PC)TAISSICJI CHLORID I S ;IrQCF,OUS L I C E T O S E
m-
J. F. SSELI.
I. INTRODUCTION T h a t potassinin carbonate added to mixtures of ethyl alco1101 and water n-ill c;iiise tliein to divide into two la\.ers has lieen knowii for centiiries, this propert!. of the salt I i a ~ i i i gbeeii iitilized by Ka~~inoncl Liill!.' in tlie tliirteentli centnr!- for the preparation of colicelitrated alcohol. Rrandes' and Schiff 3 found that iiiaiigaiioiis siilfate liad tlie same power, Traube and S e n liergq shon-ecl that t h e propertj. n-as common to a large nuinher of saltsj,and Linehargers foiuid that not onl!. could other salts be substituted for the potnssium carbonate h i t other licitiids, 1-iz. Iiropy1 alcohol and acetone could be used i n place of et1iJ.l d c o 1101. T,ineljarger foiind it possible to obtain t\.i-o-liriiiicl-pliase svstems in the case of the follon-iiig salts and bases with eth!-l alcoliol aiid water : Ak2SOd,( A ' H 4 ) J 0 4 >CdSO,, ZfL.W4> l l n S O , , AiSOH. KOH,
'\;z,Co,.
iycco,.
Those printed in italics are given also b y Traube and S e u Iierg, ~vliilethey add to the list the follon.iiig : S a l H P O , , XIgSO, K.i1( S O , ) ? .
TT'ith nieth\-l alcohol and water, Linebarger succeeded in olltainiiig two laJ-ers in the ca5e of potassium carbonate oiilj., tlioug-!i lie esperiiiieiitecl n-itli a g-reat nuniber of other salts. ITT'itIi
45s
J. F. Surll
propyl alcohol and n-ater, the follon-iiig salts gave tn-o-liyuidphase systems : SH,C1, XaC1, KC1. RbCI, CaCl,, NaXO,. S r ( S O , ) , . Li,SO,, S a , S O ; . ( S H , ) , > S O ,S. i S O , , CoSOq, CuSO,. FeSO,. F e , ( S O , ) , , CdSO,, ZnSO,, MUSO,, N a O H . K O H , NalCO,, E;,CO,, K C S , K,Fe(CS),.
ITitli acetone aiid water lie obtainetl t\vo liciuici pliases with :
LiCI, i\'H,Cl, A'aCl. KCI, RhC1. CaCl,. SrCl,, CoCl, CuCI,, UnCl.,. CH,,CO,K. (CH,CO,),Mn, Li,SO,. iI'aJ@,. ( X H 4 ) J 0 , , S i S O i . CoSO,, Fel(SO,)., CdSO, ZnSO,, !diiSO,, A>zOH, KOLY, .\ir2CO7. A*lcco,, K C S . I have cotifiriiied 1,iiiel)arger's resnlti; \vitli acetone i n the case of the italicizecl su1)staiices. His negative resiilts, lion.e\-er, are not to he taken as concliihi\.e. His procediire \vas to take n saturated solutio11 of the salt i n a tc-st-tiihe and acltl the organic liquid till layers formed or the salt pi-ecipitated. and then to repeat the esperiineiit iisiiig a salt solntioii of one-lialf the concentration. He does not state tliat he lieateti the tiilxs, bnt i n sotile cases ( e . g. KCI) lie mi1st 1iai.e done so i i i order to ohtaiii the sepal-ation. In open tilhes I lin\-e sitcceeded in obtainingtn-o laxer-5 in tlie case of the follo\viiig .substances n-liicli he gi\.es aiiioiig- those that (lo not forin t\vo la!~er.swith acetone and water: S n S O ~ . S H 4 S 0 4 ,( S H 4 ) 2 C 0 CH ,CO?Sa, also n-it11 I { ~ C in I ~preseiice of soliti salt. I ~ i a \ - calso vl)sei-~ec~ tile ~)lieiioiiieiioii in tlie case of the follo\\-iiig salts, \vhich lie did not use : S a B r , K B r , S H , B r , LIgSO,, S:i,HPO,. H S H , T a P O , . I l l .io111e otl1el. ca. , e. g-. LSO,, I:a(S(. I" and E;clo.j I find, iii ag-rcriiieilt wit 14iiieliarx-erjtliat solid 11t is prec i pit at et1 h y adtiition of acetoiie tu the nqiieoni utioiii of the salts, hut it is pos~i1)lctliat iii so~iicof tliew ca tlie foriliation o f t\vo k.!.ei-s iiiay take place a t liig-her teiliperatiires. FoI-?\\-liile it is iiiipos.4l)lt. :it rooiii tc-iliperatiii-e to g-vt t \ v o liqiiitl plia4es iu the s!-steiil potassiuiii iiiti-nte, etli!-1 :ilcoliol :11i(1 \r-atci-, I lia\-e siicceedeci in oljtaiiiiiiK the cli\isioii 1 ) ~ -licttiiig a coiiiples of tlie
tliree components in a sealed tube (see below, 11. 4/34). On the other liaii~l I got 1ieg:itii.e resiilts in tlie case of potassium iiitrate xvitli iiietlij.1 alcohol, and in the case of potassium chlorid n-ith either inetlij.1 :ilcoliol or et1:j.l alcohol. T h e esperiiiients were n;ade in each case with fift!- percent aqiieoiis alcohol m d a quantity of salt considerahlj~in escess of tlie ainonnt that n.oiilc1 dissolve a t rooiii temperatiire. In the case of potassium nitrate and methyl alcohol, the salt dissolved conipletel!~ even n-hen it \\.as so greatlj. in escess that at room teiiiperatnre it \vas merely \vetted by the liquid. Potassiiiiii chlorid neither dissolved coiiipletelj. nor gave two liqiiid layers iri either solutioii, though tlie tubes were heated to 195’. T h e influence of temperature 011 these systems lias, indeed, heen a matter of cimiiiioii observation. Tliiis Scliiff noticed that a t romii teiiiperatnre the inistiire of alcohol ant1 x-ater that di\-ided into two 1ajw-son satiiration with iiiaiigaiioiis sulfate lajbetween I j and 50 percent, while at higher teinperatiires 13,14 aiid 60 percent alcohol could be made to divitle ; Traube and S e a b e r g foaiid that the coiicentrations and relative voluines of the two layers in 11ll:jatiirated sollitions of aiiiiiioniuiii salfate in acliieous ethj.1 alcohol varied n i t h the temperatiire ; and 1,iiiebarger observed that ‘‘ a fall of a few degrees of temperatiire will liring ahont the characteristic cloudiness in a solution of potassium carbonate in a niisture of alcohol aiid n-ater on tlie point of forming laj-ers, and this cloudiness will disappear on \variiiiiig to the prei.ioiis temperatiire.” Linebarger’s deduction from this behavior of one s!.stem, that “ in general, it ma\. he stated that the lower the temperatiire the iiiore water is needed to ln-iiig abont the disappeai-ance of the laJ-ers ”, is? ho\ve\-er, unjustified. For with certaiii otlier sj-stems or even n-itli some complexes of this same sj.stein, he vioiilcl have found that a rise of teiiiperature would cause cloiidiiig which .\r.oiild disappear 011 recooling, aiid that therefore at a htc$hcr temperatiire a greater addition of water would lie necessary to caiise the disappearance of the la!-ers. Indeed. n-it11 acetone and water, the latter seems to he the more coiiiiiioii case, for of tlie salts with \vliich I have ex-
perimeiited I have found only four ( S a Z S O +9, a 2 C 0 3 ,XaZHPO4, SaXH4PO+)whose solutions in mixtures of acetone a i d water clouded on cooling. 11. THEORY
S o two of tlie three components of a sl-stem of this class form two liquid layers a t ordinary temperatures. T h e o r p i i c liquids are consolute with water ; they reach their critical points far below tlie melting-points of the salts, so a two-component system with two liqnid phases caiiiiot be obtained in the case of any of tliese organic liqiiicls with ail!. salt, anif water and salt do not form two liyiiid layers. Ab, howeI-er, it is most reasonable to ascribe the came of the appearance of the two layers to the irnmiscihility of tlie salt with the organic liqnid, we may for theoretical piirposes regard these two components as forming ( a t a high temperature) the invariant sj-stein, solid salt, two solutions and vapor. On the other liand, in \.ielv of the complete iiiiscihility a t high teiiiperatures of pot ium, sodium, aiid silver nitrates and of potassium chlorate 1 i water,' we may regard salts in general as miscible iii all proportions with ivater at their melting-points. These tiro assninptioiis bring tlie systems into Class I of Bancroft's classification of tliret-coiiii>oneiit in n-liich two liquid phases appear.' For, 1 .: being salt, 13 organic liquid, and C water, n-e hzve : melting-point of A higher than that of 13, *A and 13 forming the binary inr.ariant s!.steni solid *A9 two solntioiis and \.apor\ A x-.d C and 1: and C not forming tvio liquid phases and C iiicreaiiiig the iiiissibility of -4 and P,. One condition of tlie clas..stein uiicler Class I so far as this particular eqiiilibrinin is concerned liy taking tlie 11)-drated salt instead of the anh!-clrous salt 1
&tard. Coniptes rcn(1iis. 108, 176 ( I S S ~ ) . Joiir~Pliys. Cliern. I , 64; ( ~ 9 9 7 ) .
