65 
at the middle. Neither with this strength at ten, fifteen, or twenty 
minutes were the lice at the ends of the frame even stupefied, but with 
three-tenths gram KCn per cubic foot many of the lice were stupefied 
at the ends in ten minutes, but all soon recovered. With three-tenths 
eran for fifteen minutes, however, the lice half way between the middle 
and ends were killed. 
This frame was not only too long and of too small diameter for the 
diffusion of the gas, but was too long to be readily handled and to 
accommodate itself to any unevenness of the ground. A frame 10 feet 
long by 10 inches high by 24 inches wide at the bottom, also of a tri- 
angular shape, was therefore made, but with doors at either end 
instead of one at the middle. In the tests made with it one-half of the 
gas was generated at either end instead of from the middle. In these 
frames the cyanide solution and acid can be measured and handled in 
larger vials, and these carried in trays, as for the small covers. A 
3-dram long-style vial five-sixths full of the cyanide solution (2 ce. 
equals 1 gram KCn) and 8-dram short-style vial, with 2 cc. sul- 
phuric acid in the bottom, give one-half the amounts necessary for 
three-tenths gram KCn per cubic foot in this 10-foot frame, one gen- 
eration being made at each end of the frame. By using these vials 
the carrying and cleaning of a separate vessel in which to generate the 
gas is obviated. Using two-tenths gram KCn per cubic foot, after 
ten minutes five tests showed an average of 16 per cent of the aphides 
alive at the ends and 25 per cent alive at the middle, or that the gas 
was but slightly more effective at the ends than in the middle, and was 
insufficient to kill the lice at either point. All of these lice were stu- 
pefied and remained so for some time, but were found alive the next 
morning. In this connection it might be well to state that in such 
tests plant lice should always be kept at least for twelve hours. They 
have a remarkable power of ‘** playing possum,” and will often remain 
stupefied for three or four hours. The same dose for five minutes left 
37 per cent alive at the ends and 17 per cent in the middle, showing the 
gas to have been more effective in the middle. This shows a similarity 
in the diffusion to that found in the large box used in the laboratory in 
that the gas was at first thrown from either end to the center and was 
found to be more effective in the middle than at the end after five 
minutes, but this became so diffused that the gas was slightly more 
effective at the ends after ten minutes. Three-tenths of a gram KCn 
per cubic foot for five minutes also failed to kill the lice. Later three- 
tenths and four-tenths of a gram per cubic foot were tried for ten 
minutes, and only in one or two instances did we find from 10 to 25 per 
cent alive when the former strength was used, and four-tenths of a 
gram killed all the lice and other insects in every test. Three-tenths 
of a gram for fifteen minutes would undoubtedly be effective. With 
none of these strengths were the strawberry plants upon which the 
6878—No, 26 d 
