SULPHUR DIOXIDE AS AN INSECTICIDE. 149 



time after being removed from the fumigating chamber, indicating 

 the formation of sulphuric acid by condensation. 



SUMMARY OF RESULTS. 



(1) Sul^Dhur dioxide is very destructive to most growing plants 

 and almost instantly deadly to succulent plants • and grasses, even 

 at low joercentages. Palms and pineapples can, however, stand a 

 moderate fumigation. This gas, therefore, has probably no value 

 whatever as a means of disinfecting living plants, except perhaps for 

 the very hardiest of dormant nursery stock and palms. 



(2) The germinating poAver of grass, grain, and common garden 

 seeds is quickly destroyed with even Aveak applications of the gas, and 

 its employment is therefore impracticable for all seeds for planting. 

 It does not, however, injure the feeding value or cooking quality of 

 cereals, and the odor of the gas passes away fairly quickly and is not 

 retained except where the grain or seeds are moist. 



(3) A comparatively low percentage of the gas will kill practically 

 all free insects after an exposure of from a few minutes to half an 

 hour, but a much longer exposure is necessary to kill insects inclosed 

 in grain or seeds, as Bruchus and Calandra. The best results are 

 obtained by submitting such grains or seeds to a low percentage of 

 the gas (from 1 to 5 per cent) for a period of 12 to 24 hours. 

 Employed in this way the gas is a very effective means of disinfecting 

 stored grain or similar products, and has the additional advantage 

 of entirely eliminating the danger of explosion and fire. 



(4) The bleaching quality of the gas on fabrics and wall papers is 

 largely determined by- the moisture in the air. In comparatively dry 

 air such bleaching is inconsiderable, and in a heated house can prob- 

 ably be ignored. Its effects on metal surfaces, however, is more 

 marked, and these are likely to be tarnished if the air be at all moist, 

 and the protection of such surfaces during the treatment is therefore 

 necessary. Under conditions of considerable or excessive moisture 

 wall papers and the lighter fabrics are much bleached and all metal 

 surfaces corroded. 



(5) The penetration of a low percentage of gas (5 or 6 per cent) 

 without pressure from above into exposed surfaces of grain is not very 

 great; but a strong percentage (15 per cent) under high pressure for 

 an hour or more has strong penetration to a depth of from 14 to 18 

 inches even where a comparatively small area for penetration is 

 allowed. It should be noted here also that in the ordinary method of 

 fumigating grains with the Clayton apparatus the gas is liberated 

 through a perforated iron tube thrust into the bottom of the bin, and 

 the gas forced in under pressure is made to permeate much more 

 quickly and thoroughly the entire mass of grain. 



(6) The test made with the fumigation of a bunch of bananas was, 

 in a measure, unsatisfactory, as it was done in a very rainy, damp 



