56 
SELECTED ARTICLES. 
Sulphate of Iron.— Evidently it is meant the green 
vitriol of the older chemists. It is necessary to choose 
it in handsome crystals, transparent, of a pale or emerald 
green color, free from copper, and completely at the minimum 
of oxidation. Its formula is SFe-f-60H2, and its atomic 
equivalent =1615.24. 
Subcarbonate of Potussa. — This is the neutral carbonate 
of chemists, (CK,) its atomic weight is 866.35. But this salt 
is found in the shops in several states, and it is important to 
fix upon that which should he employed. In one of these 
states it is very impure, forming the potash of commerce; and 
although the new Codex authorizes its employment, in the 
place of the true carbonate of potassa, containing, as it does, 
chloride of potassium and sulphate of potassa, still it cannot be 
imagined that this saline compound should be used in prepar- 
ing Blaud's pills. Let us look a little farther for the article. 
There is found in the shops what is called Salt of Tartar, 
obtained by calcining cremor tartar, and lixiviating the pro- 
duct. This salt when dried presents the pure carbonate of 
potassa, and is such as is required in the formation of the pills; 
but what is at present found in commerce under the name 
of salt of tartar, is nothing more than impure potash dissolved 
in water and dried. A similar article which I examined was 
composed of 
Carbonate of potassa 38.8 
Chloride of potassium ? 49 2 
Sulphate of potassa 5 
Water 12.0 
100.0 
This certainly is not fit for the purpose. 
It is easy for pharmaciens to obtain a carbonate of potassa 
almost pure, by following the method given in the Pharma- 
copee Faisonnee, torn. 2, p. 406. The best potash is to be 
dissolved in three-fourths or half its weight of distilled water. 
After twenty-four hours, it is filtered through double paper, 
