 
phosphoTOS or turpentine, it explodes with great •violence, giving 
out liyht, and pulvcriKing any glass or porceliiiii vessels ia 
which it nuiy be contained. In cold water it undeigoca spon- 
taneous deconipoMtion with the evolution of chlorine, mtrogeo. 
hydrochloric acid, and nitrous acid. 

The following method is employed for preparing thU dangerous 
' Gladstone, L^t 0/ ParaiUty, jx lOi 



inhi(HK« in stiudl quantities, Mid fiar showinj; its exiiloaive 
propeities without risi:. A tiask of alttat two litres c«pAcit)r, 
having & long oeck, is filled witli cliloiiiie, and |i1ac««1 tiuititli 
downvahU in a tni^e glass basin filled with wmrn Mtiimlvtl 
•olution cif suJ-uniaouiiw a» altown in fig. \'29. B«]ow tlia neolc 
of the finsk it plaoed it small thick leiulcn 3aHc<^r, in wliifh Iho 
chloride or uitrogen is collected. The eolHtion of eal-aimnouiim 
absorbs the chloriae. and, tu soou u tbe flask h thtT« ]>arts Riled 
hy the liquid, oily drops are seea to collect ou the iimrncft insitto 
Lhe lb»k. These gradually increase, and at litst flru]i uiic \<y oiu) 
down into the l«adeji aaocer. Wheu a few drops have coUoctoil, 
tbe leaden sauoer may be cAi^fully renmvtHl hy ft |iiiir of clcnn 
toQgs, auuther beiu-^ {tUced in its stoad. A small quuiuity of llio 
chloride of nitrogen may bo exploded \}y loiichuiK it with * 
feath«r moistcnod witli tui-|)«i]tini3 ftttai-hcd to the end nf ft long 
rod. Another drop ol' tbe oil may be absotbi'd by llUvriuy 
1>opcr, unci whcu this ia Luld iu a llaoie a loud explo«ioii like- 
wis« ensues. 

The formatiDu and properties of chlorido of nitrogen may 
be also cxlubitud in the following way. 
A solution of sal-ammouiac, saturated at a 
temp«ratun!ar 2$", in brought into a glass 
ba»a (A, Fig. 120), and a cylinder (»), the 
lower end of which ih closvd by u piece of 
bladder, is also filled with tlif Holution 
and placed upright in the bssio. A 
layerofoilof tuqii'iitiDciillK'n poured oti 
to tbe top of tliL* Liquid iu tlie cylinder, uud 
a platinum pliit« (a> in contact with the pomitive polo of a battny 
of six cells pW-ed iu the cylimler, wliiltit tlid tK-guUve pole (ft) la 
(daceil under the bliiddcr iu the t>iL<iin. Yellow oily droi« moo 
begin to form on the surface of llie positiTe pole, and tbe»a 
gmdually become detofbc^ fntni tli« pole, and ri«e iu the lii^njd 
until tbey come in coutat:t with the layer of tarpeotine, when 
thcjr explode. 

t'l'i. 130. 


Wlien l)TOmi(Io of potftsmiim U Rrided to cUIoride of nitroReti 
tiniler wAter. potASsiam chloride and bromidG of uiLrogeD an 
fomofiil. T!ie latter is a. dark red very volatile oil, poaaeosing 
a powerful suicll, and being as explosive as chloride of oitrogen 


Iodide op Uiteoges. 

333 When iodine ia brought into contact irith aqueous or 
BlcoboUc liiumoniu, n Uack powder is forinvd which, wlicu dri«d, 
decomposes spoiHaoeously with a very violent detonation either 
wliea touched, or whea slightly heated, violet vapoura of iodine 
lieing emitlud. Tliiii com jKimid gnulually decomposes undorcold 
vater, pure iodine beiug left behiud. Wnna water facilitates 
this decomposition, and tlio body explodes violuntly wlieo 
thrown into boiling water. 

Die eoinposition of this black powder appears to van* 
according to the process employed in ita preparatJon. Serullas,' 
wlio first prepareil thia body, precipitated an alcoliolic solu- 
tion of iodine vith aqueous ammonia ; the compound thus 
obtitined posscsscj, according to Gladstone,' tlic composition 
XIIIj ; but according to Stshlschmidt/ its coui{M>siti<m is 
repnaented by the formuk NT, n body having the former 
composition beina obtained when alcoholic solntions of iodine 
and ammonia aru mixed. Bunsen, on the other hand, found 
that under these circumstances, and when absolute nloohol is 
used, a pnxipitflte baviu!:; the compogition KJiHy or NHaJTla 
is formed, and that ou pi'eci]>ilatinj; an nqueous solution of 
chloride of indtne with ammonia a black powdt-r is obtnioed, 
which consists of NH,4XI,.« These obaervationa render 
it probable that under different circiimatancea at least two 
distinct iodides of nitrogen are fonnod, one being derivwl 
from aramonis by tho replttcomcnt of the whole, and the other 

' Aim. Clum. Phi/*, xlii itO. 
» Q»aii. Joun. Chtm. Soc. it. H. 

• pBgff. Aim. cxix. i2I. 

* Attn. CSmt. JAorm, Ixxxiv. 1. 




"by the replacement of fhe portiou of the liy<!rojteD hy ioctiii«, 

(a) 4 ^•^, + 3 1, = NI, + 3 NH,I. 
(ft) 3NH3+2I,'=NHr,+ 2KH«I. 

Iodide of nitrogen would thus appvur to be callable of combininf; 
M'itli ajQiiionia, gmug rise to the compouiKls described by 


393 When a .series of (!]isi:tric sparks are iOlowed to pacs through 
dr>' aUnoAplmric air, the oitrogeu and ox)-geu combine together 
to form a conipoimd known us nitrofjea peroxide. If, on the 
other band, moisture be prescut, uitricacid is produced, and this 
acid servea as tha starting-point from vhich all the other 
oxides of nitrogen can l>e prepared. Wu are acquainlud with 
five oxides of uiti-oncn. and three oxygen acids correspondijig 
to the oxides nambcrt-d I, 3, aud 5. 

1. Nitiooa Oxide, or 


2. Kilric Oxide, or vq 

Nitrog«Ti Dioxide * 

8. Kitrogen Trioxldc ^^ \ Nittoas Acid . - ^g ! ^ 

4. Nitrogen Teroxide, or yn 

Nitrogen Tetroxide ' 

5. introgea Pentoxide ^o*}o Nitric Acid . . "^jfjo 

JfiTRic Acni. HlfOa. 

924 In Gcber'8 tract. Df InrfTifioiu Verilatis. we find the follow- 
ing descri ptiiin of a moiie of preparing nitric acid or aqua-fortis : — 
" Sumc liljnun unam de vitrioli dc cypro. tt Ubram solis petrw, 
et nnnm qunrtam Qhiminis Jnmeni, estrahe aquam (the acid) 
cum mbendine alerabici," Tliat is. by strongly heating a mixture 



of saltpetre, alnm, and salphate of cojtper, the nitric aciU dia- 
tiU ovfir, ovHng to the decomposition of Iho saltpetre hy the 
sulphuric acid of the other salts. Xitric acid was commonly 
jjrepnrcJ und used as a valuable reagent "by the alchemists, 
efijtecially as ft means of separating gold and silver. I'htt 
method of preparation which we now use from nitre and oil of 
vitriol appeaw to have l>eeii first employed hy Ohmhcr, for long 
ftflerw&rds the acid thus obtoLued vfoa called Sjnritut nitn 
/uman* GlauherL 

Ihe first llieoi y reepectiug the composilion of uitric acid 
waa proposed by JIayow in 16G9.' He believed that the acid 
contained two components, one deriveil from the air and 
having a fiery nature, and the other derived from the earth. 
More thoM a century later, in 1776, Ijivoisier showed (bat 
one constituent of nitric acid is oxygen, but he was unable to 
satisfy himself as to the nature of the other coniponcnts, and 
it yr»a reserved to Cavendish' to prove the exact composition 
and mode of formation of this acid or its salts by the direct 
comliination of oxyj^m aud uitiogcn pisKS in presence of water 
or alkaline solutionB. Priestley had already obiserved that when 
a series of electric sparks was made to pass throtigli commou 
air included between short coluoina of a aoluliou of litmus, the 
solution acquired Q red colour and the nir was diiuini»hed in 
volume. Cavendish r(»i)eated Hie experiment, usinj» lime-water 
and soap'leea (caiietic potash) in place of the litmus, and he 
concluded that the lime-water nud soa^^lees became satimit«d 
with some aeid fonued dtiriug the opei-alion. He provud that this 
was nitric acid by passing the electric discharge through a mis.- . 
ture of pure dephlogi»ticated nir (oxygen) and pure ])ljlogi8tioated 
air (nitrogen) over soap-lees (cnustic potash), when nitre (potos- 
siani uitrute) was furnied. Cuveudi^h' clearly expresses his' 
views in l!ie followitig words : — " We may sufely conclude that 
in the present experiiiient« the phlogisticated air was enabled, 
by means of the electric spark, to unite to, or form a chemical 
combination with, titu dephlogistieated nir, nnd was thereby 
reduced to nitrous ac'ld, which united to the soap-lees, and 
formed a solution of nitre ; lor in these experiments those two 
airsactually disappeared, and nitrous acid waA actually formed iu 
their room." The apparatus which he employed, represented in 

■ Mhvow. Dd cal-iiltiQ «t tipiiita aitd uano. 
* PAU Triirti. l?.H<. ». liji. Dft 1786, J. 872. 
' lUa. 1J85. p. 378. 



In onier to exhibit the dircut cuiiiUuiiiioii of ox.yigiai ami 
nitrogen, it is only uucwssary to allow the sparks from an in- 
duction-coil to pass from two platinum wires placed in tbo 
interior ol" a lai^e yhiss jjlobe Lxintainiug dr>' air. as shown iu 
Fig. 1-il. Cod fwiiios of iiitioguii peroxide unr rapidly formed, 
and Uwir presence may ha distinctly recognised by plunging 
a piece of iodiieJ starth paper into the globe, when the blue 
iodide of starch will at ouce be produced. On pouriug a few 
drop% of water into the globe nnd shaking it up, the red fumes 
are absorlwd and nitric acid formed, us may be showa by the 
acid reaction of the liquid. 

Id 0, similar manner, if a flamo of hydm^n be allowud la 
burn in a lar^e flask into which oxygen ia led, but uut in such 
quantity as to displace the whole of the air, nitric acid is 
formed inki'go quantity.' The same acid is also produced wlmn 
ammonia biirua in oxygen, Tlie formation of uilric acid by 
tlie discharge of electricity through the air accouiile for tlic pre- 
sence of this scJd in the atmoaphore. 

Another and more productive source of the nitrates has yot 
Co be described. When nitrogenous oi^ganio matter is exposed 
to the sir the aitrogen assumes the form of iiiiiuioniii ; hvt whea 
alkalies, such as potash, soda, or lime, are iireHunt, a furtlier 
hIow oxidation of the aitrogen takes place, and nitrates of 
these nietah arc formed. Ucuee these nitrates are widely 
diHused in all surface soiK es^H-dally in hot countries suc-h 
as India, where oxidation takes place quickly. Soil ia the 
Dcightionrliood of the Indian villnyvs, whicli cunhuii» con* 
fiiderable ainouiits of potash, thus becomes rich in nitre 
or potassium nitriito, KNO,, originating frnm the dex:omposition 
of the niea of the urine.' It is from this source that the 
large^st quantity of uilre imported into this country ia obtained. 
Another nitniti*, liiue-i^iUpetrc or calcium nitmtc. Ca(NO,),, is 
often lound as aa eiHoii'scence on the walla of buildings, such as 
stahles, or evlhini of inhaliited lioiis^s, and this som-ce wan made 
use of during the French revolution for the manufacture of 
niti'O. Chili eullpetrv, or Kodiuiu nitrate, NsKO^ occurs in 
hirgti deposits in thn province of Tarajiaca, a rainless district 
on the Pemvian coast l}*ing near the 20t-h degree of ponth 
latitude. The nitrate of soda is found mixi'd with chloride 
of sodium and other salts, ■ probably pointing to the fact 

■ Kolbn; Aim. Cfi4m. fiiamt. cxix. 174 ; HofiaiukD, fftr, DsaUoh. CAmu 0*»- 
0) iii. fiOS. 



Uiut. tlic lucuUly hua U-en covered iiy the sea, unil that the 
nitrate is a product of the ducompositiou of cea-plajita and 

2as FrcparatioA, — la order to prepare pure uitricacid, soltputre 
which hiM hecu previously well iliicd, is plftced in a tubulated 
retort together with an equal weiylit of caiiceiitrated sulphuric 
acid. Od heating the mixture, tbo vglatile aitric acid passes 
over, and is collijcted in a well-cooled receiver, see Fig. 132, 
hydrofien potassium sulphate (commoDly called bisulphate of 
IKiUudi), Tonuiining Ixdiiiid in the retort ; tlius : — 

KNO, 4Hj SO. == HNO, + KITSO.. 

TIte distillate thus obtained has a yellowish colour, caused by 

Fio. 1S2, 

tlie presence of nitrogen peroxide, and It ia not free from. vat«r, 
u Uie concentrated acid, when heated, dpcomposcs partially into 
peroxide aud water. In order to purify the acid tliuB obtained 
it must be s^^u distilled with il« own vohuue of concentrated 
aiilphuric acid, and the dintillitte fiuoil from traces of the 
])croxiJe by gently warming tlie acid, and K-ading a current 
of dry air through it until it is cold. Thus prcpure<l it 
conUuDS from 99'5 to 9tl'8 por cent of the anhydrous acid 

326 Propcrtiet — Nitric acid is a colourless liquid fuming 
atroiigly in the uir. It ijossesaea a peculiar though not very 
powerful emell, and abeorbs moistitro from the air 'with the 



greatest avidity. Kitric acid is an extremely corrosive sub- 
6t«nce. vrhicb, wUen broiigbt in oontaot with the akin, producea 
painful ■wounds, Iwiiig iiied in surgery as a powerful 
cautery. Tlie dilute acid nets less euurgflicolly, and colours 
the sktQ, iiaiU, wool. silk, and otLer organic bodies, of a briglit 
yellow tint 

When pore concentrated nitrio acid is lieatetl, it bt^Ins to 
boil at 86*, and becomes of a dark-yellow colour owing to 
the decompoBition of a purtluii of tlie acid into nitrogen 
p«ro:xide, oxygen, and water. As eoon as about Uiree-fourtlis 
of the acid has diatillcd over, the raiidue becomes colour- 
less, aud then contains only 9iJ8 per cent, of acid.' If the 
distillutioD is pushed further, the baiting ]Kiiut coulinually rises, 
B strDii)^ acid diitiU over, and the residue bocoiuef! oonstanUy 
weaker until it contains 68 per cent of aciil, when the liquid is 
found to boil un.iltcrcd nt 120°'<'i under the norma] atiuoapheric 
preaeure. yielding an acid of tlie above coiiatant compoflitiou, 
and with a specific gravity of 1-414 at lo'O. Tliia constant 
acid is always obtained, whether a stronger or a weaker acid be 
subjected to diatillation. If thi-i aci<l of constAnt composition 
be distilled uuder an incrmsed, or under a diminished prts- 
sure, tlie compositiou of tliu residiuil acid again undergoes a 
change, until fur each pn>s.<iure a cou<ttaat lioiling-point in 
reached. Thus, under the pressure of l'32m. of mercurj-, an 
acid containing GSC per cent, of UNOj distils without alteratioa, 
whilst under a prcfwure of 007(*m. an acid distils over at a tcm- 
peralure of from 65* to 70", linviiig a constant cotapoaition of 667 
per Cent. AVIicn a current of dry i»ir is paasL-d tlirougb mjucoua 
nitric acid, either a stronger or a weaker acid is volatilised, 
according to the concentration or tlie temperature of tiie acid, 
until at length a ivsidue is obtained which volatilizes unchanged. 
Thus, when the experinient is made at 100°, the residual 
acid contains GG'2 per cent^ ; when at 00'. 64"o per cent ; 
and at 15* the residual acid contains G4-0 per cent, of HNO, 
From this it will bo seen that nitric acid behaves in a 
similar way iii Uiis respect to hydrochloric and the other 
aqueous acids. 

Wien tlie concentrated acid is mixed with water an in- 
crease of temperature and a contraction of bulk is observed, 
^lis attains its maximum when one molecule of the acid is 
mixed with three inolcculM of water (Kolbc). The following 

' Boscoe. CVn. Soe. Joarn. xiH. HJ. 



tdblo gives the spccilic gravities of aqueous aci<ls at 0° ami 
15= ;— > 




100 Oil . . 

, 1-559 , 

. I-530 

90-0 . . 

. 1522 . 

. 1-495 

80-0 . . 

. lAU . 

. 1-460 

70-0 . . 

. 1-444 . 

. 1-423 

600 . . 

. 1-393 . 

. 1-374 

500 . . 

. 1-334 . 

. 1-317 

400 . . 

. 1267 . 

. 1-251 

300 . . 

. 1-200 . 

. 1185 


. 1182 . 

. 1-120 

150 . . 

. 1-Ofi!) . 

. 1-089 

100 . . 

. 1070 . 

. lOGO 

S-0 . . 

. 1031 . 

. 1-029 

It hu been already remarked tLat concentrated nitric acid 
begins to decoiDposc, at a t<-miierft1ure of 86', into water, oxygen, 
and nitrogen peroxide. If the acid be more strongly heated in 
closed gluAS tiibc3 this cliungL- tukcs jtlacc so rupiilly timt at 
200* the whole of tlie nitric acid is thus decomposed (Carius), 

In order to exhibit this decomposition t^y incana of heat, tJie 
same apjiHratus serves which was employed for the dccomposi- 
tioQ of aulphnric scid, Fig. 18^. Stroug nitric acid is allowed 
to fall on the hot piimiee-stone coiitAincd in the platinum 
flask. ImmoUnli'ly red vapours ar« emitted, and tliuae are 
condensed in pustiing througli a U-lubu placed in a freezing 
uixtuTo to a brown li(jiiid, KO,. whilst the cylinder placed 
over the poeumatic trongh becomes filled with a colourless gas 
which call be easily shown to be oxygen (Hufiminn). 

337 CtMimertial SSanu/—'ivi order to prepare nitric acid 
OD the commercial scale, sodium nitrat« is substituted for nitre, lU 
it is much cheaper, and the aalt is deconipowd with sulphuric 
acid as before. The pioportiona of these two substances em- 
ployed are not the same in nil woiIcr If one molecule of 
aulpboric acid and two of sodium Litrttte be taken, tlie follow- 
ing are the reactions. In the fint place we have: — 

H,SO^ + KaNO, = NaHSO^ + HNO,. 

* Kolbe, Ann. Chim. Hgt. [i] x. HO. 

TBZ »am4a:txijuc EUJCESTs. 

Whm tie hot ii nind. IW kU nfin 
■Boad ■decBte ofaodna utale; dm: — 

l^HSO^ + S*XO, = X«^, * HXfV 

la Ikw caw, bo«ev«r, a pot of tlie and b 

tothehj^ teuipeiaUi e. wid ailwigBe pgnnda ia miiI ibJ ia A> 

fima of red fiuMs vhidi doBolve is tiie t oo tc n tirta d acid, ^na% 

it tW ned a ppt at ance ntaaSy aotioed ra tbe stroog 

piodoet When a lanjB exeeH of wlphwie acid n 

a colaio qnaatjnr «f acid aedhnn tolpfcate is tarmeA, lAoA 

hmn the tadting poiat of tbe readnal maaB eo that it cut 


lie withdrawn from the retorta id the fwwxl state, wherets in 
the other com the residue cnn onlj he removed in the solid 
■tato after Oie cylinder has been cooled. Tlw ordinary com- 
nicrciiil acid Iiaa a specific gravity of from VZ8 to 1-41, and le 
uBunlly pivpnrod by means of cliainlter (sulpharic) acid ; but if 
n morn cotinontrated acid is required a stronger siilphnric acid 
must be amployed. The Htroii>{usL nitric acid <>ccurriiif; in com- 
merce ho* a specific gravity of 1'53, and this ia oblnincd by 
disUllira wcll-dried Cluli Baltpetre with sulphuric acid having a 
spcciflo gnvity of 1'85. The retorts in which nitric acid is 

usually prepared on Uit Inryc senile io England conxiKt of cast- 
iron vyliuders buUl in a lUniucu iu aucli a uay ibaL lb(7 may 
be beatwl us uniforuily aa possiblv, ua sUuwu in Fig. 1?4. £k>nie 
mtnufiwturcre cover the upper half of the cyliiiJor with firo- 
hficlcs in order to protect the iron from the action of tlte iiitrio 
aoid vapours. Tbi*, howwver, i« unnccessan-, if ihc rutort* aro 
80 tliorouglily heated tbat do nitric acid condenses on llie surfat-e 
of the iron. The ends ol the cylhi.ler-i which are not exposed to 
the avciou of the thniic are clo6«d hy plates o( Yorkshiru ftng, 
which aro cvuicntod on to thi> itDn with a mixturu of iraa EiliagM, 
sniphur, sal-ammoniac, and vinegar. In the upjK^r part of one of 
these Hags is a hole, throu}{h which tlie solphuric acid is iuu-o- 
(luced urier the cliariju of Chili «altp«trc. Tlie hole i« UicocIuaihI 
hy a clay plug. A tiuiilai- hole in the otli«r tla^ is furnished 
wiih Q beut cartheunai'e tnbo (c) pusGiug iuto a series of lar^e 
AVoulfTa bottles (Ih), one placed Whiiid llie other, containing 
small quantities of water in which the nitric ac-id condenses, 
nnd from -which iht- acid is witiidrawn by leaden syphons 
The last of these Woulff's bottles is placed in conn«ciiou mih a 
towi'T tilled n'itli ooku, down whiuh a current of water runs. 
Any uiicoud^used mtrogcii peroxide passes np this tower, aud. 
coming in contact with tlio water and the oxygi>n of tlio sir, is 
(txidized to nitric acid, ^^^le^ the operation is complete, one of 
the dags is removed and the residual fused sulphate of soda 
scraped out. 

A usual charge for one retort is 305 kilos of Cliili 8iiU[wtru 
snd 240 kilos of strong isulphuric ucid. Tlie uiixluni u 
htiiitcd unifurnily for about eighte«n hours, and the qnuntity 
of wat^T pliwcd in tlie Woulff's bottles is such that a yield of 
303 kilo* of nitric acid, of specific gravity I'io, is obtained, 
whilst 295 liilos of fased sodium sulphate remain bchitK] in the 

In a Genunn factory, where the strongest nitric acid is made, 
a caat-iron vessel is employed for its gi.-nuratioii, the con&tniction 
of which is seen in Fig. 135. Tlie cliurRe. in this caw, -of 

700 kilos ofaulphuric Hcid,of specific gravity 1-84,111 ili« 

of CbiU saltpetre. The retort is placed in connection -with two 
series of receivers, twenty-five in number. Acconling to this 
piDoots 100 parts of Chili ealtpotru, coDtaining 9l) parts of imie 
nitrate, yield G8 parts of nitric acid, of specific gravity |-5, and 
17 parts of weaker acid. This corresponds to about 95 per 
cent, of the theoretical yield. 



Commercial red nitric acid alivsys contains cblonne. and 
sometiDies iotliiic in tim rnrm of iodic acid, originating from the 
Chili saltpetre. In addition it also contains nitrogen peroxidt*, 
iron 03:ide, s'jlpharic acid, and sodium sulphate, wliicti have been 
ctrrietl mechanically over. lu order to purify the Mid, it must 
be distilled iti glu£S rvLort^, clilonnu uiid nitrogen peroxide 
coming over iu the first portion. As soou as tJie acid distillate 



I'll., i:u 

is free from chlorine the rcceivpr is changed, nnd the liquid may 
be distilled until only n email residue is left, containinp the 
whole of the iodic acid, sulphuric ncid, Hnd sodium sidphate. 
Concciitmtcd, ns well as dilute nitric acid ia Inr^ely used in the 
arts and manufHClure-i. Lai^ge quantities arc employed in the 
mtinufacture of the various coal-tar colours, of nitro-glyeerine, 
of gun^ottoii, of sulphuric acid, and of nitrate of silver, which 
is now ased in tnr^e quantities for photographic purposes. The 

Acid is also used in Inrg^ quantitios fortH« pre]iamtion of eeitun 
uttratos, especially lead nitntt«, iron nitrate, and alutniDinni njtnte, 
all of wliidi ure'einplyyt'd in tlie iirts ot'tiyeii^ oud calico-printing, 
whilst the nitrate* of barium and sttontiuiu are used for iijTx>tecli- 
nie purposeB. In the labomtory it k ah indispensnblc reagent, 
and 13 used in the preparation of a largi; number of inorganic 
and orf^iiic $ul)stunoc», 

aaS Mthc acid is a mono'iMsic acid forming a series of sails 
which mx) titrmcd the jn'trulix. Tlieee are almost aJI easily soluble 
in water, and as a rule crystallixe well. Tliey may be obtaiuod by 
neutralizing th« acid vitli an oxido or a carbonate, and tliey 
arc almost uU fortuttd by dissolving the motal in nitric acid. In 
thia ca^e the metal is oxidized at the expense of a portion of the 
acid which, acconlinjr to tho concentration or the temperature, is 
reduced to NO3, X,Oj, NO, NjO, and even to uitrogeii and 

Several otliar bodii>9. aiich as flulplmr, phosplioras, carbon, 
and many orgnnic siibstanceA, are easily oxidized, especially 
liy llie concenirated aciiL In order lo oxhiliit this action, 
some nitric acid may l>e poured upon piatnilatetl tin, which Ij 
thv:D oxidized with the evolution of dense red fumes, wliilst 
a white powder of tin oxide is deposited. Turpentine when 
ponrod into tiio concentrated acid ia likewisa oxidized witb 
almost explosive violence, lijiht and heiit being evolved. In 
like manner ignition may take place when straw or sawdust 
becomes impregnated with the stmng acid. 

Other oi^anic bodies treated with nitric acid undergo no 
apparent alteration. Thus, fur instance, wIlli cotton-wool no 
ignition or evolution of I'od tutne^ ocetir«. If. liow«vcr, the 
cotton-wool after having been thus soaked in strong tiitric 
acid is wn^iivd and dried, it is found to possess very different 
properties from ordiuaty cotton, although in appearance it can 
hardly be distinguislied fTOiu it Cotton-wool, or cellulose, has 
the funiiula C,jH2aO,p, whilst after treatment with nitric acid it 
consists of gun-cotton or ratluloste hexanitrate,f-'jjH„0,C?IOj)y the 
cbange which has occiured being represented by the equation : — 

C„Hj„0,„ + 6 H>-0, = C,eH„0/NO^, + 6 H,0. 

Nitric acid acts in a similar way on many other orgniiio bodies. 

a2g J>ct€c(ion find Estimation. — The presence of uicricacidorof 
its salts ia easily ascertained. Thus, for iiistaiico, if we heat a 
lew drops of not too dilute nitric ncid with copper lumiugB. 


IjiowniBh red vapours of nitrogen peroxide are emitted. The 
nitiatea give the same rcactiou it tbcy, or their ooaoeotrated 
aqaeous Holntions, are treated with sulphuric acid and copper. 
In order to detect nitric acid, or a nitrate in a very dilate 
solution, a cold aolutioo of fcrroiia salphata is sddt-d to the 
liquid, and atout an e<nial volume of strong sulphuric acid is 
tJien allowed to flow slmrly down to the bottom of the lest-tnlw, 
which is lield in an jnclioed position. In thia way a brovn ring 
is seea to form at the point whcru the drnsu sulphuric ncid 
jniii!) the lighter aqueous eohitioii if any uitric acid be present. 
This dark-coloured ring depends on the formatioa of a peculiar 
compound of nitric oxide with ferroii-S sulphate, which will he 
described hereafter. 

Another very delicate teat for the presence of nitric acid is 
aniltBc. In ordi-r to apply this test, ten drops of aniline are 
brought into oO chc. of a dilute siilphnric acid contdining 15 
per cent of pure ncid, and 5 cbo. of this solution is poured on 
to a watch-glaas together with 1 chc. of concentrated sulphuric 
acid. If a glass rod moistened witli the solution under exami- 
oatinn be nov brought in contact with the edge of the 
Uc^uid ia the watch-glass, a red slfcak v-ill ho produced if a 
nitrate is preseuU and the colour will increase in intensity until 
tbo whole liquid becomes red. 1 f a lai^ger quantity of nitric acid 
bo preuMit, the whole iiiilss will assume more or less of a brown 
tint (C. D. Braun). 

