Circular 21 - Insecticides and Subsidiary Materials 37 
HYDROCYANIC ACID GAS 
Hydrocyanic acid gas (HCN") is a widely 
used fumigant for the control of fabric pests 
such as clothes moths and carpet "beetles; 
flour and grain beetles; flour, grain and meal 
moths; granary, bean, and pea v/eevils; and 
similar food insects infesting grains, dried 
fruit, meats, cheese, and other stored foods. 
In certain situations where this fumigant can 
be used it provides an effective means of 
eradicating fleas, lice, bedbugs, and 
cockroaches. 
A detailed discussion of fumigation 
procedure is given in Circular No. 22. As 
explained therein, hydrocyanic acid gas may 
be obtained in several ways. The chief ways 
are by evaporation of hydrocyanic acid in 
liquid form or from discoids impregnated with 
the liquid, by the action of dilute sulfuric 
acid on sodium cyanide, and exposure of calcium 
cyanide to moist air. 
The gas, from whatever source derived, 
is extremely poisonous to all animals and 
plants. It is colorless, lighter than air, 
and has an odor resembling that of peach 
kernels or crushed almonds. 
Liquid hydrocyanic acid is a colorless 
liquid, boiling at 70° F. (26.1° C), which 
gives off the gas having the characteristics 
described above v/hen the material is exposed 
to the atmosphere. The liq^uid may be obtained 
in 30 or 75 pound cylinders which are more 
conveniently used for fumigating large ware- 
houses than the barrel or pot method. It 
should be used only by a professional fumigator 
equipped with suitable masks. 
