3o6 INSECTS 



Hydrocyanic acid gas is produced by the action of 

 dilute sulphuric acid on cyanide of potassium, and is 

 intensely poisonous to all animal life. It effects vege- 

 table life to a somewhat less extent and more slowly, 

 so that there is usually a fair margin of safety between 

 its effectiveness on insects and the danger of injury on 

 plants. For the destruction of insects on dormant 

 nursery stock, and for the treatment of rooms and 

 buildings to destroy household or other pests, the fol- 

 lowing formula answers for loo cubic feet of space: 



Cyanide of potassium, 90% pure (by weight) ... i ounce 



Sulphuric acid, sp. gr. 1.83 (by measure) 2 ounces 



Water 4 ounces 



The gas is lighter than air and is generated in an 

 earthenware jar, pot or basin as follows: First pour in 

 the water, add the acid slowly, and finally drop in the 

 cyanide broken into small lumps in a thin paper bag. 

 The order of mixing is important, for if the water be 

 poured into the acid, the amount of heat suddenly 

 developed will be so great as to spatter the material 

 in every direction. The cyanide is dropped in, bag 

 and all, to somewhat delay the development of gas and 

 permit the operator to escape or close the fumigating 

 chamber. The method of dealing with household pests 

 has already been given. Greenhouse fumigation forms 

 a study by itself, because of the difference in efifect on 

 the many sensitive plants there raised, and for which 

 no generally applicable directions can be given. 



Orchard fumigation is not much practised in the 

 east where most of the trees have a dormant season 

 permitting their treatment with sprays. On the Pacific 

 coast, fumigation of citrus and olive trees is quite largely 

 practised and elaborate apparatus for covering trees 

 with gas-tight tents is in use. But even there the prac- 



