T H E SOLUBILITY O F GYPSUM IN COPPER SULPHATE SOLUTIONS' B Y J. M. BELL AND W. C. TABER
In studying the mutual solubility relations of copper sulphate and calcium sulphate t o which reference was made in the preceding paper, a series of solutions of copper sulphate was prepared, ranging from 0.1percent to a saturated solution, and toeach solution an excess of powdered calcium sulphate was added. After constant agitation for two weeks in a constant temperature bath at 2 5 O the solutions were analyzed for lime and for copper. ~~~
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Density of solution Grains CuSO, per liter
at 25' -C
Grams CaSO, per liter
25'
I . I44 3.564 6.048 7.279 14,814 19.729 29.543 39 407 49 382
1.002 I ,005 I ,007 I
,009
I .016 1.021 I
,030
,041 ,051 ,061 I ,098 I . 146 I ,192 I ,218
,I
'
I I
'
58,880
I
I I
,
97.950 146.725 196.021 224.916
2.068 I ,986 1.944 I ,858 I ,760 1 736 I ,688 I ,718 1 ,744 I ,782 1.937 2.048 2.076 2.088 '
These results have been plotted and show a decreasing solubility of gypsum as the concentration of copper sulphate increases, until a minimum is reached a t about 30 grams of copper sulphate per liter, at which concentration there is nearly 1.7 grams of calcium sulphate in solution. From this point the curve shows a rather sharp rise to a concentration of about 150 grams copper sulphate per liter, when there are about 2.05 grams calcium sulphate per liter. From this point the curve shows a slight but gradual rise till the point of saturation with respect to copper sulphate is reached, when Published by permission of the Secretary of Agriculture.
J . Ad. Bell and W . C. Taher
638
there are 2.08 grams calcium sulphate per liter in solution. At this point there are two solid phases, calcium and copper sulphates, and the solution has a constant” composition. The remainder of the isotherm is the curve representing the solubility of copper sulphate in various solutions of gypsum. As the solubility of gypsum in water is relatively very small, its presence even in saturated solutions will probably have but little effect on the quantity of copper sulphate in solution. The correctness of this follows from the work of Trevor,l who found that a saturated solution of copper sulphate in
water contained 22.29 g r a m of copper sulphate per IOO grams of water, while in the present experiments the solubility of copper sulphate in a saturated solution of gypsum was found to be 22.49 grams of copper sulphate per IOO grams of water. It will be observed that copper sulphate in common with all the sulphates, excepting sulphuric acid,’ decreases the solubility of gypsum, as might be expected of compounds with a common ion, but at higher concentrations its solubility increases. Bureau of Soils, U . S. Department of Agriculture, Washmgton, D. C. _
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Zeit. phys. Chem., 7, 470 (1891). See Cameron and Bell: Bull. No. 33, Bureau of Soils, U. (1906).
S.Dept. Agr.
