INDUSTRIAL FUMIGATION AGAINST INSECTS 



21 



oughly before turning on the gas and to wear a gas mask while 

 manipulating the valves of the cylinder. 



THE DISCOID METHOD 



For the fumigation of warehouses that are divided into sections, 

 of mills containing machinery that cannot be easily opened up, or of 

 apartment buildings, etc., the use of <some form of solid from which 

 hydrocyanic acid gas can be produced is often desirable, since it 

 does away with the necessity for an elaborate piping system or for 

 crock or barrel generators. 



Figure 22. — Lobby of apartment house being fumigated with hydrocyanic acid gas 

 generated by the discoid method, showing round white wafers distributed over the paper 

 runner and the empty cans from which they have been shaken. These wafers are 

 wet when distributed, but after the evolution of the gas they become dry and harmless. 



There are two types of such solids now on the market. One of 

 these consists of liquid hydrocyanic acid absorbed in some inert 

 material, from which it evaporates on exposure to air. This inert 

 material is pressed into waferlike discoids each containing approxi- 

 mately one-half ounce of liquid hydrocyanic acid (fig. 22). These 

 discoids are marketed in tightly sealed cans of various sizes and sold 

 on the basis of the net content of hydrocyanic acid. The other type 

 of solid is calcium cyanide, and the hydrocyanic acid is produced by 

 chemical reaction with the moisture in the air. Its use will be dis- 

 cussed under the powder method. 