The organic base called hrucinc, bearing a close resemblance 
to stryclmine, serves as a test for nitiii; acid cveu more delicate 
than aniline. If to half a drop of a gulutioiiof oiiopart of nitric 
acid to 100,000 parts of water, one or two drops of a solution 
of bnicina be added, and then a few drops of concentrated 
sulphurif. acid, a distinct pink coloration will be observed if 
the solution be seen again&t a white ground.' 

In order quantitatively to ilclcnuini; the amount of nitric acid 
contained in potoflsium- or godium- saUjK-tre, tho wdl-diied sub- 
stance is heat«d to <luU cednvss for h»lf an hour with freshly- 
ignited and finely-|xjwdered quartz or silica, SiOj. The nitrates 
are thus completely decomposed. nhiUt any eulpli^tes or chlo- 
rides "which nLiy be present undergo no olinugc. Tlic dvccmposi- 
tion which here takes place may he rvpresented as follows : — 

2KK0a = K,0 + 2N0, + O. 

> Bekhudt, JaMrtaitriJtt, 1S71, B93. 

Oxygen and nitrogeu pijroxide ore evolved, whilst Uio potash 
cotnbiDca with tlie silica to rurni sillccito of [lotash. From Uie 
loss of weight tliua eosuii^ tbe amount of iiiire present can 
easily be calcuUtvii 

Another gooil uietliod, wbioli is jtaiiicularly tucful in the 
deteniiiiialioii of the iiiti-ates ooutaiucid in drinking water, (Ie])eiii]s 
upon tUe fact that a thin nuc pluU-, which ha» been COT'erwi with 
a deposit of spongy metallic copper by dipping it into a solution 
of copper sulphate, on beiiif; beateJ with water containing uitratea 
redacos them to umnioiiia, itinc hydroxide and fieo hydrogen 
being at the aasae time formed (Gladstone and TriW) j thus : — 

KNO, + 4Hj = NH, + KOH + 2H,0. 

The ammonia thna obtained is distilled over into an exceaa of 
hydrochloric acid mid determined in tlio usunl way, or IT present 
to only aiuall quautiliea by nea^lenjialioii (seep. m). 

Aqua Reoia. 

130 This name is given to a mixture of nitric and liydro- 
chloric aoidg which is frequently employed for dissolviDg tliu 
noble Dietals, such as gold and platinum, as well as many 
iiieiallic opps and other bodies. A method of preparing this 
subiitunco was described by Guber in his work Ue Iiiventume 
Verilalis, by dis-^tving sal-ammoniac in nitric acid ) and ha states 
that the liquid thus obtained has tbe power of dissohing gold 
and sulphur. The name, aqua rcgia, is finsl found in tltc writings 
of Basil Valentine. He, like Geber, prc^paii-d it by ilissolving 
four ounces of gol-ammoniac iii 1 lb. of aqim-fortis ; liealsostates 
that strong aqua regia can bo obtnined by mixing hydrochloric 
and nitric acids. The solvent [wwer of aqua regia depends upou 
tlie fact that, on heating, this mixture of acids evolves chlorine ; 
llius ;— 

UNO, + 3HC1 = 2HsO + NOCl + CI*. 

The comjiound nilrosyl clJoride KOCl which a libented at the 
9ame time is described on pnge 425. 

Njteooen Pk-vtoxide, NjOj. 

331 Thissubstance, which iscommonly called nitric anhydride, 
M-as discovered in 1849 by Doville,' who obtained it by leading 
) ^nh. Ckfm. nyi. f3] xxviiL Sll. 



perfectly dry chlorine gas over diy silver oittate contaiucd in a 
U-tube placed in a wntor-bath. Tho reaction begins aC 95*, 
and urbiiD cooled to 6D°, Ihu decomposiliou of the nitrate goes 
on regularly- The pentoxide is voUected in a bnlli tulte siir* 
rounded by a freezing mixture. In tht.<t prepamtion or nitrog«n 
pcntoxide two reactions occur. In the first one ft very volatile 
liquid called oitroxyl vliloride, XOjCI (see p. 415), ia formed; 

fc S°'}«^c!} =?."'} -Age.. o. 

I Hie nJtroxyl diloride then reacts on tlie excess of aQver nitrate, 
wtlh the formation of nitrogen pentoxido and silver cUloride ; 
Nitrogen pentoxide may, therefore, be easily obtained by passing 
the vajiour of nilroxyl ehloride. which can be prepared in otJier 
ways, ovcrtlry eilvcr nitrate (Odel and Vignon). In the prepa- 
ration of the substance by either of these methods all jointR of 
cork taul caotitchoue must be avoided, and each part of the g}at» 
apparatus must be connected either by fusion, or by pkcing tho 
end of one tube iusidc (Uc other and closiug the space between 
the tubes vith aslieatos, the pores of which are filled up tyith 
meital paraffin. 

Nitro(icu [^lentoxide can be alao prepared still more simply 
from pure perfectly siihydrous nitric acid, by wiliidi-avml from 
the eutistance of the eliiinents of water. For tliis purpose 
two molecules of the acid are brought into a bcaker-glass 
placed in ice-cotd natcr. and one molecule of plioxplionis prit- 
oxide is added in small portions, the mixture bein;; cniefully 
atined. This addition ia accompanied by a loud hiKiiug noise, 
and touai >>c proceeded with gently, so that no ritte of temperature 
occurs. T1)e reaction which here takes place may be thus 
^lepreacnted : — 

P 2HX0, + P,0, = N,0, + HPO,. 

The syrupy liquid ia then poured into a perfectly diy retort to 
which a cloae-fitting woll-coolcd receiver is wttachcd. Bygently 
heating tlie retort, & dfvp oranjp-coloured distillate ia obtained, 
which on standing separates out into two layera. The upper, or 



lightBT layer is tlieii pounHl into a Uiin stoppered tube fttwl 
cooled Jowu by plun^'in;; tbe tube Into ice-culd water. OrystaU 
or the pcntusidu euoD Beparate out, and tliv.s« nmy l)e pariGtMl by 
pouring oGT tbu omngo-coltnin^d litjuid fmui w-liioli tlivy nrn 
(it^poiitod, iiicUin^' the cryslaU lit a nioderata licat ind ii^ici 
allnwin)^ tlicni lu ikiKuii, and u);-.!!!! jnoriiig off Lite nmlhor 
liquor ( Welier).' if the tempcratiini diiripg tbc process of addiD;^ 
the phosplinnis p«ntoxide b« uot kept low. bitiwu-omiiye vjiiKiare 
nrt: fonutKl in Isr^e quantity, and the D|>unitioii does uoL Huccuvd. 
If, howuvcr, the prtK«ss ba cArvfully u^tiiduolod, und osjMM'uiIly 
if care be taken that tbe teiupcmlure dois not riso alxiveO', the 
pure anhydridn uiny be still more readily obUaiiKd as ru11ow«. 
Tbe pasty vaa^ obtained \»y mixii^ tbe pyntoxide and nitric 
scid is iK)ured into a lurge retort and vuiy card'ully heated. 
The anhydride then distils over, the liquid in tJie retort frotliin;; 
up, and the di^iilluU:- cTystaltizin}* in tlic wcll-coolcd rvccivur, 

flja Prajierties. — Nitroj,'pri pentoxide isa white colourless ftoUi!, 
crystallising in bright riionibic crystals, or in Mx-«i<lwl prisms 
derived fiom thfise. When heated from 15° to 20° the cryatrJa 
become of a yellowish colour, and molt nt nbont SO' to oi daHc 
yellow liquid, which decomposes between 45' aud 50' with die 
evolution of dense brown fxunta. Wlieo suddenly h««ti!ij, the 
p«ntoxido (tpcoiiipnses with explosive violuuee into nitrn'irn 
pt:roxide and oiygen, and ttiis sudden decomposition occurs 
Eonictiiiics even at ordinnrj' tcmpcmtTircs, if tbe crystals havo 
been kept for soinctinio. The lower the to-mpenitnre is kept 
the longer does tliti substance remain unaltered, aud lielow i>0, 
it may he eubb'nied in a cloacd vessel, depositing in crj-stals in 
the cool part of the tube. In dry air the pcntoxide \-oliitilizea 
very quickly, whilst in moist air it deliquesces with formation 
of nitric acid Tlirown into water, it dissolves with evolution 
of heat, fomiing nitric acid ; thns : — 

The pentoxide possesses Tory powerful oxidizing prop 
Thua, if brought in contact with sulphur it formii white vapours, 
which coiidctis<^> to a white sublimate of nUrosvlphamr flii/ty> 
dritU S,0^(NOj),. Fliosphoms and potassium biini uith 
brilliancy in tlie slightly warmed anhydride. Cbarcoul docs 
not decompose even the boiliu<> anhydride, but wbeu ignited 

I /«.m /V,<.-(. (-Arn.. [21 ii 311 

Rimoxyii OHLOBIDE. 


ami brought into tho vapour »t bonis with a brilliant light. 
"When brought in ooDtact with nitric acid, tho flnhydridc com- 
bines U) tovai the conipouBii NjOj + 2nN0y Tliis siibstanc* is 
a liijuiil nt the ordiiiaiy t^mpemttire, it possc8«>c« at 13° n specific 
gravityofl-MS. and it solidifies at 5' to acryataUine mase. Tliia 
oomiKnind. which forms the lieuvy Inycr in the preiaration of 
ttiL' jiL-ntoxid«, docoaipuiios with explosion when licateil. Its 
formution ia perfectly analogous to tbat of disulphnhc acid, and 
the oonstitulioQ is probably represented by the formula — 

XOj— 0— NO— OH. 

NiTHoxvL Chloeidk, NOjCl, Vapour density = 40 65. 

333 This body, vhtcb is the chloride of nitric acid, is formed 
wlii'ii » mixluTuof Diln^genpcroxidttuiid cbloriite is piiss4.-d lhr«>ti^b 
n heated giaas tube (ilassenbach). It ifi likewise formed by the 
action of clilorsulphonic acid on nitric acid (AViltiainson); 
lliua : — 

SO, { ^," + NO,OH = SO, { 3JJ + No,a 

This componnd is aho obtjiined, ae has been already mentioDed 
by the action of (;lili>rin<> npoii silver nitmte. 

The best tuetbod of pi«pariug tbia substance is by acting 
upon phosphoms oxychloride with the nitrate of lead or of silver ;* 
thus; — 

TOCI, + 3NO,0Ag = POCOAg), + 3N0CL 

This compound ia a heavy yellow liquid which boils at 5', and 
is decomjxisei] by m-at«r into uitric and hydrochloric acids. 

NmtooES MosoxiUE oi: Xitrods Oxide, N,0. DeQaity= 2r99. 

334 Tltis ;;8s 1.1 formed by the nction of easily oxidtzable sub- 

atauoes, sucb aa potassium sulphide, moist iron fiUngs, tliceal- 

philes, and otlkcr bodies upon nitric oxide, and according to these 

methods it was first prepared by Priestley in the year 1772. It 

■ OiUt an*) VijEiHD, Campta Undiu, txx., M. 


is moreover fonnud when zinc and otlier tnetals ftrc dissolved in 
very dilute nilric acid. 

Prtparatit/Ji. — la order to [>rcpare the ^-iw w« do uol, how- 
ever, usually eniploy aoy of these methodd, but we have re- 
couree to the decomposition wliicb ammoniam nitrate (oitrale 
of amoionia) undurgoet ou beating. This »alt splits up into 
water and aitious oxide giu ; thus : — 

im^NOj = N,0 + 2H,0. 

It is be4t, before the experiment, to molt the nitrate, io order to 
(let it free from moisture; and the powdered dry substance is 
then introducfd into s flask fumislied with a cork and delirory 
tube. The flask must be lie-ttwl gently until a regular evolution 
of gas begins, and then the flame moderated, as sometituea. if 

Fio. 134. 

tlte heat applied be too great, the decomposition takes place so 
violoutly with evolution at the same time of nitric oxide, tliat nti 
Qxptoaiuii may occur. In nrdor to frt-e the giw fruui traces of 
nitric oxide it cau bo shaken up with a aulution of ferroos 
sulphate, which combines with the latt«r ga.s ; whiUt in orJer bo 
remove traces of cltlorino derived from the chloride of ammo- 
nium, wliicli the commercial nitrat^c often contains, it must be 
allowed to stand over a solution of caustic potash or soda. 
Tliese precautions ore especially needed wlien the gas is u&ed 
for iulialing. 

Aa nitroKE) oxide is somewhat soluble in cold, but nob nearly 
so soluble in hot water, it is be^t to fill the pneumatic trough 
with warm water before collecting tlic gas. Xlie aTTAiigement 



used forthis purpose is scwi ia Fig. 13(J, and reqnbes no furtli«r 

335 iV'j*"'''"*-— Under ordinarj- circumatenccs nitrof^eii mon- 
oxide is a colourless gas posecssing a pleiunnt snivU and sweet, 
acreeable taste. IiaviDg a specilic gravity of 1'52 (Colin). Itl 
soliitnlity in vrater between U* and 25° is represented by tlie 

c= 1-30521 - 045620i + 00006843(»; 

I or its coefficieiiU of absorptioa are as follows >- ' 

(T 5' KT 15' 20' 25" 

1-3052 1-0951 09196 0-7778 6700 0r,962 gnus. 

Il ia still more miluble id alcohol, one volume of this liquid 
»bflorbing, according to tli« expcuDicnts of Caritis, a qunnlity 
of tlie gafi found by Uie formula 

c = 4-17805 - 0-0698130/ + OOOOGOdCK* 

Kitroiia oxide is a condeiisible gas; it was first li<iuefied by 
Fatadny in I8'2:l by lit^atinij; nilntu* of ammoaium iu a bent lub« 
(Fig. 137). In order to prepare Uiuid oitrous 
oxide, tlie gas contiiioed in a caoutctiouc bag ia 
puuipcd by a rnnd<-iisiiti;-pun>p into a strong 
copijcr cylinilvr. Tlie arraii^^ttiieiil u^etl for this 
purpose ia known aa Katterer's condensing pjg -^gj^ 

apparaliis (see Carbon Dioxitii^). Tlia gas 
is compiesaed by tlie pump inlu tbo cooled uppur cylinder. 
and wlion tita pr(*it4tiru witliiu this cylioder amouuta to 
'iO alniospboTcs at 0°, or uhcn the gas ia condeniwd into 
1^ of its original bulk, it liqneliva to a colourless very mobile 
li(]uid, which, under a pressure of 7(J7-3 mm. of mercury, 
boils at -87°*9. In order to obtain the liquid, tbe cylinder 
ia UDScrewed from the pump, the valre at the liotlom, 
through which the gas entered, being closed by the pressure 
within the cylinder; it is then plnecd in a sluuliiig position 
with ibe valve downwjinls, so that on turning the scn-w-hi-ad 
the ]i<itiid rushes out in a fine stream by the nozzle. To 
receive the liquirl, sovemL glass tubes 10 cm. long and 3 to 4 
cm. wide, closed at one cikI, are fixed in the cork of a wide- 
oeclcbd bottJet, and some liquiil drawn off by tlie nozzle into 
' Csrinib Ahm. Chem. narm. zl-iv. NO, 




each of these tubes. For, nlthough the liii»i(l boib at a tem- 
peniture monj than 80 deyiijes btlow the fieGziug-point of water, 
it may be kept for more than half an hour in such tubea. The 
spocitic gnt^'ity ot liijuid nitrous oxide ia 09369' at 0^ 

Like othtir coudeiisiblo gases, Uquid nitrous oxide hasaTeiy 
high coePRciciit of cxpiuiaion ; one voluiuii of the liquid at 0° 
becoming 11202 volumes at 20", whereas one volume of the 
gag at 0° becomes only l'U732 volumes when laJsed to 20". A 
drop of the liquid bronglit on to the t^kin produces n blister, and 
whvn water i» tbrovrn into thv lii^tiid it at once freezes to ice, 
at the Bftiue time producing a daugerously explosive evolution 
of gss. Pbosphonis, potassium, and charcoal do not undei;gO' 
any change when thrown into lit^uiO nitioits oxide, but if »' 
piece of burning charcoal is thrown on the liquid, it swims 
on the nurface and continues to bum with great brilliancy^ 
By (>ouriiig a little mei'cury itito a tube containiug the li<]uidJ 
nitrous oxide, the metal eolidifics, whilst at the soma moment a 
piect! of ignited charcoal may be »een to be brUliouUy buroing 
oa the surface of the liquid. 

Wien liquid nitrous oxide is pouted into carbon disniphide 
the two liquids mix, and if the mixtiiTe he brought under the 
receiver of au air-pump the texuperatui'e sinks to ~ 140'. If a 
tube filled witli liquid nitrous oxide be dipped into a bath of j 
solid, carbon dioxide and ether, and if thLi mixturo be allowed 
to cvaporatG in vacuo, the liquid nitrous oxide freezes to 
colourle^a cryalaht, whuse tension is le^s than one atiuosphete. i 
Poured into an open vessel, liquid iiitruus oxide cools down by 
Bvapotation to a tempomturo of — 100', and if tliu alcoholic 
thermomolor bo taken out of the liquid, a portion of the ad- 
hennii aubsUiUee Bolidifias and the temperature sinks to - US'. 

Solid nitrous oxide in the form of enow has also been prepared 
by Wills,* who obtained it by a niodificatioii of Thilorier's method 
of obtaining solid carbon dioxide. 

336 Gaseous nilroiia oxide, like oxygwi, supports the combus- 
tion of bodies. A iitd-hot splinter of wood r«kindlo.s when brought 
into the gas. a watch-spring burns with bright aeintilktions, and 
a blight iiaine of sulphur continues to bum with a brighter tlanie. 
If, however, the aulplmr be only just kindled, the flume is cx- 
liuguished ou bringing it into the gas, as then the temperature 
of the dame is not aulBciently high to decompose the gaa into 

* Andre^r. Jna. Chem. Pharm. ex. lU 
■ CAen, S«, Joum., 187 1, p. VI. 

its constituents. All combustions id this gas itre simply 
oombti3Hon<i in oxygen, tliR burning botly nol uniting -vrith Ihe 
DitTOus oxide, bul vritL its oxj^n, ttie nitrogen boin" liberated 

Potassium itntl sodium tilso biiru briglitly in tlw gas M'lien 
aligbtly li«at«d, with formation of the p«rt>xide3 of these metals; 
and tliese again when more strongly ignited in the gas yield the 
tiitratea of tlie mctala. 

The very remarkable eflVcts on the organism produced by 
tlie inhalation of nitrous oxide, first oLsL-rved by Davy, have 
been recently invt^tij^uted by Hermiinn.' Tlio lir&t cffecta 
noticed are ainging in the ears, then insensibility, and, if the 
inhalation l)c continued, death throu<:h suHocation. In the 
caSB of email auimals, »ucb as bii'da, fatal elTecta are obscrvud 
in 30 seconds, and in rabbits; aflur espirfttion of a few minutes. 
If, however, air be again allowed to enter the lungs as soon 
as insc-usibilily has set in, the ed'ecta quickly jam away aiid 

Fi<i. 139. 

Mi:MKKU HBults follow. VMien a mixture of four volumes of 
jAli^^ Mad one volume of oxygon is bix-iuhed for fixim oue-and- 
ihlialf to two uunut«s. a curious kind of iiervooft exdtcmcnt or 
tniti<itent intoxication is produced, without loss of conaciousoess, 
and this soon passes oEf without leaving any evil cou«fquences. 
Hence this substance received the name of laugbing-gos. Nitrous 
oxide Is now largely employed a* an aniesthetic ajj;mit instead 
of chloroform in ca^c^ of sli^jUt soigical operationa, especially 
in dentistry, whore only a short period of unconsciousness is 
needed. Cure niu^t, hnwnver, Ijg taken that for these purposes 
the gas IB free fn>m chlorine and nitric oxide. The nitrous 
oxide oacd for iuhalation in prepared on the large scale, and 
preserved in strouy iroa cyliudera forty ceutimetreB in length 
and fifteen oeutimvlrvs in diametur, into wliich the gas is pumped 
under piessoie, the cylinder being closed with a woU-fittiiig 
screw tap. 

> JakrmientU. 188% BSt 



The composition of citrous oxide may be ftscertoined in vnrioua 
ways, thus, a {jiven vnliimt; of tlm gas ia brought iuto a bent 
glass lube over mercury iu tlie upper part of Fig. 138, 'm wliich 
ft suiall piece of potnssiuui is pUced, The lower and open ead of 
the tube is llien dosed under llie mercury by the fiiifjer, and the 
part of the tube coatuniog the potasaiuiu buutcd witb u lampb 
After the combustion, the tube is allowed to cool, and the volnmo 
of the residual gas measured. This is found to bo Uic same u 
tho on;{iual voluiue tikken, and to constat entirely of uitcogen. 
Sow, a» two Toliimca of nitrous oxido are found iiy expcritnent 
to weigh 43'98, and two volumei of nitrogen are known to weigh 
2802, it ix cK-ur that tlio dilfereucc, or iiidC, U due to the 
oxygen. Hence we see that nitrous oxide consiata of two atoms 
of niltogt'n combined with one of oxygen. 

The same rciult h attained when s spiral of steel wire ia placed 
in a given volume of the g&s and heated to redness by a galvanic 
cuneiit Tlie iron then burns iu the gas, and a volume of 
nitrogen ri'inuius equal to that of the nitrous oxide employed. 

By ineanR of cudioiuetric analysis we may likewise determine 
the composition of the gns, and for this purpose the nitrons oxide 
must be mixetl with hydrogen and the niixtare exploded by an 
el&otric spark, when wnter is formed and nitrogen gus ia left 
behind; thus;— 

Utpokiteoits Aao, HNO. 

337 When sodium amalgam ia thrown into an aqueous solu- 
tion of potassium nitrate, potassium nitrite is at (Irst formed. If 
more sodium amalgam is then added to the cooled liquid until 
four ntoms of sodium have been used for one atom of the nitrate, 
the solution contains the potassium salt of hyponitrons acid, 
potassiiun byponitnte, NOK; thus: — 

NO,K + 2 H, = NOK + 2 H^O. 

The alkaline liijiiid is (hen neutralized with acetic acid, and to 
this a solution of nilrata of silver ia added, when the yellow 
almost iusoluble ailver hyponltrite AgNO is precipitated. The 
acid corresponding to the wilt has not yet been prepnn;d. The 
silvor salt can indeed bn dissolved i» dilute acida without being 
at once decomposed, and the salt may be obtained auain by again 
neutralizing the acid solution ; but the acid solution undergoea 


decompOMtion rotj readily. If tho acetic acid solatiou of the 
potassium sulti be warmed, iiitrvus oxide gas is given ofT; 
tiins: — 

Tho fctintly alkaline solution of a liyponitrilc dccoloriiws 
imlinc solutiuu tuid iircvuiita thu rornuitioa of iodide of sUrdi. 
With acetate of lead eolutiou it pi-oduct'9 a white piocipitate, 
nliicli niter a tiniu liecuiuoH densi; and ytdlow. Tht> acid solu- 
Lion does not culour ferrous snipliate. but on thi; addition of 
solphui'io Rcid tlio black colorulioD cboractemlic of nitric 
oxide is Dli^erved. Peniiangtiimtcs are ducolorizud liy the acid 
solution (Divers),' 

KiTEOGEN Dioxide, ok Niteec Oxide, NO. Density = 14-99. 

238 Tliis gafl was first observed by Van llelmont, who 
tiowever mistunk it for what he tvniied gas syletttre. It via» 
nflerwards mora fully iDveatigated by Priestley, who named it 
nitrous air (see " Historical Introduction "). 

frrparation. — The gas in roiiued when uitric acid acta ou certain 
raetaU such as co]>per, silver, mercury, zinc, &c., as also upon 
phosphorus and seme other easily oxtdtsaUe substances. It ix 
usually prex«red by dissolving copper foil or copper tiuTiinRs in 
nitric acid of specitic K'^vity 1*2, wushiiig the gu by pustiin}; it 
through vAt«r and caustic soda, aud collecting it over col-i 
water in the pnetiuiatic trough. The reaction occurrii^ in this 
case is expressed as followa ; — 

3 Cm- 8 HNO, = 2 NO + 3 CuCNOJ, + 4 UjO. 

TIiL' gas thus obtained w, however, not pure, aa it iuvarjably 
contains free nitrogen and nitrou.* oxide, the quantity of the 
latter gas increasing with th« amount of copper nitrate which 
is foriiu'd.' lu order tv obtain nitric oxide gas chemically pure 
it must be passed into a cold coacentrated solution of ferrous 
Balplut<>, with which it forms a singukr oontpouitd, to be 
described hereafter, and which dissolves id water with formation 
of a deep blackish-hrown colour. On beating this solution pure 
nitric oxide gas is given off. Tlie pure gas cau also be obtained 
by healing fprrous sulphate with nitric acid, or by heating a 
mixture of ferrous sulphate and sodium nitrate with dilut« 

■ Proa. Rw. Sut. xix. 425. 

' AAwmh, fyvm. Ottit. See. sxtIU. 83& 



sulpliuiic acid ; or again, by acting upon a solotion of femnu 
cbloride containing an excess of hydroctiloric actd -M-ith nitra 
(Gay Liisaac.) 

939 Prc^peTt\f$.~'Sitvie oxide i» a colourless gas having n 
specific gravity of 1039 CBerard), and not showing any eigns of 
liciuefactlon either when exposed to s temperature of — 1 10° or 
to a pressure of 50 atmospheres. On exposure to air, this gaa 
at once conibioes with the atmospheric oxygen, with evolution 
of heat and foTmRtion of rud fuincs of uitrogen tetroxtde. 

If a spiral of imn wire be heated to redness in this gas by 
means of a galvanic current, the iron biinis brilliantly 90 long as 
any nitric oxide ruinuiiis 11 nileconi posed, and after the combustion 
tho residual gas is found to consist of nitrageii exactly equal iu 
volume to uuts-half that of tlie gas employed. 

When a stream of the '^1 is parsed over hcot«d pota^ium this 
metal takes -fire and burns briilinittly ; whorea<< metallic sodium, 
even when UeaU.-d with a spirit-lamp, remains unaltered iu the 
gas. Phosphorus also burns with a dnzzHog brilliancy in nitrio 
oxide, but only when it i.^ brought into the g&a already brightly 
burning The flame of feebly burning phosphorus, as well aa tliat 
of sulphur and of n candle, are on the other himd extinguished 
OR plungiuf; them into nitric oxide, because the temperature of 
these f!Dmi-» is not sulticicntly high to decompose this gas into 
its elementary cnii»titiieiitA. If a few drops of ciirbon digul- 
phide be poui-cd into a long glose cylinder tilted with nitric 
oxide vapour, aiid the cylhider well sliakea so tliat the vapour 
of thu disulphide is well iiiixed with the pas, the ntixttire 
burua with a splendid blue and intensely luminous tlamo, which 
Es characterised by its richness iu the violet or cliemicaJly active 
raya. So intense in this light for the violet «nd ultra-violet 
rays, that a lamp in winch the two gases are burnt has been 
constructed for the use of photographers, who can thus obtain 
pictnres at ni^ht.^ 

Tho name nitrogen dioxide has been given to this gas because 
for the same qunntity of nitrogen it contains twice as mncfc 
oxygen aa nitioua oxtde or iiitrn;^'cn monoxide. As is seen, how- 
ever, from the density, this gas has the fornuila XO, and con- 
sequently it possesses !i 5im])ler coiistilution than nitroiLs oxide. 
The chemical and physical profierties of nitric oxide bear out 
this view. Thus, it docs not condense under circnmstaiiccs 
which cflect the lii^uefactJoii of nitrous oxide ; it is also much mem 

I Sell, Btr. Dnil. Chm. Ou. HI ISiZ. 

stable t4iaa this lultcr gaa, ao that it ToUows u luw wtiich we find 
to hold good with ro{>anJ to natilogous (faseoos bodies, \-ix., tliat 
those pos<v<;<tsiiig the simpler consiituiioD are ranch le$s patity 
eondenailiW, and much kss easily decomposable, than llioM of 
more complicated constitution. 

NiTEOfiKN Trioxide, NjO, Density = 37'95. 

340 'W'bcn starch, sugar, arscnious acid, and other easQy 
oxidissble bodies &re heated together with nitric acid, red fumes 
are given off, consisting of v'arying qiiiintities of the trioiiide 
and the tetroxide of nitrogen, and capable of being condensed 
to a very volatile green coloured liquid. Tlils liquid nmy be 
employed for the pm-poae of prapariog pure nitrogeu trioxide 
by pasfiing a current of nitric oxide gas into tlie warmed liquid 
and allowing the gas which is evolved to pass through a heated 
glass lube, tho product being condensed in n tube phinscd 
into a freezing mixture.' 

