THE MONTHLY BULLETIN. 



329 



CHEMICALS. 



The chemicals used for generating hydrocyanic acid gas in fumigat' 

 ing work are potassium or 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 potassium cyanide 98-99 per cent pure 

 was thought to be the best and only reliable source of hydrocyanic acid 

 gas. It was formerly used to the exclusion of all others and is still 

 preferred by many who do not wish to add the injurious residue of 



Fig. 316. — The McFadden tent-hoisting machine. (After W^oghim. ) 



sodium cyanide to their soil, and also by those who do not see enough 

 advantages in sodium cyanide to warrant a change. 



There are two grades of sodium cyanide ; the 98-100 per cent pure, 

 which is totally unfit for fumigation purposes because of the impurities 

 it contains, and the pure 129-130 per cent sodium cyanide, which is used 

 almost exclusively for fumigation work. This product, though some- 

 what more expensive than the potassium cyanide per pound, has much 

 more available hydrocyanic acid gas and consequently a smaller amount 

 is necessary, which is enough smaller to make the cost of dosage less 

 than that for potassium cyanide, and is therefore fast displacing it. 

 Much has been said for and against the sodium cyanide relative to the 

 burning of fruit and foliage, but this is still an unsettled point. 



