490 



INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 



CHEMICALS 



The chemicals used for generating hydrocyanic acid gas in fumi- 

 gating work are potassium and sodium cyanide, commercial sulphuric 

 acid and water. The cyanide is usually handled in the 200-pound 

 cases and the acid in steel drums weighing from 1,200 to 2,000 

 pounds. 



Cyanide. — For many years previous to the last two, potassium 

 cyanide, 98-99 per cent, was almost entirely used in fumigating. 

 At the present time, however, it has been practically replaced by 



Fie. 488. 



-The McFadden tent-hoisting machine. 

 U. S. Dept. Agric.) 



(After Woglum, Bur. Ent, 



129-130 per cent sodium cyanide. Sodium cyanide costs more per 

 pound, but because of the greater cyanide content less is needed, thus 

 making it actually the less expensive of the two on the basis of the 

 amount of gas generated. It is also put up in pieces weighing just 

 one ounce each. 



Both of the cyanides are good and reliable, and the deciding 

 features will probably always be the supply available and the price. 



Sulphuric Acid. — Fumigating sulphuric acid has a specific gravity 

 of about 66 degrees Baume, containing only traces of nitric acid 

 and arsenic, lead or zinc. It has been the current belief that espe- 

 cially nitric acid caused the burning of the fruit and foliage so often 

 the results of fumigating work, but R. S. Wo glum in Bui. No. 90, 

 Part I, page 42, U. S. Dept. Agric, Bureau Entomology, states that 

 this is an erroneous belief. It should always be the aim of every 

 fruit grower to get good grades of sulphuric acid, which is not at 

 all difficult at the present time. 



