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. 
