368 DUNNINGHAM : THE SYSTEM : ETHYL ETHER-WATER-XL.-The System : Ethyl Ether- Water-PotassiumIodide-Mercuric Iodide. Part I. .The Under-lying Three- Component Systems.By ALFRED CHARLES DUNNINGHAM.THE formation of three partly miscible liquids in a four-componentsystem has been observed from time to time, but has never beenstudied quantitatively with a view to elucidate the conditions ofequilibrium underlying such a phenomenon.The most convenient system f o r the purposes of such a studyappeared to the author to be the system ethyl ether-water-potassium iodide-mercuric iodide, in which three liquid layers wereobserved by Marsh (T., 1910, 97, 2297), who, however, made noattempt to investigate the question from the point of view ofheterogeneous equilibrium.Sime ether has an appreciable vapour pressure a t 20°, it wasnecessary to devise a special form of apparatus in which to agitatethe mixture whilst equilibrium was being attained.This apparatusis shown in Figs. 1 and 2. It consisted of a glass tube c, that couldbe fixed into a metal clamp d, which was free t o revolve in thejaws ab. The top of this tube was connected to a short shaft gh,which was fixed eccentricaiiy to a pulley m, so that when thispulley revolved the tube was shaken violently backwards andforwards. This motion served to agitate the contenh of the tube,and stir the water in the thermostat, in which it was immersed.The temperature was maintained constant t o Oslo. The tube wi19closed by means of an ordinary cork tied firmly with string.The composition of the various solid phases was, where necessary,determined by the residue method described by Schreinemakers(Zeitsch. physikal.Chem., 1893, 11, 81; 1907, 59, 641). Theappearances of potassium iodide and mercuric iodide, however, areunmistakable, and i t is only possible for confusion to arise betweenpotassium mercuri-iodide and its hydrate, KHgI,,H@, which havea similar appearance.I n analysing solutions and residues, the ether was first expellePOTASSIUM IODIDE-MERCURIC IODlDE. PART I. 369by the passage of a current of air previously dried by means ofanhydrous calcium chloride. A special weighing bottle was there-fore used, as shown in Fig. 3. The air leaving the'bottle was thenpassed through a weighed tube containing anhydrous calciumchloride, in order to absorb any water-vapour carried over by theether.The water was then expelled at a temperature slightlyabove looo by the further passage of dried air. The potassiumiodide in the solid residue was then estimated by Bray and MacKay'smethod (J. Amer. Chem. SOC., 1910, 32, 1193), in which the iodineis liberated by the addition of potassium permanganate in slightFIG. 1. FIG. 2.aIApparatus.excess in the, presence of an acid, extracted with carbon tetra-chloride, and titrated with standard thimulphate. The mercuriciodide, which is not affected by permanganate, was then obtainedby difference.The System : Potassium Iodide-Mercuric Iodide-Water.This system has been studied a t 30° as well as 20° in order toconfirm the existence of potassium mercuri-iodide, KHgI,.Theresults obtained a t 20° and 30° ar0 given in tables I and 11, andshown graphically in Figs. 4 and 5 respectively, and since they arealike in type, a discussion of the isotherm a t 20° will also servefor that at 30°370 DUNNINGHAM : THE SYSTEM : ETHYL ETHER-WATER-TABLE I.The System : Potassium Zodide-Mercuric Zodide-Water at 20°.No.123466789101112131416Percentage composition Percentage compositionof solution. of residue. - - KI. HgI, KI. HgI,. - - - 59.250-9 19.3 86.2 5.647.5 25.4 85.3 7.644.4 32.5 82-4 10.241.3 39.6 76.2 16.439.0 48.0 82-7 13.638.2 51.2 83-6 13.537.4 63-6 42.6 50.937.8 52.6 35.1 67-436-1 62.2 32.1 60.036.6 51.2 30.3 61.126.7 60.3 17.6 74.326.6 49.4 10.2 82-423.7 40.2 - -14.9 22-5 4-1 83.4Solid phase.KIKIKIKIKIKIKITABLE 11.The System : Potassium IocEide-Mercuric Iodide-Water at 30°.1617181920213223242660.640.039.640.040.239.333.733.03 1.429.1-63.062.762.261.260.349.862-061.752.2-61.036.133-636-933.629.630.329.126.6-37.060.762.169.260.462.761.060.667.1KIA t 20° the following phases are stable in equilibrium with solu-tion : Potassium iodide, potassium mercuri-iodide, potassiummercuri-iodide hydrate (KHgI,,H,O), and mercuric iodide.It has been shown by Schreinemakers (Zeitsch. physikal.Chem.,1909, 65, 553) by means of the 3 function (thermo-dynamic poten-tial) that the type of an isotherm in a system of two solid and oneliquid components, the liquid component