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 man}^ of the lice were stupefied 

 at the ends in ten minutes, but all soon recovered. With three-tenths 

 gram 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 ])y 31 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 cc. 

 equals 1 gram, KCn) and 8-dram short-style vial, w^ith 2 cc. sul- 

 phuric acid in the l)ottom, 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 foiuid 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 pc^verof "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 5 



