ON THE DENSITY OF CERIUN SULPHATE SOLUTIONS. 357 XXVL-Note on the Deizsity of Cerium Sdphate Solutions. By €3. BRAUNER Ph.D. F.C.S. late Fellow of Owens College. (Communication from the Laboratory of the Bohemian University, Prague.) SINCE the publication of MendelBeff’s paper on the Density of Salt Solutions (Russ. Chem. SOC. Jourgz. 1884 184 in which this eminent chemist shows that the density of solutions regularly increases with the molecular weight of the salts dissolved) and especially since the publication of the same author’s important work on Solutions,* the interest of chemists has been more than ever directed t o this subject ; every new exact determination therefore may be regarded as useful material for a further study of this important subject. In the case of the rare earth metals not a single solution has as yet been studied from this point of view partly on account of the rarity * A.fi1eHde.IkB.b. 13 3C~X%~OBa€lie BOdHbIX% paCTBOp0B.b IIO yJ%dh-Holly B$c~. C.-Tl[eTep6ypra 1887 (D. Mendelkeff. “ Research on Aqueous Solutions with regard to their Density,” St. Peteraburg 188’7 21 and 520 pages large SYO.). I n this important work which on account of its theoretical and practical value ought to be translated into a Western-European language the whole of the material relating to the density of aqueoue solutions is collected and unalysed with an originality peculiar to the great Russian chemist. YOL. LIII. 21 358 BRAUNER ON THE DENSITY OF of the material partly because only a very few of the rare earths can be regarded as homogeneous bodies.For the present investigation cerium (cerous) sulphate was used, which served me for the determination of the atomic weight of cerium (Trans. 1885 879) ; cerium sulphate as regards its solubility in water exhibits two peculiarities by which it is distinguished from the majority of salts. It is more soluble in cold than in warm water, and the anhydrous salt is not only more soluble but far more easily soluble in water than the hydrated salt. Many chemists assume that each of these salts is dissolved in water as such and that the solubility a t a higher temperature decreases, because on heating the cold saturated solution of the anhydride, hydrates of the salt which cannot exist in solution a t that high temperature are formed and deposited.The question whether a solution of an anhydrous salt is identical with that of the hydrated salt has been discussed of late especially by English chemists and therefore in the present case I tried to deter-mine whether there was any difference observable between solutions of the anhydrous and hydrated cerium sulphates of equal concentra-tion. The following experiments show the unequal solubilities of the anhydyous and the hydrated salts. If anhydrous cerium sulphate is added to water a t 0-3" little by little with continuous stirring it dissolves quickly and completely until 60 parts of anhydrous sulphate have been used for 100 parts of water. If more of the salt is added it is not only converted into crystals of the hydrate but crystals of the hydrate are also gradually deposited from the solution this being accompanied by development of heat.When the temperature of the liquid (and salt) has risen to 15" it becomes converted into a kind of crystalline paste. On stirring this for some time a t 15" until no further separation of crystals takes place and then separating the liquid from the solid portions a solution is obtained containing 27.88 parts of the anhydrous sulphate to 100 parts of water. If 31.62 parts of the anhydride be dissolved in 100 parts of water a t 0-3" no salt separates out from the solution on raising its tem-perature to 15". This is however the maximum of concentration of a solution whose density can be determined in the usual way for after standing for some time a t 15" crystals of a hydrate begin to separate out in the picnometer.When the solution has been standing for some days exposed to the air a t 15-18' in an open vessel so that spontaneous evaporation occurs a great part of the salt crystallises out and a solution remains containing 17.69 parts of the anhydride to 100 parts of water CERIUM STJLPHATE SOLUTIONS. 