Potassz'zini ChZoYz'd iiz A pzicozis Acetnizc
461
as component ,4. If, now, we have tlie further condition fulfilled that ice and salt (or ice aiid lijdrate) cannot coexist iii equilibriuni with t\vo solutions and 1-apor, no '' secondar?. " quintuple point is possible and the system falls into Sub-class IC'. All the above conditions are fulfilled in the case of the sj.stern t h a t forins the special snbject of this research, tlie solid that appears in equilibriiiiii with the tlvo liqiiid phases heing iii this instance the anhydrous salt. T h e siihsequent treatment will be with special reference to this systeiii, lint i t may be generalized for all systems fiilfilliiig the same conditions. Some applications of the theory to other systems will lie iiitrodacetl. T h e temperature-concentration diagram for a sJ-steiii of this nature is represented in perspective in Fig. I and in horizontal projection in Fig. 2, the theoretical assumptions as to the miscibilit!. of the coinpoileiits a t teniperati!res not actnally attaiiiable being therein embodied. The concentrations represented iipon such a diagram are those of the liqiiid pliases. Conseqiiently, a t temperatures above which no liquid phase can exist (critical temperatures'), the s).steiii hecomes incapahle of representation on the diagram. Eacli coniplex of a tliree-cornpoiieiit q'steiii h a l i n g its ow11 critical temperatiire, tlie a c t i d diagram \vould have a surface as its upper teriiiination. Ikcause, 1iou.e \ w , we have no ineasiirenieiits of tlie critical plienoiiieiia of tlirercoiiipoiierit sj-stems lixviiig t\vo liqnid pliases aiid also liecnuse tlit. theoretical relatioris are liereby more c1e:irly indicated, I have thought it better to dm.w the diagram as if iio critical points appeared. I t ilia). be well to point out the distinction lxtw-cen this dingrani and that eiiiplo~.edby Sclireineinakers.' His diag-rani represents tlie teniperature-colicelitratioticonditiolis of eqiii1il)riiii:i nt coitstnizt $ w s s z w c , n.liile this represents those coiiclitions 01 thr qtiz'/ibi-il/iizfii-c'sszfye [f thc sysicm. T h i s di:igraiii is, tlierefore, tlie strict analogue of the plane temperatui-e-coiiceiitratioii diagram coiiiirionl>-used for two-component s\wt.iiis. It slionltl also be iiieiitioned that m y experiiiients were inade under coiidi___~______ I Zeit. pliys. Chem. 23, 429 [rSg7).
tioiis not esactly those for n.liicli the diagrani calls. Some of them ivere coiidiictetl iri corked bottles and test-tulies. tlie rest in sealed tiilies from wliicli 110 attempt vas made to espel tlie air. In the first instance KC liai-e atniospheric pressiire instead of the equililiriuiii pressiire of tlie system, and i n both cases air is present as a fourth jiiiore stricti!, a fourtli and fifth) coniponent.
1
C
7 .f
Fig.
i
In Figs. I and 2 , H represents the cryoh>.dric point for the three components, 12, 11’ and h” are the cryoli! chic points of tlie three hinarj- systems and PUP’ is the boiudar\- curve for salt, two solutions and vapor. I n tlie solid fignre, 31, 11’ and 31” being tlie melting-point of the pure components, /AI is the
jiigate point of equal teinperature tipon the same curve, the two representing the two solutions which a t that temperature can coexist in equilibrium with solid salt and vapor. By drawing the tie-lines joining these successive pairs of conjugate points, we obtain a ruled snrface j’Spcr. I n other words, the ruled surface is developed by a liorizoiital line whose motion is guided by tlie curves j P c r and j’P’cr. Between tlie ruled surface arid the dineric surface is eiiclosed the region of temperature-composition conditions for the formation of two liquid phases and vapor. T h a t is to say, any coiiiples whose composition a t a given temperature falls within this enclosed space is instable as a homogeneous ten1 aiid will divide into two liqiiid layers atid vapor. Tlie enclosed space inay therefore be appropriately teriiiecl the O ‘ ~ J Z ~ ? / * ~ sjact,. C Reyond the dineric surface is tlie region of utisatiirated solutions, and beyond the ruled surface lies another enclosed space representing instable complexes dividing into solid salt, two liquid phases and 1-apor. T h i s n-e n ~ a y call the .rl~~,~’ci-c(l;lzc’i-2C.$wco. Its boundaries are the ruled surface of the boundary cnrve aiid another ruled surface developed by the motion of a horizontal line guided aloiig tlie straight line .%.I’ aiicl tlie curve #qb’ as directrices. T h e latter ruled surface separates the stereo-dineric space froin tlie two divisions of the region of supersaturated coinplexes that divide into solid, one liquid phase and vapor. T h e results of an experiment with a complex of potassiiiin nitrate, ethyl alcohol and water may serve to illustrate the changes that take place aloiig a temperature ordinate that passes through all the spaces into which the triangular pris~ii is divided by the surfaces. A%trooiii temperature, the coinplex consisted of a saturated soliltion of potassium nitrate in j o percent alcohol and a quantity of solid salt in excess. n‘lien this complex was heated in a sealed tube, the following states were realized : ( I ) T h e complex consisted of three phases -solid salt, one solution and vapor.