being regarded as solute,does not alter, provided that the solute does not combine with thetwo solids; thus he showed that in the system silver nitrate-ammonium nitrate-alcohol-water, in which the two solid com-ponents form two compounds, these compounds persist in both thethree-component systems, and right through the four-componentsystem. By an analogous process of reasoning, one may deducethat potassium and mercuric iodides do not form mixed crystalsat 20°, as there is no evidence of this in the threecomponentsystems.This is remarkable when the great tendency of mercuriPOTASSIUM IODIDE-MERCURIC IODIDE.PART r. 37 1iodide to form mixed crystals with other iodides is remembered;on the other hand, the heterogeneous area often widens rapidlybelow the eutectic point, and in this case may have done so to suchan extent that mutual miscibility has, for practical purposes,vanished.One may also deduce from the above that a compound, potassiummercuri-iodide, occurs in the two-component system potassiumiodid*mercuric iodide, probably a t all temperatures.The isotherm under discussion presents some remarkable featuresFIG. 4.20".for a system in which the components are two salts and water. Therestricted extent of the threephase areas, and the great extent ofthO unsaturated and two-phase areas, me very unusual.The following is' a resume of the more important features of thediagram (Fig.4):Point e represents water ; f , potassium iodide ; g, mercuric iodide;m, potassium mercuri-iodide ; and n, potassium mercuri-iodidehydrate (KHgI,,H,O).Line ab represents the range of saturated solutions co-existingwith solid potassium iodide; bc, with solid potassium mercuri-iodide372 DUNNINGHAM : THE SYSTEM : ETHYL ETHER-WATER-cd, with solid potassium mercuri-iodide hydrate (KHg13,H,0) ; andde, with solid mercuric iodide.Point b represents a saturated solution coexisting with solidpotassium iodide and potassium mercuri-iodide ; c, with solidpotassium mercuri-iodide and its hydrate; and d, with solidpotassium mercuri-iodide hydrate and mercuric iodide.Area fab represents mixtures of saturat.ed solutions on ab + solidpotassium iodide ; bcm, on bc + solid potassium mercuri-iodide ;end, on cd + solid potassium mercuri-iodide hydrate; edg, onFra.5.3 0".ede + solid mercuric iodide ; f bm represents mixtures of solutionb + solid potassium iodide -t solid potassium mercuri-iodide ; mcn, ofsolution c + solid potassium mercuri-iodide + solid potassium mercuri-iodide hydrate ; ndg, of solution d + solid potassium mercuri-iodidehydrate + solid mercuric iodide ; and m n g represents solid mixturesof potassium mercuri-iodide, its hydrate, and mercuric iodide.On attempting to prepare a saturated solution of either of thedouble salts, the following phenomena occur. If water is added topotassium mercuri-iodide the composition of the mixture followsthe line me.When 9b is reached, all the salt is converted intPOTASSIUM IODIDE-MERCURIC IODIDE. PART I. 3’73potassium mercuri-iodide hydrate. Further addition of watercauses the formation of kolution d, together with solid mercuriciodide, until a t p all the double salt is decomposed, and onlysolution CF and solid mercuric iodide exist. As the- mixture thenfollows the line pe, the solution follows the curve de, more mercuriciodide being formed as the proportion of water becomes greater,until at e the solution is almost pure water, since the solubilityof mexcuric iodide is negligible.When solid mercuric iodide is added to a saturated solution ofpotassium iodide represented by a, the composition of the mixturefollows the line “9.The first solid phase which separates is thuspotassium mercuri-iodide hydrate (KHgI,,H,O).The System : Potassium Iodide-Water-Ethyl Ether.The results obtained in the investigatio,n of this system a t 20°are given in table I11 and shown diagrammatrically in Fig. 6,where point qz represents potassium iodide, rn water, and r ether.TABLE 111.The System : Potassium Iodide-Ethyl Ether-Water at 20°.Percentage composition Percentage composition - - KI H,O Et,O KI H,O Et,O Solid phase.of upper layer. of lower layer.26 - None. - 59.2 40.8 - K127 0.0 3.9 96.1 0.0 93.0 7.0 None.28 0.4 0.4 99.2 55.6 40.7 3.7 KI29 0.1 2.2 97.7 25.0 72.1 2.9 None.The base line mr represents the heterogeneity which occurs in thesystem water-ether. On the addition of the third component, thelimits of miscibility are naturally altered.I n this case there issome indication of approaching homogeneity after