Nitrogen trioxide is also ohtuined when a mixture of one 
volume of oxygen and four volumes of nitriu oxide ia allowed 
to pass through a hot tube ; thus : — 

2N0 + = N,0,. 

intzogon trioxide fomia a deep blue mobile liquid, which when 
cooled to -10^ assumes a splendid indigo colour and doea not 
solidify at - 30*. Kven at so low a temperature as — 2° the liquid 
trioxide begins to decompuao with evolution of nitric oxide, 
whilst on warming, the decomposition into this gas and nitrogen 
tfttroxide becomes complete. Hence this substance possesses the 
remarkable property of being onallerablc both at high and at 
low t«mpcratiirc«, but of undei;going spontaneous decomposition 
at temperatures intermediate to these. 

NiTRoirs Acid, HNO, 

241 Nitrogen trioxide di^'tolvcs in ice-cold voter, giving rise 
to a bc-autiful blue liquid, nud to the foiTnation of nitrous acid, 
lis the follovviiig equation shows ; — 

> HuwnlMcb, Jmirs Prae. ChtM. [3] fr. 1. 



Nitrous acid is not known in tbe pure slat«, it beiog a very 
unstable substAnc^ which even in aqueous solution rapidly 
undergoes decompasition when warmed, giviug rise to nitric 
Held and uilric oxide gaa; thus : — 

3HNO, = HN0,+ 2X04H,O. 

Tlie salts of this acid, or the nitrites, are, on the contrary, very 
stable bodies. They nr« not only formed by the action of the 
acid upon oxides, but also by the redtictioa of nilniteg ami 
by the oxiUalion of amiuuiiiii. Thus, for instance, pouuaiuiu 
nitrite, KXO,, ia formed either by fusing saltpetre, or, more 
easily, by heating tliis salt with lead or copp«rt thus : — 

KNO, =K>rOj + 0. 

Nitrites alao occur iu nature. Thus tha atmospb^n contains 
flinuil ti^uuatitius of ainniimium nilritv, and traces of nitrites have 
been detected in the juices of certain plants (Schonbein], All 
tlie normal nitrites aw solnbla in water, and most of them 
soluble in alcoUoL Tlie silver salt is the nitrite wtiich is most 
diUiciiItly soluble iu cold water, crystallizing out in long glitter- 
ing; needle-shaped crystals u'lien the hot aqueous solution is 
cooled. Tiie nitrite) defli^rate when thrown on to glowin;; 
curbou, OR do the nitrates. They may, however, be distiDguisbt-tl 
from the latter aalta by the action of dilute ncida, which produce 
Hii QYoluliou of rud funics from tho iiitrilts but not fioni tlie 

In a similar way aqueous solutions of the neutral salts becODU 
of a lisht brow-n colour wlien mixed with a Bolutiiiii of ferrous 
Dulplmte, and this colour d^pcns tc a dark brown on tlie addi- 
tion of acetic acid. Iu order to detect the presimce of n nitrite 
in dilute solution, iodide of potadaium, starch paste, and dilute 
nitric acid are added. The latter acid liberates tho nitrous acid, 
and tliis instantly decoiuposea the iodide with liberation of 
iodine. As. however, other oxidising agents act in a similar 
way, a small c^iuiutity of potaa.<<iui:i pcrmati^iumte solution is 
added to another portion of the liquid ; if a nitrite is really 
present, the colour of the peruiau^'ouato solution will be at 
once destroycd- 

In the CJiso of the presence of nitrites in VC17 small quantiti»s, 
Hs iu ccrtuin waters, fi-escuius rccommcuds the distillation of 
the water previously acidified with acetic acid, tlie firat few drops 
of the distillate beia;' allowed to fidl into a solution of iodide 



of potasaiuni and starch, to wbiub a small ci^uanlily of stilphuric 
acid has been added. 

NiTKOs?L Chloride, NO CL Vapour Ucnsitj- = 32-67. 

242 Tliis chloride of nitrous acid ia formed by llie diiect 
anion of nitric oxide and clLlorine, as vtiHl us \>\ tlm action of 
{>ho3{>liorus pontachiohde upon potassium nilrile, thus : — 

PCli + NO OK = NO CI + K CI + PO 01, 

It is likewise formed together with free chlorine when a mixturG 
of hydrochloric and nilidc acids, the so-ctilled aqiuc rtgia, is slowly 
heated ; thus : — 

HXOj + 3 II CI - XO CI + CI, + 2 H,0. 

In order to obtain the cliloride in the pure state, a mixture of 
one volume of nitric acid of sp. gr. 142 and foiir volumes of 
hydrochloric acid of s]). gr. Mfi is gtijitly warmed, the gnscs 
which are evolved being first dried by piissiug through a chloride 
of calcium tube, aud then led into strong sulphuric ncifl. Tlit- 
chlorine oud hydrochloric acid gases thus escape, whilst nitrosyl 
su1pluit«, SO^H (NO), a body to Imj dvKritKid later on. is 
formed. A» soon as the sulphuric acid is saturated, the lirjuid in 
heated with an e:tcess of perfectly dry 8odium chloride, when 
nitrosyl chloride i.i evolved ; ' thus : — 

SO, I J5^ I- Na 01 = SO. I g*+ NO CL 

Niliwyl chloride ia un orange-yellow gas, the colour of wliicli 
is <^uite different from that of chlorine. It liquefies readily 
when passed llirou^h n tube surrounded by a freexing mixture, 
forming u deep oranjio limpid liquid which boils about -8°. 
This substance combinea with many metallic chlorides, forming 
peculinr compounds, whilst, brought into contact with basic 
oxide3,it is decomposed with formation of a nitrite nitd chloride ; 

NO CI + 2 KOH = KNO, + K CI + H,0. 

NriBosyL Bkomuje, KOBr. 

243 lu order to prepare this compound, nitric oxide is led 
into bromine at a toropenturc of —7° to — W as long as it is 

' TilJcs, a<*m. Sot, /num. [3] lU. 030. 



absorbocl. In this way a blacklBb-brown licj^uid u obtained, 
which begins to decompose at the temperature of — 2* nitric 
oxide beiug evolved If the temperature is allowed to rise 
to -I- 20°, a daxk-brownisb red liquid remuins bvbiud, which 
has the composition KOBr, ; and this ie also formed when 
bromine is saturated with iiitn(: o.\ide at the Drdimtry atmo- 
spheric temperature. This, nitroai/l tribrovLid*, NOBrj, is 
volatihzed when quickly heated, almost without dGcoinposition. 
but if it is alowly distilled it decumposes into its coitstituents 


Density = 22-96. 

344 Tlie rod fumes which are fonned when nitric oxide comes 
into coutact with oxygen or air, consiat of nitrogen peroxide:. 
Keaoe if one voltimtt of dry oxygen l)e mixed with two volumes 
of diy nitric oxide and the red fumes produced led into a tube 
surrounded by a freezing mixture, tbo peroxide condenses in the 
tube either as a liquid or in the form of crystal.*;. 

Nitroj^en tetroxide is also formed by tlte decomposition which 
many nitrates ujuif i^-o whe.n heated, and this substance is usually 
prepared by strongly heating lead nitrate in a retort of hard 
g]a»A, as shown in. Fig. 139, when the following docomposilion 
occurs : — 

Pb(NOj>,= PbO + 2NOa + 0. 

This mode of preparation is, however, not very couvenient, 
and & con.sid).trahlc loss of material occtirs, as the oxygen which 
is evolved carries away some quantity (jf tlie ]>eroxide even 
when the tube into which the fumes are led is plunged into 
a freeitiig mixture. 

The following method is free from the above objactions ; arsenic 
trioxide (white arsenic) in the form of small lumps is placed in a 
(task and covered with nitric acid of spec grav. 1*393; the red 
fumes, which are given olf in quantity on gently heating, are led 
into a receiver auirounded by a freezing mixture, where a mixtUTB 
of trioxide and tetroxidc of nitrogen collects. liy pftssiuy a 
current of nir, or hotter still, of oxygen. throuij;b tliU liquid, the 
trioxide is all transformed into tetroxide, and the product can 
then be rcctilied and purified.' Nitrogen t«troxidc can alsobe 

* HuieEibKh, Joum. Praxt. CAcm. [S] it. X. 



obtiuQcd bythe Action of nitn^LehlorideoQ silver aitrite heated 
to 40° (Kxner) thus :— 

AgXO, + CINO, = AgCl + 2K0, 

245 lyopcnits. — Nitrogen tetroxide 15 a liquid at the ordiaaiy 
atnu>sjili«ric temperatures ; at — 9° it »oIiditi«3 to a nia-is of 
co1o(iTt«83 crystals. .SLglktly above this tcmperaturo the liquid 
compouud is also colourless, but wben warmed above this, it 
first bccuiiif» of a pale greenish ydlow, then at +10' it attains tt 
decided yellow colour, wltikl at 15' it becomes oiaoge-coloured. 
and at higher tempcnUurcs it assuioes a still darker tiuU Tbo 

riii. 139. 

absorption Rpectrum of (gaseous nitrogen tetroxide is a cha< 
lacteristiic baud spectrum which hua beeu mapped by Brewster 
and Olodslone. 

Liijuid nitrogen tetroxldo boils at 22*. forming a brown 
vapour, possessing a very strong and unpleasant smell Wlicu 
the tuiujieniture of the gaa is raised, the colour becomes darker 
aud darker, until at last it appears almost black and opaque. 
This is well shown by sealiof; some of the gaseoua tetroxide in 
two wide gliiHS tube». healing one for some little time in the 
flame of a lamp whilst the other remains at Die onllnary 

Tlicsc remarkable changes in appearance cannot be recognized 
by any equally striking changes in the absorption spectrum of 



ths gas, although it is j^ruliablu that tbe peroxide exists in two 
distinct furms, an indeed has 'bcvn eliown hy the vsriatioos 
which its density exbibitfi. Thus, at low temperatures the 
density coiTes[)onds to thu forniulD. Hji},. and at higher ones 
to XOf The den&ity of the vapour at different temperatures 
VBM fonnd by PUyfoir and Wanklyn,' to be as follows >- 

97-5' . 


Air- ]. 

1-7 8« 



Ccim»ponJiii(; mole- 

cuUr vrrjghl. 
. . 6l0 


The denaity required for the compound NOj is 45-93, whilst 
for the compound X,0^. the doublo of this, or 9VSG, is rc^juiicd. 
It will be men that the iminbcra obtained oil lie between these 
two, thu density ut the highest tcmpcrfiLure not lying far from 
the lower number, wiiilst those found for tlie lower temperu- 
tnres corresponcl more nearly to the density of the sobstauce 
NjO,. from these facts we draw the conclusion Uiat at low 
tempcntturca the iiiolccido oF the compound is represented by 
the formula KjO,, and lln- density Aft, but thiit as the tempera- 
ture rises a gradual chanjje in the density of the moleenle takes 
plaue, one molecule of N,;0, sjdiUiiig up, or b<-coinii>g ili»»oci;(t«d, 
into two of NOj. poiscssiiif; a denaity of 23. From DeviUe and 
Trooat's' experiments the foUowiiig percentage composition of 
the gafi at various temperature^ haa been calculate^l :— 




2fi'-7 . 

. . 20-00 . , 

. . 8000 

00''3 . 

. . 5004 . , 

, . 49-96 

lOCl . 

. . 89-23 . . 

, . 20-77 


. . 98-6(> . , 

, . 104 

140' . 

. . 10000 . , 

, . 000 

We thus see tliat at 140° the black vapour consisla entirely 
ft the simpler molectde NO, 

Nitrogen IHroxide itt decomposed by coltl water with pro- 
dtictiOD of nitric and nitrous acids, thus: — 

2N0, + H,0 = HNOj + UXO, 

This decomposition, however, only occors at low teiuperatures 

1 Oktm. S«t. Jaitm. xv. 1S4. 
» /rtrwi., IMT, p. m. 



and with small quootitiea of water. When nitrogen t«troiride 
ix added to an excess of water at the ordinary tempcmtore, tho 
uicious acid is at once decomposed iato oicric oxide and nitric 
auid ; thus : — 

3N0, + H,0 = 2HN0, + NO. 

It oxygeu be present at the mme time, this oC course com* 
bine^ ^nth the nitric oxide, tormiug nitrogen peroxide, which is 

7;4. 140. 

agnin decomposed by water, nnd in this way the peroxide may 
be completely tranaronned into nitric noid. In order to exhibit 
thi« dccompOKition, its wtdl as to i^how tJie rormation of 1}ie 
peroxide and nitric oxide, the following apparatus may be used : 
Fig. 140. Tliu upper vessel, containing a little wat«r, is fiUed 
with nitric oxido, end is connected with the lower vessel by tho 
tube (/t), which is dniwn out to a point. Tliie lower vessel 



ooDtoins wulor, colourcil with blue litmus. If oxygea l)eDO»' 
led slowly inui Ihe upper vessel by means of the tube (£), red 
fumes are formed, wlikh are abaoilwd by tbe vntet. A vacuum 
is tliu« proiliicetJ, iirid tlie eolinitvil water rises in the form of u 
fountain into the upptr vessel, and becomes eolourftd red. If 
the Ditric exidv liu jiurfcctty puiv, and if care be tukcii lliat tlw 
oxygen is allowed to enter but slowly towards the end of the 
operation, the whole of tlje uppi-r vessel may be filled with 




946 This body is obtiiiiiL-d.tugctlivr with other compounds, by 
the action of dry ammuuiu upuu chloride of sulphur, or upon 
thionyl chloride II is a yellow powder, crystallizing ftom 
HolutioR in IjiAulphide of carbon in yellowish-red rhombic 
prism*. When heated to 120' it becomes darker coloured, and 
emits vapours which attack tlio mucous membrane violently. 
Heated to about 135* it subhmes in the forms of fine yellowish- 
rod cTystals, and at 1 58° it begins to melt with evolution of gas. 
At HiO' it decomposes rapidly with tiie evolutioa of l^hl and 
heat, and on percusaioii it detonati?s very violently. 

Wlien sulphur dicbloride is added to a .lolution of nitrogen 
sulphide ill bisutphido of carbon, several different compounds 
are produced, according to the quantity of the chloride of 
sulphur which is present. If this last body bo present in excess, 
a yellow CTystallinc precipitate is formcil, having the com- 
position NjSjSjCIy which, on heatiim, sublimes in ueedlea. If, 
alter this tompouud lias separated out, more nitrogen sulphidti 
solution be added, the yellow powder is chau^d into a red 
substance (N^S^jSCIj, and this again, on addition of more 
nitrogen sulphide, or on heating, yields a compound (N,Sj)jSCl,, 
whioh fonna a beautiful yellow powder, unalterable in contact 
with the air (Pordos and Ot^lis). 

Nitrogen SfJenvic, N^Sc^.— This compound is foi-med by tlia 
action of ammonia on selenium tctmchlorida It is an orange- 
yellov maaa, which, on heating to 200" as well as by slight 
preasurc. detonates strongly. 



DnrnwMO-ScLPBosic Acm, H^, (KO), 

347 ^'^ alkaline salts of this aci<], wliicli are colourtesa awl 
oryaulliiw, on fonncd vbcn nitric oxido gas is pacMd into an 
aUBline solutioo of a su]]^t«. In Lhe free state tlie acid a 
Dot kaowii, and aU acids, even carlwnic acid, ilecompoee ibe 
salts ioto 9ulp]uit«8 and nitrogen moBOxide ; thns : — 

K^SO,CNO), = KSO. + ^%0. 

When the potassiuia salt is licatcd by itst^lf it (IflconipOMa 
into potaasium sulphite and nitric oxide (Feloiue). 

SuLPUo-smio Aciofi. 

248 A scries of nanarkable cotnponniis, which may be rfr< 
ganlvd as salts o( hitberto nonosolat^ acids, has boea diacoTered 
by Trimy. Thoy Are obuiined either hy mixing itohuions of 
potassium nitrii^ ami nomial potassium sulphite, or by passtii;; 
a cniTeut of sulphur dioxtdv into a solution of potn-ssiuin 
nitrite. Thus : — 

rotasxiitm'ammon Mnsulpkcnatf, NH(SO(K)j, ia prepnrtd as 
a crj'stallinu preoipttot« by adding ud excess of i>otassiuni 
euli>hit« to a solution of potassium nitrit« ; thus : — 

4K^0, + KNO, + S1I,0 = Nn(SO,K), + 5K0H. 

This reaction is rcmurkablc as being on« in which one of 
tlie most powerful alkalies is produced by mixing togetlier two 
Donnal salts. 

Tliie salt is decompoised cither on oontioued contact vrith 
water or on boiling with dilute potash into bydric potassium 
sulphate aiid potassium ammoa-trisvtjAoHate, NHj(SO,K), ; 
thus: — 

NH/SO,K), + 11,0 - KHSO4 + XH,(SO,K), 

Tlie last suit separates out in the fonn of cryatnlliuo needles, in- 
soluble in cold watur, but soluble iit hot dilute potash, from 
which solvent the i-Tystals can be again obtained. If boiled 
nHth addified water a decomposition occurK, und the potassium 
salt of Ammort'difuip/ioau! add, NH,(SOjH)j, is formed ; thus; 

NH,(S0sK)3 + H.O = NHa(SO,K), + HKjSO,. 
Thu salt crystallizes in six-sided prisms, and when boiled for 



aOTa& time with a dilute acid, or even irhea heated in the dry 
stale to 200°,* it decomposes as foUovs :— 

Nn,{SOjK), = NHj + SO, + K^,. 

Mf/droxi/lamine-disulpluntie Acid {Sulpkatatie Aeid) 
N(0H)CS0,1IV— The potassium salt of this acid is formed 
vrhcu solutions of potaasium nitrite and potassium sulphite ar« 
mixed in such proportions that tlic mixtnto conttiiiis to on« 
molecule of the first less than four molecules of the second. 
The salt frj-stallincs in long, briglit, ttaospnrent ucedlee; whi'o 
boUed with water it forma polassittm hyilroxj/lamine-nuinosHt- 
phomte.mi{OK)HOfK: thus:— 

N"{oir){so3K}, + ir,o = nh(oh)so,k + hkso^ 

This salt can be crystallt/ed from its solution in hot water, hot 
when boiled ^vith caustic potash it dcoomposoe into amiaonit, 
potassium sulphate, and nitrous oxide ; thus : — 

4NH(OH)SOsKf4KOH = NjO+2NH3 + 4K,S04+3njO. 

lu atlilitioii to iK^'^e, several other series of salts of ftulpho- 

tiitru-adds have been prepared hy Claus,* 

NrrBosuLPiioKic Acid, SOj-j ^u' 

349 Thiseompound is commouly known as the crystals of the 
leaden ihamliers. which are produced dnriu}; the procces of the 
manufiiodiru of sulphuric acid whmu'vcr the supply of steam la 
insufficient to produce sulphnric acid. XitroAulphonic acid is, 
however, best prepared by acting upon sulphur dioxide with 
conoentratcd nitric acid; thus: — 

SO, + NO,OH=SO,-f2J5 

For this purpose, dry siilpliiir dioxide is led into cold 
fuming nitric acid until the nitua becomes syrupy. Tlie semi- 
sohd mass is then drained on a dry porous ptntc over sulphuric 

' dtDSjUid Koch, Jnn. Chtm. Pfiarm. rlii. 3B6. 
* Anil. (Mm. Plutrrn. clvili. M uiil ISl. 



Another mode of preparing the substance is to pasa the 
vapour of nitrosyl cliloridts into sulpliurio acid :-~ 

UOCl + so, I 2h = ^^^ { OH^ + "*^'- 

It is likcvbc romied vIicd nitrogen peroiide aod sulphuric 
acid are brought together : — 

2N0,-^S0,{gJ{ = ^•0,0H so,^2g« 

The substance obtained by these rcactioua crjsLallizes in 
four-sided rhombic prisms, or soiuetiiiics in tubulur or tigdular 
crj'stalhne :nas3e3, which begin to melt at 30', -witli evolutioa 
of vapour. 

Thu crj-stals dissolve iu small quuiititteft of cold water withont 
any evolutioD of gas, forming a bluo li^aid, which contains 
sulphuric and citrous acids. 

so. {«-,f+j;}o = so. {on + HOxo. 

Kitro-sulphuric acid dissolves in concentrated Rulphiinc acid 
vithout decomposition, and this solution can be distilled. 

NiTBOSDLrnoNic CnLoitiDB, SO, ■] (ji 

250 This chloride is formed hy the direct union of sulphur 
Irioxide aud nitrosyl chloride. It fonas a white crj-stallino mass, 
which molls on bcatiug, with sepuraiion of iiilrosyl chloride. It 
is decomposed iu contact with water into sulphuiic, hydrochloric, 
and nitrous acids (Weber). 

KtTRoauLraosic AsnrDHiDB, 

SO. (no 


451 Vfhen nitrosulplionic acid is heated, it decomposei into 
water and Ibis anhydride, but the latter substancv uaunot be 
obtained in a pure state in this way, as sulphuric acid is formed 
by th« further decomposition of nitroEul phonic acid, aud th(?se 
bodies cannot bo separated, as they both boil nearly at the 
same temperature (Michaelis).' It is, however, eaay to obtain 
< Ber. Jkut. Ckfn. (7m. *ii IOTA. 



this auhydriJe by pawiog dry nitric oxide into sulphur trioxidc. 
so long fts it is absorbed nnd warming the solution uutU lh« 
Ixjiling-point of tJie liquid is nearly reached ; thus : — 

3S0,0 + 2N0 


SO. f ON 

= o 

SOj-^ ONO. 

+ S0, 

The ume compouud is fonnud when sulphur dioxide acts 
upon nitrogen pei-oxide. as well as when Ihe uext conipoiind to 
be described is htfated. Kitrosulphonic nnliydride crystallizes 
ia Jiard colourless quadralic priams, which melt at 217' to fonn 
a j-ellcjw li<^i)id, which hevomes darker on furthor heating, and 
distils over unchanged at about 360°. The compound dissolves 
readily in strong sulphuric acid, forming aitrosu1p\iuiiic acid. 








353 When sulphur trioxide and nitrogen peroxide are hronght 
together in. the cold, the above c:ompound separates out as a 
wliitv ctyatalliue mass, which on heating gives off oxygen, and 
forms the anhydride last described (Wcbor). 


SO, \ 0.N0« 

353 When sulphur trioxide and nitric acid nre mixed together 
in the cold, a tliitk oiiy liquid in formed, from which the above 
compound crystullii:i^s out iiiidur certain conditinns of concen- 
tration. It is soluble without decomposition in warm dilute 
nitric ticid, and on cooling, the litiuid crystals of Ihiit substance 
separate out, containing one molecule of water of cryetuUizatioo. 


954 The ti>rra(ii> Mas usL'd by iheolder chemists in thegeaeraT 
sense in wliicli wo now t mploy the vfotA gas, to signify the various 
kinds of aerifomi Uodiea with wliich chenisii^' lias made us 
familiar. At the present dny, however, wc eouflije tJie signi- 
fication of the word nir to tbe ocean of wriforin fluid or 



otmosptiere (ar;i4ic vapour, and a^aipa a sphere) at the boltom 
of which we live und move 

or tbv existence of aa inviaiblo gaseoii3 
envelope lying bIwvc the solid mass of the 
earth's crust, wc become aware by the resiat- 
(uice offered to our bodies when we pnsa rapidly 
from place to place, as well as by tlie elTeuta 
ptodnced by the motion of tlic partic-les of the 
atmosphere which we t«rni wind. The moat HL ^, 

convincing proof of the exiatt-nw uf Ihe air is 
however given by showing that air has weight. 
This can readily bo done by linnging a luigo 
glass globe, closed with a cork thrtiu^li which 
a tube passes, furnished with a stopcock, on to 
one cmt of the bc«in of a batiiD'Cc, and plnciiig 
weights in the opposite pan until the arrauKe- 
ntent is in equilibrium. On eKhaualiiig tho 
globe by placing it in comtiiiini cation with aii 
air-pump, and again weighing the globe partially 
frtcd from air, the weight will be swiu to be 
cooaiderably less than that which it possessed 
before the evacuation. 

A knowledge of the composition of the nt- 
moephere forma the beginning of the present 
epoch of chemical science, experiment having 
ahown, in oppoaition to Ihe older views, that 
the air 13 not a simple body, but cousi«t« iiminly 
of two dillerent kinds of air or gases, oxygen 
and uittogen. 

Although some of the ancients, e^ipecially 
Vitruviua, appear to have held the view that 
the air possesses weight, yet it is to Torricelli 
that we owe the first distinct proof that this is 
tlie ca^w. In the year 1010 a Florentine pump- 
maker observed that liia lift -pumps would not 
rai.-<e water to a height groBt«r than thirty-two 
feet, and consulted his great townsiiiau Galileo 
as to the cause of this phenomenon. Gableo 
does not app«-iir tu have given tlio correct itolti- 
tion, as he comitaied the water-column to an 
iron i«hl hung np by one end, whicU, when long 
enough, will at last Weak with its own weight. Fis. 1*1. 



ToTTicelli. liowevcr, ia 1643. iiiflrie an oxpcriment which gave tTie 
true explanation of tlie puoip-iaakcr's dilTiuiiUy. Filling witli 
locrcuiy a glass tube tliree IViet in length, and closed at onfi 
end, but open at the other, ho closed the open end with his 
flngor and invi'rtcd the tube in ii liosiu tilled 'w-illi mercury. Tim 
mercury then sank in the tube to a given level, whilst above 
this level there was an empty space, which is still called tht; 
Torricellian vacuum. Above the mercury in tlie basin Viiis 
wat«r, and TorriculU then mi8<;d thi; tuhu so that the ojica cud 
came into the water. The mercury then tlowed out and the 
water nislied up, completely fiUinj; the tube. Fig. 141 represents 
the actual tubes ciii[)Iuyi'd by Torricelii, pliotographeil from 
the original instrUDients placed iu the Science Loan Exhibition 
ot South Kensington. Tlie rise of mercury or water iu a vacuous 
tuba ia caused by the pressure of the atmosphere. The water 
is. however, 135 times lighter than the mercury; hence the 
colunm of the former liquid which is supported by the atmos- 
pheric pressure is Vifi tiinu^s us high as that of Iho httter 
li(]uid. Thus was the laromtUr diseovered, though this name 
was first made use of by Doyle.' 

Hearing of Torricelli's discovery Blaise Pascal I'esolvod to ynt 
this theory to a furtlier test If. fligucd he. the suspension of tlie 
mercury in the barometric lube is dne ia the pressure or weight 
of the air, the mercurial coluttiii must .titik when the biiroiiicier 
is taken to the top of a mountain, owiog to the pressure ou the 
mercury being lessened. Unable to try this cxiwrimcnt himself, 
Pa^eal instructed his brotlior-in-law, Perier, to ascertain whether 
this is 80 or not, and on September 19, 164S, PtSrier look a 
biiroiiietcr to the summit of the I'uy-do Dtime, and showed 
that the mercury sank as ho ascended, proving conclusively the 
correctness of Torricelli's explanation. 

A Kimplc arrangement enables us to reproduce this experiment 
ia the lerfure-room; a barometer lube being filled with mercury 
is inverted over mercury contained iti a trough, when the mereury 
will be seen to sink to a certain level, the apace above this being 
vacuous. A tubulated receiver furnished with a tight-fitting 
csontchouc stopper is then brought over the tube, and the air 
})umped out from the interior of tlie receiver. As the pressure 
of the air is by degi-eca removed, the level of mercury >n the 

' Seo .Vtw E3^rimtnU tm Cottl, jmliHthfd IHi-S. BotIc'b Wartt (EJu. I7T2), 
vol. ii,, p. *87. "Tlic boranii/rr, if lo nroid clnrumWution* 1 may to »«II 
thft wlinTn inxtnimant, trlicrfin ■ mtri-'urial rj'liudor of UD ot 80 indic* is lie|>t 
■lupcndcU, •ftor tli« m«au«r of the TvrrictllUu ex]>mnienl." 




