454 



AN ECONOMIC ENTOMOLOGY. 



previously referred to. Bisulphide of carbon is very inflammable 

 and explosive, and in no building where it is used should a fire 

 or open light of any kind be allowed. Lighted pipes and cigars 

 must be avoided, because even a spark may cause an explosion; 

 but with ordinary precautions entire buildings may be safely and 

 effectively treated. In all cases where vapors are used their effect 

 depends on their poisonous action when breathed ; therefore, the 

 rooms, enclosures, bins, or other spaces must be as tightly closed 

 as possible, and in large spaces an excess of material should be 

 used, that they may be more rapidly and completely filled. 



Hydrocyanic acid gas is a vapor exceedingly destructive to all 

 life ; but more fatal to animals than to plants. Its use has in- 

 creased to such an e.xtent during recent years, that the general 

 term fumigation has come to have a specific application to the 

 exposure of infested plants to the action of this gas, produced as 

 follows : 



Cyanide of Potassium, 98 per cent, pure i ounce 



Sulphuric acid, specific gravity 1.83 2 ounces 



Water 4 ounces 



Use a glazed earthenware vessel of any kind. Put in first the 

 water, then pour in the acid slowly, then, in a thin paper bag, 

 drop in the cyanide broken into small lumps, and get out. The 

 amount above given is sufficient to fill one hundred cubic feet of 

 lightly closed space with a vapor that will kill dormant scales or, 

 in fact, any other animal life in an hour, and will be harmless to 

 all dormant stock save peach, and to most trees other than coni- 

 fers, which should never be fumigated. 



This whole matter of fumigation has become so important that 

 Professor W. G. Johnson, now editor of the American Agricul- 

 turist, has published a book to cover the subject. Naturally, a 

 brief reference is all that is possible here ; but a few well-estab- 

 lished points may be noted as essential : 



First. — The fumigating house, bo.x, tent, or cover must be as 

 nearly gas-tight as it can be made, and should hold the gas, 

 practically intact, for at least one hour. 



Second. —The chemicals should be as nearly pure as possible, 

 and the cyanide, especially, should be of high grade. 



Third.- The order of mixing should be followed absolutely ac- 

 cording to formula, to avoid unpleasant results. 



