184 
ON THE IMPURITY OP SOME DRUGS. 
I. II. III. 
IV. 
Silica, 50.15 47.31 .... 
Peroxide of iron, 22.69 32.96 31. 
Alumina, 11.46 
Lime, 6.43 
Water, .... 
Sulphate of lime, .... 
Magnesia, .... 
49,38 
30.44 
6.90 
7.04 
8.30 
1.98 
To determine if any silica was contained in the sulphate 
of barytes of the adulterated calamine, the sulphate was 
fused with carbonate of soda, the fused mass washed with 
water until the sulphate of soda was removed, and then 
the residue was digested in dilute muriatic acid. A por- 
tion of silica remained undissolved ; the quantity was not 
determined, but it is obvious that the calamine contains all 
the substances existing in American bole, and the conclu- 
sion is scarcely avoidable that the color is caused by the 
presence of this body. 
This substance, also termed milk of sulphur and washed 
sulphur, is properly prepared by boiling sulphur with lime 
or potash, precipitating the solution with muriatic acid, and 
throwing the precipitated sulphur on a filter and washing it. 
If this form of sulphur were always prepared in this man- 
ner, no impurity would exist in it. But it has been observed 
that this article, in London, at least, contains always above 
one-half its weight of impurity. To ascertain if this sub- 
stance in Glasgow was equally impure, 53.85 grains were 
ignited in a platinum capsule, and Avere found to lose 29. 
grains. This would make the composition of the sulphur — 
sulphur, 49.27, and sulphate of lime, 50.73. But as the 
gypsum was in crystals, it obviously contained its water of 
crystallization, which must therefore be calculated. The 
constituents of hydrous gypsum are — Ca = 3.5 S 3 = 
5 2 H 0=2.25=10.75. The quantity of water belonging 
2. Precipitated Sulphur. 
