CARBON DISULPHID AS AN INSECTICIDE. 7 



since every effort is made to keep carbon disulpliid from the presence 

 of fire, while gasoline is used principally in connection with fire. 

 The only peculiar thing about carbon disulphid is that the vapor 

 ignites at a lower temperature than does that of gasoline. It may 

 ignite from any form of fire, or even without the presence of flame 

 but with a temperature of above 297° F, There must therefoi^e he 

 no smoking or carrying around of lights where carhon disulphid 

 ■vapor is strong^ and it is hardly safe to have steam> pipes very hot^ or 

 to turn on or off an electric light or fan. Even the heavy striking of 

 a nail with a ho.mmer might cause an explosion if the necessary 

 density of vapor were present. Carbon disulphid should not be 

 applied to corn in the bin or to other grain when the mass is known 

 to be in process of heating spontaneously. The disulphid should be 

 stored in a cool, dry outhouse away from fire and where the con- 

 tainers will not rust out and allow the liquid to escape or evaporate. 

 As a further precaution, all containers should be labeled in red, 

 '^ Danger — Fire." 



CONFINEMENT OF THE GAS IN FUMIGATION. 



Carbon disulphid is applicable only where the vapor can be con- 

 fined quite closely. The period during which it is necessary to keep 

 the vapor confined varies with the resistant power of the insect 

 species, but in nearly all cases must be for more than 30 minutes, even 

 when a heavy dosage is being used. It is possible for the gas to be 

 confined sufficiently by the soil, the burrow, a tight room or bin, etc., 

 or even by the large volume of a material through which it can only 

 diffuse slowly. 



GA^»TIGHT MATERIALS. 



Many writers have referred to tightly closed rooms which are 

 plastered or carefully ceiled as being " gas-tight." As a matter of 

 fact, no such room can be made anj'where near gas-tight. Ordinary 

 living rooms, even in well-built houses, are so very far from gas-tight 

 that a large excess of the fumigant is necessary to get anything like 

 satisfactory results in them. It is not strange, therefore, that a wide 

 divergence appears between the results of experiments made by a 

 scientist in some laboratory in glass receptacles which are truly 

 gas-tight and the results of fumigation work under ordinary build- 

 ing conditions, both in the strength of gas required to kill all in- 

 sects and in the time in which this can be accomplished. 



A somewhat extensive testing of materials has shown that ordi- 

 nary 10-ounce duck, untreated, Avill transmit practically 85 per cent 

 as much air under a slight pressure as though there were no such 



