162 
SELECTED ARTICLES. 
Repertory New Series, vol. i., p. 178 — 181, in the number 
for March, 1834). Mr. Barry has also put me in possession 
of a means as elegant for the testing of the presence of minute 
quantities of hydrochloric or sulphuric acid in hydrocyanic 
acid, viz. : put some of the acid on a watch glass, add two or 
three drops of liquor ammonias, put the glass on the sand bath 
and evaporate to perfect dryness, when all ammonia and hy- 
drocyanic acid pass off, leaving only, if any hydrochloric or 
sulphuric acid be present, a little hydrochlorate or sulphate of 
ammonia behind; a drop or two of distilled water will dis- 
solve these, and by nitrate of silver added to one half, and 
nitrate of barytes to the other, the presence or absence of the 
above acids will be determined. If the hydrocyanic acid be 
quite pure, the watch glass, after evaporation, is scarcely soil- 
ed, and water dissolves nothing: this method is far preferable 
to that by means of carbonate of lime usually recommended. 
In a paper which I read to the Medico-Botanical Society, 
on Thursday, December 9, 1834, on the methods of assaying 
medicinal hydrocyanic acid, I stated that I had examined 
samples of the acid procured from various shops in town, and 
that the frightful difference of strength had induced me to 
make the results known, with a view of calling the attention 
of the medical profession to the evil. Thus, samples from 
Allen, Hanbury & Co., yielded 5.8 per cent.; from Apothe- 
caries' Hall, at different times, from 2.1 to 2.6 per cent.; and 
from several sources I found acid containing only 1.4 per 
cent. These samples I procured from the several shops per- 
sonally, and asked for Scheele's strength. They were assay- 
ed within 24 hours after they were in my possession, both by 
the nitrate of silver, and the oxide of mercury method, and 
the results in no cases varied more than 1.10th of a grain from 
each other. Now it is true we have no fixed standard, and 
therefore it is impossible to say whether Allen & Co.'s is too 
strong or the others too weak; but thus much is certain, that 
if a medical man were pushing the exhibition of hydrocyanic 
acid gradually to a maximum dose, the prescriptions being 
carried to a shop where the acid had only 1.4 per cent., and 
