MARSH : DISSOLUTION OF POTASSIUM MERCURI-IODIDE. 2297CCXL I .--Pheriomena Observed when Potassium Mercuri-iodide is Dissolved in Ether and Water.By JAMES ERNEST MARSH.POTASSIUM mercuri-iodide, KHgI,,H,O, crystallises well fromalcohol, but is decomposed by water with separation of mercuriciodide. A crystal of the salt changes in colour from yellow to redon being moistened with water. The salt is, however, soluble inwater if heated with a very small quantity; also, when heated inVOL. XCVII. 7 2298 MARSH : PHENOMENA OBSERVED WHEN POTASSIUMa sealed tube, the dry salt melts at 119O, and this liquid may beregarded as a solution of the salt in its water of crystallisation. Thesalt is very sparingly soluble in dry ether, but is somewhat readilydissolved by undried ether, especially by ether which has beenshaken with water and then separated from the latter.The salt,which dissolves in the ether with considerable rise of temperature,is much more soluble in cold ether than in hot. The followingexperiment illustrates this property. A sealed tube was employedcontaining 3.32 grams of powdered potassium iodide and 9.08 gramsof mercuric iodide with 52 C.C. of " wet " ether and 0.6 C.C. of water.A t Oo the contents of the tube are completely dissolved. I f the tubeis now placed in warm water, crystals begin to form, and at 50°the contents of the tube become nearly solid, with the formation oflong, yellow needles of the salt KHgI,,H,O. The crystals re-dissolve in the ether on cooling. Analysis of the salt obtained inthis way gave:Found, H,O = 2-69 ; KI = 25.7.KHgI,,H,O requires H,O = 2-82 ; K I = 26.0 per cent.If potassium iodide and mercuric iodide are mixed with ordinaryundried ether, no apparent solution or other change occurs.Thered and the colourless salts remain unchanged in presence of thesolvent. After many weeks, however, the red colour of the mercuriciodide begins to fade, and its place is taken by the characteristicyellow, crystqlline double salt. This does not dissolve appreciablyin the ether now deprived of its water, but requires '' wet " ether€or its solution.When potassium iodide and mercuric iodide are mixed with etherdried either by sodium or by long keeping over calcium chloride,the double salt which contains water of crystallisation cannot now beformed, and a quite different action occurs.The two salts rapidlyliquefy in the ether, and take up four molecules of ether t o form aheavy, yellow liquid compound. If any excess of ether is taken,i t is left floating on the surface as a separate layer which containsvery little of the salts, and a large excess of ether does not appre-ciably diminish or increase the volume of the liquid compound.If the ether taken is not enough to supply four molecules, thensome of the salts are left undissolved. If mercuric iodide is taken inlarger quantity than one molecule to one of potassium iodide, theexcess is left undissolved.The compound, KHgI3,4E~O.-l.66 Grams of well powdered anddried potassium iodide and 4.54 grams of mercuric iodide weremixed with 4.4 C.C.of dry ether in a sealed tube. On shaking, allrapidly passed into solution. The liquid compound measured 5 c.c.,and the ethereal layer 0.1 c.c., at 7.5O. From these figures thMERCURI-IODIDE IS DISSOLVED IN ETHER AND WATER, 2299formula of the liquid compound and its specific gravity, 1.87, at7 . 5 O are derived. It should be noted that the solubility ofpotassium iodide and of mercuric iodide separately in dry ether isvery slight. The solubility of potassium iodide in ether at theordinary temperature was found to be 0.016 per cent., and ofmercuric iodide 0.3 per cent., and in neither case is there formedany liquid not miscible with ether. The liquid compound of etherand potassium mercuri-iodide is also formed by exposing a mixtureof the two salts in a tube t o the vapour of ether, but in this casesome crystals are also formed in the tube, and the action is veryslow. 