SULPHUR DIOXIDE AS AN INSECTICIDE. 143 



Results on insects. — Of insects at bottom of jars merely covered with 

 cloth 2 out of 10 mealworms (Tenebrio) killed; in small sack made of 

 ordinary grain sacking or heavy drilling everything was killed. The 

 capacity of the sack was about half a peck. 



Experiment No. 5. 



Treatment for 1 hour with 7 to 8 per cent gas, machine running 

 30 minutes. Test at the end of the hour showed that the box con- 

 tained full per cent gas. Insect tests made with four jars, two of 

 which were covered with cloth and two lightly plugged with cotton, 

 merely sufficiently to retain the insects. In the cloth-covered jars the 

 insects were alive at the end of the hour, but the cotton was sufficient 

 to retain more or less of the gas over night, and the insects were all 

 dead the next day, indicating the value of the longer time gassing at 

 a low percentage. 



Experiment No. 6. 



Two and one-half to 3 per cent of gas for 16 hours, the machine 

 running for 5 minutes. At the end of the If) hours less than 0.5 

 per cent of gas was found in the box. The free insects on the exterior 

 of the bags were killed, and those deeper down in the bags were unin- 

 jured. This test was made with three bags of rye infested witli Cal- 

 andra — ordinary grain bags, capacity of each about 2 bushels. It 

 is probable that the machine, running but 5 minutes, had not at the 

 end of this time caused the gas to penetrate these large bags, and the 

 subsequent ^^artial penetration of these bags would reduce the per- 

 centage of the gas considerably. 



Experiment No. 7. 



Five per cent gas, machine running 15 minutes, and then left for 

 a total of 22 hours. At the end of 4 hours a sample of the gas taken 

 from the fumigating box indicated a strength of over 2 per cent gas 

 remaining. Some of this gas had doubtless escaped from the box, 

 but probably a good deal of it had been absorbed by the grain in the 

 large bags. The following morning the box was opened, and an 

 examination of the contents showed the apparent destruction of all 

 insect life. The bags of infested grain placed in the center and at 

 the bottom of the large sacks with many living insects (Calandras) 

 showed no living material. The same was true of Bruchus in cow- 

 peas. All of this material was held for later examination, and there 

 were no revivals. "When the box was opened the gas was still very 

 strong in the box, probably exceeding 1 per cent. This test seems to 

 indicate that a low percentage of gas, say from 5 to 1 per cent, con- 



