ON THE IMPURITY OF SOME DRUGS. 
185 
to the sulphate of lime found in the analysis will therefore 
be 13.42 per cent. The true constituents, then, are, — 
Sulphate of lime, 50.73 
Water of crystallization, 13.42 
Sulphur, 35.85 
100. 
3. Oxide of Zinc. 
This oxide generally effervesces on the addition of an 
acid, proving the presence of carbonate of zinc, or of the 
carbonate with which it has been precipitated. When, to 
the solution of this oxide in muriatic acid, an excess of 
caustic ammonia is added, some brownish-red flocks of 
peroxide of iron remain undissolved, containing, perhaps, 
a little alumnina, amounting to about one-half per cent. 
4. Red Oxide of Iron. * 
This oxide, as sold in the shops, has been examined by 
my brother, Mr. James Murdoch, and found to contain a 
small percentage of alumina. 
5. Tartar Emetic. 
This salt generally contains a small quantity of peroxide 
of iron. 
Glasgow College Laboratory, April, 1844. 
Pharmaceutical Journal. 
NOTE BY DR. R. D. THOMSON. 
The first person who published an account of the extra- 
ordinary mixture called Calamine in the shops^ was Mr. 
Brett, in the British Annals of Medicine, vol. i., p. 485. He 
found, however, traces of lead and zinc in the specimens 
which he analysed, a circumstance which has never occur- 
red to me, either before or since that period. It is possible, 
vol. x. — NO. III. 17 