0.83 Gram (1 mol.) of potassium iodide and 2.27 grams(1 mol.) of mercuric iodide exposed to the vapour of dry etherincreased in weight by 1.1682 grams (3.1 molecules of ether), whenthe red mercuric iodide justl dissolved? and gave a further increase,in all, 1.5334 grams (4.1 molecules of ether), after keeping for manydays.The compound was also analysed by determining the loss ofweight due to the ether given off on passing a stream of dry air overthe substance. The liquid, when it had lost a certain quantity ofether, began to crystallise, and soon formed a solid mass of crystals.It was then weighed, and the stream of air was continued until allthe ether was expelled.4.2914 Grams of the liquid compound gave3.7086 grams of crystals, and finally 2.6314 grams of potassium andmercuric iodides. These numbers agree with four molecules ofether in the liquid compound, and with 2.5 molecules in thecrystalline compound. As it is difficult to stop when the crystalsare just free from liquid, i t appears more probable that thecrystalline compound is represented by the formula KHgI,,3Et20.When the liquid compound is exposed to moist air, crystals of thehydrated salt KHgI,,H,O a t once form on the sides of the tube.The addition of a small quantity of water causes the liquid to setto an almost solid mass of crystals with total expulsion of the ether.The experiment was carried out as follows.I n a tube, containing 1.83 grams of potassium iodide, 5.0 gramsof mercuric iodide, and 5 C.C.of dry ether, was placed a sealed bulbcontaining 0.22 gram of water, and a small piece of glass rod. Thetube was then sealed, and, on mixing carefully so as not to breakthe bulb, the liquid compound was obtained with a small surfacelayer of ether. The bulb was then broken by a jerk, and the tubequickly became filled with a mass of yellow crystals insoluble in theether.Solution of Potussium Iodide and Mercuric lodide in a Mixtureof Ether and Water.-As stated above, the addition of water to thecompound KHg13,4Et,0 causes the precipitation of the saltKHg13,H,0, and on the further addition of water the crystals7 L 2300 MARSH : PHENOMENA OBSERVED WHEN POTASSIUMbecome soluble in aqueous ether, to separate again on warming thesolution.By continuing the addition of water, these crystals nolonger separate on warming, nor does the water cause the separationof ether, but eventually red mercuric iodide is precipitated. Thisoccurs when the amount of water added is just double the voluiueof the ether; the addition of a little more ether clears the solution.With a larger amount of ether than four molecules to one of thesalts, the addition of water may cause the liquid to separate intotwo layers. When there is separation, it is found that there is atemperature, the critical point, below which complete mixture takesplace, and above which there is a separation into layers. Thiscritical temperature depends on the concentration of the doublesalt in solution and the relative amounts of ether and water.Itis to be noted further that, whereas the addition of water to themixture of potassium and mercuric iodides brings about partialsolution with absorption of heat, the addition of ether brings aboutcomplete solution with evolution of heat, and the further additionof the water to the aqueous ethereal solution also causes an evolutionof heat. The following example shows the effec:t of increasingquantities of water, the amounts of potassium iodide, mercuriciodide, and ether being constant. One molecular proportion ofpotassium iodide and one of mercuric iodide were mixed with 12.5molecular proportions of water ; the temperature fell 2O, the solutionnot being complete.On addition of 12.5 molecular proportions ofether, the temperature rose loo, the solution being now complete.The critical point of this solution was 31O. Successive additions of12.5 molecular proportions of water were made, and a rise of tem-perature in each case was noticed until it became too small to bemeasured. The critical point was determined after each additionof water. The results are illustrated by the curve in Fig. 1. Itwill be seen that the critical point falls to a minimum and risesagain. It was found that the solution of lowest critical point frozewhen the temperature was reduced to about -15O. The com-position of the liquid of lowest critical point, and therefore also ofthe frozen mass, is represented nearly by the rather complex formulaKHgI3,12-5E~0,75H,O.The volume relations are more simple,being nearly 1 vol. KHgI, : 3 vols. Et20 : 3 vols. H20. When partlymelted and no longer adhering to the sides of the tube, the solidmass floats on the surface of the liquefied part.There is a further point to be noted with regard to the criticalpoint. It is found that, when the most concentrated solution,namely, that which has the critical point of 31°, is heated, aheavy liquid layer separates at the bottom of the tube, increasingin amount as the temperature rises, and being redissolved as thMERCURI-IODIDE IS DISSOLVED IN ETHER AND WATER. 