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ORIGINAL COMMUNICATIONS. 
It may be objected to this, that such nicety is not required, 
and that the presence of so small a quantity of iron in the pre- 
paration cannot possibly injure its effects as a medicine. This 
may be true, or it may not; I do not intend to discuss it, and 
will admit that absolute purity is not so imperatively called 
for as in the salt before treated of; but we all profess to sell 
pure medicines, and a sulphate of zinc containing iron, is not 
pure sulphate of zinc. The time occupied in preparing this 
notice it is believed has been well engaged if it serve to attract 
the attention of any one to a fact which had hitherto escaped 
his notice. As to the modes recommended, the author speaks 
from his own experience with them. 
Carbonate of Soda. The extensive manufacture of artifi- 
cial barilla, as it is called, has introduced into our markets a 
carbonate of soda, containing a sulphuret of soda, which is ex- 
ceedingly unpleasant, to say the least. My attention was 
once or twice called to the smell of sulphuretted hydrogen 
arising from carbonate of soda, before I paid much regard to 
it, passing it by as the result of accident, or neglect in clean- 
ing out the mortars after they had been used for some pre- 
vious preparation; but upon one occasion when I saw that no 
cause of this kind could have produced it, I at once recog- 
nised the cause; at least, such a cause as was adequate, in my 
opinion, to account for it. Having seen no reference to this 
subject in any of the books, it occurred to me that it could not 
prove uninteresting to your readers to have some account of 
it. The artificial barilla of this country is made by the de- 
composition of sulphate of soda, by means of charcoal and 
lime. The effect of this combination when heated is first to 
convert the sulphate into sulphuret of soda, which is decom- 
posed by the lime, leaving as the product, soda and sulphuret 
of lime, mixed with carbonaceous matter, of which there is al- 
ways an excess. This is the theoretical effect, but in practice, 
some sulphuret of soda is always left, which it is found im- 
practicable to separate, at least with due regard to the economy 
which prevails in large manufacturing establishments. I have 
