1816.) E xperiments on Prussic Acid. 363 
hydro-cyanic vapour are capable of acting upon carbonic acid at a 
high temperature, and of partly decomposing it. 
-L have already shown that the oxide of copper decomposes hydro 
cyanic acid completely at a red heat, and that water is obtained, and 
a mixture of one volume carbonic acid and half a volume of azote. 
But I wished to ascertain if the action of these two bodies would not 
be different at the common temperature. | accordingly introduced 
peroxide of copper into a tube with hydro-cyanic vapour mixed 
with hydrogen. ‘The absorption took place by degrees; but was not 
so great as it would have been if all the vapour had been destroyed. 
Having turned up the tube to ascertain by the smell if any hydro- 
cyanic acid remained, I observed with surprise that cyanogen had 
been formed, easily recognizable by the strong and penetrating 
odour which characterizes it. On exposing the oxide to a gentle 
heat, a good deal of water separated from it ; so that it appears that 
hydro-cyanic acid is acted upon in the same manner by peroxide of 
copper as muriatic acid by peroxide of manganese. On putting 
oxide of copper into the liquid acid, diluted with water, the smell 
of cyancgen became very sensible in a few days, and the oxide 
became white on the surface. ‘The peroxide of manganese absorbs 
completely hydro-cyanic vapour in a few hours. Water is formed ; 
but cyanogen does not become sensible. I shall examine more par- 
ticularly hereafter what takes place on this occasion. 
The red oxide of mercury, when assisted by heat; acts so power- 
fully on hydro-cyanic vapour, that the compound which ought to 
be formed is destroyed by the heat disengaged. ‘The same thing 
happens when a little of the concentrated acid is poured upon the 
oxide. A great elevation of temperature takes place, which would 
oecasion a dangerous explosion if the experiment were made upon 
considerable quantities. When the acid is diluted, the oxide»dis- 
solves rapidly, with a considerable heat, and without the disengage- 
ment of any gas. Nothing is obtained but the substance formerly 
called prussiate of mercury. 
When the oxide is placed in contact with the vapour of hydro- 
eyanic acid, mixed with, hydrogen, without applying heat, the 
vapour is absorbed in a few minutes. On emptying the tube of the 
hydrogen in order to fill it with a new mixture, that the result might 
be the more sensible, the absorption of the vapour was as complete 
as the first time, and the hydrogen remained with the volume which 
it ought to have had, which shows that it had no part in the pheno- 
menon. After some similar operations, the oxide adhered to the 
sides of the tube. Having collected it at the bottom of the tube, 
and applied a gentle heat, a good deal of water was evaporated. 
Hence when the peroxide of mercury acts in the cold on hydro- 
eyanic acid, the oxygen of the first combines with the hydrogen of 
the second, which by this last is reduced to its radical. We ought, 
therefore, to obtain, not hydro-cyanate of mercury, but cyanuret 
of mercury. Common prussiate of mercury, which is exactly the 
same, must likewise bear the same name. 
VA 3 