2301temperature falls, until at 31° i t disappears altogether.On theother hand, all the other solutions, when heated above their criticalpoints, expel a light layer, which increases with the temperatureand is re-absorbed by the bulk of the liquid just below the criticalpoint. It will thus be seen that a solution of one molecular pro-portion of potassium mercuri-iodide in 12.5 molecular proportionsof ether and 12.5 of water expels, on warming, a heavy liquid layer,whereas a solution containing the same quantities with an additionof 12.5 molecular proportions or more of water expeIs, on warming;FIG. 1.0- 52 4 6 8 10 13 14Volume of tenter.a light liquid layer. I f , now, we take an intermediate amount ofwater, namely, 18.75 molecular proportions, the other quantitiesremaining the same, a solution is obtained which, on warming,expels both a heavy liquid layer and a light one, so that threedifferent liquids appear in the tube.I n one experiment a sealedtube was used which contained 5-53 grams of potassium iodide,15.1 grams of mercuric-iodide, 10 C.C. of water, and 44.2 C.C. of" wet " ether. This solution is homogeneous a t the ordinary tem-perature, and between 50° and 60° a, good separation is obtaine2302 MARSH : PHENOMENA OBSERVED WHEN POTASSIUMinto three liquid layers. These layers are permanent and notaltered by shaking while the liquid is still hot, but on cooling theyform again a homogeneous solution.It is possible to obtain other solutions which, on heating, givethree liquid layers and have concentrations different from that justmentioned.The one which was first obtained contained equalmolecular proportions of water and ether. As has already beenstated, with the concentration of 1 to 12.5, a lower layer begins toseparate at 31O; with the concentration of 1 molecular proportionof salt to 25 molecular proportions of ether and 25 of water, theupper layer separates above the critical point Oo. By trying con-centrations between these two limits, it was found that with theconcentration of 1 molecular proportion of potassium mercuri-iodideto 17.3 molecular proportions of water and 17.3 of ether, the solutionseparated into three layers. I n a calibrated tube, 1-66 grams ofpotassium iodide, 4.54 grams of mercuric iodide, 2.6 C.C. of water,and 18.2 C.C. of ‘ I wet ” ether were sealed.The calculated volumeof the constituents is 22.0 C.C. The volume found on mixing was21.4 c.c., so that there was a slight contraction. The tube was thenheated to different temperatures, and the volumes of the solutionswere determined. The curve plotted from the measurements isgiven in Fig. 2. In what follows, the top layer is termed“ ether ” solution, the middle layer “ mixed ” solution, andthe lower layer “ water ” solution. At 22O, “ ether ” solutionbegins to separate, and increases in amount as the tempera-ture rises. A t 33-5O, water ” solution also begins to separate,and both layers increase with the temperature. At 51’5O, the“ mixed ” solution disappears, and only two liquids are present.These two liquids do not appreciably alter in volume on heatingfurther to above 70°.Correction was made for expansion by heat,which was regular, and nearly the same as the expansion of etheritself. In order to determine the amounts of mercuric iodide andpotassium iodide in the water layer, a tube was taken with a bulbof 4 C.C. capacity at one end, the mixture in the tube being madeup of 2 molecular proportions of potassium mercuri-iodide (12.4grams) to 25 of ether and water. On heating, the heavy aqueoussolution just filled the bulb at 63O. The tube was cooled withoutmixing the two solutions, opened, and the solutions separated.The aqueous solution measured slightly less than 4 C.C. The mixedsalts contained in it weighed 4-77 grams, of which 1-58 grams waspotassium iodide.The solution contained scarcely any ether, itdid not take fire (water containing 0.5 per cent. of ether takes fire),and had scarcely any odour of ether. It was thus found that anaqueous-ethereal solution of the salts, which is homogeneous wheMERCURI-IODIDE IS DISSOLVED IN ETHER AND WATER. 