50 



BULLETIN 918, U. S. DEPARTMENT OF AGRICULTURE. 



the summer time, when the temperature inside the house was 75° to 

 80° F. Experiments 13, 19, 29, and 30 were made to decrease the 

 dosage needed. All larva? were not killed in experiments 13 and 19, 

 where the dosage was 1 pound disulphid to 100 cubic feet with long 

 exposures, but all were killed in experiments 29 and 30, with 1 

 pound to 85 cubic feet and a 24-hour exposure. 



Table XXVI is a summary of the carbon disulphid experiments. 

 From these experiments it is seen that satisfactory results were 

 obtained by using 1 pound of carbon disulphid to 80 cubic feet for 

 24 hours or longer when the seeds were not over 5 feet deep. 



Table XXVI. — Fumigation of cotton seed with carbon disulphid. 



Experi- 



Dosage. 



Expo- 

 sure. 



Per cent 

 larvae 

 killed. 





ment 

 No. 



Pounds. 



Cubic 

 feet. 



How seeds were placed. 



1 



2 

 11 



20 



21 



22 



23 



29 



30 



20 



19 



13 



10 



9 



31 



27 



7 



32 



6 



5 



8 



4 





102 

 101 

 80 

 SO 

 80 

 80 

 80 

 85 

 85 

 80 

 100 

 100 

 54 

 82 

 90 

 80 

 102 

 90 

 161 

 161 

 124 

 161 



Hours. 

 90 

 48 

 42 

 42 

 48 

 48 

 24 

 24 

 24 

 12 

 48 

 108 

 24 

 48 

 24 

 15 

 48 

 24 

 48 

 23 

 48 

 23 



100 

 UOO 

 100 

 100 

 100 

 100 

 100 

 100 

 100 



95 



94 



91 

 2 90 



88 



85 



82.5 



80.5 



60 



51 



37 



17 



13.3 



Seed in bags. 



Do. 



Do. 

 Seed in bulk, 5 feet deep. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 

 Seed in bulk, G feet deep. 

 Seed in bulk, 5 feet deep. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 

 Seed in bags. 

 Seed in bulk, 5 feet deep. 

 Seed in bags. 



i Record doubtful. 



2 Larvte iu corked vials. 



Hydrocyanic- Acid Gas. 



The fumigation of cotton seed with hydrocyanic acid gas proved 

 very unsatisfactory, as the gas is so light that it will not penetrate 

 the seed more than a few inches. In some of the experiments an 

 earthenware crock containing the sulphuric acid was set directly on 

 top of the seed pile and the cyanid lowered by a string from the 

 outside in the usual way. The penetration was so poor that a 

 special generator was designed. A section of 10-inch pipe 14 inches 

 long was fitted with gas-tight caps on both ends and a lead inner 

 pot to hold the acid. The generator was placed outside the house 

 below the floor level and the gas conducted to the inside, where it 

 was allowed to escape in the bottom of the fumigation chamber 

 through perforated pipes. It was hoped that the penetration 

 upward would be greater than downward, but there was very little 

 difference. 