IvHiQ will gi-aduall^- becauie lower, until nl last it will nearly, 
bat not quite, reacli tlie level oF the mercury in the trough. Oa 
opi'iiiiii^ the st<»pec)rk tliR nir will nisli in, aud tlie level of the 
tnvrcur)' id the tub« w-ill rise uuUl it has attoiiicti its former 

ajs Obeying then the laws or "ravilntion, the nir forms part 
of tbtj earth's body, and aucompimius tin; foliil and liquid I'ortioiis 
ID Uieir axial «ncl orbital motions. The absolute height to 
which the atmosplii^i'e extends above the earth's surface luus not 
been ascertained accuracy. As its density is not uiiiforoi, 
but diininiKltcs as th« distAnce Froni tho earth's <urfB<:o in- 
oeofies. the exact point at which the atuiottphere t«nuinat«a ia 
difiicalt to detennine. The height is certainty not unifonn, 
iDa»much as owin;;; to the variation of the force of gravitation 
at the ]}ole8 and at iho equator, and nwing also to tho action of 
centrifugal force, as well as to chaiigi-s of teiupuruture, a 
column of polar air is considerably shorter than a cotumn oF 
cqnatonal nir. 

The almosphcric pressure at the sen's surface would naturally 
bci constant if it were not that owing tu the variations in the 
fiolor radiation, the tempei-ature, and, therefore, the prei^iiire of the 
air, undergoes frequent altemtions. These irregular variations 
necessitate our rending off the height of the barometer when- 
ever volumes of gas have to bo mp-nsured. There ig no doubt 
that the atmoKpheru bus a dcfinitu limit, and, fmni observatJODS 
of tlie time during which tho twilight ext<?nds to the zenith, it 
appears that the alniospherL* reaches in a state of sensible 
density to a hci{;ht of from forty to forty-five miles above the 
earth's siirfHce. Tho n-lution hutu-et-n this height and tho 
diameter of the earth may be ilhistralcd by the statement 
that if a globe of one foot in diameter represents the eailh, 
a GIm of air ]s of an inch in diameter will represent tlie 

If the air were an incompressible fluid, instead of being on 
clastic one, and if it had throughout the density which it possesses 
61 the sea's level, the height of the atmogpheio trould bo 

10513 X 0'760 = 8360 meters, or 5 204 English miles. 

As. however, the nir is elastic, it diminish*s in density as the 
disloncc trom the earth's level increases; thus at a hci-fht of 
5S2S meters, the air expands to twice its volume; whilst at a 
height of twice 5528 meters ttie density of the air is only ^ of 

that wliicb it posseS9i3s at the soa's luvcL At grcalvr clevatioua 
the volume iucreases iti tiie following ratios : — 

GcnK^pliicAl Milei. VoIuhm. 

0- 1 

0-587 2 

1-17* 4 

1-761 8 

2-348 16 

2-935 :i2 

3-522 64 

Tbe weight or the air at the level of the sea in our Inticode ia 
equal to that of a column of niercur}' at 0' of u height of 
76fJ luilliitiotcTS, uTid this is tnkoii lis thu iiortnal barometric 
pressure. Hence, iis ouu clic. of mercury weiybs 13-596 grams, 
the pressure exerted by the air oa oue square coutinieter of 
surface at tlie »ea'» level will be K^.'jOG X 76 = 1033-3 grama 
(or nearly 15 Iba. ou evff>' square inch). 

Accordiiij; to ttiu urvurale dutvnuiuatious of lie^auU, one 
liter of diy pure nir nl 0', mid \iiider the prcsauie of 760 mm, at 
the latitude of Paris is l-2;i.'i20l yraiii. Whilst according to 
Laach ' the weight at Berlin is 1 -293035 gram, or eJuioat exactly 
ylj of the wuiylit of water. 

356 lu cotiuiLou with all bodies at the earth's surface, the 
huinau frame baa to support this weight, but, under ordinary 
circiiiiLttancea the prossure is exerted in all directions, and it is 
not. feit. If. however, the pressure iu one dirc-L'tiuu be removed, 
OS yihea the hand i^ placed over tltc open end of a cylinder A'om 
which the air is heinj; pumped out, the weight of the air is at 
once perceived. As the air obeys Boyle's law, iU density being 
directly proportional to the pressure lo which it is subjected, it 
followa that when the height above the sea's level increases by 
ecjuttl intervals, the density of the air decreases in a geoinelrie 
ratia Henr,a the diH'erence in height of two stations in theaune 
vertical line is in the ntUo of Ihe difference between the 
logaritlims of the harametriu readings at tlic two stations, and 
if tha temperature of the two stations be the same we need 
only multiply the diflerenro of tlie IctgdHlluiis of tlio two read- 
ings (reduced to 0° for the expansion uf mercury) by the number 
18363 to obtain the elevation in meters. 

■ P^. Ann. XiyttnsiDigiM. UL SSI. 


Tlio average or raetui annual temptmttin of tiic air, like its 
density, ill not tlie fiauid Uiroiigliout the mass. It (liminishea 
as the elevation above tlie earth's siirfacQ increaitt'it, so that at 
a certain height., diirering for diflerent laliludes, a. line is readied 
at wliicli tbti nit:aji tcniporaturc of tliu air docs col rise above 
tlie freezing-point. This 18 called the Hue of perpetual snow. At 
latitude T-i" it reaches the eea's ieviO, in the laCitudo of 60° it 
is found ut u height of 3,818 feet, whilst under the equator the 
snow-line exists at a height of 1J,207 feet nbovo tho sea. 
The height of th« snow-line is also alTecled by local causes, 
Olid it a found to vary considerably even in tlie same latitude. 

Owing to tho uneqnal beating effect produced by the sun on 
different portions of the enrth's surface, great variations are 
observed in the temperature of the atmosphere in different 
plticos, aiiil thcsv give rise to thoso motions of the ntmosphci'e 
which are termed winds. Wiuda nmy either bo caused Ijy 
local aUcnitioita of temperature conllncd to narrow limits, as 
with the laud and sea-breezes of our coasta, or they may be 
produced by a general unequal diffusion of heat over the sur- 
face of tlie globe, as with the so-called trade-winds, which are 
oau-'tcd by the temperature of the air in tlifi equatorial zoaia 
being liijjher than tliut of the iiir in llie polar regions. 

Tub Composition or tub Atmosphkbe. 

357 Atmospheric air, in addition to oxygen and nitrogen, 
contains as normal constituents, aqueous vapour, carbon dioxide; 
ammonia, and ozonu. OUier guscs and vapours do indeed oooiir 
in diffeient places, umler a variety of circumstances, and in 
varying quantities. Furthermore certain chemical compounds, 
such as common salt, ammonium nitrate, and some other chemi- 
cal salts, occur as finely-divided solid particles, together with 
Other minute lloatiug paiticles of animal, vegetable, and iniQeial 

Tlie discovery of th« composition of the ntmoaphere has been 
(l«soril«d in (he Histoncnl Introduction. AVe savr there 
that we owR to C' the fiist exact determination of the 
relation existing l>etween the two importAnt constituents, oxygen 
and nitrogen^ " During the last half of tlie year 1781," he 
writes, " I tried the air of near sixty different dnye in order 
to find whether it was more phlogisticated at one time than 
> mi. Tram». ITS3, p. )0d, " An Account of a new Eadiamelir." 



BQOtlier, but found no diflerencc tlial I couM be sure of, though 
the wind and wcatliflr on these days was very vaiioiis, som« of 
them being very fair and clear, others very wet. and otlicrs very 
foggy." ' This result was fouuded on a long series of eipcrimenta, 
lor eeren or eight andyses of air coUcvtcd on the sutne day 
were luivJc by different processes, 8o that altogether Cavendish 
cannot have made fewer than 4tl0 detenninntions of the com- 
position of atmospheric air. Expcriincnts u-ei'e likewise made 
lo see whether I^ndon air differed from that of the country, and 
Blight difi'erenceg were sometimes found in favour of London air, 
in Marlborough Street, aometimes in favour of country air, in 
Kenaington. On taking a mean of the numbers no diffwcnco 
whatex'er vrn.% perceptible, the result of all his experiineuls 
being that 100 volumes of air contain 20*83 parta by volume 
of dephlogisticatid air or oxygen. 

The constant results thus obtained by Cavendish led several 
chemists, such as Trout, Uobeminer, and riioinsen, tomainlaiu 
that the air ia a chemical compound of one vohinie of oxygi.>ii 
witli four volumes of nitrogen. AgaiuGt this assumption 
JoliD DaUon protest&d,' insisting that the air is merely a 
mechauiail tntxttire of coii»tant composition, and contendiDg 
that, because iiitrogon is lighter than oxygen, the relative 
amounts of the two ^uscs must vary at diffeiont heights above 
the earth's surface, the oxygeu diminishing and the nitrogen 
iucreasiiis as we ascend. This view was, however, shown to 
be erroneous by Gay-Lussac and Th(;nard, who colloclcd air 
in a balloon at an elevation of 7.000 meters, and fuund it to 
contain exactly llie same proportional quanlity of oxygen as 
that collected at the same time in Paris and analyzed in the 
same way. Their results have since been corroboratod by 
the more exact invegtigations of Brunner, who analyzed tlio 
air collected nt the top and at the bottom of the Panlhom and 
found in each case exactly the same proportion between the 
oxygen and llie nitrogen. 

Tlie very iuiportanti question whether the composition 
of the air undei-j^es vaiinllon, wndor vai^-ing conditions of 
time and place and what h the perccntflge of oxygen it 
contains was further invcatignted by many chemiiits. Gay- 
LusSac and Humboldt in Paris found that the air contiiined 
from 20"9 to 21'I per cent, of oxygon ; Ua^y in London obtained 

' FtM. Travj. 1783. p. 1S8. 

■ UandiaUT llttairin. Sad wrin, Tol. L p. Hi. 

from 20-8 to 2M per cent.: Thoiiujon in Glasgow 211, and 
KupRer iu Kasao 21'1 per cent, of oxygen. It was, however, 
oeeessaty tUnt more accurate methods of annlysis sliould be 

258 Two processea are now used, viz., (1) tneasui-cmpnt of 
the voUimes of the component gases, (2) deter mi nation of their 
weight. Xlie lirst of these processea, or the eiidiouietric method, 
has been practised by Ih^gnault, Biinsen, Lewy, and Angus 
Smith, whiliit the latter method lias cWefly been used by 
Dumaa and Houssingautt iu their cdcbrated I'esearcb carried 
out in the year ]ft41.' In their analyses of air by tlie latter 
method, the tm-o French clieniists employed 011 apparatus 
showQ in Fig. 142. The lai;ge balloon (v) was rendered m 
perfectly vacuous as possible, uud brought iu couneclioo with 


Pio, us. 

vacuous tube fa h), coDtaioiDg inetollic copper redwct-d 
by means of hydroj:;en. and placed in a furnace in which it 
could be heated to redness by means of charcoal or gas. At 
the other end thia tube was connected with the tubes c and 
B, and with the bulbs A. these last contained cau.«tic pot:i<ih, mid 
the others pumicc'Stone moistened with strong sulpliuric acid 
.ftir the purpou of taking iip all molsuiro front the air, us well 
i"^ of al^trncting from it tlie whole of its ammonia and carbun 
dioxide. As noon as the tube a b had been heated to dull red- 
ness the stopcocks r wr-i-n opcued so a.t to let the air pass slowly 
into the apparatus. Entering the tiibo a b, and coming in 
contact with the glowing copper, Uie whole of the oxygen was 

' Ann. C/iim. J'ky. [3] iiL Sfi7. 

absorlied, only ttie nitrogen going over into the thcuous glob& 
WUcn the experiment was complete, the stopcocks were closed, 
the tube and balloon detachod from Hie apparatus and each 
accunitvly weighed. Holb lube and ballooa were then again 
rendered vacaous, and weighed a third time. The tube contain- 
ing the copper oxide, which had heen weighed empty to begin 
with, is thus weighed fuU of nitrosen. after wliich the nitiO]»en 
is withdiawD by thu ntr-pumji nnd its vcight again dewrmiued. 
The foUowiug details of an actual experiment may iltoatrate the 
method : — 

Vacuous tube containing copper before the } 

expcrimenl i ^"^'^^^ 

Tube filled with nitrogen and copper afitr the ) rri.jic 

experiment ) 

Vaciioii8 tube after experiment CiiX'346 

JJalloon containing nitrogen at 19* and under ( , ,-,, --„ 

pressure lOi * nirn ) ■ 

BaUoon. vacuous, at 19*-4 tnd 7627 mm. . . I391'554 

Hence the weight of oxygen is found to be 3*680 grams, whilst 
tlie weight of uilroKon in tJie balloon was 12304 grams, and the 
weight of uitrogvu iu tlie tube 0069. giving a. total of 12*373 
Or the peicentago composition is : — 

Oxygen 22-92 

KiUogen 7708 


Dumas and Boussingfiult wsed two balloonB, with which Ihcjr 
obtained the following results :— 

Pa^etitafce hy weijiht or oKycta. 
With •.ninll With larn 

1S41. hilliwu. balloon. 

April 27 22-92 . . . 22-92 

,. 28 2303 . . . 2;i-09 

„ 29 23-03 . . . 2301 

Mean. . . . 22-993 23-016 

The menu of these deteraiinations is 23-005 parts by weight of 
oxygen and 76995 of uitiogen. 



Knowing the specific gravities or the two gases, we obtain bjr 
calcolatioD the fbllowing compojiition of air by volume: — 

Oxygcu 2077 

Nitrogen 79-23 

10(1 00 

These experiiiiGiiift were subsequently repeated by other 
chemists, with the following results: — 

Mwin PorconURe by 
weiglit of ux jgok 

Lewy, in Copenhagen, 1841 22 998 

St«8, ill Brussels. 1842 23-100 

Marignac. in Geneva. 1842 22990 

V Th 

[ cbem 


[ According to these txperimcnts, titfrefore, tke air contains 23 
^■^HHs liy weight of oxygon and 77 parts by weight of nitn^n. 
^^^V^sg This uielhoil, aUhou;i;h caijable of givinj; exact results, 
requires lai^ce appaiatus and good air-piunps and babiiices. It caa 
only be caTriud on io a Iftlwraloiy, and it necessitates the employ- 
ment of large volumes of air. The atdivmdrie, or volumetric 
oietJiod is less difficult and tedious, so that the determinations 
may ba repeated by thousands and require a much smaller volume 
of air. This method is liable to so email an exi»'rimcntal 
«Tror that, with an oluerver welbskilled in its vige, it never 
teaches the rv^n,; psrt> and may sometimes uot exceed tho 

^ rvimv pa't of iIiB wliola 
^B The process di>pendA on the welbknown fuct that when 
^^ oxygen and hydrojjpn gases are mixed and fired by an electric 
spnik, they unite lo form water in the cxiicb proportion of 
one volnme of tlie former to two volumes of iJie lattur. TIio • 
volurao o( the liquid water formed is so small in proportion 
to that of the constituent gases that, except in casw of vtry 
exact estimntions, it may be altogether neglected. Hence if 
■w« bring together a givi^n volume of air and more liydwgou 
than is needed to cnmbino with the oxygen in it, and if an 
electric spark be jiis^ed throiij^h the mixture, oiic-lhird of tho 
observed cfmtraclwn will be due to the oxygen. In order to 
obtain by this method exact results' a very carefully calibrated 
tadionietcr is enijdoycd 1 meter long and about 0*025 wide, and 
' fat lUutla Ml thtM |iotati Buntm'a OoMUKfrjt miut b« cooaulttd. 



the observations are comlucted ia a space within which th*' 
changes of temperature are as small and as gradual as possible. 

The air for these tieteniiinations is collecleil either iu small 
Eaaks of aljuul hulf a liter in ckjmcity, lh« necks of which have 
been previously elougated before the blowpip"^- " i" ^on-; tubes. 
Ihe ends of which have heen drawn out. Inside the flask or 
lubu a siiiiill piece of fused chloride of calcium ia placed for 
the purpose of Absorbing Eho amtnonia, and a similar piece of 
fused caustic potash to nhsorb the carbonic acid, nnd both 
euhslaiices arc ullowod to crygtjillizi: on tliu stdu-t of the glass 
by the addition of a drop of water. It is quite necessary to 
remove the carbonic acid of the air previous lo analysis. Even 
if the ijimiil-Jty prcMjnt were only OOS per cent, of the total 
volume, it would produce au appreciable error in the oxygen 
determination, carbonic acid when exploded with an fxceaa of 
hydixjiien in presence of the detonating mi.\tnre of oxygen ajjd 
hydrogL-n being decomposed into an equal volume of carbonic 
oxide, while an equal vulitntc of liydmj^cu disappears, so that 
the volume of combined gas would be 0*05 per cent, too lai-ge. 

Li cnriTi'itig nut this method \vil!» exactitude a number ofj 
manipulatory precautious have to he alleiidcd lo. Increase of] 
temperutarc of the mercury by handling muBt bo avoided h 
much as poftsihle ; the air must always be measured saturated 
with the niaximuni aniotint of aqtieou-s vapour, for , which 
purpose one dfop of waiei- is pluccd into tlic ht-nd of the cudio- 
metw and allowed to run down through the whule length of 
the tube, so that tlie aqucini!! vapour may adjust itself at once 
throughout the mass of ga.s to coniespond with atterations of 
temperature. It is nece.*»ary to subtmct Mie vohinio of tlio 
water formed by the couibuslioii from the volume of gas -which 
has disappeared reduced to 1 m. pressure and 0° C, which i8 
done by multiplying this volttnie by Ihe fraction 01)007 and 
subtracting the product from the observed coiili'action. 

The following numhers ' tliow the approximation obtained 
by Bunsen in two aualyeea of the same sample of air collected 
in Marburg on 9th January, 1846: — 


Air employed .... 841-8 
After addition of hydrogen 1051-" 
After the explosion . . 8788 



Tin p. 


VqL lit 0» 
n-ad 1 m. 





480 09 

> EhutMii'i Oatmttrt, 'i. 



Compositiim, of Air in 100 parts by volume. 

Nitrogen 79030 

Oxygen 20-970 


Air employed .... 859-3 05225 06 
After additionofhydrogenl051-9 07079 0-6 
After the explosion . . 870-3 05317 6 

Composition of Air in 100 parts hy voluvie. 

Nitrogen 79037 

Oxygen 20963 


743 01 

Bunsen, who has brought all the processes of gas analysis to 
a marvellous degree of perfection, points out^ that in normal 
determinations of the composition of the air still greater 
precision may be attained by repeating, several times, and at 
regular intervals, the observation of the height of the mercury 
in the eudiometer. From the agreement between the reduced 
volumes which are read off, the point in the aeries of observ- 
atjooa is found at which the temperature has been most con- 
stant. As an example of such an accurate analysis Bunsen 
gives the following : — 




VdL at If C. tnS 1 mstcT 

Air Employed 

6l> C 

75* -9 





360-52 1 

360-63 > 360 62 
360-70 ) - 

After additioQ 
of Hydrogen. 









657-20 } 
657-24 i 557-20 
657-17 ) 

After the Ex- 
plosion. . 








330-6* I 

33045 f 330-5* 
330-5* ) 

Hence Nitrogen 79036 volumes. 

„ Oxygen 20964 „ 


» Loe. dt. 77. 



As the result of tw«Dty>eiglit nnnlyscs Bunsen found 
avcragft percentage of oxygen to ba 20'92t volumes, whiUt 
rlie lowrst percputflgc found was 20840. 

360 ItegimuU,' uaiug a difTerent -volumotrio method lias 
anfllysod a very ]a.Tv;e iiiimbcr of i*raplds of air collected in a 
uniform inanupr in various (Quarters of the globe, according tojj 
in&lTQctions wliich lie Imd given, TIjc error of two anal} 
made on tlie siimG sample rarely readied 0*02 p«r cent In 
more than lUO samples of air collected in or near Pu^i^ Reg- 
nault found a maxiniiiin amount of 20*1>1>9, a minimuia of 
20 31.1, and a mean of 20'0C percentage of oxygen. The dif- 
fei'puce of 008C per cent, is too large, according to Itcftnanlt, 
to l>e due to errors of cxfK-niDoiit, mid il must, tlierofore, be 
ascribed to vanationa in tlie composition of the air occurring 
tiom day to day. 

Air collected from other locsHtios gave Eegnnult the followinfl 
results : — 

PeromUKT of oxj 

9 samples fi-om Lyoua gave 20-918 to 20-9S8J 

30 samples from liorlin 20-908 „ 20998 

10 „ „ Madrid ' . . 20916 .. 20-98! 

23 „ „ Geneva and Chamounix . . 20909 „ 20993 
17 „ „ Toulon Roads and Meditcr- > 20-912 •>0-982 

6 „ „ Atlantic Ocean 20918 „ 20-961 

2 „ „ Ecuador 2096 

3 „ „ Summit of ricliincba . . . 20949 „ 20-98al 
2 ,. ., Antarctic Seas BOSS „ 209* 

The conclusion which Eeynault draws from these dvtcrmi- 
nalidns ia, that the atmosphurc shows perceptible, though very 
aiiinll. alterations in the amount of oxy^^i-u nt different times and 
in diffi;rent localities, Tliis vanalioii ranges from 20'I) to 21'0 
per cent,, but from special unknown causes the amount of oxygen 
aeems somi-limvs to sink iu trcjiical Cdunlries as low as 204 per 
cent, as was &epn in the Day of liengal on March 8, 1849. 

261 Ih. R. Angit5 Smith ^ lias recently extended out know- 
ledge of the variutioaa which the percentfl;!e of oxygen under- 
goes in the air of towns and that of closwl inlmbitcd spaces. Ho 
finds tliat tlie percentage of oxygen in flir from the sea-shore, 

» j(nn. C/itifi. PAyi. m Hxvi 3S5. 
* On Air and JCatn, l.Migiiun«, 1S73. 



BDct from Scotch moors nn<t mount&ins, is as high &s 20'd09. In 
the fre« air of tiiwns, and especially durinf; foggy weaUier, it 
may sink to 20 82. In inliabited rooms and crowded tlieatrcs, 
ihe percentogo of oxygen may sink sonietuncs to 20^8 {Lvvty), 
whilst according to the very numerous (339) anolj-s&s of Angus 
Smith,' the percentage of oxygen in mines docj) not average 
more than 20'2G. 'J'h« exact cniuposition of the ait at high 
elevations haa heen investigated hy Frankland,' who hu ahown 
thaty 83 far as nitrogen and oxyguii arc coiiccrnwl, the composi- 
tion of tho air up to an elevation of 14,000 feet is constant, 
and that the variations exhibited in air collected at the above 
height, fall within thu limits noticed hy former exiwriineiitcis. 

If we compare the percentage composition of air by volnme 
(see p. 44.1). as obtained by calculation from llie )rravimetric 
annlysiFi, with the moan results of Bunsen's volumetric analyses, 
ll>c difftrence (20-924 - 20770 =0154) is greater tlian the 
differences observed by Regnault in his volumetric nnalyses of 
air collected in voiioue situattoaa, This is to be ascribed to the 
fact that in the operations of weighing the latge balloons, kc, 
cOTstanl experimentril errors are introduced from which the 
volumetric method is free. 

aSi That the air is a ruechaiiiciil nixttire and not a chemical 
combination of oxygen and nitrogen, is seen from the following 

(1.) The quantities of nitrogen and oxygen in the air do not 
present any simple relation to the atomic weights of these 
elements, and, indeed, the propoitions in which they are mixed 
are vannhlc. 

(2.) On mixing oxygen and nitrogen gases mechanically in 
the prt'i>ortion in which they occur in oir, no conlracliou or 
evolution of heat ie observod and the mixture behaves in every 
way like air. 

(3.) When air is dissolved in water, the proportion beUveen 
(he oxygen and nilTOgen in the dissoU-ed air is ({uite dilfereat 
from that in the nndistwlved air, the difleronce being in strict 
nccordanvo with the laws of gaa-absorption ou the assump- 
tion that the air is u mixture. When water is saturated with 
air at any temperature below 30°, the following is the proportion 
of oxygen aud nitrogen contained in the dissolvcil and uodis- 
aulved air : — 

■ (H Air md Rnin, y. 104. 



Oxygea . 
NUrogea . 

Air <liMnIv«d 
in water. 

. 34-92 . 
. C508 . 


Air nndisaolred 
ill wnfr. 

. . 2oao 

. . 79-04 


If iha air n-ore a chemical eombinfttioa of oxygen and 
nitrogen, such a separuMon by soliitioa would be impossible. 

2$3 Id order to ahow the compositioa of the air, ttie appanitus 
Fij,'. 14:! U often used. Tiiis consists of ft calibrated and divided 
glass tube filled to a giveu poiut wilh air over mercury. Into 
this is iatroducvd a smull piucu of pliospHoi'Us supported upon 
a copper wire. Gradually- all the oxygen is absorbed and llie 

Fw. IIS. 

Fio. 141. 

mercury rises in llie lule. After a while tho volume of residual 
nitrogen is read o8", and, correctioiis haviiif; been mndc for tem- 
perature and pressure, it is found itat 100 volumes of tbe «ir 
contiiin nbout 21 rolumcg of oxygea. 

Acotber less exact but mora rapid method of exhibiting the 
tAtnc fact is carried ont by help of the arrangement sbovro in 
Fig. 144. In tlie beaker glass (r) is placed the iron stand (d) 

carrying tlie iron cup (e), containing a muall piece ot phosphorus. 
Over this stand is placed the tubuliited cyliuder (a). The upper 
port uf thb cvlindiT is KnidimtvJ iiilo five equal division?, 
and water is poured into tlie heaker glass until the level reaches 
the first division. The phosphorus in the cup is i^ited by 
droppiog dowa ou them a chaiu vliich has been heated in a 
flnnia The phosphonig then bums, the fwmcs of phospliorua 
pentoxide are absorbed by the water, oiul, when iJie gas hiL*i 
cooled, and the pressure been equalised by bringing the level of 
the water outside up to that iiiKido the cylinder, four'tifths of 
the original volume of the air remain uiiabBorbed. 

The carbonic acid, aqueous vapour, organic ntatttir, and the oilier 
constituents of the atmosphere varj* in amount in different places 
and at difTercat times much iiioiv than the oxygen and nitrogen. 

264 Atntosphem Varbtiaic Acid. — Reffrein:e bos already been 
made to tlie pait played by atmospheric carbon dioxide (car- 
bonic acid). The wliole vegetable world depends fur its existeuCQ 
on the presence of this gas, which serves, in the 8iiiili;;ht, as Ibe 
chief food of plants, wliilst, when present in certuiii quantities, 
it acta most prejudicially nn the higher furtna of aiiiuial life. 
Nor ia the amount of carbonic acid whicli becomes hurtful 
very much removed from tlio amount at present existing in 
the air. So far as tee can ascertain, nil aii- which contains 7 
volumes of carbonic acid in 10,lM)0 ia hurtful for reepiratioQ, 
while the normal amount is ■( volumes in lO.DUO. 

The queJition whellier the atmasplicre is now slowly under- 
going or has in post times undeigoue any perceiitible clianges 
in the amount of its carbonic acid cannot be answcied witli 
certaitily. hnl it Is piftty clear that if th»re are any snch 
changes tlity must be and must have been veiy slow in their 
notion. The carbonic acid present in the air, atlhough apjMrently 
small in it« relative amount, is in fact enonuoiu in absolute 
weight, reaching to upwards of 3,000 billions of kilograms, or mote 
than would probably bs obtained by the combustion of all the 
vegetable and animal matter now existing on the earth's surface. 
The quantity of atmospheric carbonic acid varies occoi'ding to 
the Situation and occonling to meteorological and other circiun> 
stances. Thus tlie average amount in free open country sir is 
4-0 volumes in 10,000, whilst in toiivns where much cool ia 
burnt the amount may rise to GO or even 70 per 10.000. Over 
the tea. the amount of carbonic acid is somewhat less,' being on 
' Tborpe, Cbut. Soc Jatn. :ll. 18». 



an average aboHl y*0 volumes per 10.000. At high elevations iu 
tlie fttinoHplicrc Lh« proportion of cnrboiiic acid is geoeraily, but 
not invariably, greater Uian at lower levels. In closed inhabited 
epaccH tlic volume of carbonic acid, proceeding from ntsptimtioQ 
and from the combustion of illumiiiating materialB, is usually 
much biglicT in the open air,' end the amount is much 
higher iji uum» thau iu tlie air above ground. 

