360 Experiments on Prussic Acid. [May, 
3. And consequently that the potassium has absorbed 100 parts of 
‘prussie vapour ; for there is a diminution of 50 parts, which would 
obviously have been twice as great had not 50 parts of hydrogen 
been disengaged. 
When the yellow matter is put into water, it dissolves entirely, 
without the least effervescence, and exhibits all the characters of 
simple prussiate of potash obtained by combining directly the acid 
and alkali. If we suppose the water to be decomposed, which is 
very probable, but which must necessarily happen by the joint action 
of an acid, the potassium combines with its oxygen, and the 
hydrogen, which is precisely equal to that which the potassium dis- 
engaged from the prussic acid, reproduces this acid with all its pro- 
erties. 
Here, then, is a very great analogy between prussic acid and 
muriatic and hydriodic acids. Like them, it contains half its volume 
of hydrogen ; and, like them, it contains a radical which combines 
with the potassium, and forms a compound quite analogous to the 
chloride and iodide of potassium. The only difference is, that this 
radical is compound, while those of the chloride and iodide are simple. 
Since prussic acid contains 
One volume of vapour of carbon. 
Half a volume of azote, 
Half a volume of hydrogen. 
And since I have just proved that potassium disengages half its 
volume of hydrogen, it is obvious that the substance which com- 
bines with the metal, and which ought to be distinguished by the 
name of prussic radical, is a compound of carbon and azote, in the 
proportion of 
One volume of vapour of carbon. 
Half a volume of azotic gas. 
This radical combined with potassium forms a true prusside of 
that metal. We ought, therefore, to consider prussic acid as a 
hydracid ; and with the less hesitation, that a great number of other 
facts lead to the same conclusion. 
The name prussic acid, then, will no longer suit it; but it must 
be called Aydro-prussic. We must likewise invent a name for its 
radical, from which this may be derived. Were we to preserve the 
term prussic, which has never been adopted in Germany, and which 
never can be, we should be obliged to give it a meaning different 
from that which it has hitherto borne. ‘These considerations have 
induced me to invent a new name for the radical of prussic acid. 
That of cyanogen* having appeared very proper to the chemists of 
this capital, I have adopted it, and sha!l use it afterwards in the 
course of this memoir. Common prussic acid will receive the name 
of hydro-cyanic acid, and the prussiates that of hydro-cyanates. 
The combinations of cyanogen with simple bodies, when it performs 
. * From waves, blue; eyed», I produce, = 