saturation withpotassium iodide is reached. It is therefore conceivable that a t ahigher temperature there would be an uninterrupted solubilitycurve from the solubility of potassium iodide in water to the samein ether.The folIowing is a brief consideration of the system.The solubility of ether in water is represented by the point x,that of water in ether by the point 9.The solubility of potassium iodide in water is represented by thepoint d , that of potassium iodide in ether by the point c. This, inpractice, is negligible.The curve da represents the saturation curve of potassium iodidein water containing ether, ch that of potassium iodide in ethercontaining water. Further addition of ether to solution a i374 DUNNfNGHAM : THE SYSTEM : ETHYL ETHER-WATER-contact with solid potassium iodide causes the separation of asecond lighter layer, the composition of which is represented by h .Similarly, the addition of water to solution h in contact with solidpotassium iodide causes separation of a second, denser layer, thecomposition of which is represented by a ; a and h are thereforeinvariant solutions ; a is an aqueous solution saturated simultane-ously with solid potassium iodide and ethereal solution h, whilsth is an ethereal solution saturated simultaneously with solidpotassium iodide and aqueous solution a ; a and h are thereforeFIG. 6 .mconjugate solutions in equilibrium with one another and with solidpotassium iodide.In Fig.6 the curve ax represents aqueous solutions unsaturatedwith respect to solid potassium iodide, but in equilibrium withethereal solutions represented by points on gh, whilst gh representsethereal solutions unsaturated with respect to solid potassiumiodide, but in equilibrium with aqueous solutions represented bypoints on the curve ax; ax and hg are therefore conjugate curves.A solution represented by a point on one of these is in equilibriumwith a solution represented by a definite point on the other.These curves, ax and hg, naturally end in the points 5 and grespec tivel pPOTASSIUM IODIDE-MERCURIC IODIDE. PART I. 375We can now distinguish the portions into which the trianglew w is divided.Area dnu represents mixtures of aqueous solutions on da + solidpotassium iodide ; chm represents mixtures of ethereal solutions onc h +solid potassium iodide ; nah represents mixtures of the twoconjugate solutions a and h + solid potassium iodide; duxm repre-sents unsaturated aqueous solutions ; chgr represents unsaturatedethereal solutions ; and axgh represents mixtures of two conjugatesolutions (aqueous and ethereal) represented by conjugate pointson ax and gh respectively.The behaviour of a mixture of two components when the thirdis added to it is as follows:I f nu is drawn and produced to meet mr in p, whilst nh is drawnand produced to meet mr in q, the line mr is divided into threeparts, namely, mp, pp, and qr.We will first consider a mixture of ether and water representedby a point k; on mp.If, as in Fig. 6, k lies between m and x, thismixture is homogeneous, whilst if k lies between x and p , twolayers, of compositions represented by x and g respectively, areformed. I f now potassium iodide is added to this mixture, itscomposition follows the line kn. This line cuts the curve da, andenters the area dna. The addition of potassium iodide to themixture k therefore finally gives a homogeneous saturated solutionrepresented by a point on da. Similar considerations show thatany mixture represented by a point on q~ gives, on addition ofpotassium iodide, a saturated homogeneous solution repraented bya point on ch.It will further be observed that if k lies between m and x it ispossible for the line kn to cut the curve xa in two places, c and f.When thi8 is the case, the addition of potassium iodide causes theseparation of an ethereal layer at e, which disappears again a t f,where the mixture becomes homogeneous.This ethereal layer is,of course, very small in amount.Any mixture of ether and water represented by a point j betweenp and g exists throughout as two layers. These are first representedby x and g, and as potassium iodide is added, they follow thecurves xu and gh until, when the mixture reaches b , they havecompositions represented by a and h respectively. Further additionof potassium iodide leaves these layers unchanged.The phenomena occurring when potassium iodide is added to anether-water mixture lying between g and q can be seen at oncefrom the figure.When ether is added to an