( 2 j T h e liquid divided into tu-o laj.ers, making the total iiiiniber of phases four. ( 3 ) T h e salt dissolved coinpletelj., leaving the three phases - tn-o solutions aiid x-apor. (4)T h e two liquid phases coalesced, leal-ing o d y one liciiiicl and \-apor. Thiis the temperature ordinate for the complex traverses : ( I ) Tlie region behind the surface lii’rZ‘Z, ( t h e region of supersaturated solutions). ( z ) Tlie stereo-dineric space. ( 3 ) T h e diiieric space. (4)T h e regioii of unsaturated solutions. El-erT- point of the dineric surface has a conjiigate point a t the same temperatiire, the two representing the coiiipositioiis of the coexistent liquid phases. But aloiig a limiting ciirx-e n-liicli we may call the c ~ ~ s t - c z i ithe ~ u two ~ , coiijiigate points for anj- given temperature coincide, that is, the coiiipositioii of the coexistent phases are identical and therefore equal also to that of the whole liquid. T h e point u is tlie p/nz’t-juin~of the surface. Its temperature is the niiniiiium temperature at which tn-o liquid phases can coexist in siahle equilibrium with vapor, and as the point lies also on the curl-e Po-]‘,solid salt can exist in equilibrium with the two solutions and vapor a t this iiiiniiiiuni teniperature. ;1peculiarity coininoii to many, if iiot to all, of these sj.sterns of salt, water and organic liquid is that the diiieric surface extends out so far as to ol-erliaiig the bouiiclar\. ciirve pup’. T h i s is indicated in Fig. z n-here pu)’ is tlie horizontal projection of the bouiiclarj- curve, while pS’p’ is the projected limit of tlie diiieric surface. ( I have assiiiiied that the two ciirl-es meet in $Jand j’.I t is possible, however, that the!. may meet in soiiie other conjugnte points of u - aiid u)’. KO experiments have been macle to settle the question.) T h e phj.sica1 fact expressed 13)- this property of the surface is that certain solutions iiiisaturated with respect to the salt can be made to divide into two layers bj. heating. For exaniple, a complex of the composition,
us’s,
water j1 g,acetone 39 g,potassium clilorid I O g,forms a hoiiiogeiieoiis solution at 30' and at i o " , hut is divided into two liquid layers at S O @ . T h e temperature ordinate for this coiiipositioii niiist therefore pass throngh the diiieric snrface at a point between 40" and 50'. T h e same belial-ior iiiaj. be obser\-ed in the case of iiiaiij- other salts nitli acetone and n-ater. T h i s peculiarity in tlie form of the diiieric surface di.qtiiiguishes the systems possessing it from some others bdoiiging to h n c r o f t ' s Siib-Class I r . For esaiiiple, with iiaplitlinleiie, acetone and water Cad>-' found 110 iuisnturated solution that formed tn-o layers oii heating:. In such a s>-stem the limit of the diiieric surface does not overhang the boiuiciar). cnrve. T h e cliff ereiice between the two varieties of sj-steins is expressed in the projected diagram (Fig. 2 ) bj- tlie presence or absence of the ciir\.e
ps'p'
*
Froiii Fig. I it \\-auld appear that b y followin:: iip tlie temperature ordinate for water 51 g. acetone 39 g,potassiiiiii chlorici I O g,w e should ex-entually pass through the diiieric surface a second time aiid come back into the region of unsatiirated solntions. In other words, the coniples that clix.ided into two liquid laj-ers below jo" ~ o i i l dbecome lioniogeneons again at soiiie higher teinperatitre. T h i s I have not heeti able to realize with the sj-stein acetone, water and potassiiitii chlorid. On account of the steepness of the diiieric surface, the temperature at which the liqiiid becomes hoiiiogeneoiis lies so high !at aiiy rate in the case of the coiiipleses used in the fen- experiments made) as to be irrealizalile bj- iiiy method of experimentation (see p. 479). Rut by taking 11.6cc water, 3.; cc absolute alcoliol and 2.93 potassium carbonate ( = 66.40 g water, 16.8 alcohol and 16.8 g salt to 100 g soliition), I obtained a complex xvhich is a11 1111saturated solution below 40' arid above 70" and a two-liquidphase s)-steni between these two temperatures. TTitli such a q - s tem i t is possible to realize i n an open test-tube tlie formation of two laj.ei-s 011 heating aiid their disappearance on fnrtlier heating. I t will he observed that in systeiix of this class the plait-
point is tlie point of iiiiiiiiiiiiiii temperature for the coexistence of solid and two liquitl phases (aiid also for that of tlvo liquid phases). while in tlie systeiii \\-ate?, sodium cliloritl and ethylene c!.aiiid studied h!. Sclireiiietnakers' it is tlie point of iiiasiiiiiiiii teniperature for this qtiililiriiiiii,2 Tlie latter .i).steni helongs to a different class, for liei-e the appearance of tlie two 1ajw-s is diie to the incoiiiplete iiiiscibilitJ- of v-ster ant1 etli!-leiie c!.anid and the third coiiipoiieiit is siicli as to ni'ci-cns/ the iiiisciljility of the other tn-o. If we neglect the possibilit!- of the reciirreiice of two liqiiid la! ers at a liiglier temperaturt. (clue this tiiiie to the incomplete miscibility of socliuiii cliloricl \\.it11 etliJ-leiie cjaiici )> this s!-steiii collies iiiider Sub-class 3'2 of Bancroft's paper, -1being etli!.leiie, c!.anitl, B water and C sodiuiu clilorid. Tlie esperiiiieiital datti of Sclireineinaker's paper fulfil the predictions of Bancroft tliat iii the projected teiiipcrature coiiceiitratioii diag-ani for s!-stems of this Sub-class, ( I) the tn-o liraiiclies of the l,ouni:ar!. curve for solid Ai7 tn-o solutioii.5 m d \ - a p ~ rwill diverge as die!. leave the side AI3 of tlie triaiigle ; ( 2 ) tlie temperature will rise aloiig this ciirve as n-e pass :iv-ay from tlie side of the triangle; and ( 3 ) tlie teiiipernture will rise froiii the qiiiiituple point aloiig the t\vo h i i c l i e s of the boiiiidar!. curve for solid C,tivo solutions and vapor, tlie cur\-e having therefore a point of 1ii:ixiiii:iiii teiiiperature.' For \vhile the coliceiitratioiis of the eth!.lene c!-anid i t i the two liciiiicl pliases at the liiiiarj. c~iiaclruplepoint (on the side of the triangle) ;ire : Upper layer '72 g-niols to roo g-rnols Lower 2.5 '' . /
"
"
all
it1
"
( L
"
at the teniarj- quintuple point the!- ha\-e divergecl to Cpper layer 82.79g-mols to Lower " 1.99 '' "
100 g-mols "
' C
in all i
i
,
'
The teiiiperatnre of the quatlruple point is IS.j " aiid that of the quintuple poiiit 29'. a rise as lve pass from tlie side of the triangle. ;Iiicl, finally, tlie teiiiperatnre rises as we pass from tlie
quintuple point along the bou~iclary ctirT-e for solid sodium cliloricl, tn-o solations and vapor, and reaches a iiiaxiiiiiiin a t 145.5’. In assigning this sj.steiii to Snb-class 30, we h a r e assumed that sodium chlorid aiicl ethj-lene cyanid d o iiot form ti\-o liqnid phases. It would be iiiore consistent, liowe\-er, to make the same assumption in this case as in that of tlie acetone and potassiniii clilorid, i. e. to regard the two components as forming tn-o laj-ers at a temperature iiot actually realizable. T h i s assumption n-ould require that there shonlcl proceed froiii tlie -\C side of the triangle a second diiieric surface, v h i c h xvould be analogous to that of Fig. I , for here, as there, the effect of the third coiiiponent, water, is to render the other two iiiore miscible. Though it seems probable tliat not far above 1 4 j . j ” clieiiiical action hetu-een water and ethj-lene cjmiid will occur to sucli ai1 extent as iiiaterially to alter the iiatitre of the system, still i t is just possible tliat a portioii of the secoiid diiieric surface ma>-be realizable ; in other n-ords, inistiires of ethylene cyanid, water, and sodiuiii chlorid tliatclear a t or helow 145. j ” iiiaj- cloud again a t higher temperature. Eiit Sclireiiieniaker’s work shows that at least this second ditieric surface does iiot ciit the first. T h e loner diiieric surface will therefore not clifier in anj- respect from that of systems of Sub-class 30 and this application of Bancroft’s predictions is legitimate.
