PRUSSIC. 
157 
Having thus traced the gradual progress of philoso 
Chap. IV. 
phers in ascertaining the nature of the prussic acid, it 
only remains to give an account of its properties, which 
were first examined by the indefatigable Scheele. 
Prussic acid obtained by Scheele’s process is a co- Properties. 
lourless liquid like water. It has a strong odour, re 
sembling that of the flowers of the peach, or of bitter 
almonds. Its tase is sweetish, acrid, and hot, and apt 
to excite cough. It does not alter the colour of ve 
getable blues. 
It is exceedingly volatile, and evidently capable of 
assuming the gaseous form; though it has never been 
obtained apart, nor examined in that state. At a high 
temperature (when united to a base) it is decomposed and 
converted into ammonia, carbonic acid, and carbonated 
hydrogen gas. 
It unites difficultly with alkalies and earths, and is 
separated from them much more easily than from me 
tallic oxides. Mere exposure to the light of the sun, or 
to a heat of 110°, is sufficient for that purpose. These 
combinations are decomposed also by all the acids. 
It has no action on metals, but it unites with their 
oxides, and forms with them salts, which are almost all 
insoluble, if we except prussiats of mercury and man 
ganese. These compounds are not decomposed by 
acids. Yet the prussic acid is not capable of taking the 
metallic oxides from the other acids. 
Prussic acid has a great tendency to enter into triple 
compounds, combining at once with an alkali and a 
metallic oxide; and these compounds are much more 
permanent and difficult to decompose than its single 
combinations.