10 FUMIGATION METHODS 
and sizzling similar to that produced by a piece of red- 
hot iron in‘cold water. ‘There is also a dense cloud of 
so-called steam given off. This bubbling is due to the 
action of the acid on the cyanide, and the so-called 
steam is the gas being produced. ‘The result of this 
chemical action is the production of hydrocyanic acid 
gas (HCN), known in the liquid form as prussic acid, 
according to the following equation: 2KCN + H,SO, 
=2HCN+K,SO,. The gas has an odor somewhat 
similar to that of peach pits, but do not stick your 
nose over a vessel in a house or under a tent to test it. 
These fumes, if inhaled, would prove fatal, and thus 
the necessity of great care. 
The vessel.—Various kinds of vessels can be used 
for the acid and water. Usually an ordinary earthen 
jar, china dish, or bowl is used. In some cases a 
wooden pail or tub can be used to good advantage. 
As a rule, earthenware vessels are employed in orchard 
and nursery fumigation. ‘The size of the vessel will 
depend upon the amount of material to be used for 
generating the gas. Sometimes in mills, warehouses, 
elevators, and other enclosures large jars or wooden 
pails containing from two to three gallons are necessary. 
Under no circumstances should tin or iron vessels of 
any kind be used, as the acid would quickly corrode 
and ruin them. For small boxes a china bowl or tea- 
cup can be used. 
Residue tn the jar.—After a charge of gas has been 
liberated there will be a residue left in the jar. At 
first, and while still warm, it is a whitish liquid, with 
a bluish cast, but as it cools it becomes thick like paste 