359 How difficult it is to attain the final point of saturation without starting with a supersaturated solution may be seen from the following. Anhydrous snlphate 14.56 parts was dissolved in 100 parts water at 3". After standing for a few days exposed t o the air numerous crystals of a hydrate separated but the saturated solution con-tained only 15-59 parts of anhydride to 100 of water. Crystals of the hydrate Ce,(SO& + 8H20 were stirred from time to time with water at 15" during two days in such proportion that a great part of the salt remained undissolved ; in this case only 17.52 parts (anhydrous salt) were dissolved by 100 water.On one occasion a solution of 19.80 parts of the anhydride in 100 water was obtained on concentration by spontaneous evaporation but on trying t o obtain such a saturated solution of the hydrate once more in the same way solutions were obtained containing after two days 11.66 parts and after five days only 12.24 parts in 100 water. From this it will be seen that on saturating water with cerium sulphate at the mean temperature of 15-18" solutions may be obtained containing from 12-24! to 31-62 parts of salt in 100 water ; it is however difficult t o determine the point at which " saturation " ceases and " supersaturation " begins.For the determination of the density of the solutions two Thorpe picnometers of 18.9 C.C. (a) and 22.5 C.C. ( b ) capacity were used. In the middle of the narrow neck two fine lines 1 mm. distant were engraved and the volume of each of these intervals was determined by putting into the vessel full of water a drop of mercury of a known weight (MendeGeff). This volume was found to be for a 0.0054 and for b 0.0042 C.C. As one-tenth of that interval can be measured by optical means the corresponding sp. gr. can be estimated to within about 0.00002. The temperature was determined by means of a normal Geissler thermometer showing distinctly O*0lo the zero point of which was corrected several times duying the investigaticn.All determinations were made at 15" ; and in order to keep this temperature constant for a sufficient length of time in the glass vessel (with flat sides) containing about 4 litres of water into which the picnometers were plunged the temperature of the surrounding air was kept artificially at 15-5-15.6". The weights used were carefully corrected and the weight of the liquids and vessels reduced to a vacuum. By using the method of vibrations the error does not exceed 0.1 mgrm. which makes the error 0.00001 in the density. For calculation of the sp. gr. 0.999159 was taken as the mean density of water at 15" water at 4" = 1. The air was pumped out of the solutions before weighing, but this could not be carried too far in the case of the more con-centrated solutions.2 3 360 BRAUNER ON THE DENSITY OF Calculated. After each determination the contents of the picnometer was transferred to a weighed platinum crucible and this was weighed in a thin glass weighing bottle so as to prevent any loss which might be caused by evaporation. The solution was then carefully evaporated on the water-bath and the anhydrous salt obtained by heating the crucible at 440" in the sulphur-bath described in the paper quoted above. The experimental error caused by inexact determination of the amount of salt in solution has the greatest influence on the final result for a difference of +0*005 part of salt i n 100 parts of water makes as much as +0.00005 in the density. The first series of experiments was made with solutions of the anhydrous sulphate the second series with solutions of the hydrated salt of nearly equal concentration; these were prepared afresh for each experiment by synthesis.The first column of the tables A and B below shows the quantity of anhydrous salt contained in solution €or 100 parts of water present (not the percentage) the second the Difference. A. Solutions of the Anhydrous Sulphate Ce2(S04), at 15'14". 1'03006 1 y' -0'00001 5 __ 100' 21.19 _ _ _ _ ~ -31-62 Density found. 149.1 99.9 Density mean. 1 -19649 - 0 '00009 1 -030026 1 '030071 1 * 03005 3z 0 -00002 1 -058082 1 *058151 1 -080026 1 '079983 -__-1 '05812 -+ 0 -00004 1 -08000 f 0 * 00002 --1.05795 1 +0-00017 -I-1'08003 1 -0*00003 1 -090810 1 090880 1 -09085 f 0 *00004 1 -09939 f O -00003 - ~ -1.09077 1 +0*00008 328 -7 299 * 5 -249 -5 ---1 '09952 - 0 *00013 I -___-1.11905 1 +0-00012 ~ 1.099418 1 *099362 1.119153 1 *119169 1 - 119171 1 -119196 1 '1191t f O ~00002 12 -66 1 -136646 1 -13665 1.13651 ~ +0*00004 I -- " X I " V 1 -146212 1 -146247 1 - 14623 zk 0 *00002 1 *196426 1 *196367 1 '28'777 -1 -19640 &0*00003 1 -28'778 1'28788 1 -0'0001 CERIUM SULPHATE SOLUTIONS.36 1 number of molecules of HzO holding 1 mol. of the respective salts (anhydrous and hydrated) in solution the third the density found, the fourth the mean numbers the fifth the numbers calculated by the interpolation formulse given below the sixth the differences between the numbers calculated and found.B. Solutions of the Hydrated Xulphate Ce2(S0& + 8HZO. ~ ~~~~ Calculated. 