442 : M. Vauquelin’s Memoir on [June, 
to be perceived, otherwise the hydrocyanic acid will be mixed 
with it. However, we may avoid this inconvenience by placing 
a little carbonate of lead at the extremity-of the tube. As dry 
hydrocyanic acid is only required for chemical researches, and 
as it cannot be employed in medicine, in which that acid in a 
dilute state begins to be used, I think it may be worth while to 
bring to the recollection of apothecaries a process of M. Proust, 
which, perhaps, has escaped their attention. It consists in 
passing a current of sulphuretted hydrogen gas through a cold 
saturated solution of prussiate of mercury in water,* till the liquid 
contains an excess of it; to put the mixture into a bottle in 
order to agitate it from time to time, and finally to filter it. 
“ Ifthe hydrocyanic acid, as almost always happens, contains 
traces of sulphuretted hydrogen, agitate it with a little carbonate 
of lead and filter it again. 
“« By this process we may obtain hydrocyanic acid in a much 
eater degree of concentration than is necessary for medicine. 
t has the advantage over the dry acid of being capable of being 
preserved a long time, always taking care to keep it as muchas 
possible from the contact of air and heat.” 
Conclusions. bl 
From the important set of experiments of which we have just 
given an account, M. Vauquelin draws the following conclusions : 
“ }, Cyanogen dissolved in water is converted into carbonic 
acid, hydrocyanic acid, ammonia, and a peculiar acid, which 
may be called cyanic acid, and into a charry matter. This hap- 
pens in consequence of the decomposition of water. These new 
compounds arrange themselves in the following order: The 
ammonia saturates the acids, producing soluble ammonical salts ; 
while the insoluble charry matter is deposited. 
“2. The alteration produced by the alkalies, strictly so 
called, in the constitution of cyanogen is exactly of the same 
nature as the preceding ; that is to say, there are formed hydro- 
cyanic acid, carbonic acid, probably cyanic acid, charry matter, 
and ammonia, which is disengaged in consequence of the 
presence ofthe other alkalies. This is the reason why the solu- 
tion of cyanogen in an alkali gives at once (as Gay-Lussac has 
observed) prussian blue with the acid solutions of iron. 
“3. The common metallic oxides produce the same effects on 
cyanogen dissolved in water as the alkalies, but with different 
degrees of rapidity, according to the affinity which each of them 
has for the acids developed. But in this case triple salts are 
formed, as we have shown when treating of oxide of iron and 
oxide of copper; so that cyanogen, similar in this respect to 
* Experience has shown that a solution in the proportion of a gros (59-06 grs. 
troy) of cyadide of mercury to an ounce of water gives a hydrocyanic acid suffi- 
ciently strong to be employed in medicine. This is the strength of the acid 
employed by MM. Hallé, Magendie, &c. 
6 
