12 



CIRCULAR 3 6 9, U. S. DEPARTMENT OF AGRICULTURE 



which combines with moisture from the air to form hydrocyanic acid 

 gas — the powder method. 



THE BARREL OR POT METHOD 



The barrel or pot method of generating hydrocyanic acid gas is so 

 called because the chemicals used are placed together in a barrel (figs. 

 1 and 12) or some similar container (fig. 13). This method, while 



Figure 12. — Man wearing gas mask about to lower bag of sodium cyanide into a 

 barrel containing sulfuric acid and water. If tbe cyanide is put in a gunny 

 sack, there is no danger of the bottom of the bag breaking and spilling the 

 cyanide. The cyanide should not be dropped into the acid-water mixture ; it 

 should be lowered carefully. 



more laborious than others, gives excellent results and is the safest 

 for the use of other than professional fumigators. It can be made 

 the cheapest method of fumigation. 



CHEMICALS REQUIRED 



Sodium cyanide (96 to 98 percent, containing 54 percent HCN), 

 a commercial grade of sulfuric acid (66° B.). and water are the 

 only materials required. Sodium cyanide is a white crystalline sub- 