1 * 03015 -1 *0599 1 1 '07902 ----1 '08029 -1 *09936 --1 * 09960 -1 * 10981 --1 * 11521 1 *13605 1 -Y' X -100' Density found. Density mean. Difference. 3 -18 -6.31 -x *35 994 -2 1 *030060 1 '030068 1 * 030075 1 *030106 1 *03008 ~0~00002 - 0.00007 1 -059561 1 -059957 1.05956 -f 0 - 00000 + 0 *00005 500 -3 378 *4 -372 -3 299 *9 --+ 0 -00008 1 '0'79062 1 -0'79130 1 -07910 & 0 '00003 8-48 -10 -53 -10 -56 -11 a 66 1 .Of30337 1 * 050282 1 -08031 f 0 -00003 + 0 -00002 1 -099292 1 '099273 1 '09928 ,J 0 '00001 1 -099606 1.099564 1 -09959 f 0 * 00002 - 0 *00001 1 -109857 1 a 109883 1 '10587 f 0 '00001 + 0 '00006 1 -115294 1 *115300 1 *136180 --+ 0 -00009 1-11530 f 0 ~00000 1 * 13618 12 -24 14 -52 -+ 0 WO13 In order to see whether the densities of the solutions of the anhy-drous salt are identical with those of the hydrate of equal concentra-tion the densities for equal concentration had to be calculated.Dr. A. Seydler Professor of Natural Philosophy in our University has kindly calculated by a complicated formula involving the use of the method of least squares the equations for parabolas showing the dependence of the density on the concentration in both series of experiments but as the equations were calculated only from the data obtained by me without regard t o the fact that water at 15" has a density of 0.99916 the corresponding values in the equations had fo be extrapolated which makes them somewhat uncertain (0.99966 an 362 0.99964 instead of 0,99916) Other methods of calculation however gave no better results.The equations are ( d = density at 15" x = salt for 100 parts water) : (A,) For the anhydride d = 0.999665 + 0*00964010 - 0-0000166~~. (B.) For the hydrate d = 0.999636 + 0.0096646~ - 0*00001839~~. The values calculated by the aid of these formulze for 2 to 14 parts of salt in 100 water (14 being the maximum of concentration of the solution of the hydrate) are given in the following table :-BRAUNER ON THE DENSITY OF D emit y of anhydride solution. ~--0.99967 -~__--X -100' Density of hydrate solution.0 * 99964 0 1 *03796 1 *05691 1.07572 1 * 09441 1 -11296 1 *13137 ~---~-----___-___ 2 4 -1 * 03800 1 '05696 1 '07578 1 *09444 1 -11296 1.13134 -- G 8 -Difference. - 0.00003 + 0 *00001 + 0.00004 + 0 * 00005 + 0 *00006 + 0 *00003 0 ~00000 -0 *00003 From a comparison of both series it follows-1. That the densities of solutions of anhydrous cerium sulphate are identicaZ with the densities of the solutions of the hydrated salt. 2. That the differences in both series fall entirely within the un-avoidable experimental errors for the differences never exceed those between the numbers found and calculated as is seen from Tables A and B. Finally it should be mentioned that if solutions of the hydrate and those of the anhydride of equal concentration be evaporated in vessels of equal size and material on the same water-bath those of the anhydride will show an inclination to deposit monoclinic prisms of the salt Ce2(S04) + 5H20 whereas solutions of the hydrate + 8H20, are more inclined to deposit rhombic octahedrons of the salt, Ce2(SOa)s + 8H20.This difference in behaviour of the two solutions holds good only for those concentrations in which the salt begins to be deposited not on merely heating the solutions but only after some water had evaporated. I cannot say definitely whether this may no CERIUM SULPHATE SOLUTIONS. 363 be due partly to chance; that it is reaJly the case however is seen from the following analyses :-(a.) EvaToration of a Solution of the Anhydrous Salt. The salt Ce2(S0& + 5Hz0 is stable at 100". Weight of salt-(a.) Directly after evaporation at 200". . After drying at 100" f o r 5 hours After drying at 100" for 10 hours . After drying at 100" for 15 hours . Weight of anhydrous salt (440") . (p.) Salt at 100" Salt at 440". . (y.) Salt at 100" . . . . . . . . . . . . Grams. 1.4677 1.4474 1.4458 1.4445 1.2547 1.1828 1.0204 1.2244 1.0577 Water in Calculated for per cent. Ce2(X04)3 + 5H2O. 14-51 13.66 13-31 13.19 13.14 13.72 13.62 (b.) Evaporation of a Sohtion of the Hydrated Salt. The salt Ce2(S04)3 + 8H,O loses 4 mols. H20 at 100". Water in Grams. per cent. Hydrate. Requires. Weight of salt-(%.) After evaporation at 100" 1,4975 19.92 8H20 20.21 100" . 1.3479 11.03 4H,O 11.24 ( / 3 . ) Salt at 100". . 1.3093 11.11 4H20 11.24 Aft,er drying 2 hours at Anhydrous at 440". . 1.1992 Salt at 440". . 1.163