unsaturated solution of potassiumiodide in water, such as that represented by t , the composition o376 DUNNINGHAM : THE SYSTEM : ETHYL ETHER-WATER-the mixture follows the line tr.A t 21 an upper o r ethereal layercommences to separate. I f the line fr coincides with the conjuga-tion line through 27, as in Fig. 6, the composition of this upperlayer is represented by zu. As the mixture moves along vw thecompositions of the two layers remain unchanged, but the relativeamount of w increases. At any point y t.he ratio of the two liquidsis given by the relationship:amount of v - length of wyamount of w lengtt-1 ot vy’-When w is reached all the lower layer ZJ has disappeared.Thesolution then remains homogeneous on further addition of ether.I n most cases, however, tr does not coincide with a conjugationline, but cuts through a number of them. This means that thecomposition, as well as the ratio of the two liquids, changes asether is added. Since, however, in reality the curve h g is veryshort, the line tr always approximates to a conjugation line, andthe compositions of the two layers vary only slightly.The addition of water to a mixture of ether and potassium iodiderepresented by z almost immediately (at u) causes a separation intotwo layers, represented by a and h, in contact with solid potassiumiodide. A t b all the potassium iodide just dissolves, the solutionsstill being represented by a and h.As the mixture then movesfrom b to s, these solutions follow the curves ax and hg, whilst therelative amount of the ethereal solution decreases. A t s the etherealsolution just disappears, and the aqueous solution remains homo-geneous on further addition of water.The System : Ethyl Ether-Potassium Zodide-Xercuric Iodide.The equilibrium obtained in this system is of a remarkablecharacter. The results are) given in table I V and shown diagram-matically in Fig. 7, and the more important features of thisdiagram may first be briefly considered.Point a represents potassium iodide; s, ethyl ether; c, mercuriciodide ; and i potassium mercuri-iodide.TABLE IV.The System : Potassium 1od:ide-dlercur.ic Iodide-EthylEther at 20°.Percentage Percentage Percentagecomposition of composition of composition ofupper layer.lower layer. residue. -- - KI. HgI,. KI. HgI,. K; l332. Solid phase.30 1-1 2.8 None. KI + KHgI,31 1-1 2.4 17.6 53.2 25.6 67.4 KHd,HgI, 32 0.8 2.5 16.5 56.1 - -33 None. 17.0 58.2 18.3 71.6 KHgI,+HgIPOTASSIUM IODIDE- MERCIJRIC IODIDE. PART r. 377Line d e represents the range of saturated solutions co-existingwith solid potassium iodide; lines cf and hk represent the range ofsaturated solutions co-existing with solid potassium mercuri-iodide ;by/ and mk, with solid mercuric iodide; and f g and hm representthe ranges of two series of conjugate liquids in equilibrium withone another.Point e iepresents a saturated solution co-existing with solidpotassium iodide and solid potassium mercuri-iodide ; points f and ILrepresent two conjugate solutions co-existing with solid potassiummercuri-iodide; i~ and m, with solid mercuric iodide; point k repre-FIG.7.a, (KI)sents d saturated solution co-existing with solid potassium mercuri-iodide + solid mercuric iodide.Area defgb represents unsaturated solutions containing a smallproportion of dissolved salts ; h.km represents unsaturated solutionscontaining a, large proportion of dissolved salts; a d e representsmixtures . of solutions on de +solid potassium iodide; efj, onef + solid potassium mercuri-iodide; fhmg represents mixtures oftwo conjugate solutions on fg and hm respectively; bgc representsmixtures of solutions on b y + solid mercuric iodide; hjk, on hk +solid potassium mercuri-iodide ; kmc, on mk + solid mercuric iodide ;ae j represents mixtures of solution e + solid potassium iodide + solidVOL.cv. c 378 DUJSNINGHAM : THE SYSTEM : ETHYL ETHER-WATER-potassium mercuri-iodide ; fj?L, f and k + solid potassium mercuri-iodide; gmc, g and m +solid mercuric iodide; and jlcc, k+solidpotassium mercuri-iodide + solid mercuric iodide.It will be noticed at once that the saturation curve of potassiummercuri-iodide is divided into the two parts ef and hk, whilst thatof mercuric iodide is divided into the two parts b y and mk. Thesetwo saturation curves intersect at I%, which thus represents asolution saturated with both solids. Both these saturation curvesare divided into two portions by a binodal curve, E,xfgl~2m?L~,which cuts across them.Only the parts f g and hm, representingtwo