T i c Jsofii~i-nisarid L ~ o t i c r - r i i ~P/aiics ~Z An isothermal plane is, of course, a horizontal section of the triaiigiilar prism and the i.sot/~ci~ii~ is made u p of the cur\-es of intersection of this plane with the diiieric aiicl solubility surfaces. For temperatures, xt which oiily oiie solid aiid one liquid phase exist, tlie isotherm is a single curve (an element of the surface, I ) representing the solubility of the salt in yarj.ing mixtures of acetone atid water. For teiiiperatiires a t which oiie solid and two liquid phases can appear, the isotlieriiial plane has tlie form of Fig. 3, the isotherm consisting of the three curves LP,PSP’atid P I 4 ’ . T h e solubility of the salt -1i n water a t the given temperature is represented by the point L and tlie
Fig, j
solubility of the salt in the organic liciiiicl li? L’. (-Asthe diagrain is draw11 to represent the system alcohol, water and iiiaiigatiese sulphate, the point L’ is practicall!. coiticideiit with I;, T h e smie is true iti the sJ-stein acetone, water and potassium clilorid]. The field CLI’SP’L’I3C is a section of the region of unsaturated solutions, PSI” P,a sectioii of the diiieric space, aiitl the triangle ,\PP’a sectioii of tlie stereo-diiieric space. Therefore a t the teinperatiire of tlie isotlierin. coiiiylexes ~ v h o s econipositions are represented 11y points n-itliiti tlie field CI,I-’SP’I,’HC are stable as lioinogeneotis liqiiid (and vapor) ; coinplcses n+ithin the fields, &ALP, ;1I,’P’ are instable as honiogeiieoiis liquid and break c l o ~ i into i solid salt and solution represented 1)y points of the curves LP, L’P’ respectively ; complexes n-itliiii the triangle XPP’break c l o ~ \ ~into i solid salt and two solutioiis hax-ing the composition P,P’, atid complexes within the diiieric field PSI” P break into tn.0 solntions represented by conjugate points
of the cliiieric curl-e PSI”. S heiiig the m>st$oi/zt the point of the crest-ciir1.e for this temperature - the coiiipositioii of tlie lower la!-er in a s!*steni of two liquid pliwes aiid vapor \vi11 11e denoted liy a point S lietween Saiid I’, that of the upper la!.er 11)the conjugate point S’ liet\reeii S aiid I”, lvliile the coiiipositioii of the whole coiiiplex will be denoted 11)- tliat point of the tieline SS’, n-liicli \voiilcl l~ tlie center of g-rai.it!- of the ivhole mass if the iiiass of the lower la>-ern.ei-e situated at S and that of tlie upper la!-er at S’. If, to a mixture of organic liquid and \vater, ~ l i o s ecompositioii is represented 11)- a point K lietxvcen \- and Z, \ve coiitin~ioiirl>.add salt, tlie coiiipositioii of the mixtiire \vi11 \-ar>. a l o i i ~ the liiie K-1 iiiitil it readies the diiieric cur1.e PSI’’, nhere the soltitioil \\-ill di\-ide into tnv liciiiid pli oi coiiipositioiis represented b y conjugate points of tlie diiieric curve. A i sthe coiiiposition of the n-hole coniples proceeds alon:: tlie line K-1) tlie two la!.ers will differ more and more in coiiip~~sitioii, the coiijiigate points separating farther aiid fartlier. At the same time, the relati1.e m(iss(~s of the tn-o la>-ers will \-ai-!. coiitiniiousl!., 1:ecause tlieJ- must ali\-a!-s lie sucli that their ceiitei- of grayit!- will lie a t tlie intersection of tlie tie-line with the line K.1. IT‘lieii the coiiipositioii of t h e ivliole has renclied tlie i x l u e R,the coiiipositioiis of the two l a ~ will ~ ~ hes P, I”, and their masses as 1°K : PK. Further addition of salt will ha\-e iio effect on either the conipositioii or the relati\-e iiiasses of tlie two pliases. I t is evident also that mixtures of the organic liqiiicl and n-ater ha\-iiig coiiipsitioiis between C and ’i’ or between Z and 13 caiiiiot he made to divide into two la!-el-s h!. addition of salt. 111 both cases we should get first a homogeneous solution, then a solid salt in eqiiilihriiini with a 1ioiiioKeneous soltitioil of a composition represented by a point of the ciirve LI’ in the one case or of the ciirve L’P’ in the other. I n like iiiaiiiier, S and 11 being the points of iiitersectioii of 131’’ and 131’ with tlie side -IC,i t is evident t h a t we get difiereiit results by coiitiniioiis additions of org-aiiic liqiiid to acliieous salt solutions of difierent concentrations. In the case of the inost dilute solutions, C to S,we ~
get first homogeneous solutions, then solid salt and a solution of the curve P’IZ. Jlore concentrated solntions, AI to S , gi1.e first hoiiiogeiieous liqnid, then t\Yo liciiiid phases of chatigiiig c o i n p sitiori ant1 re1atii.e niasses, tlieii solid salt and two liquid phase5 of constant composition h i t 1-aryiiig relative inasses, and fiiiall!. solid and solntion of tlie curve RP’,tlie iiiass of the lower la ye^. having now lieconit zero. Solutions of coiicentratioiis betn-een ?,I aiid L ( t h e latter being the coinposition of the satiirnted aqiieoiis solution) give first hoiii(geiieoiis liqiiitl, then solid salt aiici solution of the curve I,P, theii solid salt and two solutions. the iiinss of the lower la!-er coiitinuonsl!, clecreasiiig, and finall!. solid arid solutions (of tl:e cur\-e I i P ’ , the lower layer lia\.ing disappeared. 1-erj- f e n quantitative rsperiinents have been made n-it11 systeiiis of tliis clam. (If iiieasurenients a t constant teniperattire there are a fen- 1 ) ~ . Schiff,’ Tranbe ancl Senberg,‘ I h d lander,; and L i i i e b a r ~ e r . ~ Schiff oliseri-ee. that :it rooiii teniperatnre aqtieous alcohol of froiii r j to 50 p2rceiit strength separated into two layers 011 satnration witli i i i m i g a i i c ) ~sulfate. Table I gives his iiieasureiiients of tlie pel-ceiitage weight of crj.stallized salt (lIiiSOt.i H z O in the satiirated solutions. T h e data for tliis sented in Fig. 3? \\,liere the hydrated salt is taken as one of tlie coiiipoiieiits. .As Schiff‘s iiieasiireiiieiits were of saturated solutions in all cases, tlie!. xive the points I>, 1)’ niid points of the curl-es LP and P’13. Tliey can lie iiiiiiiecliatelp plotted on the tiiagrani froiii the f i p r e s of Table I by iiiarkiiig off tlie giveii percentaxe of salt on the straight line joining the point A with tlie point for tlie strength of alcohol. If iiiore accurately iiiacle, Schiff‘s iiieasiireiiitiits of the compositions of the two layers \vould iuic1onl)tedly have been esactlj. the saiiie in the 2 0 , 30, m c l 30 percent alcohol. .A few points of the diiieric ciirve are obtained from tlie iiieasiireiiieiits of Linebarger. Xs lie worked Lieb. Ann. 118, j ~ (n1 5 6 1 ) . Zeit. phys. Cheiri. I, 509 ( I S S T ) . .‘Zeit. pliys. Clieiii. 7, 31s ( r S 9 1 ) . - h i . Clietri. Jour. 14,jS0 ( r S 9 2 ) . I