As the quantity of cEubonic acid serves oB the Tefldicst and 
most reliable t«6t of the healihiuess or otherwise of an almo- 
aphere, it becomes a loatler of importnnce to iuMx;rtain iiM 


Fia. Hb. 

amount with accuracy. The methods in use for tliis purpose 
ere (I) the gravimetrio and (2) the vohiinctric nielhod. In Iho 
first of these* the carbonic acid is absorbed from a known 
volume of air, freed from ammonia and aqueous vapour, through 
weighed tubes containing c&ustio potash. This necessitates the 
passage of not less that forty liters of air. drawn by means of 
the aspirator (v. Fig. 14')), fiUe-d with water, over the tubes, in 
order thata sufficient weight of carbonic acid for an exact weigh- 
ing may be obtained. The tubct A and B are filled with 
pttmic«-«tone moistened with sulphuric acid. Tlie oir is thus 
dricdand freed from ammonia, o and d coutuin moist bnt solid 
) EtoKM, (7&1M. Set. Journ. x. S&l. * fiauasiir*, Piijf. Ann. xlx. 381. 



caustic potash for th« absorption of the carbon-dioxide. E and 
p are also drying-tubes, prepared liko the tubes A and li. and 
ser\'riig to bold back any moistm-o which tlie dry gaa might 
have tjtkua up rrom the tubes c and n. The following cxtimple 
of & detecniuiation made by this plan illustrates tlio process :— 

Grasimetrie Determination 0/ Carbonic A i:ul in London Air, 
Ftb. 27, 1857. 

Volume of aspirated air at 8' and anderl _^™^ i-, 

772*5 mm. of mercury J 

Weight of absorbed carbonic acid . . . =0'O30SgTin. 

Hence 10,000 volumes of air contain 37 volumes of carbonic acid. 
265 A mnch more convenient proccas is the vohimetric one 
proposed by I'ettenkofer.^ For thia a volume of aSont 10 fitera 
of air only is needed, a glass cyliniior closed by a camitchonc cnp 
bein;; employed, ajid do bal&nce being required. I'he method 
depends upon the fact that a solution of hydrat« of baryta of 
koovn strength wliea shaken up with a closed volume of air 
containing carbonic acid, abstnict« the whole of that carbonic 
acid from the air with formation of lUfiolubld carbonate of 
bariom ; thus : 

Ba(On), -H CO, = IJaCO, + H,0. 

Hie quantity of baryta in excess which remains in solution, after 
shaking up with the air, is asc(>Ftained by adding to an aliquot 
portion of the milky fluid a standard solution of oxnlic acid 
nnti] the nlkaline clinracter of ilic baryta wnter disappeara. When 
tltia point is reached, tli« whole of the restdunl soluble baiyta 
has been ncntraliscd by the oxitlic ncicL The hiuyta and oxalic 
acid solatioim are made of such a strength that equal volumes 
oxMtJy DCUtTfdiM each other, and so that 1 ctw. of bnrj-ta solu- 
tion will ptwipilate exactly 1 msnn. of carbonic acid. The 
following example will serve to explain this process : — 

Votuutdrie Deierminaiion of Carhoitic Add m Manekeater Air, 
Nov. 10, 1873. 

Volume of air employed, 10'80 liters at T*and underapreasnre 
of 765 nun. of mercury, 

> CktA. Sot. Jaum. t. ttL 



SO cba of Standard baryta sotution (1 cbc. = 1 ingm. COg) was 
shaken up with this air. Of tliis, after tlie experiment, 25 eta 
needed '2'i cbc. of standard oxnlio acid (I clic. = I nigui. COj) for 
complete neutralization. Ilencc C cbc. of tiaryl-a aolution were 
neutralized by tlic carbonic acid In 10 S liters of air; or 10,000 
volumes of air contain 2 85 volumes of carbonic acid. 

a66 The moisture contained in the air is liable to much more 
extcuslve chaugcs than even the carbonic acid. Amongst the 
circumstances which affuct Uic atmosphciic moisture, distance 
from masses of water, and the coiifi<;uratioD of the land, seem 
Che most important A given volume of air cuunot take u[> 
more than a certain quantity of aqueoui; vapour at a given tem- 
perature, and then the air is said to bo saturated with uiotstui'a 
The weight in grams of water capable of being Liken up by 
1 cubic meter of air, at different temperatures, is given in the 
following table :— 





C. 43 num. 





35* 39-252 





40* 50700 





100' 588-73 





This quantity is wholly depoident on the tcmpcratuTo of thej 
air, being representc-d by the tenaon of the vapour of water at 
that temperature. Thus the veight of ivjucoiis vapour nhich 
can be taken up by 1 cubic meter of air at 10', at which tem- 
pcraliin; the tension of its vapour is 91G3 mm., ia obtained aa 
follows: — 1 cubic metei of aqncous vapour at 0' and 760 mm. 
weighs 804-75 prams. Hence one ciibie meter of air needs for 
satuatioD tlie following quantity of aqueous vapour : — 

804-75 X 273 x 9163 

283x760 9-362 grm. 

When the temperature of saturated air ia Towered, the aque 
vapour is precipitated in the form of ruin, innw, or hail, accord-' 
ing to the temperature of the air during, or alter, the depoaition. 
If one culiic mile of air eatiiratod with wiitcr at 35* be cooled 
to 0°, it will deposit upwards of 140,000 tons of water as rain. 
for one cubic meter of air at SO" ia saturated when ib contains 
39*35 grams of aqueous vapour, whei-eos at 0" it can hold ooly 



4'87 groins Id tJie state of vapour. It seldom happens tliat tho 
air is completely saturate ivitli moisture, and as seldom tliiit the 
amount of moisture sinks bc)ow ^'g of tlie saturatio); quonlitj. 
Even over tbe sea the air is nevt-r conii)Ift«ly sittiiratcj wilh 
moisture. Large uinounts of watery vapour are, however, driven 
l)>- the winda into the iuterior of the continents, and mnre in 
snnuiicr than in winter, when the land is colder than the aco, 
and when, therefore, the aqueous vapour is more easily condensed, 
and wlien it does not so readily penetrate for great distances. 
Tlie following mean tensions of aqueous vapour in tlio air at 
clifTcreot places exhibit this fact clearly : — 

Hvan Tniiion of AqvMiu Vapour in mm. 

London . . 

Vtrecht . . 

Hallo . . . 

Berlin . . . 

Warsaw . . 
St. Petersburg 

Kasan . . . 

Barnaul . . 

In order to determine the amount of moisture in the air, we may 
cu)]iloy either a chemical or a physical method. According to 
the lirHt. a known vuluniu of air is drawn over weijjhcd tubes 
contamiii}; hygroscopic substances, the increase in weight of 
these tubes giving the weight of tlie aquvous vapour. Thus 
43'2 liters of Ijondon air at 8^ and 1725 mm. : when passed 
through diying tubes, deposited 0241 grni. of water. 

In the Bticond method Uy<jrQmtlcrt are employed ; of these 
Bcgnatilt's dew-point hygrometer is the best.' for the physical 
detenu inittion.1 of atmospheric moisture, works on Hygrumetry 
must be cooaulted. 

367 Ammonia is another important constituent of the air, 
originating in tlie decom position of nitrogeaoiu orgauic niotler. 
Tliu relative proportioD in which this substance is contained in 
the atmosphere is extremely small, and prolmhiy very vatying 

> Afoh Okn> Fhy*. [91 xr. lO. 



inasmuch as it is not present as free ammonia, but coiabincd 
vith atmospheric cnrboD dioxide and othor ocida. and ibOM] 
ammoiitac&l sait» ore wiuhud down by the Tain or ubeorbod 
by the earth. This oonatituent plays an important pott in vege- 
tation, for it U from it alone that unmnnurcd crops derive the 
nitrogen which they require for the formation of seal and other 
portions of their structure, it having been shown by LawtB, 
Gilbert, and Piigh,' as well as by Schltteing and A. Meyer, that 
plants growing in an atinoephera and in a soil tne from ammonia 
or otfaer forms of cuinbinod iiUrogcii do not contain more nitrogen 
tluin the seods from which tliey grew. 

It has alrcad>- been Blated that ozone is almost always con- 
tained in the atmosphere. Its amount is, of course, but i»mall, 
owing to it.<» powerful action as an oxidizing agent Its presence, 
however, ia the atmosphere explains the occurrence of hydrogen 
dioxide and of the uitrate n-iid nitrite of aininonium which have 
been found iu snow and rain. Carius has proved^ that the whit« 
fumes given off when oKone and ammonia are brought together 
are due to the formation of these compounds, a-t the following 
equation shows : — 

2Nn, + 40j = NH.NO, + H,0, + 40, 

The rain which falls during thimderstoruis is found to contain 
more nitrite oiid uitrate than ordinary rain, whence wc are led 
to conclude that electric diaeliarg*s also eifect thia combination. 
According to the experiments of Goppelsroder,' the rain water 
collected ab Basel contained the following amouots of amiuouia in 
parts per miHion : — 

1671. Miniintun. Max imam. 

January .... 4-6 .... 78 

February ... 3-2 .... 6-5 

March .... 3-8 .... 18-3 

April 3-2 .... 6-8 

May 3-2 ... . 14-8 

June 3-2 .... ^1 

According to thd experiments of Anj^is Smith/ ouo kilogaml 
of air contains the following amount of ninmonia: — 

> CA«m S«: Jmrn. xvi. 100. * Ber. Dnttek. Chtm. Oa. rlii. 1481. 

* Jonm. Ft. Ottm. [2J fr. la's and 383. * Ok Or and Sain, 439. 

luneUan (Fiith of Cljdo) . . . 004 

Loruioa 0-05 

01a3£;ow 006 

Slftucliijster 010 

Near a midJen 0'26 

The following observations have been mode by Bechi ' ou the 
amount of animoiiin und nitric acid contained in the rwiii water 
folliiig in Florence and at Vallambposa in the Apennines fly? 
metera above the aea-lcvel for one square hectometer of surface : 

Eain in cobic meten 
Ammonia in grains . 
Nitric acid in grains. 











. 20278 
. 10433 
. 11726 

368 Atmoa}3iime Organic Hattet: — flie atuiosphere also, of 
oonne, contains gases arising fiom the decomposit-ion of putre- 
factive organic substances. Tliese gases do not remain in the air 
length of time, but tindet^o pretty rapid oxidation, llie 
articles of dust which wo see dunciiig in the air 03 iiiotea in the 
aunbeam are partly oi;ganio and portly inoignjiic. Bechi found 
that a thousand liters of rain 'water vhich fell in Kovember 
1870 iu a garden in Florence contained 4*123 grams of total 
wlid residue, of which one half consisted of organic bodicfi and 
amnioniaRal salts and one quarter of gypsum and common salL 
Amongst the organic substances the gertii! of plnnte and animals 
always occur, as has been proved by the classical labours of 
Partew,* ITiesa bodies are the propagators of fermentation and 
putrefaction, and air which has been freed from tlicsc particles 
either by flUr.ition through asbe:jtt09 or cotton-wool, or by igni- 
tion (Postcar). or by subsidence (Tyndall), may be left in contact 
for any length of time witii Itijuids such as uiiiie, milk, or the 
juice of meat, without these organic Uq^iiids undcigoiog the 
slightest cbnnge. Air which hfw thus been filtered is termed by 
Tyndall optically pure. When a ray of light is allowed to 
pass through air thus freed from solid particles no reflection 
19 noticed, and the space appear* perfectly empty, the mot03 
which ia ordinar>* air reflect the light being absent 

* Dttiltek CWni. (?/«. Brr. «iii. 1203. 

* ^ttti. C/iim. I^i/t. [8] Ixtf. 5, 



Hie orgumc nilrogeu contaiued io t]i« air, probably cliiefly 
CQiitaiui>rt in suvh gcmtitutl bodies, liaa been quaatitattvely 
determined by AngtiR Kniitli' in the fonn of ammoniju He 
obtained tlie foUoring results;— 

1 kilogram of air eonUtas of MnmonU 


Inaellan Cl^rith of CIvdc) . . . Oil 

London ....'.... 012 

Glasj-ow 0-24 

Mancbeeber 0*20 

Near a midden 0-31 

The volatile organic products arising from pntrefnction whicli 
arc always present in the nir, appear to exi.«t in larger qiiantiUes 
in Qianiliy disU'icts tbun oiscwht;iv, uiid in »U probability tlivy are 
the cause of the uuhealthineasof such eitiiationa. The unpleasant 
odour iiivariahly noticucl on enterinH from the (resh air into a 
closed ii)lial>ited space xs also due to the presence of the same 
organic putrescent bodies, whilst tli<j opptxisstvc feelings which 
frequently accompany a contJiiu<;d habitation of such spaces do 
not proceed from a diraiuished supply of oxygen, or an increase 
ill the fitmosiili«rio carhonic acid, but are to be ascribed to tlie 
influence of tlie&e organic emanations. Hence the subject of 
rtntilation is one of the greatest consequence to well-being as 
well as to comfort, ajid it is ueeesBaiy lo provide for a continual 
renewal of the deteriorated air. Fortimately this renewal takes 
place to a considerable extent in a mom, cvcu when doors and 
vfindows iiro Khut, by what may be called the nntnral means of 
ventilation, by the chimney, by craeka and crevices in doors 
and Viindows, and cijpccially ihruugh tlie walla. Almost in- 
stinctively man appears to have chosen porous building materials, 
thus permittius. by fjascoua diffii.'iiou, an exi:lmnge of fresh 
for deteriorated air. The well-known unhealthiness of new aud 
damp houses, as well as of those built of iron, is to a great 
extnet to be attributed to the fact that tlie waUs do not permit a 
free dillusion to go on. 

269 This fiwt, that gases readily pass throngli an ortlinary 

dry brick- or Eandsloiie-wall, is clearly shown by the following 

experiment proposed by Tettenkofer. (A) Fiji. 146 is a piece of 

uulL built of ordinary brick or saudstone 82 centimeters ia 

> Jir aM Bain, 4a. 



b«iglit, 40 cm. broad, and 13 col thick. On each side of 
the wall two rectangular plutcs of iron (C) are fixod, oiid 
the wholv of tlie outside of the wall is then covered over vrith 
a coating of tar, uiid tlius toadt! utr-tiglit. A tubo (c c) 
is soldered into a bole in the centre of each iron plate. If 
a condli'-flainc be held in front uf thi; opcDing of Uie tube 
at one side of the wall, and a puff of air be blown from the 
lungs through the open end of the tube at the other aide 
of the vail, the cuudle will at once be blown out; whilst if 
tbe one tube be connected by a caoutchouc tube to a gas jet, 
and the coal gas be allowed to pass through tlio tube, a flame 


ri«. lis. 

of g»8 can, in a few secoods, be lighted at the open end of the 
oj^site tnb& If the bricks or «tones of the experimental 
wall be veil wotted, it will be found very difficult to blow out 
the candle as described. 

PHOSPHORUS. P = 30-96. Vapour Density - ei'^a.' 

170 A considerable amount of unceTt«)Uty auirounda the di» 
corery of phoephonis. inasmuch as sevenl chetniats have claimed 
the fint preparation •.( thi» body, whdc «ach tuis contradicted tbo 
other in a variety of wuys. It seems, however, tolerably certain 
that pbospbonu was lint prepared by the alcliemitit Hrand. of 
Xlaiabarg, who obtained it from urine in a process which bad 

' TIm nloBW ce c ofui by Ui« Bbxa of fiw rn hcrm wtq^m SO-M u only InlT 
ai U/f* at that o uup tei bjr «kIi of Uw |ine«ilni| eueoo* eloneou. 



been previously made use of for tbe purpose of preparing a 
liquid supposed to have the power of turning silver into gold. 
By a eecret process. Brand succeeded in prepariiig phaiphoroa 
jrom this litj^uiil, and lie is aatd to have sold tha necret of tlie 
manufacinre to Kraftl, from whom it Bppears that Kunkol 
learnt what he knew, and published in the year 1678 a pam- 
phlet on tlii» rvinarknbtc! product.* 

In theae early days phosphorus was a vflry costly body, bein;; 
valued as one of the moat remarkable and interesting of 
cliotnicol substances. Ki-afTl oxliibiU'd it us one of tho wotidcrv 
of nature to various crowned heads, amongst others, in tho year 
1677, to King Charles II. of Englanil ISobert Koyle became 
acquainted uith ita existence without, aa ho t«Ha us, having 
been inforiacd by Krnfft of the mode of preparation except 
so far aa that it was obtained from on animal source, and 
he succeeded tu lUe year 1680 in tlie preparation of phosphorua, 
a-^ Kunkel and Brand had done before him, by strongly heating 
a mixture of evaporated syrupy urine and wliite sand in an 
earthenware retort * The dillieulty of ibus preparing phosphorus 
was considerable, and so taauy chemist!) failed in tlie attempt, 
that the price, as Iat« as the year 1730. was extremely high, 
ranging from ten to sixteen ducats the ounc«. Gahn, in 1769, 
discovered the existence of calcium phosphate in bones, but it 
was not until this fact was published by Sclieele in 3771 that 
phosphorus was obtained from boiie-ash, which has from that 
time invariably ser\'ed for its preparation. 

The name phosphorus (^i, lights and ^e/xo, I bear) was 
originally u.*ei:l to dcslgimte any substance which was capable 
of becoming luminous in the dark. The first chemical substance 
in whith tliis property was noticed was termed Jioniwnian 
pkonpfiortu (see barium sulphide). In order to distinguish 
true phosphorus from this body, the name of phoBphonu 
mirabilU, or phospliorua ignaui, was given to it. In the 
eighteenth century it was usually termed Brand's, Kunkel's, 
or Boyle's phosphorus, op sometimct Etiglii^h phoi'phorus. 
because it was then prepared in Loudou by Uaokwitz in 
quantity according to Boyle's receipt; 

Up to the time of Lavoisier, phosphorus was considered to be 

* " OirmtlJclu> Zufclirirt vom rtioijibor MintbilD and il««Ka Imrlitcnden 

• Bojie, rS'L Trans., 1503 :— '• A TiifTr of llic Urn. Robert Buj-Ic. dcporitad 
with tfi* Sfi:rrt«iy of the RoyU Sociely oo Uin Ulb of Ui.tober, ISSO, aod 
ftpeued liuuc liu deutli." 


a compotmd of phlogiston with a peculiar acid ; but is ITT? 
ths gniit Frcncli chemifit stiowed that the acid hoAy fomwd by 
the ootabustioD of phospbonts, weighed more than the pbos phtntt 
itmsii, niigaK-iitation in irnght being duo to a comhinatioQ wiUi 
tlie oonstitueul of the air.' In a ntQinoir commtmieated to tbe 
AcMtemy in 17S0, be re^ffeeented phosphoric acid aa a contpoand 
of photphorus and oxygen, and investigated it» sa1t«. 

aji Phosphorus, being a very easily oxidizable body, does aol, 
of course, exist in the ftee state in uaiurc. It in, bowcvrx, rery 
widely distributed, especially in combination with oxy^n attd 
calciam, as calcium phosphnte. The most impurtnnt minerais 
containing pbosphonis are, estramadourilo or phosphorite 
CaCPOj),; apatite 3Ca(I'0J, + CaCl,; wavcUite 2a4(1'0,;, 
+ Al, (OH), + OH,0 ; vivianite FbsCPOJj + 8H,0. Calcium 
phosphate also forms the chief oonstituent of coprolitcs. and 
occins in small quantity throughout the gmnitic and volcanic 
rocks, whence it passes into Uie seditncotary strata, and thus 
6nds its yr&y into Uie soil. 

The original obseiration of Gahn, that phoophoros fumis an 
essential constituent of the animal body, niif;ht, it may be 
thought, have led to the coucluaiou tJtat tliis cleuciit is 
veiy widely distributed. It was, however, reserved for a later 
time to show ttuLt ulmost all sutslancea found on the earth's 
cmst contain plioaphoms, that it is always present in sea-water, 
and in all river as well as in aluio«t every sjiring-water. 
All fVuitful soils contain phosphorus, and no plants will grow on 
a soil destitute of it, as it is required to build up certain 
essential ports of the vci^etahle structure, cipecially tlic fruit 
and seeds. From the plant the phosphorus passes into the 
limal body, where it is found in the juices of the tissues, but 
ecially in the bones of vertebTate animals, the a.4he9 of which 
'congist almost etitir-ely of cnlciuin phosplmte. I'bospbonis is 
likewise connected with the higher vital I'uuctions of the animals, 
Ute substance of tlie hriiin, ns well ns nervouti matter in general, 
always containing it. When the animal tixsues, whether 
mnsculnr or ncr\'ons, are worn out, they ore replaced by fresh 
material, and the phosphorus in tliem is excreted in the urine 
chiefly as sodium nmnioniiim phosphato or microcosmic salt, 
Ka(>'HJHPO, -t 4HsO. I'hosphonis is likevfise found in small 
({itimtity in meteoric stoues, a fact which indicates its wide 
coEJuical distribuUoiL 

■ CjMwiiitt Pkyrif*" " Cl(m£rw, 1774. 



973 J'rtparation. — The preparation of phospliorm from bonu 
■was first descrilffid by Schccle m 1776. Ho warmed boiie-ash For 
mnny ilaya with dilute nitric acUl, precipitatud the lime with sul- 
pliortc acid, evaporated the liquid from wliich the gypsum haA 
separated out to n tliick ajTop. and distilled tlie residue with 
charcoal.' This process was uft«rwan.l» siinplilicd by Ktcol&s 
Aud I'cllcticr,* inasmuch aa tlioy treated tlio baae-ash at oikw 
■Willi sulphuric acid. The yield of phoephoriis liy this prooeas 
was, however, but small, until Fourcroy and VauqocUn* i3«t«ff- 
mined the exact proportion of sulphuric acid reqnired for the 
complete decoiwpoaition of the bone-aah. thus prcpsiring the way 
for lJ)c economical productiou of the element. 

In order to obtain calcium phosphate from bones, tlie bones 
were fonnerly burnt in ovens. At pn-st'-nt, however, the 
organic material contained in them 13 made of uae in several 
ways. Thus the bone« are either boiled with water, or treated 
with superheated slcnui, to extract the gclutme which they 
contain, or they are ditvtilled in iron retorts to obtain the 
ammonia and other volatile matters which they yield. In the 
Utter case the hono-hkck or animal charcoal, which conaisia of 
a mixture of charcoal and calcium phosphate, ia left behind. 
lliis bone-black is lai^guly used by sugar rclinerA for clanfying 
t)ie syrup, :ind it is ouly wlien it has become useless for this 
purpose that it is completely burnt in an open fire, and obtained 
in the form of bone-iuih. In order to prepare phosphorus, the 
bone-ash is first mixed with ao much dilute aulphoiic acid as 
to form the acid phosphate : — 

Ca, (VOX + 2H^04 = CaU^ (P0,>, + 2CtS0, 

The tohitiou of lliis soluble acid phosj^ate ia next poared off 
from the prijcipitated gypsum, atid eva|iorated to drj'neits, aA«r 
which, the solid reaidue being heated to redness, water is givea 
oil and calcium metaphosphnte formed :— 

CttH. (I'O^, = Ca (PO^j + 2H,0. 

Tliis salt is tht?n carefully mixed with charcoal, and heated 
to bright redness in earthenware retorts shown in Fig. 147, whoD 
the following change takes place :— 

SCa (POj), + IOC = P, + Ca, (POJ, + lOCO. 

> OmMt Saltttairt A BmiWen, 17TS. * Journ. Myi. xi. K. 

* fyurm. /VkATM. i. 9. 



Tbns only two^thirila of tliQ phogphoms coutained in the 
metap1ios[>liutc aro reduced, oov-tliird n-mainiiig »s trtcnlciiim 
phosphate. If sand be dddeil to the mixture, the whole of the 
phosphorus is driven off, calcium silicate being formed ; thus :~ 

2Ca (POJa +■ IOC + 2SiO, = 2CaSiO, + lOCO 4 P4. 

The mixture uf the vapour of phosphorus and carbonic oxide 


Pio. HJ. 

escapes throu;jh a bent eartlienwaro pipe (a). Pig. 147. which 
dips under the surface of water coiituiiied in the vessel (J), 
whareby llio phosphorus i-apour is condensed. 

A large proportion of the phoaphoms made in Englnnd is pre- 
pared from sombreritc, an impure calcium phosphate found ou 
the Island of SombTero in tlie \V\-?tt Indies. IL appcan tliat 
almost the nhols of the phosphorus made in the world u 



iTianuractureil in two works — namelj, tiiat of Mi^sats. Albright and 
Wilson, at Oltlbury, near Birmingham, and that of M&L Cognet 
et fiis, in I-yoDS.' 'i'he manufacture of plioB|ilionis is somewliat 
dongeroiu, ou account of the easy istlanimabiliiy of the product, 
and it is also difitcult, inasuucfa as tli« distilhition rcq^uires forty* 
eight hours for its completion, and iiweseitates, during the whole 
of this time, roiistaat watching. The crude phosphoras alwayg 
coutuiiis small particles of carbon mechanically carried over. 
To |:!et rid of this and other impurities, the phosphorus is either 
melted under water, and prcas(-'<l Ihruugli chiimois leaUier, 
or, more frequently, the crude melted materiiJ is mixed with 
sulphuric acid ami bichromate of potash, three-and-half parts 
of each being used for every 100 pmta of phosphorus. Thia 
oxidizing mixcun; acts upon the impurities, vhich rise as a scum 
to the aiirfuce of the liquid, whilst the pure phosphorus remains 
clear and colourless ut the boUoni. It was formerly cast into 
sticlcs by the workmen eucking Uie melted pho^pliorus up with 
the mouth into gloBS tubes, lumtcad of this dantiiToas operatioii 
an apparatus is now employed by which the phosphorus is cast 
in brass or copper tub&s by a continuous process, proposed hy 
Seubert.' The apparatus consists of a copper vossel. in which 
the phosphorus is incited under water ; fn)m this the molten 
phoaphoma is allowed to flow into a tnbe coosistini; of glass or 
copper. One-half of this tnbc is surrounded by hot and the 
oilier by cold water, the phosphorus being thus obtained in the 
form of solid sticks, and cut under water into pieces of a 
convenient length. 

Tlie quantity o( phospbonis manufactured in the year 1874 
amoiuitc<l to 1,200 tons, the greater portion of which is used for 
the manufacture of luoifer mnt<'ha<t, a certain amount being 
employed ns a vermin poison, and a small quantity being used in 
chemical laboratoriia. 

The distillation of phosphorus can easily he shown in 
tho lecture-room, by placing some pieces of dry phosphorus 
in a small tubulnted retort to which a tubulated receiver 
containing water, which comTnanicAt«a with th« sir by mwos 
of a tube one meter in length dipping under inercuiy, is 
attached. A current of carbon dioxide gas is passed through 
the tabuing of the retort so as to drive out tho air. As 

> HoTniiuin'fl Ripurt m Ihr Vifn* £»kA<tiam. 
' JHK. Ck4tn. J^rm. xtix. Ste. 

soon aa all the air lias been lenioved the phosphorus can he 
hekted and is seen to boil, the colourless vapour condensing in 
transparent yellow drops on Il)e neck of the retort and in the 
receiver. Tbe barometvr-tube preveDts the entrance of utmo* 
eplieric oxyj^cu. 

373 Proprrties. — Like sulphur and uther elements. phoiiphomA 
exists in different alloiropic ioodi6catJons. 

Common eolouriat or odohedrai pJtosphtWJi i», wlion fruslily 
prepared and kept in the dark, a slightly yellow or almost 
oolou^ll^sa btjdy. which, when elowly aulldified, is perfectly 
traii9par«Dt, but wbvn quickly cooled ia tianalucent, and of 
a vax-Iik'c cbnracter. At low t«!mpciatuies phosphorus ia 
brittle, but at 15* it becomes soft like wax, so that it may be 
easily cut with a knifa The mass of the substance hna, how- 
ever, a crystalline structure. Tliis may be seen by leanug the 
solid for some timn in conUict with dilute nitric acid, vrbcn the 
surface becomes distinctly er^'Htn-Uiiie. According to v. Schrotter 
its specific gravity at lO' is 183, and it molts at 44*3, fonii- 
ing a colourless or slightly yellow struitgly refracting li()uid, 
having a specific gnvity of 1*764. Melted phosphorus, under 
certain circumstances, remains liquid for a long time at tempera- 
tures much (jelow its melting point This is especially the cose 
when it is allowed to cool slowly under a Layer of an alkaline 
liquid, or when the solution iu carbon di3nl]>hi(ie is slowly 
evaporated under water, Neither solid nor melted phosphorus 
conducts electricity (Faraday). 

When heated in an atmosphere free from oxygen to a tem- 
perature of 290°, phosphorus boils, yielding a colourless vapour 
which, according to the experiments of Mitseherltch, has a 
epccilic gravity of 458 at Slo", and of 4*50 at 1040* accord- 
ing to those of Devitlc and Troost (Air =10). ITctico the 
molecular weight of phoephcriis is calculated to be 123*84, or 
Uic molecule consisU of four atoms. 