series of conjugate solutions, are stable. The metastable parts,both of the binodal curve ar,d of tlie saturation curves, areindicated by dotted lines.Unfortunately, the actual range of all the curves is exceedinglysmall, but the form of the isotherm as shown in Fig. 7 is deducedfrom the experimental evidence given belo,w.There is no formation of two liquid layers in any of the threetwo-component systems from which the three-component system isbuilt up.Both potassium iodide and mercuric iodide are practicallyinsoluble in ether, so that in the ordinary way it might be expectedthat the addition of a small quantity of mercuric iodide to asolution already saturated with potassium iodide, and containinga considerable quantity of that salt as solid phase, would merelycause the solution t o become saturated with respect to potassiumiodide and potassium mercuri-iodide ; tlie formation of the doublesalt can be premissed on the law of corresponding isotherms.Theactual course of events, however, is different from the abovescheme.The experiment described above causes the separation of aheavy liquid rich in potassium iodide and mercuric iodide, which,on continued shaking, disappears, and leaves the solution saturatedwith respect to potassium iodide and potassium mercuri-iodide.The transitory formation of this heavy liquid may be readilyexplained by reference t o the diagram, in which the whole of thebinodal curve is shown, the stable part by complete lines, themetastable part by dotted lines. A consideration of the 3 surfacesshows us that if the metastable prolongation of the saturationcurve of potassium iodide cuts the metastable portion of thebinodal curve, we can obtain two liquid layers in equilibrium withsolid potassium iodide.The conditions for such a metastable equili-brium ar0 shown in the diagram by the area axy, in which z and yrepresent the two liquid layers. This area is divided up into twostaEle areas representing the following equilibria : (1) potassiuPOTASSIUM IODIDE-MERCURIC IODIDE. PART I. 3’19iodide + potassium rnercuri-iodide -t solution e , and (2) potassiummercuri-iodide + solutions on ef.Since we started with a solution containing a considerable excmsof solid potassium iodide, it is evident that the ultimate stableequilibrium will be potassium iodide + potassium mercuri-iodide +solution e.If we take some of solution e saturated with potassium iodideand potassium mercuri-iodide, but containing only potassiummercuri-iodide as solid phase, and add mercuric iodide to it, asecond liquid layer is formed almost at once, which does notdisappear on continued shaking.This means that we rapidlytraverse the small range of solutions on ef saturated with potassiummercuri-iodide, and arrive in the complex area, fjh, which repre-sents mixtures of potassium mercuri-iodide with solutions f and h.I f a complex consisting of it small quantity of solution f anda large quantity of solid potassium mercuri-iodide and solution his now taken, and solid mercuric iodide added to it, the solutionf disappears, and if sufficient mercuric iodide is added, we obtaina solution saturated with respect to two solid phases, namely,potassium mercuri-iodide and mercuric iodide.This means thatthe complex of solid and solution has entered the area jlic.I f , on the other hand, the two solutions f and h saturated withpotassium mercuri-iodide and containing this salt in slight excessare treated with small quantities of solid mercuric iodide, the solidphases disappear, and w0 enter a twoliquid region. This is shownin the diagram by fhmg.The addition of a large excess of mercuric iodide causes theformation of two liquid layers saturated, with respect to mercuriciodide. This equilibrium is also attained when potassium iodideis added to a saturated solution of mercuric iodide in ether, con-taining an excess of that salt. It is represented by the area gmc.The author is carrying out a further series of observations onthis system at, other temperatures.The System : Mercuric Iodide-Water-Ethyl Ether.Since mercuric iodide is practically insoluble in ethyl ether andwater, and in all mixtures of these two components, no pointshave been determined in this system, which is similar in type t o thesystem potassium iodidewater-ethyl ether.I n conclusion, the author wishes t o acknowledge with gratitude agrant from the Chemical Society, which has enabled him to carryout this research.SIR JOHN DEANE’S GRAMMAR SCHOOL,NORTHWICH, CHESHIRE