430 =: M. Vauquelin’s Memoir on [JUNE, 
acid. This produced a desire to see some skilful chemist under- 
take this difficult task, and give it ail the perfection which the 
great improvements i the means of analysis induced chemists 
to wish for and expect. This task was accordingly undertaken 
by M. Gay-Lussac, and the results to which he arrived would 
have been astonishing had they not been produced by a philoso- 
pher possessed of very uncommon sagacity ; yet he acknowledged 
that experiments were still wanting to complete the subject. 
This confession occasioned the memoir of M. Vauquelin, of 
which we propose to give an abridgment in the present article. 
Even M. Vauquelin himself still admits that his own labours are 
far from completing our knowledge of this intricate subject. 
“Though I found the road struck out, and easily followed,” 
says he, “ 1 am yet far from pretending that I have traversed 
the whole of it. Many lateral paths issuing from that road still 
remain to be discovered. But these routs will gradually be laid 
open.” 
Of the Alteration which Cyanogen dissolved in Water gradually 
undergoes. 
The phenomena presented by the decomposition of cyanogen 
dissolved in water are very important to be known. Upon them 
depend the explanation of a multitude of changes observed in the 
reaction of this body, and of hydrocyanic acid on other bodies. 
This is the reason why M. Vauquelin begins with it in his 
memoir. 
The fresh sclution of cyanogen in water is quite colourless ; 
but after an interval of some days it becomes yellow, then brown, 
and allows a matter of the same colour to precipitate. Then the 
liquor has lost the penetrating odour of cyanogen, and possesses 
the peculiar odour of hydrocyanic acid. If tron filings do not 
occasion the formation of prussian blue, as would happen if they 
were brought in contact with pure hydrocyanic acid, this 
depends upon a cause which will be understood immediately. 
We may, however, produce prussian blue in the liquor separated 
from the iron filings, by adding to it a slight excess of sulphuric 
acid. When, on the contrary, the iron is superabundant, the 
sulphuric acid combines with it by little and little, and the blue 
colour, which was at first manifest, disappears; but it always 
appears again when a new dose of acid is added. 
Water seems to be the sole efficient cause of the alteration of 
cyanogen in the present case. M. Vauquelin has ascertained 
that the solution of this body in ether, though quickly and easily 
made, does not become coloured, and that alcohol alters it so 
much the less the stronger it is. 
The aqueous solution of cyanogen, altered by standing, yields, 
when distilled, a liquid, having a strong odour of hydrocyanic 
acid, which contains hydriodate of ammonia and subcarbonate 
of ammonia. The residue of this distillation is a liquid, holding 