Pliosphoma also evaporates at temperatures below its boiling 
pointy If a small piece of phosphorus be placed iu the Torri- 
cellian TRCuum, it gradually soblimes and dejiosits a^in in the 
form of bright colourless crystnla. Tj»i;ge crystals of phosphorus arc 
obtaioed hy placing phoitplioriis in a flaxh tilled with carbon 
dioxide, then hermetically seating it and allowing the bottom of 
the fiosk to be heated on a watvr-luith for some days to 40°; or 
in another way by keeping phosphnras in ■vacuoua tubes in the 
dark for some time, when it sublimes and crystallizes on the 



side of tJie tube in colourless transparent brigliUy sliiaiug 
cryfltaU (Hermann and Maskelyne). 

I'hosphonis is ttearly insoluble in water and elii^btly soluble in 
elher, oil of tur]:ientin9, and tlie essential oils. It ia readily soluble 
in cliloride of sulphur, ])ho:4phanis tricliloridc, sulphide of phos- 
phorus, ftnd carbon disulphide. of wUich on« part by weij^bt. will 
dissolve from sevcotcea U> ci^bt«cu purt^i of pkospbonis. From 
solution in carbon disulphide, pbosphonis can easily be obtained 
in the crystalline sl«t«, ustiitlly in tlie form of rhombic dodeca* 
btidro. Tlie same crystals wi obtained, accotxlitig to Mitfichcrlioh, 
by boating under water a mixturo of oac part of sulpliur wilb 
two parts of pho*phorus. lu this case a cnm|wumL of phos- 
phorus and sulphur is formed which dissolves the excess of 
phoaphonis, but this crystalliftfis out on cooling. In order to 
obtain phosphorus in the state of fiue powder, the incited 
substance is well shuken with cold wator containing u little 
urea^ the small drops thus fonncd congealing into solid particles^ 

Phosphorus is an extremely inllammable substance, and 
is ttl^tuys kept under water. In presence of uir uiid Li^ht it 
becomes coveted under water with a white crust, which gmdtially 
falls off. wliilgt the phosphorus becomes darker coloured. The 
crust U coiuiuou phoapboius. which falls olT from an unequal 
oxidation of the mass, and on melting it under water it 
assumes the oixlJimry appearance of the element. 

Fho»phoni3 appears luiuiaous in the dark, when in contact 
with moist air, unil it ovulves fumes possessing a strong garlic-like 
smeU. These lumtw are poisoiiHus. producing phosphorus- 
necrosis, a disease ill which the bones of the juw arc destroyed, and 
one by which scrofulous subjeotJ* are the most ensily nffected. The 
luminosity of phosphorus in the nil- depends upon its slow oxida- 
tion, with formation of phosphorous acid. In this act of combina- 
tion so much lieat is evolved, tliat if a large piece of phosphorus ba 
allowed to lie exposed lo the air it at last melts and then takes 
£re. The himinosity and oxidution of phosphorus is best scon 
by pouring a few drops of the solution of this body in carbon 
diaulphide on lo a piL'cc of filter paper and allowing the solution 
to evaporate. In the dark the ptiper soon begins to exhibit a 
bright phosphorescence, and after a short lime the pliosphorns 
takes fire and bums. It wn,i fornietly believed that phosphorns 
becomes luminous in gases upon which it can exert no chemical 
action, such as hydrogen or nitrngen. This is, however, not so. 
tbc Imninosily wbii:h has been obscncd in these ca^cs being dua 



itidiffereat giu, or if it be rarefied, tlie pfatie|ihore8ceuce is Kt once 
obserred (GrahamX Xho phenomenon can be very bcnutifiilly 
shown b; placing u Mick uf phospliorus iu a long tube (a. Fi^'. 
\4S), closed at one end and opuu at llii; olbc-r, and pertljr' fillip 
vitli m«rcury. into wbicli some pure oxyjtea is broaght. The 
oppn end of tJje tube is connected by a caoutchouc tube with 
the vessel (fi) containing mereuty, so iheit-, by nusing or lower- 
ing the ve»Ael the pressure on the gns can be reguluted. If the 
pressure be so arranged thnt it does not amouut to more 
tluui one-fil^h of ua itttuospbcrv, the iiliottpltnma will be seen 
to be brightly luminous in the dnrk. If the pressure lie 
then gra{lually increased, tlie light will become less and 
less diiStinct, until, whi^u tlio level of the merciirj' is llie »nmv 
iu botli vessels, the hiniinoaity has entirely ceased. The phos- 
phorescence can, however, at once be brought hack sgaiu by 
lessening the pressure. Tiie luminosity of phosphorus is aUo 
fltopped when certain gases, auch a& aulphvrettcd hydrogen, or 
tlie vapours of certain compounds, such as ether or turpentine, 
are present even iu miuule tjiiantilies. 

374 Deledion 0/ Pkoaphorus. — Tin- water in whicli phosphonia 
has been kepL is also luniinniiH in ihf dark, as phosphunis ia 
eoluble, thoiiijh only very slightly so, iu water. When phoa- 
phon.i$ is lioilud with wdter, it is )iiirli«lly voliitilized, issuing in 
the etJit« of vapour togwther with steauL This proiwrty of 
pliospUorus is made use of f<jr its dctoctiou in cases of phoa- 
phurus poisoning. Tlie apparatus which is used for this 
pur]ins(! is shown in Fig. 14!). The contents of the stomach 
supposed to couUiin the poison tiro diluted with water and 
pl-jccd iu the flask A. This flask is eoiinectud by the tube h, 
with a condeuHinj^ tubu ecc, surruundeil by cold water. As 
soon as the liquid contained in tho flask is heated to boiling, 
some of the phosplioru-s, if present, is voI*tili/.ed togcllier with 
steam, and if the whole of the apparatus be placed iu the dark, 
a distinct luminosity, usually in the form of a ring, is observed 
at the point where the steam is condensed. If tho r|UHutity of 
pliosphorus is not too small, some of it is found in the receiver in 
the form of email solid globulin (Mitschorlichj. 

When phoaphonis ia heatod slightly above its nielling-poiut, 
it lakes tire and hums with a hriijlilty luminous flam? nud with 
evolution of denso white fumes of phosphorus pcutoxide PjOj. 
Tha giT-atest prpcautions are ncf*sst»rj' in working with phos- 
phorus on uccoiint of its highly inflammable character. It must 



always be cut> u well as kept, under water, and nnust not be 
robbed either in contact with the skin, or when it is being 
dried with blotting paper, m burning pbosphonis produces deep 
vounds, which \ica\ only with ^rcal difficulty. 
Pbofiphorus combiner direutly with the elements of the chlorine 

\'A ^ 


and salphur jiroupa of elempnti, but not directly with hydropen. 
If it is heated with aqueous vapour to a teinpcraturo of 250°, 
the water is dceoiiiposcd with furmation of phosphorous acid 
and phospliHTctted hydroge.n. It also combines with most of 
the mctnls at a high temperatmY>, and on account nf its v*sy 
oxidizability, it acta as a {)Owerfut reducing agent, depositlllg 



oertajn metals, sucli as goM, silver, and copper, vfaca it is 
broiigbt into a solution of tW salts of the mctuls. This t«- 
action may also be niiuic use of for tJie purpose of detecting free 
phosphorus. Thus, if the Diateriul under vxsminntion be boiled 
vitli water, and the escaping vAjxiur allowed to come in cont«ct 
with R piece of pappr wliicli has bt-en wetted with n soliuion 
of iiitratti of silver, any piio^phoms present v. til cause u black 
stain of uielallio silver la appuar on Ihc paptT. No reduction, 
however, takes place of a lead salt undi^r similar ciiviiniRtnuct^, 
whiUt if the black etain be due to the presence of aulpliui-etlml 
li^dro^n, the lead as well as tbe ailvcT paper will become 

275 Actiom 0/ rftofphorut at a 7^i'«i«. ^-Ordinary pbospliorua 
is a powerfully poisonous substance capable of inducing death 
in a few hours, or, when piven in smiill closes, of producing 
a renifirkiiblft train of poisonous symptoms lasting for niaiiy 
days, or even for wveks. Red or ainorphone phosphorus ap- 
pears, on the oUier hand, to be without Hotion on tJie animal 

Although cases occur in which the administration of pbm* 
phorua is followed by death in a few honrs, more commonly 
some days dapsi; betwceu tbe date of adminialratiou mid death. 

In tbe more commou cases of phnejihunia poisoning, some 
time after the poison has been taken there supervenes jiaiQ in 
the stomach, with vonuting of garlic-smelting eiibstanc.e8.aml not 
unfrccjncnlly diurrhtt'a; all these symptoms of giuttrodntc^tinal 
irritation may hn, atid often arc, absent. "Wlietlior they are 
present or absent the patient .soon bcconirs vrry wnak, a febrilo 
condition ensuea, and the akin assumes a janndici^d hue. 
Mieinorrbases may occur, and, towards the end, convulsions or 
coma usually make their uppearanee. 

The apjtearances obKer\-ed in the bodies of aiiiinala and men 
poisoned with pbnsphoius are very interesting and indicate that 
lliis sub^itauce praiuces a powerful I'lTect upon the tiiili'itiun of 
the body. Minute extravasations of Wood arc frequently seen 
in the lining munihmno of the stomnch and intestines, end 
nut nnfrerpiently siiuU ulcers occur in Uio«c organs. The 
commoa and remarkable appearances are fatty degeneration 
«f the liver, kidneys, heart, and voluntary niuselcs. It is tu 
ta remarked tliat the same changes are obser\'cd, nllhough in 
u lew marked degree, ftft<.T chronic poisoning by ai-Hcnic, an- 
tiuiony, and vanadium. TlieJie fatly degenerations probably 



iniliL-ato tbat ])li<j8[i1iorus uitd llie allioti poisoiis exert aa 
influeiict; ulici-eliy the oxidation clianges, wLich liave tlieir seat 
in tti« aiiiuiul tissues, are moro or \&>a slowed or ureslvd 

IViitli lifts in iiiaii rollowcd the administration of dosea of 
phosplioniH not exceeding a decigmm. 

276 /M or Aniorp/tous rhospfuiTtM.~^Th\s\iecuUiirmoi\ificalion 
of phospboms was discovered by v. Sclirilttcr in 18-15.' Othtr 
clKMiiisU had iiideifd pix^viimsly noti(-ed tlie exisleiict! of tliis 
eubstittiGc, butilH iiuturi'bnd beenioisuiideretood. It isolituine<l 
liy Uie tkctioD of li^^bt oiid bent on ortliiiitry pbosplionii;. Tbis 
cbaiige occurs willi tolornble mpidity wlicu the yt-IIow piios- 
pbonis is beulc-d from 2-^0° to 2H0'. Above the tompcmture 
of SfiQ" red pbos|^boni3 begins to uiiderj^o the opposite change, 
vliite phosphoriis being formed. Hence the passage fiom on« 
utiotrupic inodilkittioti lu uitoUn^r i^ inuiu readily slio'wu in the 
case of phoflphorua tban iii that of any other olcoiciit. For 
this ptiriiose all tbat is needed is n glass tube contuiiiiug thrct* 
bulls (Fig. loO), aud having the open end beut at right angles 
nud dipping under lucrcurj-. in the lu«t of these three bulb* 
is placed a piece of jdmBphuru-i. Tbe phospliorus is then heated. 
Ibe wbole of the oxygen cont.iined iu the apparatus is vcvy sooa 
nbsorhed, niul tbe rvinaindci- of tiic phosphorus is distilled from 
Ibe laat into the middle bulb, ity gently boating this, it ia 
tninHfoniied into the red mud ifi cat ion, which by a further 
iipplicatiou of heat, is n^fornied into llie ordinary modification, 
which distils into the tbiixl bulb. This cxperimeut should be 
made on a leaden table or on u surface covered with a conting 
of aand, in case the bulba tshouM buret. 

Ued phosphorus ia also formed when ordinnry jdiosphorus is 
heated in closed vessels to 31)0', or about lb" above the 
boiling point. In this cu»e the change takes place in a few 
iniuutea. Tlte eonversioii of ordinary into amorphous phos- 
phorus can also he bi-nngbt about by certain cliuuucaJ nctions. 
£. Kopp' found, in 1845, that by the action of iodine on 
phosphorus a red body is formed, which on healing ^'ields tbe 
ordinary niodificatioa of phcxspboriw, and K C. Hiodie' has 
shown that only a trace of iodine ia needed to bring about tlie 
change from the yellow to tbe red iiiodilieiition, and that vheo 
conuiiou phosphorus ia heated with a trace of iodine to 200*, 

' Aff. <*iiit. hxxL 37a. ' CompL Raid, xriii. 871. 



a very violent reaction takoa place and the red modificatwn is 

Red phosphorus is a compact solid substance, which has a 
dark rcddisli-brown colour, and geuerally posacsses u metallic 
iron-n^cy lustre. It has a apedlic gravity of 2'tOQ, exhibits 
a conchoidal fracture, and yields a reddisli-hTowa coloured 
powder closely rcsembliag tinoly divided oxide of iron, lis 


-- 'tJ 

Kir.. 1.'.0. 

tai'dness lies between tJiat of calc-spar and that of fluor-spar. 
It is a tast^jlefis and odoinlesa body, insoluble in ail (hose 
solvent* which dissolve common phogplicinia, and when it is 
perfectly fri-c from lliu ordiasry modification it is not poisonous. 
\Vhen introduced in fionto quantity int<i the nniiDHl economy, tlie 
whole of it is excreted, so that it is capable of withstanding the 
strong oxidizing actions of the animal ny-steni. This eiibstonco 
can be exposed to the air for years wilJiout undergoing any 
alteration. Friction does not bring abnut its oxidation, and 
to take fire it miial be heated to a teuiperaliirc of 240*. ITie 
ordinary phosphorus takes lire spontaneously when brought into 



chlorine gu, but the red i>}iosplion» requires heating licron: 
iguitioa tAkes place. SimiUr difTercncna l}etwc«n thu ttt-o modi- 
fications present themselves in & targe number uf oUier cliemical 
reactioui!, mid iht red modiliculiou conducts rU^ctricity, although 
but feebly, whilst the yoUow does not do so at all 

The mode of mRiiiifaotnring rod phosphorus is Himple. 
^Miitc phdt^pbonis is pliiced in au iron ve&sel and heated to a 
temperature of 2-40°. Thia vessel is closed by means of a cover, 
thronjih which pnssPR a. Inn;,' imrrow pii«! open nt both ends, so 
that tlio nir has limited acces^i to the phosphorus contained in 
tlio vessel Thus all danger of explosion is itvoidixl, and tbv 
air in the uftrrow tubo UDder:goiiig but little change, only a 
little of the phospliorns takes lire as soon bs the oxygen 
lins been ■withdrawn from it by the combustion of the first 
portion of the phosphorus. The rt-d phosphonis thus prepared 
is groiuid andcr water, and tri'inl from eonimon pliusphonia 
by boiling vritb a solution of caustic soda, washing and drying. 
The GOtntnercial amorphous phosphurii», when in large comiuict 
masacs, tdoiOHt always coutains a small ipiautity of enclosed 
yellow phosphorus, aud nob uufreijHently takes fire when 
it is rub1>ed or briikon. In consequence it is usually packed 
in vcaeels coutoining water, vhilsL the groniid snbetance. as 
above dcscribod, may bo sent in tlie dry statu in tin lioxes. All 
the oommereial aniorphoufi phospboruB. howevBr. contains traces 
uf the white modification, and this undergoes oxidation in the 
nir, so that the moss always lias an anid reaction, owing to the 
formation of phosjihorous and phosphoric acids. It fivfiuently 
also ooiduiiis truc(':3 of gmphitUj origiuatiiig from the iron pota 
in which it is heittfd. 

377 Mctaiiuter RkomMudral Phosjihonu. — Whenphosphorns 
ja heatdd in sealed tubes in cnnlact with mrtallic lead for ten 
hours at a t«n)peratur« approaching a red heat, a third modi- 
fication of plo^phonis is formed. On cooling, the whole mass 
uf lead is found to be punucatcd with siujiU crystals, whiob 
have been formed by the phosphorus dissolving in the melted 
lead at a high temponittire and by its crj-stidlizing out on 
cooling.* Jn order to separate these cr>'8tals from the metallic 
lead, the mti^^ is plnix'd in dilute nitric acid, when the lead is 
disaolvbd. Tlie crj'stala of phosphonis are still fiirther purified 
by subsequent hoiling in strong hydrochloric acid. Ttletallic 
phosphorus is a brightly lustrous dark otyKtullino mass, which 
■ ililtorf. Fo}f. Jnn. caxrl. 193. 



in thin p1ate» possesses a red colnitr and consists of mioro- 
KOpic rhombohcdm. Its epcciiic gravity nt lo''5 is 2'34; it 
»ppoars to couduct etectricitj' better thiui tlic amorplious variety, 
ftiid it requires to be boalcd to a teinjieralura of 'SjS" before it 
18 converted into ordinary phosiihonis. Tliia variety is uUo 
formed vhen amoriiiiniis phosphonia is heated under preesare 
to a tempcniture of 5S0'' (Troost and llawtefeuille), 

According to Thonard a fuurlli modilication of pliosphonis 
existi This siihstance lias a black colour, and is oblaiced when 
tnt^lted phospborus is(|uiel(!y cooled. Itecent observations have, 
however, shown that this black pliosphoiiia is only fonned when 
foreign bodies, especially mercury or other luviub, are present, 
thcsii bodies uniting with pbosplioriia to form a black metallic 

Wlien liydroj.Tn is pnfiH<!d over pliosphoru-s, or when phos- 
phnteii, li^'pophospbitea, or phospliitcs, or tliR correii ponding acldit, 
ftto brought into n vessel in which hydrogen is Iwing evolved, 
the hydrogen is seen to burn with an enicmld green llaiue ; and 
if the quantity of phosphorus be not too sniall, a white poice- 
kiu phit« held in the i;^ Gained with a red deposit.' Tbi« 
reaction dots not occur iu the presence of alcohol, ether, or 
auimal matter.' The spectrum of the phosphorized hydrogen 
flame exhibits three bright green lines, of nhich one is almost 
coincidoDt with one of the hues of the bariiiin epectnini, Uie 
third beipg not quite so bright, uud lyiuy beUvecn tliu two bright 
ones and tite sodium Hna^ 

Fhoaphonis is frequently used in the laboratory. It ia 
largely employed in the manufacture of the iodides of methyl 
and ethyl, bodlL-s much used in tlic preparation of cortain aniline 
colours. Tlie main purpose forM-hich phoxphoruH is employed in 
the arts is, however, the manufacture of lucifer matches, lor which 
purpo^ic no less tliftn 1,000 tons are employed every year. 

278 Lucifer MiUcJtfs. — The application of this aubxtaiice to 
the artiiicial productJou of hunt and light is only of recent date. 
The oldest mode of artificially obtaining lire is that, still imiA« 
use of by certain rude tribes, of rubbing together a piece of 
hard wood and a piece of soft wood, tiu'ning the former quickly 
on the latter until it takes fire, ^t a later time it wa:ii found 
ttiat, when a piece of iron pyrites was struck with a mass of 

• Dnsart, Compt. ittnd. xliii. 1128. 

* lilondlnt. Campt. Htnd. hi. 11I>7. 

■ Chrutofla Mid IkUttoin, Ann, Chcm. Pkyi. [4] iiL 28(L 



iron, sparks flew off", hy means of which, <Jiy inflammnble 
tiiateriais, Bitch as tinder, might b« i^piUed. In place of iron 
pyrites flint was next used, aiij thu mm replaced by a rough 
piece of steel. The titider isuiployed was made either ul' 
chaired linen, or of shiivinys of wood which luid been dipped 
ialo melted sulphur. Up to ihe year 1829 lhi.'» wiis the «.-«ual 
method employed for striking a light ITie first hicifer maichea 
consisted of pieces of wood, the cud* of which hud been 
dipped into sulphur, and which were coat<d in addition wilh 
u mixture of sugar and chlorate of potash. In onler to bnn<{ 
about the ignition of thf^e matches, they were dipped into a 
t>ottlc containing o-^hestos moistened ^^'ith fiitning sulphuric 
acid. Frictioa matclies were invented in the year 1832, the 
material composing the infliiiainuhle mixturo coueisting of two 
parts of Eulpludc of antimony aud one part of chlorate of 
potash, mixed together to a paste with gum nnd water. The 
matches, which had hecu previously coated with sulphur, wctc 
then dipped into this mixture and dried. In order to ignito 
them, these matches were drawn through two layers of sand- 
paper, held between the thumb nnd first linger. The antiinouy 
«idphidc was soon m-placod hy phosphorus, and the first miittchcs 
which were made in lliis way were sold in boxes containing 
from 50 to 60 for twopence. Chlorute of potash is now supplanted 
hy uiti-e, especially in thn case of the Coutiiieiitnl makers, inu- 
mnch as the latter substance is less liable to give rise to tn 
cxpltioivc ignitiou- A further improvement consiiitod in the 
replacement of sulphur and its disagreeable smell by wax or 

Tlie discovery of aniorphona phosphorus uatumlly led to tlni 
idftn of the citiiployiuent of this Bubetancu in tba manufacture 
of Iticifer matcheit, and this improvement was especially valu- 
aMe, as, in flpite of all care, the phoaphorus disease made 
its appcamncc in iiiiitch nuinufnctovies, wlici-c ordinary pho»- 
phortis was employed. The Bubstitntiun of tho ri^d phos. 
phonis for tho white modilicatiou rcudurcd its recurrence 

Many difiicidticK had to bo overcome in the employment of 
this new substance, and it was only after some time tliat the 
following mixture applied to the head of the matches waji found 
U> ser^'e tlie req^uLmd purpose : 



Polassiuiu Chlorate 32 

Potaasiuiu Bichromate 12 

Red Uad 82 

Sulphide of Antimony 24 

This mixture coulaiua &o pliosphorus, oud, aa a nilo, it will 
only ignite on a surliici! Btrewcd witli u tuixLuru of amorphous 
jihusphuius luid bulpbidc of aiitiiituiiy. IT, liowrevLT, these so- 
called safety oiatches be (juigkly rubbed over a surface of glus 
or a siiioutli slicet of paper they can be made to tuke lire. 


%ig Three cotupotmds of phosphorus and bydrogcu aro 
known — 

1. Gaseous Hydrcgen Phosphide PHj. 

2. Liquid „ „ 1*!^^ 
2. Solid „ „ P,H^ 

"Gaseous HvoitoGES Phosphidb or PhosphixEjPITj =33-96. 
Density = 16-98. 

By hcntiiig together pliftapliomsaml caustic potash OengembTQ 
In 1783' oUaineJ a gas \itiich wns spontnneously iiifia.minable. 
Some years hiter Diivy ■ and IVlli'liur-* prepared a verj- airnUar 
Ras by heating i>ho.s]>]iopou3 acid. Tliis gaa dirTLirL'ti, liuwevcr, from 
the fonuer, inasmuch as, although v^ry easily inllamiimble, it did 
not tukc fire spoutnuuously on coiniiiy in contact with tlie air. 
Both compounds were at thut time recogiiixi'ii to be compounds 
of hydrogen and pliti.'iphunis. Tlie tme explanation of Iho 
ilifference between these two gases was given hy Paid Tlii;nanl.* 
He showed that the spontaneous iiiflnttmiation of the one gaa 
waa due to the preacnee in it of small traces of the vnponr of a 
liquid hydride of pliosiihoms. 

280 Prvi>a.rntwn.~(l) In order to prepare spontaneonsly in- 
flaminablo phoaplniretfed liydrojcn, as the gaa has been called, 
phosphorus is heated wltli milk of lime or vith a aoluUon of 

> Crtit. .^mt. L <SOl 

■ CirtU. Anm., 17M, U. 148. 

• j%i7, Travs.. leoa. t. 67. 

* Ann. C\rin. Ph^., 3U atrit, zir. S, 



caustic potash. The spontaneously inflfiinmablo gaa is evolved, 
and calcium or potassium liypophospbile letl behind ; thus : — 

aKOH + P^ + 3H,0 = SlUIji'O. -i I'llj. 

(2) The same substance is ttlso readily fontied wlit!ti pliosphide 
of calcium is Ttimwn into water. Eiich hubbic of the "as iguttes, 
on coiiiiiig to the surface of the water, witfi n alinrp explosion, 
buruiug with a bright white ilnme, and a ring-like cloud of 
phosphorus pentoxide b formed, v.-hich on ascaiding shovi^ the 
remarkable vortex motions. In order to exhibit this phenomenon. 


Sia. IS I. 

A ixniSl fiaslc (a, Fig. l."I) is three-quaptera filled -with slronj; 
potash solution, a few piects of phosplionia are thrown in. and 
tlie whole is gently watnu^d. As soon as small flames atx> sceu 
a( the nio«th of the flnak, a gaa df' (c) is fixed hi with 
cork, the lower end dipping nnder wntpr. 

"When the sponlaneoualy inflammable phosphnretted hydrogen 
IS exposed to the light, or whi>ii it Is imsscil tlirouj^-h a freenin;* 
mixture, or left in contact with carbon oi potassium, it loses its 
power of spontaneous inSammahility, iniismuch as the liquid 
hydride coutaiued in it is either decomposed or condensed. 



(S) Tlic Duii-apuDtaneuasly iriflaniiniilile j>liu!iphnrctte<l b^dro* 
gen is obtained hy waniiiiig i)}ioj[))iora9 wtlli au alooliolic 
solution of potash, or by dccoiiipusiiig phosphide of calcium by 
meftns of lijiliDcliloric acid 

The pliosphiiie prepared hy any of these Dietliods is, liowever, 
not pure, but contnias moix; or less hyiiro^en mixed with it 
lu order lo obtain pure phospbureltcd liydroycii we make use 
of its property of combining with hvdriodic acid to form tlic 
crystalliMR compound tinned plionidionium iodide, I'H.L Tliia 
substance, when tlirowu into water, detuiiipuaes iulo its cou- 
Btitucnts, naiiiely, phospbinu, Pllj, uiid bydriodic acid, UI. The 
BoUd iodide, tlie pripavatiou of wliicU will bp herenflrtr described, 
13 employed as follmvs lor tlic prepanition of the pure ga&i 
Some pieces of the iodide of t!ie size of ppas, mixed with brokea 
gloss, nrc bixxiglit into n small Hasb. The flask ia closed by a 
coik bavins two hules horcd tbrongli it, in one of which is 
pisccd a Bloppercd funncl-tubc, and in atiotber a gas-delivery 
tube. The fmiuul ia filled with conccntrntod sciliition nf potash, 
and this is ntlowcd to nin into the daslc filowly, when the 
following decomposition occurs: — 

nij. + KOH = rn, + ki + n,o. 

The gas tliufi obtainpd is not spontaneonsly inltninniable, at nny 
rate at the beginiung of the operation, nithongh if the evolution 
be ciinied ou foi' a cousidenible lenj-th of lime the spontaaeously 
infliimmable gas is formed (Rommelsberg). 

261 PropcrlUs. — I'lKJspliine is a (■olonrless gas, possessing a 
very disagreeable smell re*enibling that of rotten fish. The 
pure gM takes (Ire only above a teiiipeiatii re of 100°, and is 
»o iulla unliable that the beat evolved by the friction of the 
stopper oil opening the bottle containinff the gas is sometimes 
kuDicient to produne its intUniniatioii. It may he mixed with 
oxygen without midci^oiiig any alteration, but if this mixture 
bu suddenly exposed to diminished pretsuru an explosion occurs. 
This remarkable phenomenon reminds one of the nonduuiinoaity 
of phosphorus in pure oxygen and its luminosity in diluted 
oxygen at tbc same temperature. 

Phosphine aUo takes fire when a few drops of dilute nitric 

acid nre brought in contact with it, or when il is mixed with 

the vapours evolved from chlorine- or bromlue-water. If th« 

gaa free from air be led through common nitric acid conloiuing 

' IlofinAnn. Btr. J) yiiaU. Ckfn. (}<$. iv. 200 



nitrous fuiucs, it bi-coincs sjiODtaDcoiisIj inllammalile. and it 
explodes in chlorine gas with great violence and with tlie evo- 
lution of a liriyht grcenisli- white liyht. I'horiphinG is somewhat 
soluble iu water, aiid impiirls lo il a peculiar and disagretaUe 
tast«; Lhe solution di.-coiii poses in the ]t<;ht with the evolution 
of hydrogen and the spimrmion of amoqihous phmiilionis. When 
& series of electhu sparks are passed tliioiigh the gas it also 
decon>[>usi>.s iuto phos{j1ioni« nnd hydrogen, the vdlnnie of Uio 
latter bearing to tliat of the original gas the proportion of three 
to two. lu order lo sliow this a eudiometer similar to the oiw. 
alrrady dty^cnhed (Fig. 128) may be employed, but instead, how- 
ever, of havin;:; platinum M'ircs. pieces of r^as-coko arc melt«d 
through tht; ^Inss. tniisn]uc)i ilk phitinuiu nnd phoi^phorus in 
contact unite, forniin}; a silver white compound vhich ia hrittU 
aitd CflsUy fusible (Hol'mann). 