at 20’ liis results ilia! faill! lie plotted 011 tlie 5ame isotherm a< Schiff Is. Table I1 g i l es 1,inebarger’s results, recalculated 011 tlie basis of grains I\ ater, nlcohol and I i r clrated manganous sulfate respecti1 el! to oiie hnticlred grain3 solution. T h e letters in Table I and 11, refer to Fig. 3. T h e poiition of the point P’ is uncertain. I I i a ~ e plotted Linebarger’i last cletermiiiation a5 probablj tlie nearest approach to that point, though he does not ineiitioii that salt wa\ precipitated in the experiment. -1s alreadj intimated, Schiff $ 5 anal! ses of the upper la! ers in tlie 2 0 , 30 and 40 percent alcohol do not accord nitli the theor!. The same is true of liis anal! sis of the 50 percent alcoliol solution. But the discrepancies ilia1 eaiil! be due to experimental error. I t appears from tlie cliagrain (points S and 11) tli‘it t h e range of iiiaiigaiioiis sulfate solutions that can lie made to dil ide into two layers at room temperature by addition of alcohol is 5 ery n ide, rnnning from solutions containing about 3 to solutioiis containing over 51 percent of the tetralijdrate, i. e. 2 to 34 percent solutions of iiiaii,vanoiib sulfate. Schiff $ 5 observation that in presence of the crystals the s.olume of the tipper layer is the greater the stronger the alcohol is evidentl! in accord with the theor!.. For the nearer the point K approaches Z , the qreater is the ratio PR PR’. Traiibe and S e u h e r g determined a number of conjugate points of the dineric c u m e of the 333 isotherm of the sjsteiii alcohol, water and ammonium sulfate and Bodlander deteriiiiiied tlie position of the intersections of the dineric with the salt solution ciirves (i. e. points P, P’, Fig. 3) on the 15‘ isotherm of the same s! stem. T h e methods of the phase ride having been already applied to these nieasureiiients by Schreineniakers,l i t is unnecessar! to discuss them here. Linebarger conceived of the layer formation as taking place in systems of salt, a n organic liqriid and water only witliin certain limits of composition and defined the ‘‘ upper ” limit as ( ( t h e limit attained vi-hen the forination of a lajyer is rendered impossible by the presence of too inuch organic liquid ”, and the
’ Zeit
plir
5
Clieni 23, 65 g ( 1S97)
Pof(yssiiijti
LXlwid
2'12
a-lqiicoiis
173
foiit~
lo\\-er " liiiiit as tlie poiiit \\-here a layer censes to fori11 oii x c o u i i t of tlie pieseiice of ;iii e s c of water." His iiietliod of tleterniiiiatioii of tht: lon-ei- la!-er was as follo\vs : 17ar!.iiig quantities of orgaiiic liquid and water were added froiii burettes t o a titratetl solution of a salt until a tlrop of \ v a t u 1vould clear iip the iiiilliiiiess cauied 11~-a tlrol) of alcohol." It is e\-ideiit that this pi-ocedure give..: ;i poiiit of tlie diiieric cur\-e. For he hegin.: \vith :I point 011 tlic side -ICof the Li-iaiigle a i i t l proceeds in a hti-aig-lit line toward I3 i 11). addiiig alcoliol i till lie has o\-ei-steppetl tlie diiieric tun-e, t l i t n lie proceech in a straight line to\\-ar(ls C (addiiig \vnter) until :ie has 3%-aiiioversteppecl tlie ciir\-e mid so iiio\.es in a11 e\.er-iiarron-iiig zigzag iiiitil he has apl~roacliedso close to the diiiei-ic curl-e that a di-op of oiie liciiiitl C 'T -,I ses :i c1i:uig:t. i i i m e directi8xiand a rlrop of the other caiises a cliniige in the other direction. T h e tables gil-eii in Liiieharger's paper ai-t~therefore data of t h e c!iiieric c i i i - ~of~ tlie 20" isotlieriiis of the \-arions sJ-steiiis. His iiieastireineiits are liiiiited to a siiiall portion of the curve :tiid iio coii,iuxate points are deteriiiiiied. 111 atteiiiptiiig to deteriiiiiie tlie upper ' ' liiiiit, 1,iiielm-geitook a certniii ~-olui1ic~ of salt soltition aiicl added the org-aiiic liciiiicl iii siiiall qtia1it:ties iiiitil tlie \-oliiiiie of the lower 1 a j . e ~ liecaiiie zero. -1alaiice at tlie cliagraiii n-ill slion that this result caiiiiot lie attaiiied \I ithotit precipitntioii of salt iiiiless a line joiiiiiig soiiie point o i i AC \!-it11 tlie poiiit I3 lias tn-o iiitersectioiis \\it11 tlie cliiieric curve aiid iioiie with the line l>I''$ Tvliich caii occur only in case the cliiieric curve which has been teiidiiig don.iin-arc1 t o x m l tlie side CI3 liegins to tend upward \!.lien lve get near the .side .\I:. In geiieral this is riot the case :iiid 1,iiielxirger fouiid that precipitatioii of salt pre\-eiitecl his attainilia tlie upper " liiiiit of 1aj.er-foriiiatioii iii all systeiiis but ( , l i e potassiniii carbonate, etli!-l alcohol aiid ivater. In the c n , of ~ this sJ-steiii, either tlic: diiieric ci1rT-e 113s tlie peciilix- form just referred to or, what sceii1.s more probable in T-ie\v of tlie fact that " ci->.stalsnppeai-ed as sooii as tlie I:i>.ei-clisappeared Idineliarz-er ivas reall!. deteriiiiiiiiig points on a iiietastahle tsteiisiori of the tl i ii er i c c 11rx-e. ((
L '
b b
' L
~~
''?
471
J. F. S?l€ll
An interesting confirmation of the theor>-of the tie-lines is afforded bj- some ineasiireiiieiits by Traube and Xeuberg of the variations of the conjugate solutions of a complex of aininoniiim sulfate, alcohol and water with the temperature. T h e y added 250 cc of 99.6 percent alcohol to 7 j o cc of a solution of ammonium sulfate, containing 340 g to the liter and analyzed the two layers into which the mixture divided a t four different teiiiperatures. Their results recalculated into mass-percentages are given in Table 111. -According to our theory the tie-lines joining each pair of conjugate points must pass tlirough the temperature ordinate of the coinposition of the whole complex. In other words, the horizontal projections of the four tie-lines must intersect in the point that gives the composition of the whole complex. If the tie-lines be actuallj- dran 11 on a triangular diagram the! are found to intersect, as nearl! as one can tell, in the point Water j 8 j A l C O l l O l IS I Salt 2 3 . 2 T a k i n g the specific gravity of the aiiinioniiiiii sulfate solution used as 1.16s and that of the alcohol as 0.795, I calcnlate for the composition of the complex as made up b?. Traube and S e u b e r g : Water j j 86 Xlcohol 18.42 Salt 2 3 . 7 2 T h e diagram shoivs also that 15 it11 rising temperature there is an increase in the relative mass of the lower layer, i. e. the ratio R’X’ R’X (Fig. 3) increases as the temperature rises, and Trauhe and S e u b e r g found that wit11 increasing temperature the lower layer increased in volniiie, while the upper layer decreased. TABLE: I 1Ianganous Sulfate, Alcohol and ITater - Schiff Strength of alcohol
-
56.2j 51.4
0 IO
20
30 40
50 60
1
, I
Upper layer
Loner layer
2.2
47
1.66 1.37
I 2.0
~
Point on Fig.
Pct XnSO, 4H,O
0.66
48 48.6
I
L
I
I
I
P
I I
k
j
TABLEI1 hlanganous Sulfate, Alcohol and TT'ater - Linebarger, g rvater
g alcohol
j 5.86
30.03
g salt ( X i i S 0 , . ~ H 2 O Poitit ~
20'
C
011
Fig. j
~~
13.59
52.25
49.41 45.31 42.j 6
14. I I 4.16
~
~
I
a
6
~
2.91 I .66
47.66 53.00 j6.24
C
d
1.20
P'
i
TABLE111 Xmmoniutn Sulfate, Ethyl Alcohol and Water
-
Traube and
Seuberg Composition of 100 g solution r p p e r layer Lower layer g water g alcohol g salt g water K alcohol
Temp
16.6"
52.80
33 .oo 41.8"
47.99 47.34
jj.j3
,
Ij.90
40.21 46.75 47.67 49.47
6.99 j.26
'
4.99 1.63
, '
60.33 61.02 61.16
i
61.j9
g salt
29 AS
10.19
9.80 9.71 9.46
29.18 ,
29.10
28.95
111. EXPERIMENTS
I n order to gain a more accurate knon-ledge of the shape of the dirieric surface for the system acetone-water-potassinm clilorid, I have made the following experiments : I. ,1 series of measurements of the temperatures at which different unsaturated soliitioiis of the system divide into t\vo layers, i. e. a deteriiiiiiatioii of the points at which given teiiiperature-ordinates cut the diiieric surfaces and so pass from the region of unsaturated solutions into the diiieric space. 11. A few experiments to discover whether dix-ided solutions become homogeiieons again a t higher temperatnres, i. e. Lylietlier the temperature-ordinate passes a second time througli the dineric surface- this time from the diiieric space to the region of unsaturated solutions. 111. _1Ieasnrenietits of the temperatures of division of saturated solutions, i. e. determination of points of the bouiidary curve. IT'. Measurements on the 30' and 40" isotherms.
