February, ’ 24 ] 
MOORE! CALCIUM CYANIDE 
105 
carbide, calcium cyanamid, and a small amount of sulphur in the form 
of a sulphide. 
Reactions of Calcium Cyanide 
The value of calcium cyanide as an insecticide is due to its reaction 
with water vapor to produce hydrocyanic acid and calcium hydroxide. 
Some entomologists have considered that this reaction is true for all 
cases where water is brought in contact with calcium cyanide but such is 
not the case. If calcium cyanide is mixed with water it forms a solution 
of calcium cyanide similar to a solution of sodium cyanide. A solution 
of calcium cyanide would appear to have no more value as an insecticide 
than a similar solution of sodium cyanide. 
When calcium cyanide is exposed to atmospheric water vapor the 
reaction is similar to the reaction of moisture on calcium carbide only 
hydrocyanic acid is evolved instead of acetylene. The rate of this 
reaction is more closely associated with the absolute humidity than 
with the relative humidity. A temperature of 85° F with 50% relative 
humidity actually has a higher absolute humidity than a temperature of 
65° F with 90% relative humidity. Even a low relative humidity may 
therefore have sufficient actual moisture present to produce a killing 
concentration of gas. 
vSprinkling the calcium cyanide with a very small amount of water 
will increase the evolution of hydrocyanic acid. If sufficient water is 
used to wet the material another reaction occurs in which the hydrocyanic 
acid decomposes under alkaline conditions, with the formation of am¬ 
monia and other little known compounds, one of which is often referred 
to as azulmic acid. 
The Use of Calcium Cyanide as an Insecticide 
When the calcium cyanide dust is blown thru the air the moisture 
releases the hydrocyanic acid gas. 
The possibility of using a gas such as hydrocyanic acid in the open to 
destroy insects appears at first as absurd. Further considerations and 
experiments have shown it’s effectiveness to be due to the fact that 
the concentration of the gas to which the insects are exposed is of more 
importance than the length of exposure. Better results are obtained 
when a dust is delivered from a nozzle held from 3—4 feet distant from the 
plant than when held close to the plant. It is not necessary to hit the 
insects with the dust but they should be exposed to a killing concentra¬ 
tion of gas although this concentration may only last for a moment. 
When flakes are used in chinch bug barriers, if the soil is very dry and 
