INDUSTRIAL FUMIGATION AGAINST INSECTS 25 



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 of 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. 



Fumigation With Chloropicrin 



Chloropicrin, although not so popular as hydrocyanic acid, is 

 sometimes used as a general fumigant for mills and warehouses. It 

 is a colorless or slightly yellowish liquid, a little more than one 

 and a half times as heavy as water. It has a boiling point of 233.6° F., 

 and on exposure to air evaporates slowly, forming a mixture of 

 air and chloropicrin vapor that is 1.1458 times as heavy as air at 

 the same temperature and pressure (77° F., 29.9 inches). It can be 

 purchased in cylinders of from 1 to 100 pounds' capacity, or in glass 

 bottles containing 1 pound. The gas is nonexplosive and nonin- 

 flammable as ordinarily used, is very toxic to insects and also to 

 man, and has an extremely irritating effect upon the eyes and respira- 

 tory passages of man. The last characteristic insures against the 

 possibility of anyone accidentally entering a building filled with 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. It should not be applied directly on 

 painted or varnished surfaces. Where there are several stories to a 

 building, each floor should be sealed off from the others. 



Owing to the rather high boiling point of chloropicrin and conse- 

 quent slow rate of evaporation, it is sometimes desirable to hasten 

 the process by applying the liquid in the form of a spray or fine 

 mist, or by using a mixture of equal parts of chloropicrin and carbon 

 tetrachloride or trichloroethylene. At temperatures above 70° F., 

 however, satisfactory results can be obtained by merely applying the 

 straight chloropicrin. 



In mills that are equipped with machinery for handling food- 

 stuffs, it is desirable to apply the chloropicrin directly into the ma- 

 chinery where the heaviest infestation is likely to be found. 



One-pound "automatic" cylinders of chloropicrin charged with 

 carbon dioxide are sometimes used for treating machinery. They 

 are supplied with a short length of hose ending with a spray nozzle. 

 The nozzles are inserted into holes bored into the machinery, and 

 the gas is released by opening a valve on the cylinder. The pres- 

 sure of the carbon dioxide expels the chloropicrin in a fine mist. 



An objectionable feature of chloropicrin is that considerable time 

 is required to ventilate a building after a fumigation. Because it 

 does not evaporate rapidly, it clings to fumigated commodities with 

 great tenacity. 



464673°— 42 4 