The.
.1h7
tL,rioi ~ i
Tlie potassium clilorid used i n a11 the espei-iiiients tlescribed in this paper \vas carefull>-prifiecl 1 ) ~ . three recrystallizations. tlieii fused in a platiiiuin dish. I t p 1 - e n o reactions for sulfate arid iiotie for iiiagiiesiuiii aiid a11 anal>-sis b y precipitation with silver nitrate gave : KCI taken
.IgCl fount1
0.5359 g
1.0s13 g
Calc. for piire KC1 1.032
g
Chie portion used in soiiie of the experiments of Series 111 was iiiade from acid potassiuin carbonate. ;InalJ-sis of this portion gax-e ;
r; c 1 t :Ik e 11 0 .~ ~ 3 6 g0
.lgC1 fount1 I.+IZj
Calc. for pure KC1
g
1.4115
g
Tlie acetone vas dried ox-er calciuiii clilorid niid fractionated. Tlie portions used distilled within half a degree.
( a i Temperature of Division of Unsaturated Solutions T h e salt n'as neighed out froin n-eigliiiig tithes aiid the water aiicl acetone added from linrettes. T h e coiiiples \vas then heated aiid the temperatiire at n-hicli the cloiicliiig took place noted. TYliei-e the temperatiire of division w a s lon-, tlie iiieasiireinents lvere iiiade in a \vide test-tuiie provided with a cork through which the tlieriiiometer passed. For liiglier teiiiperatures, pressure flasks were tried a t first, ixit, these proving leaky, sealed tulles were iised, the tubes being heated in a n-ater- or oilbath.' Here. of course, the temperatiire iiieasiireiiieiit was not as acciirate as for tlie lower teiiiperature, the theriiiometer beiiig iiiiiiiersed in the l n t h instead of i n the iiiner liciiiicl. In all cases a niiinber of olxer\.:itioiis of the temperatiire of diI.isioii v x r e iiiacle. For tlie lon.er temperatiire, these ol)ser\-atioiis did not in general differ froiii one another 1 1 ~iiiore tliaii a few tenths of a deg-ree, but iii the case of tlie solutions in 3 0 percent acetone the cloiidiiig was iiiclistiiict aiid the teiiiperatiire of division, therefore, much harder to distinguish. Tlie error iii all tlie
' For the
teirilxratures nho\ e I jo" an air-liath was used.
temperature readings for this strengtli of acetone :tiid iii the higher reatliiig for other inistnres i i i a ~ .aiiiouiit to iiiore than o:ie degree. T h e results are giI.en in Tahles IT--IS. TheJ, .;lion. that n-itli rising temperature tlie diiieric siirface approaches the
acetone-water plane of tlie triangiilar prism. 'I'al~le S shows tlie nearest apliroacIie:+ to that plaiic that Jvere realized and so gi\-cs an approriiiiatioii to the position of tlie li~iiit-cur\.eof tlic projected diagram - the cur!-e I S ' ] ' of Fig. 2 . Tlie liiiiitcurl-e as thus approxi::iatel!- cleteriiiiiied is slion-ii together \\it11 the bouiidarj- curl-e in Fig. '4.
-
63.46
1
62.00
I
61.75 61.68 61.73 61.19 60.50
9.36 11.43 11.79 11.92 11.55 12.62 13.60 13.71
27.20
26.57 26.47
~
~
60.40
26.43 26.46 26.22 25.93 25.85
j4.00
36.00
53.84
35.90
53-48
35.65
1
'
I
I '
47.12
46.96 46.66 46.61 46.54 46.35 46.06 45.75
I
1
. I
a *
.'
'*
150'
( ' 290'
103: 100
SI"
6z3
10.00
~
10.28 39.0
10.87
~
47.48
5.04 5.79
47.12 46.96 6.69 46.66 6.So 46.61 6.94 1 46.54 7.23 46.38 46.06 I 7.90 i 8.50 45.75 Saturated solution ~
6 '
67'
Temperature of tlirision
Composition of roo g solution g salt g water g acetone
47,48
S o division up to 2g03
1 1
__
1
No division up to 150'
1
97.ja
76 57.2 ~
I 1
56 52.6 47.4 35.4 27.4 ( ? ) Metastable
32.6
TABLE 1-11 Temper at II re of Division 60 pct acetorit. Temperature of division
Composition of 100 g solution g acetone g salt
g water
jd.SO jY.42
2.97
58.20 5 7.64 57.49 57.21 57.25
38.20 j8 oj j x 04
3.95
4.32 4.70
4.69 4.79
:;::?i
3S.00
37.95 37.78
4.51
5.27 56.96 SR t u ra t ed s 01 II ti on
TABLE VI11 Temperature of Division 70. I 2 pct acetone Cornpoiition of 100 g solutioii g acetone g salt
::Tvater 29.24 29.19 25.16 29.14 29.14
6S.61 68.j o 68.44 68.37 68.33
Ternper,iture of divisioi3
2.13 2.30
2.41 2.48
'
I
2.j3
Saturated solution
,
i o pct acetone
Saturated solution jj pct
jj . 6
acetone
Sat u rated sol u ti on
39.0
TABLE IX Temperature of Division 80 pct acetone Composition of 100 g solution g acetone g salt
Temperature of cliviaioti
g~ater
_ _
19.90 19.88 '9 84
19.82 19.80
I
79.60 79.52
;E; 79.21
1
Saturated solutio11
0.jj
I IO. j
o 65
95 67
0.so
0.93 0.99
1
55.5 45.8 45 6
380
30
11,s
50
~
Between
j.O
60
2.9
80
0. j
and j.S
( b ) Attempts t o Realize Clearing L i iiuniber of tlii%letl uiisaturated solutions Jvere heated to higher teiiiperatures to cleteriiiiiie ivhetlier the two licitiid phases becoiiie one a g a i n .\ lleaker IWS iisetl as ai1 air-bath aiid the sealed tulles were shake11 l)!. iiieaiii o f \vires u-rapped about tlieiii ant1 pi-o,jectiiig tliroiigli the xilmtos coi-er of the beaker. ITitli carefull!- iiiacle tiilxs, it \ w s found pssilile to reach :I teinperature of 2,jO' iii this \vay, h i t \\-lien lientecl to joo', tlie tubes iiiixriabl!- burst. It is iiot kiio\vii to ~vliatexteiit decoiiiposition of acetoiie a t Iiigli teniperntures may alter tlie eqiiilihr i m i between tlie pliases. T h a t tleconipositioii does take place to ai1 appreciallle extent is slionii b!- tlie coloratioii of the liquid in tlie tulles. The following coiiiplcses reiiiniiied divided at aliont 300' :
(I) ( 2 )
TT'ater 60.7: q Acetone 26.04 g Salt 1 3 . 1 9 g (30pct acetone) '' 46.30 g 4€.30g ' ' 7.40 g (jopct acetone) "
TTheii tlie approximate position of the limit-a1rx.e (Fig. 4) had been deterniiiied, a feiv coiiipleses in the neighborhood of the cur1.e were clioseii iii the hope that they would become hoiiiopieoiis at realiza1)le temperatiires : ( 3 ) TT'ater 47.0 g
Xcctotie 47.0 g
Salt 6 . 0 g (jo pct acetone)
a11d (4)
'*
4;.1g
reiiiaiiietl divided at
' >
47.1 g
' '
j.8 g
(j0
pct acetone)
2 20'-230".