2303cold, separates, on warming, into a, '' water " solution nearly freefrom ether, and an ether " solution which, from the volnmes ofthe two solutions, can contain but little water.I n order to determine how the mercuric and potassium iodidesare apportioned in all the three layers, a solution was made whichgave three layers at a temperature below the boiling point of ether.FIG. 2.2018161412w fc 10wk8642--l-- 31 xed solution.l o o 20" 30" 40" 50" 60" 70"Tempe ratzi re.The three Iayers caii then be produced in a stoppered burette, andrun off and analysed.It was found that with 1 molecular pro-portion of salt to 20 molecular proportions of water and 33 of ether,a separation into three layers is obtained at 2 9 O . The " water "layer measured 0.6 c.c., had a concentration of 1 gram per c.c.,and contained HgI, : KI = 2 : 3 mols. The " middle " layer measure2304 MARSH : PHENOMENA OBSERVED WHEN POTASSIUM6.2 c.c., had a concentration of 0.4 gram per c.c., and containedHgI, : KI= 1 : 1 mol. The (( ether ” layer measured 31 c.c., had aconcentration of 0.1 gram per c.c., and contained HgI,: KI=7 : 6mols.It will be noticed that the ((water” solution contains more,and the I‘ ether ” solution less, potassium iodide than is representedby the simple molecular proportions HgIz: KI.It was found that(‘ wet ” ether will dissolve mercuric iodide and potassium iodide inany proportions between the lower limit K I : HgI, and the upperlimit KI: 2Hg1,. The upper limit of solubility of water isKI: HgI,, whilst there is, of course, no lower limit.There seems no doubt that this separation of a homogeneoussolution into layers on warming is associated with the temperaturechanges which occur on making the solutions. There are fouroperations, three of which occur with evolution of heat, and onewit.h absorption of heat. I n the first place, mercuric iodide andpotassium iodide together dissolve in water with absorption of heat.The same salts dissolve in ether with evolution of heat.Further,ether dissolves in the water ” solution with evolution of heat, andwater also dissolves in the ((ether” solution of the salts withevolution of heat. It would be expected that the effect of raisingthe temperature would be to assist the change which occurs withabsorption of heat, and to prevent those changes which occur withevolution of heat. Thus either ether will be expelled from solution,which happens at low concentrations, or water will be expelled,which happens at high concentrations, or both ether and water willbe expelled, and further the salts will be expelled from the (( ether ”solution into the (( water ” solution. There is thus eventually pro-duced, at a sufficiently high temperature, a strong aqueous solution,together with a weak ethereal solution of the two salts.Thesechanges are reversed on cooling. I f not shaken, however, thesolutions may be kept apart when cooled; theyfmix then on shakingwithout change of temperature or volume. The great concentrationof salts in the “water” layer is well shown by heating a tube,containing 1 molecular proportion of salt to 12.5 molecular pro-portions of water, to about 70°, and then, without shaking, coolingrapidly to Oo. The “ water ’’ layer now becomes filled with crystalsof the double salt mixed with the red crystals of mercuric iodide.Compounds of Two Haloid Salts wit?& Ether.A number of compounds analogous to the compound KHgI,,QEt,Owere also prepared.The alkali-metal iodides form liquid com-pounds with mercuric iodide and ether, with the exception oMERCURI-IODIDE IS DISSOLVED IN ETHER AND WATER. 2306rubidium and caesium iodides.following f ormulze :The compounds obtained have t,heNaI,HgT,,G Et20KI,Hg I,,4Er20LiI,HgT,. 