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Proceedings of the British Association. 323 
tations. Experiments are now in progress to Aetenmine this ques- 
tion. 
New schemata process for the anideutiia of i 
Acid for medical use, by R. D. Thomson, M.D. The i importance 
- of this acid as a remedial agent, induced the author to bestow 
much attention upon a mode of producing it always of uniform 
Strength. Having tried all the processes for this purpose, proposed 
in this country, he was satisfied that none of them afforded an acid 
of uniform strength. The process recommended by Dr. Clark of 
Aberdeen, was superior to every other, but an objection to it is 
the great difliculty of procuring pure cyanide of potassium. The 
author believes the following process to be less liable to objection 
than any at present used. The first step consists in forming a 
pure cyanide of lead. ‘This may be done in various ways, either 
by precipitating acetate of lead by hydrocyanic acid, as prepared 
from the ferrocyanide of potassium and sulphuric acid, ina stop- 
pered bottle, or by distilling the mixed materials into a Wolfi’s 
bottle containing a solution of acetate of lead. In either case a 
definite compound of cyanogen and lead will be obtained, which 
is to be carefully washed and gently heated. The next step in 
the process is to decompose it by means of sulphuric acid. In 
order to obtain an acid of the strength of the Acidum Hydro- 
cyanicum dilutum of the London Pharmacopeia, or containing 
about two per cent. of absolute acid, the following formula is re- 
commended. 
46.36 grains of cyanide of lead. 
2 fluid drachms of dilute sulphuric acid. Lond. Pharm. 
6 fluid drachms of pure distilled water, 
Introduce the cyanide of lead into a stoppered bottle ; mix the 
acid and water in a glass vessel; allow the mixture to cool, and 
then pour upon it the cyanide of lead. Close the stopper, and 
agitate the fluid and salt together. After standing for some time, 
pour off the supernatant liquor from the precipitated sulphate of 
lead, and preserve it in a stoppered bottle. This formula is 
founded upon the circumstance that the dilute sulphuric acid of 
the London Pharmacopeeia contains in each fluid drachm about 
9.5 grains of oil of vitriol (SO?HO). Two drachms will there- 
fore contain nineteen grains of oil of vitriol. The quantity re- 
quired for saturating 43.36 grains of cyanide of lead, is only 17.4 
grains ; but the small excess is useful in preserving the a 
