THE WAR ON INSECTS 305 



and as the vapor is heavy, the shell should be put on 

 top of the mass of vines. 



A much more usual employment for the material 

 is to destroy insects infesting seeds like peas, beans, 

 lentils, wheat or corn. In such cases the infested seeds 

 should be put into a tight box or other receptacle, and 

 bisulphide at the rate of one drachm per cubic foot 

 of space should be placed in a shallow dish on top of 

 the mass, the box or jar being tightly covered, of course. 

 In twenty -four hours all the insects will be killed with- 

 out injury to the germinating power, but if the seed 

 is to be used for planting, it must then be aired out be- 

 fore being again put away. Eggs are not killed by this 

 vapor, hence it may be necessary to treat a second time 

 in case of badly infested material. If the grain or other 

 seed is to be used for food only, it may be kept covered 

 indefinitely, as no injury is caused to its milling or cook- 

 ing qualities. In large spaces one pound may be counted 

 for 100 cubic feet of space, or for one ton of binned 

 grain. Shallow vessels should always be used for evap- 

 orating dishes to expose as large a surface as possible, 

 and the heavy nature of the fumes must be taken into 

 consideration. Under no circumstances should the 

 material be used near a light of any kind, and if the 

 person using it has any regard for his safety, he will 

 not smoke while handling it even in the field. 



Before the development of the hydrocyanic acid 

 gas, bisulphide of carbon was used to treat even large 

 spaces like houses, barns and mills; but its cost and 

 dangers are so great compared with the newer material 

 that it is not now employed in this way. Purchased 

 in small quantities at drug store prices, this is rather 

 an expensive material; but there is a special much 

 cheaper grade known as "Fuma" bisulphide, which 

 answers every purpose for agricultural use. 



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