Circular 21 - Insecticides and Subsidiary Materials 38 
Hydrocyanic acid discoids are conven- 
ient and useful for the fumigation of houses, 
barracks, small warehouses, or storage rooms. 
As with the liquid form their use is not 
recommended for any but professional fumiga - 
tors with masks, _as the gas is a deadly poison . 
This fumigant consists of wafer-like 
discoids of an inert material, each containing 
approximately one-half ounce of absorbed 
liquid hydrocyanic acid, packed in sealed 
metal cans of various sizes, and sold on the 
basis of the net content of hydrocyanic acid. 
When sodium cyanide (NaCN) and dilute 
sulfuric acid (H2S0^) are mixed, a reaction 
takes place in which the deadly cyanide gas 
is liberated. Sodium cyanide is a white, 
deliquescent, poisonous salt. For fumigation 
purposes it should be practically free from 
chloride and contain not less than 51 percent 
of cyanogen. This salt mav be purchased in 
the form of eggs weighing I or 1 ounce, which 
provides an easy method of calculating dosages 
by counting out the number of eggs required 
for a certain weight of sodium cyanide. Sul- 
furic acid is described under that heading on 
page 75 of this circular. 
Calcium cyanide (Ca(CN)2) on exposure 
to the air reacts with the moisture in the 
atmosphere and gives off the poisonous HON 
gas. '^en the reaction is completed, the 
residue remaining consists chiefly of calcium 
hydroxide or hydrated lime. This form of 
cyanide is obtainable in granules, dust, or 
flakes. The granular form, which is dark gray 
in color, is most frequently used for fumiga- 
tion. It can be purchased in 1, 5, 25 pound, 
or larger sized containers. 
