54 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



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 317 and 435).* 



Hydrocyanic Acid Gas is extensively used for the fumigation 

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

 dwelling houses, storehouses, mills, etc. It is made by combining 

 cyanide of potassium or sodium, sulphuric acid and water. The 

 gas is slightly lighter than air and is one of the most deadly poisons 

 known. It should be used only under competent direction and 

 by persons thoroughly capable of understanding the directions 

 and carrying them out. Under such circumstances the danger is 

 negligible. Brief directions follow but these should be supple- 

 mented by first-hand advice which considers the local factors. 



Take for each 100 cubic feet of space one ounce of the cyanide, 

 one ounce of the acid and three ounces of water. Provide stone 

 jars which will not be filled more than one-third full by the quantity 

 of materials to be used. Use one or more for each room, accord- 

 ing to the size of the room. Weigh out the cyanide and place 

 the amount for each jar in a paper bag beside the jar. Pour the 

 water into the jar and then add the acid, stirring gently at the 

 time. Arrange the material in this manner for all the rooms. 

 The building should previously have been made as nearly air- 

 tight as possible. An exit on the ground floor should have been 

 provided and arranged so that it can be quickly closed and pro- 



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

 145, U. S. Dept. Agri., and see page 184 below. 



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

 manner as carbon bisulphide, and is not so explosive. 



