246 INSECTS 



And now, it sometimes happens that a house or a 

 room long neglected gets into such a condition as to be 

 almost uninhabitable by reason of insect pests of all 

 kinds from scavengers to parasites and the question 

 arises whether there is any method by which all these 

 things can be reached at one fell swoop, or at least by 

 two swoops; the second being made necessary by the 

 fact that there are always some forms in the egg state 

 and not to be reached even by fumigation with hydro- 

 cyanic acid gas, which is usually recommended under 

 such conditions. 



Hydrocyanic gas is formed by the action of dilute 

 sulphuric acid upon cyanide of potassium, and is one of 

 the most penetrating of poisonous vapors, fatal alike to 

 man and insects and even to plant life when long enough 

 exposed to it ; but harmless to fabrics and not injurious 

 to metals. The formula for each 100 cubic feet of space 

 to be treated, is 



Cyanide of potassium, 98 pure, by weight. . i ounce 



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



Water 4 ounces 



Break the cyanide into small lumps and put the 

 necessary amount in a thin paper bag. Put the water 

 into a glazed earthenware vessel a wash basin, slop jar 

 or other bowl will answer then add the acid slowly. 

 The water will heat as the acid is added and will fume 

 or bubble. When all the acid is added, drop in the bag 

 containing the cyanide and get out. The formation of the 

 gas will be retarded for a few moments while the acid 

 gets through the paper and this will give opportunity to 

 close the door and seal it as tightly as possible. The 

 order of doing this is important, for if it were attempted 

 to pour water into the acid, the first drops would cause 

 a boiling so violent as to spatter the entire volume in 



