24 



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



in a special apparatus (fig. 25). Air is forced by a small motor into 

 a rubberized sack containing the calcium cyanide dust, which is kept 

 agitated until all the hydrocyanic acid gas is liberated. The gas 

 enters the space to be fumigated through a filtering device, which 

 frees it of the dust. 



The Dosage 



To figure the quantity of calcium cyanide needed for a fumigation, 

 it is necessary to know the percentage of available hydrocyanic acid 

 it contains. This percentage will be found on the label of the can. 



If, for example, the dust 

 contains 50 percent 

 available hydrocyanic 

 acid, 1 pound will give 

 off as much gas as 8 

 ounces of liquid hydro- 

 cyanic acid or 1 pound 

 of sodium cyanide. Cal- 

 cium cyanide sells for 

 about $1.35 per pound. 



FUMIGATION WITH 

 CHLOROPICRIN 



Chloropicrin, although 

 not so popular as hydro- 

 cyanic acid, is some- 

 times used as a general 

 fumigant for mills and 

 warehouses. Chloro- 



picrin is a colorless or 

 slightly yellowish liquid 

 a little more than one 

 and a half times as 

 heavv as water. It has a 

 boiling point of 233.6° 

 F. and on exposure to 

 air evaporates slowly, 

 forming a vapor that is 

 about five times as heavy 

 as air. It can be pur- 

 chased in cvlinders of 



Figure 25. — Apparatus for passing air through cal- 

 cium cyanide dust in such a way that the hydro- 

 cyanic acid gas evolved will be free from the dust. 



from 1 to 100 pounds' 

 capacity at a cost of about $1.35 per pound. The gas is nonexplosive 

 and noninflammable as ordinarily used, is extremely toxic to insects 

 and also to man, and has an extremely irritating effect upon the eyes 

 and respiratory passages of man. This last characteristic insures 

 against the probability of anj^one accidentally entering a building 

 filled with the gas. A gas mask equipped with a canister especially 

 designed for the purpose must be worn when fumigating with 

 chloropicrin. 



There are several methods of applying chloropicrin as a general 

 mill or warehouse fumigant. The simplest of them is to draw the 

 required quantity of liquid from the cylinder in which it is mar- 