6E t,,O Li Br, HgT2,4Et,O [ LiC1,HgI2 '13LiI, HgBr,,5 Et,O[LiI,HgCI, 93 LiBr,HgCI,,Et,O '1 [LiCI,HgCl, '13Li Br, Hg Br,, 4 E t20 1 t i C1, Hg Br,, E t,O ?LiI, AgI,3Et.,OLiI,CuI,4 Et,OThe compound KI,HgI,,4Et20 is described on p. 2298. Theamount of ether (4 molecules) is approximately correct at theordinary temperature, but the compound is affected by a rise oftemperature with loss of some of the ether. This effect is found tobe a general one for this class of substances even when they arecontained in sealed tubes; it is small in the case of the lithium andsodium mercuri-iodides.The experiments which are now to bedescribed are not therefore intended to furnish accurate analyticaldata, but rather to show how the substances were obtained. Theyindicate also that the constituents are combined at the ordinarytemperature in approximately simple molecular proportions, theamount of the solvent being limited to six molecules or less. Theliquids can, however, hardly be regarded as " definite " compoundsin the ordinary sense, nor are they ordinary solutions, since they aresaturated both for salt and for solvent. They seem t o be of anature intermediate between a solution and a chemical compound.C o r n p o d s of Iodides with Mercuric Iodide and Ether.Lithium Zodide.-Lithium iodide alone is readily soluble in dryether, although not in undried and ((wet" ether.It does not,however, form a liquid compound with a limited amount of etherin presence of excess of ether.1.4 Grams of lithium iodide and 5.05 grams of mercuric iodidewere mixed in a stoppered burette with 10 C.C. of dry ether, whenall dissolved rapidly, forming two liquid layers. The volume ofthe solution was 8.15 c.c., and that of the upper ether layer 2.55 C.C.The latter left, on evaporation, 0.015 gram of solid residue, con-sisting of lithium mercuri-iodide, LiHgI,. Hence the liquid com-pound contained 1.387 gra.ms of lithium iodide, 5-038 grams ofmercuric iodide, and 7.45 C.C.of ether in 8-15 C.C. From thesenumbers is derived the formula LiI,HgI,,6EL20, and the specificgravity 1-461Sodium Zodide.-l*53 Grams of sodium iodide and 3.67 grams o2306 MARSH : PHENOMENA OBSERVED WHEN POTASSiUMmercuric iodide were sealed in a tube with 6 C.C. of dry ether. Thecontents of the tube liquefied readily on shaking, with the exceptionof some sodium iodide, of which excess was taken by accident. Theether not required was 0.8 C.C. The formula of the compoundformed is NaI,HgI,,GEt,O.Rubidium Zodide.-Rubidium iodide and mercuric iodide incontact with dry ether gave no liquid compound. There is noapparent action at first, but after some days the red mercuric iodidedisappears, and its place is taken by a yellow, crystalline substance.Caesium Zodide.-Cwium iodide and mercuric iodide gave noliquid compound with ether, and after several months most of themercuric iodide appeared to be unchanged.Silver Zodide.-Silver iodide and mercuric iodide in ether do notappear to suffer any change.Strontium Iodide.-l.44 Grams of strontium iodide and 3-67grams of mercuric iodide, with 6 C.C. of dry ether, liquefied andcombined with 2-63 C.C.of the ether; hence the formula of theliquid compound is SrI2,2HgI,,6E~O.Aluminium Iodide.-Aluminium iodide and mercuric iodide didnot give any liquid compound with ether, but the colour of themercuric iodide disappeared with the formation of a yellow pre-cipitate and, after a time, of large, colourless crystals.Hydrogen Ibdide.-1'27 Grams of mercuric iodide were mixedwith 3 C.C.of dry ether, and dry hydrogen iodide was passed inuntil the mercuric iodide just dissolved. Two layers of liquid wereformed, and the upper layer of unused ether measured 2.25 C.C.The probable formula of the compound is HI,Hg12,3Et20.Tetramethylamrrwnhm Iodide.-Tetramethylammonium iodideand mercuric iodide suffer no apparent change in dry ether afterseveral months.Ammonium Iodide.-The compound of ammonium iodide andmercuric iodide with ether differs from the other compoundsdescribed, in that its composition is different at different tem-peratures. 