(j) TT'ater 61.6s g Xcetoiie 26.43 g Salt 11.92 g ( 3 0 pct acetone) yiliicli did not di\.ide till it liad reached a teiiiperatnre of nearl!. 100' nplieai-ed to be lioiiiogeiieoiis allos-e ISO', 110 second layer k i n g i-isible and 110 cloitdiiig lleing caiised 11). shaking. But
tlie \.oliiiiit; of tlie upper la!.ei- was so vei-!. siiiall as to make i t difficiilt to decide i\-hetlier the t\vo had reall!- co:ilesced, aiitl the ~\.ideiicesof decoiiipositioii n-ere .;pecinll!- iiiarked i ii this tiihe. It is therefore iiot claiiiietl that recleariii:,. l i x becii certaiiil!. realized iii ail!. coiiiplex of the sj.steiii potassiuiii cliloi-id, acetone s aiid vxter. T h a t it caii lie realized in the a i ~ n l o g i ~ usj.steins, potassinin nitrate, etli!-l alcohol aiid n-ater aiitl potnssiiiiii carlionate, eth!-1 alcohol aiicl \vatel- is slion-ti b y tlie esperiineiits tlescrilied above j pp. 464-4661, ( c ) Temperature of Division of Saturated Solutions -The
Boundary
Curve
Iii deteriiiiiiiii:,. the teiiiperatnre of divisicm of satni-ated solutioiis, a difficult!. is met with. Here oiie caiinot make one's 1-eadiiig-s1 1 ~ lieatin:,. the tu?ie coiitaiiiiiig soliitioii :iiid salt and ol)m-\-iiigthe te1iiper;itnre a t \rliicli the liqiiid cloiids, for the soliibility of the salt increases TI-itli tlie teiiipei-attire aiid the chance.; are that the soliitioii rvill iiot be satiirated \vlieii tlie clouding occurs. Coueqiieiitlj- it is iiecessar!. to lieat the tuhe to a temperatiire abol-e tlie teiiiperatiire of diT-isioii of tlie saturateti solution aiid then, shaking it as it coolsi, ol)sei-\-e the tciiiperature at which the cloudin:,. disappears. If the tiibe be cooled i-apidl~.\a temperatiire l ~ l o wthat of the lioundar>. cur\-e i,q reaclietl, a iiieta,stable exteiisioii of the diiieric snrface iiito the re:,.ioii of the supersaturated solutions heiiig realized. Such n state is realizable e\-eu in the presence of ail excess of solid salt, for the crj.stals foriii ,ilo\vl~.aiid a teniperatiire 11clon. that of the stable eciiiililii-iiiiii is easilj- reached before cleai-iiig takes place. The coiiipositioiis aiid teiiiperatures of divisions of the saturated solutions are giyeii in Table S I . T h e coinpositions \vere tleriyed froiii the data of Taliles IT..-IS ti\- plottiii:,. tlie \.ariation o f the teiiiperatiire of di\-isioii with the salt-coiiteiit of the 1111saturated solutions ai-:d estrapolatiiig for the o1)served temperature of diyisioii o f tlic: satiirated solution. T h e relati\-e pi-opoi-tioiis of acetone and \\-atel- i n tlie soliitions n-ere, of coiirse, alrc.acl!- kiion.11. 011 the projected trian:,.iilar tliagraiii the l~ountlaryciirve, so fr.r as I have deteriiiiiied i t , lias the position
slion-n in Fig. 4. T h e data of Table SI plotted n-ith ternperature and strength of acetone as coordinates gii.es the curves of Fig. j,which may also be regarded as traced upon the nater-
Per cent Acelone. Fig. 5
acetone face of the triangular prism hJ- the horizoiital line which moves upon the salt-temperature a s i s and the l ~ o u n d a r ycnrve as directrices. Sncli a curve might he nsecl i n the estiiiiatioii of the strength of aqueous acetone. T h e error dne to the difficult>. of deterniiiiing accurately the temperatiire of dil-ision of saturated solutions coiild he eliiiiiiiated h!. making the readings aln-ays under the saine conditions, hut at best the method would be applicable onl!- to inistiires of sa!- between 2 0 percent and ti5 percent acetcne not containing any third substance and n-ould not be verj- acciirate for niising lxtn-een 50 percent and 60 percent acetone liecause of the flatness of this portion of the curve.
TABLE XI Temperature of Division of Saturated Solutions pct acetone
26
30
Temp of division
Composition of IOO g solution g acetone g salt
g water
...
....
....
59.36
25.44 35.47 45.97
I 5.20
68.25
2.66
,
40
53.21
50
45.97
60
70 r -
13
37.86 29.09
....
j6.So ,
*..
II
.32
S.06 5.34
.. .
I .oo 19.80 i9.20 so -411experiment to determine the effect of a further increase of temperature 011 a diL-ided saturated solution ~ n n ylie here described. A portion of 7 j percent acetone was heated in a sealed t u l x lvith a quantity of salt iiiore than sufficient to saturate it at any temperatiire realized. ;Ihoi.it 2 3 0 3 , tlie upper liquid phase became identical n.itli the vapor, the lower liquid phase reriiaiiiing. On cooling, tlie upper phase diyided into liquid and vapor \Tit11 the turbnlent clouding cliaracteristic of a critical point.
( d ) The Isotherms T H E 3 0 3 ISO'I"ER3I
- I t 30', two liquid phases do not appear. This isotherin, therefore, consists of a single cur\-e representing the solubilitJ. of potassium chloriclI in 1x-yin.g niixtures of acetone and water. In tlie solnbilit;; cleterminations I used sniall bottles that had been steamed out.. T h e acetone solutions n.ere macle up by weight ant1 with tlie finel!--powclered salt were heated to 40" for seven hours \\-it11 frequent shaking. T h e bottles were then transferred to an Ostn-ald thermostat set at 30'. ,liter the!. had stood over night, salt had crystallized out from all these solutions, slion-itig that the)- were saturated. T h e 40, jo ant1 6 0 percent acetone soliitions were still dil-ided into tn-o layers but became homogeneous 011 shaking. T h e bottles \yere left standing in the thermostat t n o clays longer before tlie n n a l ~ ~ s ewere s I The solubility of potassium clilorici i n ivater at 3oJ appears from I ~ J nieasurements as 27.49.5 parts in 100parts water. IIultier, scheik. Verh. 1864, 39, fount1 37.4, and .indre2i, Jour. prakt. Chetri. 1 3 7 , jju (ISSA). got h y interpolation of his results j i . z ; j .
