INSECTS AND INSECTICIDES 379 



furic acid. The ingredients are combined in the following 

 proportions : 



Potassium cyanid (98 per cent) . 1 ounce avoirdupois 



Sulfuric acid 1 fluid ounce 



Water 3 fluid ounces 



Potassium cyanid is a white, deliquescent, highly poisonous 

 substance. The commercial article is usually in the form of 

 rather hard irregular lumps wdiich are readily soluble in water. 

 Because of its tendency to draw moisture from the air, it is 

 usually sold in tight tin cans or drums. Small amounts may 

 be kept in glass fruit-jars. For fumigation purposes, only 

 potassium cyanid that is at least 98 per cent pure should be 

 used. 



The sulfuric acid need not be chemically pure, a good com- 

 mercial grade being entirely satisfactory. 



When sodium cyanid is used, the proportions are as follows : 



Sodium cyanid 1 ounce avoirdupois 



Sulfuric acid Ij fluid ounces 



Water 2 fluid ounces 



W^hen pure, sodium cyanid contains 53 per cent cyanogen 

 (CX), which is about 33 per cent more than is present in potas- 

 sium cyanid. It is customary to indicate the strength of sodium 

 cyanid in terms of potassium cyanid ; that is, pure sodium 

 cyanid is said to be 133 per cent pure. This means that 100 

 pounds of sodium cyanid will yield as much cyanogen as 133 

 pounds of potassium cyanid. For fumigation purposes, sodium 

 cyanid should be at least 124 per cent pure and should not 

 contain more than one per cent of common salt, as its presence 

 causes the decomposition of the hydrocyanic acid gas. Owing 

 to its higher cyanogen content, only three fourths as much 

 sodium cyanid is required for fumigating a given space as of 

 potassium cyanid. 