0-584 Gram of ammonium iodide and 1.83 grams ofmercuric iodide, with 3 C.C. of dry ether, gave two liquids, theunused ether measuring 0-8 C.C. This agrees with the formulaNH,I,HgI,5Et20.At about 80°, 1 molecule of ether is expelledfrom the lower to the upper layer in the sealed tube. Thus thecompound NH,I,Hg12,4Et,0 is left.If wat'er is added to ammonium and mercuric iodides dissolvedin excess of ether, no crystalline hydrate separates, but the wateris absorbed to a certain amount, and then any excess of waterremains undissolved as a light layer floating on the heavy ethersolution. The water layer contains very little of the salt dissolvedMERCURI-IODIDE IS DISSOLVED IN ETHER AND WATER. 2307Compounds of Bromides with Merczlric Bromide and Ether.Lithium Bromide.-O*4 Gram of lithium bromide and 1.8 gramsof mercuric bromide were sealed in a tube with 3 C.C.of dry ether.The mixture readily liquefied, and formed two layers. The amountof ether in excess was 1.02 c.c., hence the formula of the liquidcompound is LiBr,HgBr,,4Et20.Sodium Bromide.-Sodium bromide and mercuric bromide gaveno liquid compound with ether.Ammonium Bromide.-l.43 Grams of ammonium bromide and5.3 grams of mercuric bromide were sealed in a tube with 5.5 C.C.of ether. The salts liquefied, but not quite completely, and required3-66 C.C. of ether.NH4Br,HgBr,,2'5Etz0.This compound, however, like the corresponding iodide, loses etherwhen warmed in the sealed tube, leaving not another liquid com-pound, but a solid mass, with loss of probably all the ether. Thema-ss slowly unites again with the ether when cold. Further, whenthe liquid compound itself is cooled to about loo, it sets to a solidmass of colourless crystals without any loss of ether.This agrees with the formulaLithium Chloride arid Mercum'c Chloride.0.42 Gram of lithium chldride and 2-71 grams of mercuricchloride were sealed with 3 C.C.of dry ether in a tube. No liquidcompound was obtained, but, on long keeping, crystals formed inthe tube.Hised Halogen Salts and Ether.Lithium Bromide, Mercuric irodide, and Ether.-O*45 Gram oflithium bromide and 2-27 grams of mercuric iodide were mixed with3 C.C. of dry ether in a sealed t,ube. The salts liquefied,taking up 2-15 C.C. of ether. From these numbers the formulaLiBr,HgIz,4Et20 is derived.Lithium Iodide, Mercuric Brorn.de, and Ether.-@76 Gram oflithium iodide and 2-15 grams of mercuric bromide liquefied incontact with 4 C.C.of dry ether, and required 3-14 C.C. for solution;hence the formula of the compound is LiI,HgBr2,5Et2O. Neitherlithium chloride with mercuric iodide nor lithium iodide withmercuric chloride gave any liquid compound with ether.Lithium Bromide, Mercuric Chloride, and Ether.-@85 Gram oflithium bromide and 2.65 grams of mercuric chloride were mixedwith 4 C.C. of dry ether. The action was slow and did not appearcomplete, but partial liquefaction occurred. The amount of ethertaken up was 1.06 c.c.; hence the probable formula of the compoundis LiBr,HgCl,,EhO2308 BARLOW AND POPE : THE RELATION BETWEEN THE CRYSTALLithium Chloride, Mercuric Bromide, and Ether.--@21 Gram oflithium chloride and 1.8 grams of mercuric bromide became pastyin contact with 2 C.C. of dry ether without completely liquefying.The amount of ether taken up was 0.7 c.c.; hence the probableformula of the compound is LiCl,HgBr2,Et20.All the liquid compounds with ether mentioned above contain amercury salt as one constituent. The following are examples ofliquid ether compounds, where silver, lead, and copper iodides takethe place of mercury salts.Lithium Iodide, Silver Iodide, and Ether.-l.82 Grams of lithiumiodide and 2.67 grams of silver iodide were sealed with 6 C.C. of dryether in a tube. Liquefaction took place rapidly, two layers wereformed, and 3-6 C.C. of ether were taken up. From this the formulaLiI,AgI,SEt,O is deduced.Lithium Iodide, Copper Zodide, and Bther.--1*45 Grams oflithium iodide and 2-05 grams of cuprous iodide were sealed in atube with 5 C.C. of dry et,her. A liquid compound was obtained,but was not clear. The ether not used was 0.85 C.C. Hence theprobable formula of the compound is LiI,CuI,4EhO.Lithium Iodide, Lead Iodide, and Ether.-O.87 Gram of lithiumiodide and 2-62 grams of lead iodide were sealed in a tube with4 C.C. of dry ether. Ether was absorbed, and the compound formedwas solid and crystalline. It melted partly on warming, but a clearliquid was not formed. The composition is doubtful ; apparentlybetween 3 and 4 molecules of ether are required.UNIVERSITY MUSEUM,OXFORD