CARBON DISULPHID AS AN INSECTICIDE. 9 



liquid and forms what may be called a " cone of killing." The apex 

 of the cone is close to the point of application, and the base is against 

 the floor or ground below. 



EFFECT OF TEMPERATURE IN FUMIGATION. 



An extremely important factor that has been ignored until recently 

 in fumigation work is temperature. The effect of temperature may 

 be judged from the fact that a warm atmosphere will require far 

 more of the carbon disulphid vapor to saturate it than will a cool 

 atmosphere. To saturate 1,000 cubic feet of air at 50° F. requires 

 ^^3.5 pomids of liquid carbon disulphid; at 59°, 64.6 pounds; at 

 68°, 77.6 pounds; at 77°, 92.4 pounds; and at 86°, 109.3 pounds. 

 Thus at 86° F., which is a temperature not uncommon, the air will 

 hold more than twice as much disulphid vapor as it will at 50°. Not 

 only is this true, but insects show great differences in vital activities 

 at these varying temperatures. The higher the temperatures, up to 

 a certain point, the greater their activity; and the more active the 

 insects are, the more susceptible to the effects of the gas. In practical 

 work it has been found that it is not advisable to try fumigation 

 with carbon disulphid when the temperature is below 60° F., while 

 the most effective and economical work can be done at the higher 

 air temperatures. 



AIDING RAPID VAPORIZATION. 



In several ways vaporization may be hastened beyond the rate at 

 which it will occur naturally from the surface of the liquid as it is 

 freely exposed to the air. One common method for use in the treat- 

 ment of rooms and bins on a small scale is to saturate some absorbent 

 material with the desired amount of liquid and hang it near the top 

 of the room or bin so that the vapor may flow away freely downward 

 and produce quickly the maximum density of vapor. Another 

 method sometimes used in large warehouses is to apply the liquid 

 through a spray pump. The operator using this method must be 

 careful not to stay too long in the gas thus rapidly increasing in 

 density. Where the liquid falls upon wood it is taken up quickly by 

 the wood and is then given off again, but slowly. Spray applications 

 sometimes can be made through holes bored in the ceilings or through 

 the floor of the room above that to be treated, and the spray thus 

 distributed at various points in the room below with no inconvenience 

 to the operator. The holes can be stopped securely except when in 

 use. Still another method, which is a modification of the spraj'' 

 method, is to force the liquid under pressure, mixed with a large 

 amount of air, into the material to be treated so that the gas will 

 have to diffuse throughout the material before it can escape and lose 

 75300°— Bull. 799—17 2 



