THE SOLURI1,ITY O F CALCIUM S U L P H A T E I N SOLUTIONS O F O T H E R SALTS' BY F. K. CAMEROS A N D B. E. BROWN
T h e effect of different electrolytes upon the solubility of calcium sulphate has already received considerable attention in this laboratorya2 This paper records some results which have been obtained with solutions of ammonium chloride and ammonium nitrate of various concentrations, and with saturated solutions of certain other salts. T h e solutions employed in the work here described were contained in 8-ounce bottles provided with tightly fitting rubber stoppers, an excess of solid calcium sulphate being present in each bottle. Kahlbaum's chemicals were used. The bottles were kept in a constant temperature bath at 25" C., being temporarily withdrawn from time to time to thoroughly shake the contents. After remaining in the bath for several weeks portions of the solutions were carefully withdrawn for analysis, Determinations on duplicate series made at different times yielded results in very close agreement, and therefore, the averages only are being considered. Where ammonium salts were used the solutions were analyzed for ammonia rather than for acid radicals, but in the case of the other salts the amount present was calculated from the amount of acid radical found in the solutions. Solubility of Calcium Sulphate i n Solutions of Ammonium Chloride Tilden and Shelistone' determined the solubility of calcium sulphate in ammonium chloride solution at different temperatures, but only one concentration of ammonium chloride was considered by these investigators. F a s ~ b e n d e r ,in ~ 1876, published some results upon the solubility of calcium sulphate in solutions of both the chloride Published by permission of the Secretary of Agriculture. Jour. Phys. Chem. 5 , 556, 643, (1901); 7, 57' ('903); 8, 335, 493 (1904). Proc. Royal SOC. 38, 333 (1885). Ber. chem. Ges. Berlin, g, 1360 (1876).
and nitrate of ammonium respectively, but his figures can oiily be regarded as approximations. Cohn' and Ditte2 have also studied the solubility of calcium sulphate in solutions of ammonium chloride, their results presenting discrepancies which can hardly be explained as due to analytical errors. I n the following table are given the results obtained in terms of grams per liter of solution. For coiiiparative purposes the earlier results of Ditte and also of Cohn are given.
TABLE I.-SOLUBILITY O F CALCIUMSULPHATE IN SOLUTIONS OF AMMONIUM CHLORIDEAT 25' C. Grams CaSO, per liter Grams NH,C1 per liter
10.8 20.0
24.4 26.0 40.0 46.7 6 7.0 80.0 94.5 105.0 120.0
126.0 149.7 I 70.0 198.6 200.0 202.0 2 10.0
228.0 270.0
275.0 280.0
325.0 333.0 375.3 (saturated I
Jour. prakt. Chem. ( 2 1 , 35, 43 (1887). Compt. rend. 126,694 ( 1 8 9 8 ) ; Ann. Chim. Phys. (7) 14, 194 (1898).
F. K. Canzcvoiz am! 8.E. B Y O W ~ Z
212
.
T h e solubility of calcium sulphate in ammonium chloride solutions, as shown by the graphical representation, steadily increases with increasing concentration of aninionium chloride until a concentration of 2 1 0 grams of ammonium chloride is reached, at which point approximately 10.9 grams of calcium sulphate are dissolved. With a further increase of the concentration of ammonium chloride the solubility of calcium sulphate decreases until at the point where both salts are present assolid phases the amount dissolved is 7.38 grams per liter.
Fig.
I
From the results given in Table I it will be seen that Ditte observed no maximum point. Cohn, on the other hand, observed a maximum point, but his deterniinationsare throughout lower than those given in this paper.
Solubility of Calcium Sulphate in Solutions of Ammonium Nitrate T h e solubility of calciuni sulphate in solutions of aninionium nitrate has been determined by Fassbender', Droeze2 and Cohn'.
' 1. c . 2
Ber. chem. Ges. 1. c .
IO, 330
(1877).
SoZzihiZiiy of Calcium Su@t'zatr
Grams ",NO, per liter IO
25 55 IO0
150 200
300 400 5 50 750 I OGO I200
213
Grams CaSO, per liter
3.18 3.93 5.80 7.65 8.88 935 10.80 I 1.40 12.02 12.20
11.81
I 400
11.10 10.02
Saturated
7.55
It will be observed that the solubility of calcium sulphate in ammonium nitrate solutions increases at first. with increasing coilcentration of the more soluble salt, as in the case of the ammoniiim chloride series. The maximum solubility of
F. K.Cainevoiz nszd B. E. Bvowiz
214
calcium sulphate is approximately 12.2 grams in a solution containing 7 j o grams of ammonium nitrate per liter. From this point, with increasing concentration of ammonium nitrate the solubility of calcium sulphate decreases until both salts exist as solid phases, in which case the amount disolved is 7.55 grams per liter. Solubility of Caleium Sulphate in Saturated Solutions of Certain Salts. I n order to make more complete our knowledge of the effect of other electrolytes upon the solubility of calcium sulphate, it has been deemed advisable to obtain the solubility of this salt in solutions of other salts when they also were in contact with the solution as a solid phase. This work was also done at 2 j " C., and the results are given in the folldwing table. I n all cases duplicate series were prepared at intervals of several weeks, the results of both series being given in Table 111. TABLEIII.-SOLUBILITY OF CALCIUM SULPHATE IN SATURATED SOLUTIONS O F C E R T A I N SALTS.
Salt
saturated solution 'I1
NaCl NaNO, Na,SO,
MgC', MgCNO,), NH,C1 ",NO,
318.1 667.9 254.3 477.1 615.3 374.6
-
1
Average
318.5 668.9 254.9 476.9 614.9 380.0
-
318.3 668.4 254.6 476.5 615.1 375,3
-
Grams CaSO, per liter
I
IT
Average
5.53 7.20
5-52 7.16 2.58 I .og I 5.26 7.38 7.55
-5.51
7.12 2.58 1.10
2.58 1.08
15.30 7.31 7.47
15.22 7.45 7.63
'
I n previous work in this laboratory on the solubility of calcium sulphate in saturated solution of sodium chloride1 at 23' the following figures were obtained : NaCl = 31j.j j grams per liter of solution, and CaSO, = 5.37 grams per liter of solution which are in fair agreement with those' tabulated above. It was also found for solutions saturated with respect to both calcium sulphate and sodium sulphatez at 2 j", Na,SO, = 2 57. I Jour. Phys. Cliem. 5 , 556 (1901). Ibid., 8 , 335 (1904).
grams per liter of solution, and CaSO, = 2.65 grams per liter of solution, which is in fair agreement with the figures tabulated above. T h e results given in the above table for solutions of sodium nitrate and magnesium nitrate respectively are in good agreement with values obtained by extrapolating the results formerly obtained.’ I t is iiiteresting further to note the widely different effects of saturated solutions of magnesium chloride and nitrate respectively upon the solubility of calcium sulphate. No calcium sulphate could be determined in saturated solutions of calcium nitrate or calcium chloride. Bureau of Soils, U. S. Department of Apiculture, Washington, D. C. Jour, Phys. Chem. 8, 493 (1904).
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