Phosphine coiuLinL-s. like ammonia, with certain metallic 
chlorides; thus, for instance, with nluuiiiiium chloride Al,CI^ 
tin chloride SnC),. titanium chloride TiCl^ and antimony 
cliloride SbCly 

Phosphine is a very poisonous gas, producing, when present 
in small proportions in respired air, in turn dyspna-a and death. 
It pos-sia-Hi-s the power of cotnhiiiiug with the nspirutorj' oxygen 
linked to hn^maglohin ; in this way its toxic action has been 
explained, although in rcjdity it is almost entirely due to more 
complex operations. 

P}to*phonxum Cavipoundg. ~ Phosphine possesses f<eebly basic 
properiips, combining with hydriodic nnd hydrubromic acid* to 
form detiuile sails, produced when the two diy gases arc brought 

Phosyhoainm lirMnide, PIT, Br. — Cryatallijtea in colourless cube*, 
which boil at 'iVt. The vapour possesses a specific (gravity of 
t'906, so that wc conclude that it is a mixture of phwpUine Kud 
hydrobromic acid. 

Pkaq^ottium Ivdide, PITJ. — This iH-dutiful cunipounO, which 
ciystallizcs in large Iran.'iparenc glittering <iuadratic Jimnis, con 
easily be obtained by placing in a retort of a litre capacity (sec 
Fig. 132) 400 grama of common phosphorus, allowing an equal 
weight of dry carbon disiUphide to run in, and gradually adding 
680 gmins of pure iixline, care bsin;,' taken to keep the rctoit 
well cooled. The carbon disulphide is next completely removed 
by distillation in n water bnth, and the ri>tort connected witJi 
a long wide tube placed in a ^tightly elanting position, and 



fomislicd at its lower eod witli s tubulated leceiv^sr. "this, 
a^LR, ia coniicctcti l>y u tipriaa of buib tubes witli two absorp- 
tion-vesseU, tliti Gr^L of which contains dilute sululiuD of 
hydriodic acid, niid llie &<M;oud water. Tlie object of tbU 
RTningoiuoul 14 to absorb the liydriodic acid foifued during tlie 
ivactioii.aiidatthe itiinietiiiie lo }irf<veat the li(|iiid fiuuifjiiloring 
tbc wide tube iuto which the iodide of phosphouiuui id sub- 
limed. The ai>paratu8 is then tUlud with puit; carbou dioxidot 
a slow curreut of the ^as buiii^; passed lhi'uui;h during the 
operatiou. The ex|]eriment being Lliiu far urruii^ud, 240 granift ' 
of vater are allowed to drop slowljr by toeaDS of a stoppered 
tube-funnel into the wtort, wliich is slightly warmed. The 
heat evolved by lUe autiou Ikeu laltiug place is auSicieBt to 

Fid. 153. 

Bublime the jrreAter part of the iodide of phosphonium into the 
wide tuV, Towards the end of llic operation, inluch usually 
requires abont eiglit houre for it?! completion, the irtort u heated 
somewhat more sI,ron<:I)'. Wlien no further increase in the 
amount of sublimate tjikis plaeo, tlie upparatns ijs dismounted, 
the end of the long tube closed with corks, aiid the tliiek enist 
of the iodide of phoaplioninm loosened by means of a stout iron 
wire, and preserved in stoppered bottles.^ The formation of 
tliQ iodide of phosphooium ia reprvacntcd by tlie following 
cquatioD ; — 

51 + 9P+ 12HtO = 5PllJ + 4IT,P0j. 
An excess of phosphonia is. in practice, employed becaase a ] 

' Itormttnii, Btr. Ifria>«h. Chm. tJa. t\. 238. 



of tiiia substance is conveited, daring the reaction, into the 
red moditicntioa The foroiatioa of the hj-drtodio add which 
escapes is voiily explained by the decoiapositiou of the ioditlu 
of phosphonium in the presence of water and henl, I'hvs* 
pboaiuin iodide boils at about SO*, but it easily v-Rporizcs at 
a lower temperature It is u$etl ia the labomtorjr as a powerful 
nxluciiig ugeut, an well us for the preparjitiou of man/ oi^jauic 
phospboruii uoDipouadsc 

Liquid HYUHonEs PnospniDE, P,H^ 
Vapour Uonsity •= a2'y6.' 

38a This body, discovcied by Taul Th^nard in the year 1845, 
is formed when phosphide of calcium is decomposed by water; 

2PCa + 4T1,0 = 2Ca(0H),+ P,H<. 

T.iquid phosphtirctted hydrti^jeii is a very unstable body, readily 
splittuig up into solid hydride and plioispbiDe : — 

31»,ir.= P.Hj + PH,. 

Wlienthe spontaneously inflnnimable sulutniice is prepared, the 
fg» conies witli it a certain (]itantity nf \'apoar of liquid phos- 

Piu. ]£3. 

phnretted hydrogen ; and if the st^lf-inflammable gas be passed 
through tabes surrounded by a freezing mixture, a colourless, 
atrongly rt-fmctin*; liquid is olitaiitcd. which takes Bie at once on 
exposure to Ibe nir, buniiiij; with a bright plioaphorus-l ike flame. 
On exposure to the light, as well ns in pr&seuce of certain bodies, 
SQcb as liydriodic acid, tlii» liquid bydrido is decomposed, as 

' CraullcWi*, &>mfA. Rtn4. IxxriU. ISS. 



ahowii above, into the solid aud ga5cous couipoimds. According 
loTlicinHrd, I cbc. of hyilrochlorJc acid JSHufltcieiit to decoiDpu6« 
an iQiIafiutt« qunoutjr of the body. 

In onier to exhibit the properties of the liquid pfaonplmretled 
hydrogen. Hofmann emploj-s a U-tube made of strong glnis, 
3 to 4 turn, in diametcT, <^c:h of tliu Limbs of which is furnbihcd. 
with a glafts stopcock (Fig. 15:1). Thia tube is placed in a fieez- 
iltg mixture of pounded ice and salt aud connected with a flask.] 
into whicli from liO to 50 grama of freshly prepared calcium 
phosphide ari; gindually Uirown. This being dvcoinpost-d by 
water, tlio phosphui'cCtod hydroj:;ca evolved posses tlirongh the 
U-tube, in whit^h the liquid hydride condenstts, whilst tliu 
spontaneously inflammable gas escapes. Aa Eoon as all the 
oaloium phosphide bns bet>ii ilecoinposL-<l, ti cuiTent of dry 
carbon dioxide ts led through the apparatus; the flame of 
Ihe issuing gas is then changed to a faintly luminous cone. 
If, however, the carbon dioxide be replaced by a current of 
hydrogen, the luminous flauie is a^L=iin seen. 

Solid Hydbooks Phosi-uipe. 

This compound, the mode of formation of whkb has already 
bceu described, occurs as a yellow powder. On heating this in 
a stream of carbon dioxide to 70° it deconipoaea into phosphorus 
and hydrogen. It does not take fire iu the air until it attaitia 
a temperature of ICO*. lis conipositiou has not yet liefiHi 
ascertained with cerLuJiily. 


Ordinary pliospliunis takfis (ire in dry ehloriiu; aa^ and burnsl 
with a pate-gruunish tiaiiie, witli fomiatioii of phoHpliorus tri-J 
chloride, PCI,, or with au excess of chlorine pliospliorus pent*-] 
Chloride, VC)^. 

Phosphorus Tbichloride, PCI, 
Vapour Density = 6tl'a35. 

383 Thia conipoiiml was discovered by Gay-Lusaao and 
Tlitn.ird in 1808. It is best prfpiirnd by placing amorphous 
plioapborua in a retort (d. Fig. 154;, and heating it whilst a 



aUeam of cliloriQO gas evolvod Id the flAsk (.v), and diied by 
pasaitig through the tube (c), is led over it* Tlie distilkte is 
purified from any pentachlorido which is fomted by allow iug it 
to lemain ia contact with onlinary pbcMphoros for somo time 
and then rectifying. 

Tlte triohloriile is a mobile colowlosa liquid, which hns ft very 
pungent smell, boils nt 7i>', aad docs nut uuder<To solidification 
at- 115*. The specific gravity of the liquid at 0* ii 1-61294l* 
When exposed to the air it evolves white fumes, absorbing the 


Fie. 16*. 

atmospheric moisture, and decomposing into hydrochloric and 
phosphorous acids ; thus : — 

PClj + 3HjO = 3HC1 + P(OH)j. 

Sulphur trioxide acts violently on ibis compound, with 
formation of phospbonis oxycliloriile. nntl sulphur dioxide. 
Ticated with cuiicvntrtit^d sulphuric acid, chtoixisiilplioiiic arid 
and phoiipliottia penloxiiJo are produced according to llio 
eqimtiou : — 

2PCI1 + 3S0,{0U)j = 2S0, + 5RC1 4- ^^ | SO, + P/)^. 

' l>iKn«s vim C%im. n^B. [S] Ir, 175. 
* Tboqw. Pw. A«v. Stc ulr. 2S6. 





384 This conipouiK) was (Hficovered by Sir Humphrey Davy 
ia the ycftr lUlO, tJiougli it waa first oiialj-secl by Duloug In the 
year 1816. It ia easily formed by the uuiod of pJiospIioms 
tricbloriile with chlorine. To prcpurc it, a cum-nt of dry 
chlorine ia led through a wide tube on to the surface of the 
liquid trichloride coiitaiDcd in a flask surrounded by cold water. 
Aa the abaorpliou of Uie chlorine is accoin|jauied by tlie evolu- 
tion of much heat, it i3 ncoeHsary to take eare, in the beginning 
at least, tlmt th(! liijuid in well cooled. Tli<; mactioii is finished 
as soon aa thfi product assumes the condition of a perfectly dry 

Phosphoiiis pentoxide ia a white or yellowish-vrliite lastrous 
crystalline powder, possesatng a very aharp unpleasant smell, 
and violvntly attacking the eyes tin<l the toucoiis membrnna 
On healing, it is found In sublime bolow 100°, but it cannot be 
fused under the ordinary pressure wf the atmosphere. When. 
however, it is h&ated under increased presaore, it melts at 149", 
solidifying on cooling in transparent prifims. When heated still 
more alroiigly it boils, cmitlinjj a colourless vapour, which 
becomes coloured on farther heating, the coloration increaaing 
with the temporfttnro- This is due to the fact that the vapour 
gradually uuder^^ocs diasociation into etjnal molecules of free 
ohioriuu and phosphorus trichloride. That thia is the case is 
fully proved by Dtinia.1'3 determination of the density of tbig 
mixture at diffi^rent temperatures : — 

Uenaity . , 



200* 250" 
700 57-6 

300" 336' 
52-4 52-5 

Tliese nnnibcrs clearly exhibit the gradual dissociation of the 
TRpour, the density undergoing a continuous diminution until the 
tfinpcraturc of \iW hiis tuen reached. Above that point it 
remains constant The vapour at these teinporaturos conaista of 
amixttu-eof an equal numbor of niotecules of the trichloride and 
chlorine, possessing the density; IS?^? + 2 x '6oZ7 _ k».qi; 


That the vapour thus obtninpd contains free chlorine wm 
proved by Wanklyu and Itobiuson in tlie following way.' The 
vapour of the peutachloride waa allowed to diffuse into an 
' JVw, Jtuy. Soe. xiL 407. 



MmoRplieieof carl>on dioxide. Chlorine gns Wtiig lighter than 
the vapour of the tiichloride, must diffuse mora quickly than 
tbe laltur. Accordingly, if, ttUst tfao experiment, the vessels 
OonUimn;; the pentachloride were foaitd to contain the trichio- 
rido, whilst the ntiiiosphcns of carbon ilioxido was admixed with 
(tea cUorioc, the fuct of dissociuliou would bo piovud. Tliis 
was the result The dissociittion of the pentachloride may be 
prevented, or iit any mto much diminished, by allowing it to 
volatilize in a space saturated with the vapour of the trichloride. 
Wurtz' obtaiaed, uiiduT these circumstances, a vapour posst-'ssiog 
a density close upon 11)39 (the iiorimil density of PCIJ at 
l«raper»tures varying from 160* to 175'. 

In perfectly dry air tlie petitaclilorlde of pJiosphorus undergoes 
no alteration ; on exposure, however, to moist air, it docomposos 
with formation of phoaphorus oxychloridc ; thus >- 

H rcij + n^o = poci, +2ncL 

V Thia compound, as well as the pentachloride, dissolves in 

I n-otvr, with evolution of heat and formation of phosphoric oud 

1 hydrochloric acids ; the two roactions being : — 

P "^ 
I Tl 

I at 


K)C1,+ 3U,0 = PO(OH% + 3HCI, 
VC\ + 411,0 = PO(OHJ, + 5HC1. 

One of the most importaot properties of phosphorus penta* 
chloride ia its action on the acid-foruing oxides aad on the acids. 
Tliow it converts inU* tim noid chloriilu-s. Many exniuple* of 
this kind of deconiijositiun have already been given. For in- 
stance, it forms, with Rulphur tnoxide, chloride of sulphuroua 
acid or sulphni-yl chloride ; tlius : — 

SO, + pa, - sojCi, + poa. 

In this TeoctJOD two Atoms of chlorine arc rcjilrtccd by one 
ntom of oxygen. Wheu, on the other hand, the penloxide is 
allowed to act upon an oxyacid, clilorine ropluccs the radical 
bydroxjl, OH ; tlius : — 

^^* I OH + '^'^^ = ^°A OH + ^^^'> ^ ^^ 

In a similar way tliQ p(?ntachluriile acta upon organic acids 
aud other compounds Doatuiniii^ hydroxyl; and in couBequenci: 
' QamfUt Stmtnt, UxvL 001. 



of thin property it is much osed iu the propaiatioQ of organic 

I'liosphonis pentachloride forma a cryfitalline compound vrith 
iodine monochloride; thns:— PGl^ + ICl, as also wiLli difl'erent 
mctollio chlorides ; thus :~2PClt -f- Fe,CV &c. 


Phosphorus TsiBHoaiDE, VRvy Vajwur Density = 135-1. 

385 KrnminH imd phosphorus net violently upon etch other. 
so thiit small pieces of phoapboms thrown upoa bronune may 
cause a dangerous explosion. Iu ordur to prepare the tribro- 
mide, dry carliun dioxide ia allowttd to pass ttirough bromine, a 
small portion of tlte vapour of wliich is carried over. Thia is 
brought into oontaot with dry phosphorus (Lielien). Another 
m^tluid of preparation coiuists in dissolving both of these , 
vlemvnUt BcpiiraU-ty iudry carbon dieulpliidu.aml then graduiJIy 
ponrinj; the bromino solution into that contdniiij^ the phos- 
phorus and distilling, when the carhon disulphide boiling at 43' 
comra off. leaving behind the phosphorus Lribromide which 
boils at 175' (Kvkul.;-). 

The siiupU^et procesa for preparing' the tribromide is to 
place nniorphous phoaphorua in a tiaak closed by a doubly 
bored cork, one opening of which i» connected with an iuvurtcd 
condenser round which cold water is allowed to flow, whilst 
throngU the second opening a funm-l M'ith glnsn stopcock is 
placed, by muans of which bromine is allowed to fall slowly on 
the phosphorus. Tha first dro|)9 combine with evolution of 
li<;hl and lient, but this mptd comhiiialioti soon ccnsKR, and the 
bromine can bo allowed to drop in without causing any violent 
aotJoiL The product is then separated by distillation from the 
excess of phosphorus which rnnat be present (Schorlemmcr). 

The tribromtilc is a colourless mobile liquid posste^sing at 0° a 
sp&cific Ri'avity of 2!)25. It has a strong uiiplcasunt pungent 
odour, and is dccompotied in presence of water into phosphoioua 
add and hydrobromic acid. 




a86 This body i« obtainec] when bromine is (uldcd to tlio cold 
trilronii<Ie. It is a lemon-ycUow crj'stalline body wbicb on 
heatitij; melts, forming a iwl lifiuid -which decompose nl 100* 
into tbc tribroinide and bromine (Gladstone). Wlit-n a current of 
carbon dioxide is led tliixmgh the melted compound, the bromine 
is carried over and tb« tribroinide remains behind. Tho pcnla- 
bromide possesses aii extremely pungent odour, niid I'orms, 
when brout^ht into contact with & small quantity of water, 
pliosphorus oxybromide and hydrobromic acid 

PnoBpnostrs CuLononitomDe, PCljBr,. 

387 If equal molecules of bromine and phosphorus trichloride 
arc brought together, the liquid becomes boated and two layers 
are foniied. Ttio ujrper layer conHiat« of & soluliou of bromine 
in pho9phom3 trichloride, whilst the lower consists of asolulion 
of trichloride in bromine. If the mixture he cooled down to a 
temperature of- 20° the whole sQlidifiestoayellowish-Kdcrystttl- 
liiiv mass which iiguin splits up nt ordinary temperatures into two 
distinct layers (Wlchelhaus). If this mixture, placed iu a sealed 
lube, be ex])06ed for some weeks to the oi-dinary wintiir tempera- 
ture, a. ciystalline coni|>ound is formed whicb ia more stable, 
ioasmnch as it does sot decompose into its constituents until a 
tumpeiulure of ^5" ia reached. 

3'hosphorus cblorobromide combinps with bromint'. and foitas 
llie compound I'ClaBrj + I!r, wliicli aoliililies in large cjjstals, red 
by transmitted, but blue by reflected, light. A second compound 
PCi,Br, + 2Brj i« also formed «t the wiuie time, ciyslalliziug in 
Deedle-shaped crystals of a greenish lustre, which man turo 
brows. Tfaese compounds corruapond to those formed by the 
union of pho8p1ioru9 trichloride with iodine monochlorido and 
with the metallic elUoridcs (Mtchaelis). 


pHO&PHOBUa D[-I0D1DK, 1',!,. 

388 This compound, wliich hoa au uoalo^us composition to 
liipiid phoepliur«ttcd hydrogen, is obtained by dissolving one 
pert of phosphorus iu curbun disulpUide aw) then adding 


gndaaHj 8*2 pail of iodme. Ob gmtly ■■"■»ing t&e 
•olntioa ao u ti> dutil off the eaiboo d i wJ phJ Je, tke di-ic 
temaiiH bduod u a ydknr crjrsulliae hhh When the 
pbiile is cooled dovn to 0", the aunc w p oaad afp«la> ooi i 
long otue»-nd ciTiUls (ConnTinderX The oyBtita ndt 
llO*aodaie draonpoaed bj water with fionnatiott of i 
(iho^jboniiS pho^boTow Msd, and kydiiodic acid j thus: 

3P,r,+ 1211,0= P,+ 4P(0H),+ I2ia 

PHom-Ronts Tn-ioDiDZ, PI, 

Thu compouml is olitained in a sbnllar way to tbe 
bat ttsitig 1} timea as much iodineL By gently **'*'tt^ tlkij 
Mlalton, tbe greater poTtinn of the disolphide of ctrbon is 
rid or, aod tbe raidui! is coolud dou-ti by a mixlate uT salt 
icA S«d Mix-aided crystaU Mpante oat which melt at &5* and 
which OD (imtly cooling may be obtained of laige sixe. On i 
addition of water to tbia compound hydnodic and 
adds are fomied ; thtu : — 

PI, + 3H,0 = PCOH), + 3HL 


Phosphorcs Pestaflcobidb, PFj. Density = $3* 

289 This mtei^sling coiiipotind has bu<n recently discovered 
by Tborpe.^ it is fonned vhea arsenic irilluoride is added to 
plxwphonis peatacliloridi', a violent leactiou uccuniiig ; thus : — 

SAsF, + SPClj = SAaCI, +3PF,. 

PhMphonta iwntailuorido is a colourless gas which decom- 
poees on oontoct witli wnter into ]>liosphoric and hydrofluoric 
acids. It poesQSses a strongly irritating smell aod attacks the 
mucous tiienibmuc. Under a pressure of 12 utmospherea it does 
uot liquefy, nor is it inflaniuiable. Tlie density of the 
i« (H = 1) 03. When a st-rics of elerrlric sparks are passed" 
through tlic gas by it«u]f, or tlie gas mixed eithcrwitli oxygen or 
hydrogen, it uiidergoea no change. With dry aniniOQia it forms 

* Pn» finjf. Soc XXT. jk ISi 



ft white soliiJ compound liaving the following cwmpogitiou — 
(l'FJ. + 5NH,. 

Tliu «xiHtenoe of tbe gaseous pentafluoride, taken in mn- 
junction with the fact tlial it. i» [ictlWtly stable, ev«a at veiy 
high tempcnittirGS, is of great theoretical interests 


Oxygen fonus witli phosphorus two couipounda, to which 
two acids correspotul. A third acid is also knowu to wliicli 
iheie is no correapoadiDg oxide: — 


Phosphorus trioxi<Ie P.Oj. 
Plunpbonis pentoxide l',Oi^ 

nypopliosphorous ncid PH(01I}j, 
Phosphorous acid I'(OH),. 
Fhosphoric acid I'OCOHV 

HypopnosraoROCS Acm, HjPOc 

ago The sails of this acid were discovered by Bulong in 1816. 
They iire fonned wheii (,h« pliosphjdos of Lho metals of the 
alkaline eartlis ai-e dt-oiinpoiied by water, or when phosplionw is 
builud with an ulkidi or an iilknliuo fiarth. i'or thv purpose of 
pre]mring Uie acid, bai-yla m best employed, as it la from the 
bariura «dt titat not only tlip other salts btit aim the free acid is 
easily prwpanrd. The fonuation of barium hypopliosiiliite isshown 
in tiN followiu);; equation : — 

3Ba(0U}j + 21', + 6H,0 = 3Bn(PHjOj)j + 2PHy 

At the same time a small quanti^ of barium phosphate is 
formed, but this cjin r(.'«dily bu scpuralod from the hypuphos- 
phite by filtration. To the clear solution, the requisite quautity 
of dilute sulpliuric acid is added, nni) the lilt^-red iKiliitiun 
erapomtcd to a eyrupy consistency. On ooolinp the Holutioo, 
the bypophosphorous acid is obtained in the form of n thick vei^ 
acid liquid. Hypopbosphoroua acid can also be obtained in the 
form of u white crystiilliuo masa mvlting at 17''4 as follows.' 
The tolerably concentrated solution ia gently evaporated in a 
platinum dish at a temi>cnLture below its boiling point and then 
gtwlually lieatcd from 110° up to 130", at whidi temperature 
it is flllowcd to rc-main for ten ruiniitcs^ The eolutioQ thtu 

' Thcmnn, Ser. DniMt, Clum. Go. vii. 094 uiil M6. 



obtained is cooled, poured into a stoppered botUe, and tbis placed 
in a frueziitg mixture at a f«w degrees bclov 0°. The acid 
in then f>)u»d citlicr to crystaUiz9 spontaneously or to do so on 
being toucltcd with a glass rod. 

Hjpophoapborous acid whoa strongly heated docompoeos into 
phosphurcttcd hydrogen and phosphoric acid ; thus : — 

2H3pOj=PlIa + H,PO,. 

It« ftqiieons solution precipiUtes gold and silver from solutions 
of their soils, phosphoric acid being formed ; thus ;— 

4AgN0, + 2H,0 + H.PO, = 4Ag + iHNO, + I1^V0^. 

When a. soliitioD of tliis acid is added to merctiric diloride 
eoliition, either calomel (merciirons cliloride) or metallic mercury 
in precipitated according to the proportions in which the acid is 

HypopltosphoTous acid is also oxidixcd by chlorine oud otlier 
oxidizing agents to phoaphoric acid, and when esposed to the 
air it taken up oxygen with the fonuation of phosphorous acid. 
Nascent hydrogen reduces it to phoRphuretted liydrogen. 
Although iiypophosphoious acid contains the group hydroiyl 
twice, outy one Jitom of hydi'ogea cau be replaced by uietals. 
This is uosily explutm;d when we rvnieiuber that this acid may 

be considered as dihydroxyl-phosphine V< OH, or as a weak 

basic huiiy which hns hocome a wrnk acid by the addition of 
two ntonia of oxygen. 

7A«T }li/i>vp}iMPphitfs. — Must of the suits of by pophtisphorous 
acid are soluble in water, and some also soluble in alcohol 
and ciystallizablfi In the dry state they do not undergo altera- 
tion in the air and may be boiled in water, fi'ce from absorbtnl 
oxysen. without decora position. Like the free acid, all the 
hyi>opliosphil€9 poaseaa strong reducing propcitJes, giving with 
solutions uf gold, eUvor, and mercnry, the same reactions as 
the acid itself. 

PnospBOBca TBioxrDB, P,Oj. 

291 In tlie year 1777 Sngo showed that when pliosphonis 
undergoes slow combustion, a body is formed which is different 
ftova the substance produced in the quick combustion of phos- 



phonia ; autl Lavoisior explained thia fact by Uic siippositioa 
that two distinct oxides of phosphorus exist. 

In ordt*r to ptvpire phospbonis trioxidc a pi«c(j of dty 
phosj^oras is pkcuU in a glass tube (Kig. 155) drawa out at 
the end (a) to a fino point, and placud at the otlicr end (6) in 
coDiwction with an tLipiratoi- from which a slow cunvnt of air 
is pauod into the apparatus. If the phosphorus is alight ly 
beated, it burns with ouly a slightly luminous greeui^h tlame, 

no. ifis. 

snd the trio.-udc which is formed is deposited in the furthvr part 
of the tube as a white powder. 

Phospbonis trioxide in a white amorphous powder, veiy 
voluiiiiDous nnd easily fusil)1e,aQ that it can he readily sublimed 
froui one piut of tlic tubt^ to another. It has a peculiar garlio 
like HiDell, does uot redden blue litmus paper, and when heated 
in the air burus wiili fonnalion of the pciitoxidc. '^^Tien 
thrown into water it instantly combines with it, forming phos- 
phorous acid ; thus : — 

P,03 + 3H,0=2PCOH), 

Phosphokoto Actd, P(OH)j. 

393 This acid is not ouly formed by the action of vflter on 
phosphoiiu triuxidc, but also by thu slow oxidation of phos- 
pborua in moist air. In order to prepare the acid in tliis way, a 
number of gla^ii ttd)e}( (a h Fig. 1 5t>) drawn out at {b) to a fine 
point> and each containing a elitk of pliosphoraa. are placed in a 
gloss f'imni>l. The fitouel is tlien plncvd in a bottle coataining 
some water and tbo wbolo covered with a boll-jar oppn at tlio 
top (Tig. 157). The phosphorous acid thus formed, which, 
however, always contains some phoophoric acid, collects in the 
vater below. In order to proparc pure pliosphoroiis acid 
the reaction discovered by Davy iu 1872 is employed. This 
consists in the decompositions of tlio (ricbloridu by wolcr; 

PCI, + 3H,0 = PCOH), + 3Ba 



For iliis purpose it ia not neces&ar^ lo prepare the pure tricJitomle 
separately, for. if cliloriiw be I«d tlirougli melted phosphorus 
contained under watvr, Iho trichloridu is Ant, formeU. tuiJ, ou 
coming in contact with tho vratitr, this is dt-CODipoeiKi as ehowu 
Jo the above cquatioa Care uiut be t^ea to stop passing thu 

■ rf*' 


rm. U7. 

cliIoTine ill Ijcfore all the pho«phnnis has disappeared as tlia 
cliloriue vrotild othem'be oxidij;c the phosphorus to phoephoric 
»cid. It is difficult to prevent this altogether even if phoHphortis 
is preseut in excess. 

]\y evaporating the solution until the residae att«ias a tern- 
ptratare of ISO" a tliick ayrupy substance is obtained which is 
transformed more or less i-apidly oa cooliiifi into a ciystalline 
iiinsa molting at TO"!.' riio»[ihorous acid has an acid, garlic- 
like taato, absorts moisture rftt»idly from tlie air. «nd deliqiiesct-s. 
"Wlien strongly heated, iiho.iphoraus acid decomposes iolA 
phosphurettcd hydrogen and phoaphoric acid ; thu£ : — 

And when treated with phottphonis pcatoclilotido, pbosphonu 
tiiclilorido is formed : — 

P(OH), + PClj = PCI, 4 POClj + 3HC1. 

