1816.]} Experiments on Prussic Acid. . 353, 
acid, which he supposes is formed of carbon, azote, hydrogen, and 
black oxide of iron. He founds his opinion on this fact, that when a 
triple prussiate is exposed to the galvanic action, the alkali appears 
at the negative pole, while the oxide of iron and prussic acid appear 
at the positive pole.* In his second memoir Mr. Porrett gives the 
analysis of prussiate of mercury and prussic acid. I shall state this 
analysis hereafter. It is very different from mine, and I consider it 
as inaccurate. 
In terminating this historical sketch, I must not forget the labours 
of Proust. I have made much use of them; and if I do not speak 
of them more at length here, it is because I shall have occasion 
frequently to quote them. I pass over a good many others in silence. 
But I mentioned already that it was not my intention to state every 
thing that is known respecting prussic acid. 
That the observations which I have to present may assume a re- 
gular arrangement, I shall present them under four different articles. 
In the first I shall endeavour to explain the nature of prussic acid ; 
in the second, I shall explain the properties of a new gas, which is 
the radical of prussic acid; in the third, I shall examine the com- 
bination to which the name of oxyprussic acid has been given; in 
the fourth, I shall treat of some prussiates. I regret that time did 
not permit me to carry that part of my labours further, but I hope 
to resume it afterwards. 
I. Of Prussic Acid. 
This acid may be obtained perfectly pure by the process which I 
described in the 77th volume of the Annales de Chimie, which 
consists in decomposing common prussiate of mercury by muriatic 
acid. The apparatus which I employ at present being somewhat 
simpler than my former one, I shall give a description of it. To 
the beak of a tubulated retort intended to hold the prussiate of mer- 
cury and muriatic acid, is adapted an horizontal tube, about six 
decimetres (two feet) long, and 14 centimetre (0°59 inch) in > 
diameter in the inside. The first third part of the tube next the 
retort is filled with small pieces of white marble, to retain the mu- 
riatic acid that may come over, but which ought if possible to be 
prevented.t ‘The two other thirds contain fused muriate of lime, 
likewise in small pieces, in order to condense the water which may | 
be mixed with the prussic vapour. To the end of this tube is adapted . 
a small receiver, destined to collect the acid. It must be surrounded 
with a frigorific mixture, or at least with ice,, that the less acid may 
make its escape. ‘The prussic acid is usually deposited upon the 
marble in the first portion of the tube. But by means of a moderate 
heat it may be made to pass successively through the whole tube, 
* 1 need scarcely observe that this account of Mr. Porrett’s paper is quite 
erroneous,—T, 
+ If muriatic acid pass into the tube, it will separate the carbonic acid of the 
marble, which, mixing with the vapour of prussicacid, will prevent ite copdensa- 
tion, and occasion a considerable loss, _ 
