168 
Selected Articles. 
counters. This latter objection, I must say, is hypercriticah' 
if people will be careless, there is no means of preventing mis- 
takes, and I conceive the objection of Mr. Barry applies with 
tenfold force to many arrangements of a druggist's shop, 
where we often see tincture of opium flanked right and left 
by other dark tinctures; and who that has manipulated has 
not caught himself laying hold of, and using one acid, &c. 
for another, when the mind is also at work? 
(10.) I have made many trials as to the practicability of 
applying the cyanide of silver and dilute hydrochloric acid 
for procuring medical hydrocyanic acid. The cyanide of 
silver presents many advantages : it is perfectly stable, be- 
ing neither affected by light nor moisture ; its purity can be 
very easily ascertained, and every five grains of it will yield 
one grain of acid. It can be procured by conducting the va- 
pour from the process described in section (6.) of this paper, 
into a pint of water, holding 255 grains of nitrate of silver, 
washing and drying at 212°. It yields 201.6 grains of white 
cyanide. I should recommend that the bottle containing this 
salt be accompanied by a small stoppered phial w r ith dilute 
hydrochloric acid of such strength, that one minim will ex- 
actly decompose one grain of the cyanide : thus, suppose one 
corked phial having 200 grains of cyanide with one J oz. 
stoppered bottle with hydrochloric acid of specific gravity 
1.129, this would be enough to make five fluid ounces of di- 
lute hydrocyanic acid, of the Dublin strength, if the follow- 
ing formula be followed. Into a phial capable of holding 
rather more than one fluid ounce, put forty grains of the cy- 
anide, add seven fluid ounces twenty minims of water, and 
forty minims of the dilute hydrochloric acid; cork closely, 
shake several times for the first quarter of an hour, set aside 
to allow the chloride of silver to fall, decant the clear liquid 
into another bottle, to be preserved for use : every fluid 
drachm will contain one grain of real hydrocyanic acid. 
The only objection I had a 'priori to this process, was the 
liability of a little free hydrochloric acid remaining in the so- 
lution, since all books echo that the presence of a minute 
quantity of the mineral acids very much hastens the decom-' 