Hence Ihe trichloride is the chloride of phosphorous acid • 

The Bqttpous solution of the acid also slowly nbsorlw oxygea 
from the air, and in jift-sonce of nascent hydrogen it is reduced 
to pbosphnretted hydrogen. It acts as a strong reducing 

I J. Tbnnurn, lUr. J)rttUeh. CAcm. Ot», Til. «B«. 
» (katber, Jmrn. Pmt. CA«n. l^J liiL Sbft 



Agent, precipitating gold, silver, and mcrcuiy from their aolutiona 
like hypopbcsphoroas acid. 

The }'ho«phite9. — Although a weak acid, phospliorous nciJ is 
triLosio, but uuder ordinaiy ciruuinsttuiccit, onl^ two atoms of its 
hydrogen cau bo replacttd by niDtals. A normal tribosic snlt, 
F(ONa)y 13 known, but this lias not yet beuo olitaiuerl in tho 
aiili)'<lruiis state,' Ou the oUicr band, t-thers of phospliorous 
acid arc known in which the three of hyilroj^en are rpplaewl by 
u ladicul, 33 ethyl, C,H^, and this tri-ethyl phosphite, ^(OCjU^y 
is a body which can 1>b dUtilled witliout dL-cumpositioii. 

The phosphites wliicb are goIuhl>> iu water posseSB an acid and 
garlic-like UJjstu. They act upon tlie 6att« of the noble nititals 
like the hypophoHpbites, fi'oni which, however, they are distiu- 
guistied by giving' a precipitate with biir}'ta- or tioie-'wator. 

I'noaPBOBPa Pkstoiidb, r,Oj. 

393 '^■1= ^1 '^Ic white clouds which arc formed whim phosphorus 
bumd bn;^ht1y in the air consist of this o:iido> If a small piece of 
phosphorus is burnt, on a dry pkt« covered with a bell-jar, these 
fumes coiideiiHe p:trUy ou the sides of the g]a»i aiid partly on tjie 
plate, in the fonii of a white floecuJeiit powder, whilst tlie por- 
tion near the hiiriiing phosphorufl forma a glassy mags. This 
white powder is amorphous, and may be gtiljlimed in a test- 
tube heated over u giw lump. The pure [wwder is perfectly 
colonrlefis and odourless. If it should possess any garlic-like 
smelt it contains trioxide. and if it has n yellowish or reddish 
colour it is mixed with amorphous phosphorus. It poasessca no 
action upon dry blue litmus pajier, and is excessively hygroscopic, 
deliquescins when exposed to the air, very q^uJckly with formation 
of mctaphosphoric acid : — 

When thrown into water it dissolves with a hissing noise 
and with the ovolutioii of n large amount of heat On heating 
with carbon, or other reducing agents, phosphorus is formed: — 

P,0^+5C = P^ 5C0. 

Pboaphorua pentoxido is often uscid in tho lahoratory as a 
desiccating agent, especially for the purpose of removing the last 
tinoea of nioistaro from gases or from liquids. Owing to its 
> Qnuncrmiinn. Lifbiif» Jnulm, rlxzr. XL 


BtroDg power of combining vith water it is able to withdraw the 
elemenla of water from many compounds containing oxyges 
tnd hydrogen. Thus it is usod fur lite {>re]>anLtioii of iiiuogcu 
p«titoxide and other compounds. 

lu onler to prepare large quantities of the pentoxide the ar- 
rangement shown in Fig. 158 )» employed. (A) is a laige dry 
gltiss hftlloon, provided with three iMcks (a d ftiid g) ; the neck ((f) 
is connected with a powerful wutcr-aspirutor by means of which 
air, dried by passing through the drying tubo (f), is drawn into 


k I 

Fiii. IS8. 

the balloon ; (g) communicates with a hirge wide-necked bottle 
(B) into which a portion of the light powder is driven by the 
oiirrent of air; through the neck (a) paaaea a strajsht glaM tube, 
closed with a cork at the lop hut open at the bottom, reaching 
nearly to tJie centre of Uic balloon and having a small copper 
wucible (e) fixed to ita lower end A piece of phosplioms ia 
dropped down the straight tube into the crucible aad ignited bya 
hot wire, a good current of air being kept up until the operation ia 
complete ; a second piece of phosphorus is then dropped down 



into tbo cruuUe (e), ood trticn tbis is burnt & third piece is 
introduced, and so oo, until a sufficient quantity of tho pCQtoxide 
has been obtained. 

A more practically useful nrrangement for preparing the p«n- 
tAxide in quantity conatata of a cyliodor {a, Fig. 159), open at 
both ends, made of cominun slieet-iron. fourteen inches hi^h and 
twelve inches in diameter, having ii cover provided with a bent 
chimney (h), one incli in diameter, cloaed by a cork. Tlie cylinder 



Fig. IS9. 

is soppOTted by a wooden tripod, kud rests in n sbcct-iron 
htDnel (A), fitt.iiig into the neck (tf a wide-mouthed botUe (3). A 
copper spoon (rf). I'"*^ to an icon rod, serves to ruoeivo the 
pbospliorus which is from time to time renewed by drawing 
bock the s[K)on to th« opening («), an*;! dropping in a fresh 
piece. In order to renew the aupply of air, which during dry 
woatlicr docs not rcq^iiire desiccation, the board (t) ia occasioiiaJly 
removed, and air allowed to enter 1)etwi!en the funnel oud tho 



cylinder.' On account of it« bciiig so exceedingly hygroscopic, 
the pcnloxidetlms obtained must be preiscrved iu well-stoppered 
bottles, or, better, in heroietically-iieuled flasks. 

PnospnoBic Acid. 

394 The liistoty of tbis acid pQ!ise33c» a peculiar interest for 
Die aciL-ntific chemist. In the year 1746. Marggmf observed 
that. w\w.njmible salt 0/ urine, IfH,NaHP(\. is mixed with a 
solution of oitrate of siher, a yellow-coloured silver salt is 
procipitatmL It was aftenrards noticdd that other salts of 
phosphoric acid, as, for instance, the ordinary phosphate of soda, 
gaT« the same reaction; but Clark, in the year 1828, pointed 
out that when the ttalt i» beattid and then dissolved in water, 
the solution m obtained gives with nitrato of silver a white 
precipitate He, therefore, distinguished the ncid coDtAiiicd iu 
the heatod salt from tliat coDtainbd in tbo commoQ phosphate, 
and termed tlie former pyrophonphoric acid. In 1829 Gty- 
Lussac proved tbnt the acid thus prepared can. be converted 
into the otlicr compounds without losing its peculiar prop<.*rlic8 ; 
and lier/elius aud Eugetliardt had previously found that freshly- 
prepared eolutioii of well-iguitod phosphoric acid was able to 
ooogulute uleiir solutions of albutneii, wbiltt this i.-* not the case 
when the solution of the ncid has becu standing for any con- 
sidcmblc length of time. These and eiuiilnp obscr\-«tiou» led to 
the conclusion that phosphoric acid, with which the pentoxide 
■was then classed, can exist iu several allotropic conditions. 

The classical researches of Thomis Graham • first Uirew a 
dear light on this subjocl. Un showed, in the first platio, that, in 
additinn to the onliuftry phosphoric acid and the pyrophosphoric 
acid, a third modilication exists, to which be gave the name of 
inetapho<iphonc acid, and that tlits is thu substaaoe which has 
the power of coagulating albumen. He also ascertained that 
voiuiiion pboi^bates, when tlicy are snturated with a base, 
contain three times aa much of that base, in proportion to the 
same weiglit of phosphoric acid a.s the metaphosphates, whilst 
the pyrophosphates contain twice as much as the metaphosptiates. 
Orahftm likewise proved that, when the acids arc libt-raUsd from 
these different salts, they may be reyarJvd as containing different 

' V. Gnhovn\ii, Jnn. Chrm. FSarm. gxxxtL IW. 
* nU. rrau 18$3, ii. SS3. 



qiuiiititit:8 of wiiUr. Uvnuo tlio cuiiix>ositiun of Ibe Uiree acids 
is as follows : — 

OM notRlion. Kmt D(it;ition. 

Coiuraon, or Ortliojihospliopic acid P^O^ + KHjO H,I'0^ 
PjTophospIioric acid .... ^,0, + 2H,0 H,P,t), 
MeUiphosplioric acid PjOj + H,0 HPOj. 

Theae three acids as well as hypophosplioToiis and phoHphoroos 
acids may be considered to be derivatives of pUospbiua, I'Hy ; 
thus; — 

Hj|>optio"phorotu Acid. 


Ottlioplio«i>horic Add. 

rTiocplvaroiia Add. 






Vp_0— OH 

Pyi^pJio^p^o"^ AciO. Metsp)io>phonc AcU. 

on— I'— 0-OH 

HO— P<' I 

— P— 0-< 



The OTtho- and meU-acids ai-e also fonaed by decomposing 
PC1( or PFj wiLh water, and thi^c, ns well as pyropliosphoric 
acid, may therefore be represented as derivatives of these pentad 
compounds; thus. — 

Ortlia[A(Mpliari« Acid. 




^P = 

UetaphMpliortc AcM. 



395 Poifoiiova Action of tie Acids of PAcspAwiM.— Vhcn 
ndmiaistercd in an uQconibiiicd condition, Uie various oxides of 
plioRphorus prodtice appan-nlly riie same symptoms which 
follow the administration of other mincnd acids. Sufficient 
data do not iixist aa to the specific physiological action of all 
these compoundft 

Id tti(> case of ortho mela- aod pyrophosphoric acids it would 
appear tbnt the 6rst, wbuu in coiuliinntioii with inactive l)«ses, 
acta as a perfectly inert body. The seoood possesses some 



activity as a poison, while the pjro-fl&lts when iDtro<luc«d 
directly into the blood are fonnd to be very powerful poiaoDS 

OttTnopnosraoRic Acid, H^PO^. 

ag6 In order to prepare this acid, red pboaphoma is heat4?d in 
a retort with common coiicentraU^d iittric ncid. The pho9ph(Hiu i 
is oxidized at the expense of the nitric acid, and i«d fumes tat 
slowly evolved. When the phosphorus has dissolved, the rendoe 
is cvaporatf^d in a porcelain dish, and the concentrated solution 
r[.-peutc'dly iix^ilcd wiili nitric Hcid, in order to oxidize com- 
pletely any phosphorous acid which may have been formed. At 
soon as the further addition of nilrio acid is iinacconipanied by 
Uie evolution ofreil fumes, the operation is concluded, uod the 
residue only rcquirca to bo evaporated again, in order to get rid 
of the execss of nitric acid (v. Sclimltcr). Coininnii phw^phonis 
was formerly employed instead of amorphous phosphorus for 
this purpose ; but tliia undergoes oxidation much more slowly 
than tlie njiiurphous vsriL'ty. inasmuch ax it meltA fomiin}< round 
globules, which are only slowly attacked by the nitric acid. In 
addition to tliia, when common phoitpliorus is cniployod, weak 
nitric acid can alone be used, as tlic strong acid ia ajit to 
prtiduce an explosion when brought in contact with ordiiiaty 

The residue obtained in the preparation of hydriodic nctd 
by mean^ of iodine and phosphorus consists of a mijctare 
of phosphoric and phosphorous acids, containing a small quan- 
tity of hydriodic acid. In onler to prejiare jniTe orthophosphorio 
acid from this residue, it may be heated with a little fuming 
nitric acid, and filtered, in order to separate it from the solid 
iodine which ia liberated. More nitric acid is then added, in 
order to oxidize phosphorous acid, and the liquid is evaporated 
to a syrupy consiatency. 

Oithophosphoric acid is prepared on the laiye scale from 
bonc-asL, wUicli consists chiefly of tri-ctilci«m pliosphate, 
together with a small quantity of magnesium phosphate and 
calcium carbonala Acconling to Liebig, equal weights of 
sulphuric acid aud bone-a:ih are taken ; the sulphuric acid 
is diluted with ten tJmes its weight of water, and is allowed 
to remain in iroutaut with the boue-aMh for some time. The 
add ijolutioQ is then Jlltercd through linen, aud tbo filtmto 

uHTiioriiorfiJitJifrc acid. 


evapomUjd to a small bulk. On tke adtliLioa of strong sul- 
phuric add, the caleium, still prt-aent in si)hition. is precipitated 
u gypsam. Tlic clear solution is tht^u poured olT, cvaitoratctl to 
diyness* and ttevd fruui u» uxcuut of »ulpliuric acid by ignition. 
Tbo rceidno is free from lime aiid eulpliurie acid, but it contains 
small quantities of magnesia, which can only with ditBculty be 

In order to prepare a pure acid from bonD-aali, tlie powdered 
ash ia dissolved in tliv smnllust possible ({uantity of uitric 
acid, and to tlie clear liquid a solution of nc<!tttt6 of lead 
ia added. A precipitate of lead phospliate falla down, which 
must hp warmed for some time with the Iic{uid, in order to free 
the precipitate fitim any calcium pliospliate which is thrown 
down with the lead-salt. It is well waslied with builiny water, 
and decomposed by su]ptnlrutti;(l liydro^'ii. According to 
Berzelius's method, ib» lead-salt is decumpo»ed by dilute 
sulphuric acid, and the excess of acid removed by i^^uitiou of 
the evaporated Sltrate. The residue is tiien dissolved in water, 
and freed from traces of lend by sulphuretted hydrogen. 

Another method which may ho employed is to dissolve the 
bono-aah in its own weight of hydrochloric acid of spociSc 
gmvity IIS, diluted with four times its wcijjbt of water. To 
tills solution oiie-and-a-hulf parts of dry sodium eulphate is 
added, whereby a precipitot.f: of gypsum is produced; tJiis is 
then 61tered o^, and the boilin;^ solution iteuirali/.ed with 
carbonate of soda; the solution is again tillered, to separate 
any calcium corbouale which may fall down, aud the whole 
precipitated with barium cldortdo. The precipitate thus forme<l 
oouaists of & mixture of barium sulphate and barium phosphate, 
and this is decomposed by one part of sulphuric acid, haviug a 
specific gmvity of 171 (Neuittadt). 

Coinuinreial phospliorie acid fi-equently contains arsenic acid, 
derived from the sulpliuric ucid or hydrochloric acid employed 
in it« manufacture. In order to free from arsenic, it must be 
dissolved in water, sulphur dioxide led tbrounh the wnnn 
nolution, in order to reduce tlie arsenic acid to arseniuusacid, then 
tlte solotion boiled to remove the excess of sulphur dioxide, 
and Aulphnrelted hydrogen passed through, by which means the 
whole of the araenic is precipitated as the insoluble trisulphide. 

297 rhoifphoric acid is extremely soluble in water; it has a 
pleasant purely acid taste, and is perfectly free from smelL 
When tJie aqueous add is evaporated down until the residue 




possesses the composition, lIjPOj, it presents the appearance of 
a thick 6>Tn]), from wlitcli, on stauiHtiij^ a ci^slalline mass 
Uepcsits. If a co'^tal of ihU acid be dropped into a freshlj'- 
ppcpared solution of tlie reqiiisit* strength, crystals hegiu to 
form at ouco, and soon sprt-iuj throughout tiie mass. These 
cr^'&tals belong to lUe rhuuibic syvtviu, forming Hix-sidvd prisms 
teriniijat«iJ by six-sided pymniiiU, wliich melt at 3il-6'> Tlie 
crystallized acid may tie heated bo IlJO" without undergoing any 
altemtion, hm above this temperature it loses water, and at 213° 
is compliiloly converted into pyrophosphoric noid, Hjl',0^ This 
substance, in its turu, loses water wli«n heated to redness, with 
formation tpf metaphosphonc acid, UPOg. Tlie following table 
gives the variation, of th« specific gravity, with tlie percentage 
conipoaitioa of aqueous solutions of oithophosphoric acid: — ' 


per acuL 


Par Coat. 
























33 49 

































1-41 (i 




















1-2 U 








1-0. '2 















37 37 








398 Tlu Orlhophosphatrs. — Ortliophospboric acid, being tri- 
basic, forms thn?e classes of salts according us oni!, two, or threo 
atoms of liydrci^^cn are n]]daccd by their equivaleut of metal. 
Urns we know three orthophosphatcs of sodium : — 

' J. Thonwcn, Her. Dnitteh. Chfm. ffr* tii. 997. 
• John Vau, Chtm. A"«io(. ili. 160. 



Triaodium or aormal sodium phosphate. Na,P0j + 2U,0. 
Hydrogen disodium phosphate, HNa,PO, + 12ITjO. 
Diliydrosen sodium phosphate, HjNaPO^ + H.O. 

Of the normal salU tho»c of the alkiilU M-iili the excepUoD of 
the lithium salt arc cosily soluble iii w!il<?r and thrir si-jlutiona 
hare a strong alkaline reaction, Tht nonnal orthophosphtites 
vhicb are insoluble in wat«r are easily soluble ia dilute acida 
by which means ihwy iire converted into Uie soluhle hy.lrogen 
ortho phosphates. Theac latk-r isuUb are readily obtained froui 
the normal comiwunds ; even carbon dioxide brings alxiut the 
olmnge; thus, if the gnst lie led into a solution of trisodinm 
pboaphats the following reaction takes place : — 

Na,PO, + CO, + H,0 = HNaJ-O, + HNaCO^ 

The hydrogen disodium {ihosphalc which is liere formed to- 
gether with hydrogen sodium carbonnt* is the coomiou 
phosphate of fioda of tlie sliopa. Tliis salt alt-hougli according 
lu its conutitution it must be conaidered as an acid salt, inas- 
much as it contains bnsic hydrogen, bos a slightly alkaline 
ruaclion, and, like other soluble hydrogi-ii orthopUosphatcs, is 
easily obtained by adding solution of eoda to phgsphoric acid 
until the solution has a weak alkaline reaction. The hydrogea 
diaodium orthophosphate is coDVcrte<l on heating, witb loss of 
waUjr, into the pymplicsphate. 

The dihydrogcn ortliophospliates of the alkalis are soluble in 
wali:r, and possess a slight acid reaction. Ditiydro^tn potaa- 
sitim phoephat«, H.KI'O^. forms laiya well dc6n(?d crj'stala, and 
this salt may be heutttd to a tenipcnitnre of 400' without losing 
vrater. At a higher temperature, however, one molecule of 
water is driven off and potiutsium metapliosphute, KPOy ia 

The orthophosptuLlcs can readily be nicognizcd by tlie 
following reactions. The normal as well as > the acid salts give 
with nitrate of silver a yellow precipitate of silver orthophos- 
phate, AgjPOi ; thus :— 

Ifa^PO, + 3AgN0, = 3XaN0, + A^.PO.. 
HNa^PO* +3AgN0j = 2XaN0j + UNO, + Ag^POj. 
U,KaPO« + 3AgN0,= Na>JO, + 2HNO, + Ag,PO, 

In the esse of oommon pltosphate of soda and nitrate of 



silver, ire bave tlie stngalsr hci uf two ueutral solutioos, when 
mixed, yielding ft strongly iicid liquid. 

When to a solutioa of an ortlio-salt a mixture of sal-ammoniac, 
antmonin, iiixl uiaguf«ium sulpliato sulutious is added, a crystal- 
Itue precipiUite of amraoniuiu tnagttesiutn pboaphate 


is tliTOWU dovrn. la order to detect orthophaiphonc acid id a 
siil»iiunco insoluble in water, the body may be d^olved ia oitric 
acid aud an excess of a solution of molybdic icid iu nitric 
acid added to the liquid. If phosphoric acid be present, this 
solution o» slightly wanuinj; yields a den»e jpHow precipitate. 
The composition of this precipitate is approximately represented 
by the folloiviti^ ronimla : — 

iiMoO, + (Nn^),PO, + 4 n,o. 

MRTAPnospnonrc Aero, HPO^ 

999 Tills modification of phosphoric acid was diacovered by 
Graham in 18.13. It is obtained wbeii a solution of phosphoric 
acid ia heated until thw n-siduy doi'8 not give oCT any more 
water. The acid tlius pr<>pared solidifies on cooling to a soft 
pasty mass which oa exposure to the air readily absorbs 
moisture aiid dfliqucstus. Tliv glacial phosphoric acid of the 
shops ia metaphosphoric acid which usually contains wida as 
impurity.' Metaphosphoric acid i» also formed when cr>'stalliuo 
phosphorous acid is heated in a sealed tul>e with brouuae 
(Gustavton) ; thus : — 

H,PO, + Brj = UrOj + aiTBr. 

When phosphorus pentoxidc is allowed to delicjiicsce in 
moist air or whwn it is di.-ssulved in oold water inetnph«»phorio 
acid is formed. TUts aqueous aotutton on standing at the 
ordinary temperature of the air, gmdually undergoes change 
with fuimatioD of common phosphoric ucid iind this conversion 
takes place quickly if the liquid bo boiled without the fonna- 
tion of the iutermediate p.v-rophoaphoric acid (Gmhaiu). Mctn- 
phoephoric acid is volatile at a bright rod boat an*! when heated 
with sulphates expels sulphuric acid from tliem. for although 
sulphuric acid is a stronger acid than phosphoric acid, the 

' Breicitn, ZMIkA. An^ifi. Clum. vi. 187. 



fonner is more ctisily volatile than the latter. An aqueous 
eolulioD of metaphoaplioric acid u also obtniniMl l)y pussmg 
a current of sulpliu retted hydrt^ii gas through a liquid 
oontaining lead metapliospliati; in suspenBion. 

Tlie solution of lucUipliufipboric acid is dtstin^itsticd from those 
of tlie other two modifications inasmuch as it prodnces with 
eoluiiou$ of calciuiu chloride, barium chloride and albumen 
white precipitates. 

300 The Mrlaphospheits. — ^The salts of motaphosphoric nciit 
are obtained by ututnJixLng the aqueous soluliou of the acid 
by a ba«o or by heating a dihyUrog«D ortbophospliato ; thus : — 

No less iha.n five distinct modificitions of Oia raetaphospltates 
are known to exist.' 

( 1 ) Monotnetaphcsphates. — Of this class otdy those of the alkali 
inetal.i arc known, suck as KI'O^ Thi* moiH>iiictaplioi<pliat6s 
are remarkable as being ingoluble in water. The potassium salt 
ia formed, as ahow shnnii, when the dihydrogcn polassiuui 
phosphate is heated. The nionometapboaphatea are distinguished 
from tlie other nioditicatioDS inasmuch as they da not form 
any double suits. 

(2) J>imeUiphoirpkaiu. — These salts are formed when nquvou* 
phofipluiric acid is Iient«d to a temperature of 350" (Fleituiiiuu) 
or 31 G* (Maddroll) with the oxides of zinc, manguiese, or copper. 
if the copper salt bu th<.-ii decoinjioEed by jratatsioiu sulphide a 
fioluble potassium dimetapho!!|lhall^ Kjl'jOj. be obtained and if 
sodium sulphide bu employed a soluble eodiiim dimctuphosplmtc 
in io tike umoiier produced. In lulditioii to the dim«lapbosphat«3 
ooniaining only one metal, double salts such as CuKjfP.O^), 
can 1m ]>rcp«n!d. Only the dimetaidioaphates of the alkaline 
metaU are aolubic in water and are crj'slallizabiL' ; the remaining 
diametaphosphalfls are insoluble or only very slightly solubla 

(3) TnmtlafitMpkateg.~t\ie floHinm salt, Nn^PjO^. is obtained 
together with the niononiotaphosphate when niicrocosuiic salt. 
(NHJHXaPO, is gimlly hf^hid uutil the fused mass bucouie* 
ciyBtalline (Lindbom). By double decomposition other triineta- 
phospliates can Iw abtatned fmm this salt These are all 
soluble in water, including the silver salt, and tbi-y form double 
soJta such as >fsBaF,0„. The silvtsr salt may be obtained in the 

■ UuUnll. Htm. CKem. Soe. liL 973. 



form uF large tiaDHpaivDt muDoclintc ccyst&U hy allowii^ a 
mixture of Lhe eodiain sail and nilmte of silrer solution to stand 
for eome days. In ibe sanw way tbc crystalline luul salt may 
Iw ]tr«[)ar(nl tiy tlie Ribetitntioi of nitrate (but not of acetate) 
of lead for the eiivcr taUt, 

(4) TrirttMetaphoiiphaUa. The lead salt, I'bjP.O,^ is formt^ 
by treating oxide of lead with an excess of pLosplioric acid and 
beating np Ui a temperature of SOO*. If tbis is then deCD[ii> 
pMcd by sotlium fiulphide the sodium ealt is obtained as a 
t4;tniiiK<U|iboH|tlinli.-. TliK however, U not a crj-atallino cnlt 
but forms with a email quauttty of w&t«r a viscid elastic m&68 
and ou th« addition of a lai^^r quantity of water a gam- 
like Bolutioa n-liich will not pass through a filter. The 
tetraiaetaphosplintes nf tlie alkalis produce viscid prwipitates 
with the EoluUe salts of tbe ulkuliue earths, ir swliuu 
dimetaphoiaphate is fused with cupper dinetaphospliate and 
the mixture allowed gmdually to cool a double componntl 
harin*^ Uie compo&ition UuNajP^O^ is fonued (ncitmaiiu and 


{H) IfrMimetap/ioipfmUs. — Tbe sodium salt, XfieP^On, is 
obtained when fused sodium metaphosphate ia allowed to cool 
slowly. It is a crystiilline mass, deliqaesoes on exposure to tbe 
air, and produces with barium chloride a lloccnlent prw-ipitate. 
and with tUo salts of the heavy mt-tals gelatinous precipitates. 

It aUo forms characteiistic double salts containing (pinntili^s 
of monad metal in tlie ratio of five to one or tquivaleut 
quantities of dyad melal, the calcium salt, for exuiiiplc, luiving 
tlie composition Ca\}i^(l*0^ji or {'Sa?Oj)lC&'Pp^)^. 

The meta phosphates which are soluble in water harcanoutral 
or slightly acid reaction. Wlien their solutions are boiled they 
are conx-ertcd Into orthophoaphatfn. All the nieta))hosphates 
vndert;o this cbaii^ on boiling with nitric acid or when tlicy 
arc fua«d with an alkali 

The diflereut \fiTicti(!s of motapbosphalcs are derived from 
acid<t, all of which possess tlte same composition, but dilTer, as 
tbe double snlis show, from one another in molecular weight 
CoiDpouuds of tliis description are termed pt^f/mcrie bodits. 
The constitution of these hypothetical acids may he rcpreseuled 
graphically as follows : — 


MetAphmphoric Acid. Dimstaphoaphoric Acid. 

o - p— o— oa o— p— o— OH 


^1^0— OH, 

Trimetepbosphoric Acid. 
P_0— OH 


HO-0— P P-0— OH. 



Or if we BSsume that metaphospboric acid is represented by — 

= P=0 

I , then the two otbei polymers will be : — 



O =P— OH P 


\/ i I 

0=P— OH = P P = 


Pybophosphokio Acid, H^PgOy. 

301 Common phosphate of soda, or hydrogen disodium phos- 
phate, HNa^POj, when heated to a temperature of 240° loses 
water, and is converted into sodium pyrophosphate (Graham) ; 

2HNa,P0^ = HjO + Na^Pp,. 

The salt thus obtained dissolves in water, but does not again 
form an orthophosphate.and is distinguished from the original salt 
inasmuch as its solutions yield on the addition of silver nitrate, a 
white, and not a yellow, precipitate. This fact was first observed 
by Clark, of Aberdeen, in the year 1828.^ It is, however, to 
Graham that we are indebted for a knowledge of tlie fact that 
the heated sodium salt as well as the silver salt obtained from it 
is derived from an acid having the composition H^PjO^, and 
that this acid can be obtained from orthophosphoric by heating 
' Sdii\iwrg\ Journal of Science, Tii. 29?. 



it for a considerable lengUt of Umv to n temperature of 315^ 
Pyrophospliorio acid is also fonned when ei^aal molecules' of 
ortho- ood metapbogpboric Rcids are brought togetlier ou a 
water-bath : * 

HO— P— O— OH 
P— 0-OH HO, I 

+ ^p— o—on = O 


HO— P— O— OH. 

Pyrophoephoric acid forms either a soft glassy mase (Graham) 
or an opaque indefinite crystalline mass (Peligot). 

Ad nqueoiis solution of pyrophosphoric acid is obtaiDed by 
pre uip it'll iu^ tlm ao4ium salt with u solution of acetate of lend 
and decomposing the well-washed lead pyrophosphate with aul- 
phuretied hydrogen. The acid solution undergoes no change at 
the ordiniiry temperature, even whoa staodiDg for aonie lime, 
but when heated it is converted into orlhophoephoric acid. 

Pyrophosphoric acid m