152 FUMIGATION METHODS 



when the gas is used in an elongated space the amount 

 of cyanide per cubic foot is no guarantee, on the one 

 hand, of sufficient acid vapor to do the work, nor, on 

 the other, of too little to injure the plants. These 

 tests show also that a large amount of gas may be ab- 

 sorbed by the film of water on damp foliage, or by the 

 soil in a frame with the bottom open. 



In field tests, therefore, a larger amount of gas than 

 that used in the laboratory in a closed box was re- 

 quired to compensate the influence of soil and foliage. 

 In a ten-foot frame, triangular in cross-section, with a 

 cubic capacity of 8^ feet, or a ratio of 2^ soil surface 

 to one of volume, Professor Sanderson found just 

 twice as much gas was required to be generated 

 from two points to be effective as that in a wooden box 

 containing 10 cubic feet capacity and 5 square feet 

 soil surface, having an almost opposite ratio of two 

 of volume to one of soil surface. The materials and 

 cost of constructing frames for the fumigation of plants 

 in rows is slight. Frames, triangular cross-section 10 

 feet long by 10 inches high and 24 inches wide at the 

 bottom, have been found very satisfactory by Professor 

 Sanderson. With twelve such fumigators an acre of 

 plants, where the rows are three feet apart, can be gone 

 over in about two days. The cost of chemicals, not 

 including labor, would be about three dollars per acre. 



