20 



CIRCULAR 3 6 9, U. S. DEPARTMENT OF AGRICULTURE 



for storage and the pipes capped. In removing these nozzles, care 

 must be taken to avoid accidents from the small quantities of liquid 

 hydrocyanic acid that sometimes remain in the pipes after a fumiga- 

 tion. The operator should never stand directly in front of or be- 

 neath a spray nozzle that is being removed. The presence of liquid 

 hydrocyanic acid behind a nozzle that is being unscrewed is usually 



revealed by a well-defined 

 cooling sensation and 

 sometimes by a slight odor. 

 In fumigating with 

 liquid hydrocyanic acid, 

 there is always some 

 danger that the rubber 

 connecting hose may 

 burst under the pressure, 

 showering the operator 

 with the deadly fluid. 

 It is therefore a wise 

 precaution to wear a gas 

 mask while manipulating 

 the valves of the cylin- 

 ders, and also to have 

 the clothing covered with 

 a smock, which can be 

 snatched off in an emer- 

 gency. 



THE DISCOID METHOD 



For the fumigation of 

 warehouses that are di- 

 vided into sections, of 

 mills containing machin- 

 ery that cannot be easily 

 opened up, or of apart- 

 ment 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. 

 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. 



Figuke 21. — Various attachments for spray nozzles 

 used in fumigating a warehouse, mill, or factory 

 with liquid hydrocyanic acid. 



