1819.] Cyanogen and Hydrocyanic Acid. 44) 
ammonia, and consequently an ammoniacal mercurio-muriate. 
On the first supposition, charcoal must have been deposited ; 
and on the second, carbonic acid must have been formed. But 
neither the one nor the other of these took place, though the 
liquid assumed a light-brown colour. 
“ M. Gay-Lussac has not spoken of this phenomenon ; pro- 
bably because having employed less acid it did not take place in 
his experiments. However in another experiment, in which I 
employed only 30 grammes of muriatic acid, I obtained only 
about two grammes of hydrocyanic acid, possessed of all the 
properties described by Gay-Lussac. The residue of the opera- 
tion contained likewise ammoniaco-mercurial muriate, though I 
had conducted the process with much caution. 
“It is singular that having some time afterwards repeated this 
process twice, I did not obtain the triple mercurial salt. I do 
not know to what I ought to ascribe this difference. It is pos- 
sible that in the first processes, in which the apparatus was 
arranged the evening before, the cyadide of mercury having 
remained long in contact with the muriatic acid before being 
subjected to the action of heat, the hydrocyanic acid underwent 
‘e decomposition. 
“ The observations which J have just stated respecting what 
passes sometimes between muriatic acid and cyadide of mercury, 
would be of little importance unless they were to lead to a better 
method of obtaining that acid. 
« Considering that mercury has a strong attraction for sulphur, 
and that cyanogen unites easily to hydrogen when presented in 
the proper state, I thought that sulphuretted hydrogen might be 
employed for decomposing dry cyadide of mercury. I operated 
in the following manner: I made a current of sulphuretted 
hydrogen gas disengaged slowly from a mixture of sulphuret of 
iron, and very dilute sulphuric acid pass slowly through a glass 
tube slightly heated, filled with cyadide of mercury, and commu- 
nicating with a receiver cooled by a mixture of salt and snow. 
«« As soon as the sulphuretted hydrogen came in contact with 
the mercurial salt, this last substance blackened, and this effect 
gies extended to the furthest extremity of the apparatus. 
uring this time no trace of sulphuretted hydrogen could be per- 
ceived at the mouth of a tube proceeding from the receiver. As 
soon as the odour of this gas began to be perceived, the process 
was stopped ; and the tube was heated in order to drive over the 
acid which might still remain init. The apparatus being unluted, 
I found in the receiver a colourless fluid, which possessed all the 
known properties of dry prussic acid. It amounted to nearly the 
fifth part of the cyadide of mercury employed. 
“« This process is easier and furnishes more acid than the one 
by means of muriatic acid. I repeated it several times, and 
always successfully. It is merely necessary to take care to stop 
the process before the odour of the sulphuretted hydrogen begins 