-
the dineric curve PSP’. For, if to 9.11 aqueous solution of potassinin chloricl represented l q . the point 31, we contiiiuousl>- acid acetone, tlie coinposition of the coiiiplex will T-ary along the line :\I13 and the solution \vi11 1-eiiiain lioinog-eneous until the point I, is reached, when it will divide into t x o 1aJw-s. If, then, we know tlie composition of tlie original aqueous solution (11) aiicl the quaiitit!. of acetone added, tlie point L is deterinined. T h e points of the tliiieric curl-e so obtained are given in Table XIV. T h e compositions of the solutions that just divide at 40‘ are there expressed in two na!.s : ( I ) For plotting 011 rectangular coordinates, as grains water a i d acetone respectively per graiii salt ; ( 2 ) For triangular coordinates, as Eraiiis of each cotiiponeiit per liunclred grains solution. I n calculating tliese resiilts, the specific grax-itj. of water at room temperature was taken as equal to unity and that of acetone as 0.792, the value gil-en in Laiidolt and I3oriistein’s Tables for acetone at 19.8” a s compared with water at the saiiie teinptrature. X nuinber of pairs of c-oiy‘ic,rrntc points of the clineric curve were determined. T h i s was done by the followiiig method : T h e data of Table XITv were used to plot a curve with acetone per gram salt (x)and ivater per gram salt (1))as coordinates. two-liquid-phase sj-stein having been allon-ecl to coiiie to equilibrium a t 40” C,portions of each layer ;\-ere pipettecl off and weighed. Their salt content was then cletermined by evaporation and the cliffereiice gave the iiumber of grains of acetone aiid water together. Reduced to one grain salt, this gave the value of x 3’ and reference to the curl-e enabled one to deteriiiiiie what values of x and 1’ gave the found value of .T’ y. T h e cotiiposition of tlie con,jiigate phases is given in Tahle XV. A n approxiination to tlie position of the point I’ can be obtained by producing the salt-solution curve, K P , and the diiiei-ic curve to their intersection, and in tlie same way the point P’ can be found by producing HP’ and the dineric curve. 011either tlie rectangular or the triangular diagrain, hcwever, these approxiinations are very rough. I obtained a more accii2-
rate determination of the points liy e\-aporatiiig :I portion of each of the two liqiiid phases that existed in eyuilihriuiii with solic? salt, so deteriniiiing what percentage of the solution coiisisted of water and acetone together. and then fiiicliiig from Table SI (Fig. g) what were tl:e ~ r l n t 2 ' ; 'quantities ~' of acetone and water in the solutions t h a t coexist with solid aiid a second liquid phase at 40'. -1direct ohseri-ation there taliiilated xiyes 30 percent acetone as one of these atid iiiterpolatioii sho\vs that ;6 percent acetone is tlie other. T h e foriiier will, of coiirse, lie the lower la!-er. E~aporatioii-aiinl!.se~of the lower la\-er were made i n the case of tlie 4 0 ~jo and 60 percent acetone solutions and p l - e as an al'erage 84.23 as the percentage of acctoiie aiid \vater in this layer. For tlle upper la!.er, an average from the 50% 60 and jo percent solutions p 1 - e 9S.g j percent. Hence the figires give11 in Table XT' for the coinposition of these coexisteiit phases. T h e follou-iiig d ~ d u c t i o i i scan be drawii froin the diagraiii of tlie 40" isotliertii : I . -1t 40" aqiieoiis soliitioiis of potassiiiiii clilorid of froiii 5 to 21.5 percent streiig;tli cain he made to dil-ide into two liqiiid layers bj- addition of a sufficient quantity of acetone. From weaker or stroii,yer solutions, salt nil1 be precipitated. lye 1iai.e already seen tliat the acetoiir-\vater illistiires that caii be iiiatle to divide 11~.addition of potassium clilorid lie betweeii 30 and 76 percent acetone. 2. T h e crest-point S lies betlveeii / aiicl /'. ?'hiis there is a solution of ;I coiiipositioii of about j 0 percent acetone, 43 percent lvater, niid j. per8:eiit salt that an iiifiiiitesiiiial additioii cf salt or of acetone \vi11 came to dil-ide into two hj.ers of aliiiost esactlJ- eciiial coiiipos-itioii. 3. T h e point R being the iiiiddle point of the line PP',the line BR produced cuts the side A I C of tlie triaiigle at alioltt I j percent salt. and the line * l Z K produced cuts CB at j j percent acetone. Therefore, if we liegin with a 17 percent solntion of potassinin clilorid ai16 add acetone till salt just begins to precipitate, w e shall h a r e two liqiiid layers of equal mass, atid we
get tlie same ti\-o In!.ers 1 ) ~ . sattirating 55 percent :icetone \\.it11 potassiiiiii cliloi-id. Tlie coinpositions o f the cc~iiiplexes tliat dii.idc into In>,err of equal tiiass \r-ithout pi-ecipitxtion of salt is gi).eii 1 ) ~ .the 11iicl~llepoints of the tie-lines coiitiectiiig tlie different mirs of corijngate points.
Curve K P 0
71.3r
3
69.62 67.8s
9.09
!
0.00
2S.69
R.67 6.79
26.72 25
33
15
hj.ij
1I.jI
21 1 3 ' 34
20
62.9;-
1 j . j j
21.28
80
19.81
8j 90 95
14.94
S4.66
0.40
10.00
89.84 94.96
0.16 0.07
Curve P'A 79.34
4.97
IO0
0.00
:i' acetollc
1.95 3.I6 4.05 j.11
6.63 7.$ 3
I O . 7') 12.88 18.62 2 2 .j 2
28.47
IOO.00
o.,ji:
0.00
Fig. S
tlie esperiniental re.i;ultx of Series I and 111, n-itli the exception of tlie poilit I;which is taken froiii .-liidreii's measureriients of the soln1iilit)- of potassiuin cliloricl in xater. The sources of the figures are indicated in tlie table. Points a-f are obtained hj. iiiterpolation on ctiri.es for each acetone n-ater-mixture, tlie coordiiiates being temperature and g salt per IOO g solution. Points 1' and P' I ha\-e located by producing the diiieric curye to its iiitersectioii m-itli the lines joiiiiiig the poiat Ior ptire potassiuiii chlorid to the point for 2 j percent aiicl 81 percent aqiieous acetone. It will be observed that both the range of acetone-water inistiires that can be caused to divide by addition of salt and the rang? of acliieoiis salt solution that caii he caused to dix-ide b!- additioii of acetone are greater at 50' tliaii at 40".
T . ~ B LX1-I E Isotherin 50" C pct ,AICetOlle
Compositioii of roo K soliitioii g n..iter g acetone g silt
l'oint 011 curve
Source of figures
Dineric Curve
i
30
a
40
b
50 60
c
1
d
I
70.12 80 S I 2k
25-26 0
c
1
'
f 9'
P I k
50 91
5404 46 46 38.25 29.22 19.81
1
25.67 36.03 46.46 57.37 6S.56 i9.25
Table 11-
14.42 1 ~
9.93
7.07
4.3s
1
('
2.22
I
0.94 Saturated solution
' i
IX
( (
XI
I'
XI
1
' /
I
1
Solubility curve KP 70.0 .... ' 30.0
~
1-1 1-11 1-111
Andrea
SrlIXAIRY
T h e kiiov-ledge tlitis gained of the form of the dineric stirface for t h e system potassiuin chlorid, acetone, a i d water, may he siiiiinied tip as follon-s : Tlie plait-point of the surface lies at a temperature of ahont , 3 2 . j " and a coiiipositioii soiiien-here near water 43, acetone 50, salt ;(saturated solution of the salt iii j q percent acetoiie a t 3 2 . 5 " ). From this point the botuidarj- cur\-e extends in the
Potrrssizim Chlorid in Jqzfeviis Acciotir
491
direction indicated in Fig. 4, the temperature rising froni the plait-point in both directions. Froiii the boundary cui-ye, the dineric surface extends upward and outward ton-arc1 tlie acetonewater plane a t least a!; far as the position of tlie outer cur\-e of Fig. 4 and to temperatiires as high as 149' (See Table T.11). T h a t a t some higher temperature i t reaches its actual limit and begins to slope back in the other direction is indicated by tlie fact that solutions differing very little in composition from others that divide at about 100' can be heated to very high temperatures withoat clividing and ~ v o u l dalso seem probable froin the fact that in the analogous s\.stems, potassiiiiii cx-lioiiate, et1ij.l alcohol ancl water and potassium nitrate, ethJ.1 alcoliol a11c1 jvater, solutions that divide into tlvo layers on heating heCollie homogeneons again at still higher temperatures. In concliisioii, I desire to express iiiy heart\- tlimks to Prof. Bancroft upon whose suggestion this n-ork was undertaken ant1 \Those yaliiable advice has been e\-er at m y service. Cui-neiZ C n i z ' e ~ s i t y.~/(ZJ'. , 1,?98
