INSECTICIDES 57 



prevent any insect or fungous depredations. A generous price 

 per tree is charged, which is the only " effect " of the treatment. 



4. Gases. 



Carbon Bisulfid (or disulfid) is extensively used against insects 

 affecting stored goods and grains, and for root-feeding insects. It 

 is a clear, volatile liquid giving off fumes heavier than air. It is 

 sold in 25- to 100-pound cans at 10 to 12 cents per pound. It may 

 be thrown directly onto grain without injury to it or placed in 

 shallow dishes. For grain in store in fairly tight rooms apply 5 to 

 8 pounds to every 100 bushels, distributing the bisulfid over the 

 surface or in pans containing not over one-half to 1 pound each. 

 Make the enclosure as tight as possible; covering the grain with 

 blankets or other tight cover, if necessary, and leave for twenty- 

 four hours. Recent experiments have shown that the vapor is 

 much less effective at low temperatures and that the dosage must 

 be greatly increased at temperatures below 60 F. For fumi- 

 gating buildings " there should be about 1 square foot of evap- 

 orating surface to every 25 square feet of floor area, and each 

 square foot of evaporating surface should receive from one-half 

 to 1 pound of liquid." For fumigating clothing or household 

 goods, place them in a tight trunk and place an ounce of liquid 

 in a saucer just under the cover. The gas is exceedingly explosive; 

 allow no fire or light of any kind around the building or enclosure 

 until it has been well aired. The fumes should not be inhaled, for 

 though not seriously poisonous, they have a suffocating effect and 

 will soon produce dizziness and a consequent headache. The 

 treatment for root-maggots and root-feeding aphides is discussed 

 in connection with those insects (pages 355 and 496).* 



Hydrocyanic Acid Gas is extensively used for the fumigation 

 of nursery trees and plants, certain greenhouse insects, pests of 

 dwelling houses, storehouses, mills, etc., and in California for 

 .scale insects on fruit trees. It is made by combining cyanide of 



* For a complete discussion of the use of this gas, see Farmers' Bulletin, 

 145, U. S. Dept. Agr., and see page 197 below. 



Carbon tetrachloride is now used for some purposes in much the same 

 manner as carbon bisulphide, and is not so explosive. 



