CHEMISTRY OF FUMIGATION. 97 
conditions under which all of the hydrocyanic acid may be decom- 
posed by the hydrochloric acid and none whatever expelled into the 
medium which it is desired to fill with the gas. 
This action of acids on hydrocyanic acid has been known to chem- 
ists for years, but the first work the writer has seen in which its bearing 
upon the subject of fumigation had been brought to the attention of 
the public was by Newell, x in which he shows the decomposing action 
of hydrochloric and nitric acids on hydrocyanic acid and points out 
the necessity of using pure cyanids for fumigation work. 
ACTION OF SULPHURIC ACID ON HYDROCYANIC ACID. 
When potassium cyanid or sodium cyanid is treated with sulphuric 
acid, the first action which takes place is the liberation of hydrocyanic- 
acid gas, as shown by previous equations. This is then acted upon 
to a greater or less extent, depending upon the conditions, and a 
portion of it decomposed: The principal products of decomposition 
are ammonia and formic acid, according to the following reaction: 
HCN + 2H 2 = HCOOH + NH 3 . 
The ammonia formed combines with the excess of sulphuric acid 
present and forms ammonium sulphate. If the sulphuric acid is 
concentrated, it attacks the formic acid, extracting water therefrom 
and liberating carbon monoxid, CO, thus: 
[hIcoJoh] = H 2 + CO. 
Wade and Panting 2 have shown that, on treating potassium cyanid 
with sulphuric acid, by suitably varying the concentration of the 
acid a practically quantitative yield of either hydrocyanic acid or 
carbon monoxid can be obtained. With dilute sulphuric acid and up to 
a strength of 1 part acid to 1 part water, which is as strong as it is ever 
used in fumigation work, nearly pure hydrocyanic acid is formed. 
With a stronger acid, however, ' ' a certain amount of carbon monoxid 
is formed, and as the concentration of the acid is increased the volume 
of gas increases, while the amount of hydrogen cyanid diminishes; 
and finally, when ordinary concentrated sulphuric acid is allowed to 
act on the cyanid, nearly pure carbon monoxid is evolved in almost 
theoretical quantity/' Concentrated sulphuric acid at a high tem- 
perature is reduced by hydrocyanic acid, sulphur dioxid, carbon 
dioxid, and ammonia being formed. 
HCN + H 2 S0 4 = NH 3 + C0 2 + S0 2 . 
As sulphuric acid stronger than 1 part acid to 1 part water is never 
used in fumigation work, we need not concern ourselves with the 
1 Georgia State Board of Entomology, Bui. 15. 
2 Journ. Chem. Soc, vol. 73, pt. I, p. 255, 1898. 
