118 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



to the "pot method," which consists of placing dry cyanid with diluted 

 sulphuric acid in an open vessel beneath the tented tree. In 1912 a 

 simplified portable machine for generating cyanid gas outside the tent 

 was invented and this method of application rapidly and successfully 

 displaced the ''pot method." The latest development, liquid hydro- 

 cyanic acid, has proved the most revolutionary of all changes in field 

 fumigation, promising ultimately to completely supersede current 

 practices. 



In 1915 C. W. Mally,^ working in South Africa, prepared and 

 experimented with liquid hydrocyanic acid. It happened that Wil- 

 liam Dingle, of Los Angeles, one of the inventors of the machine 

 method of generation, began to develop simultaneously but entirely 

 independently the same method and, in the early spring of 1916, pub- 

 licly demonstrated the fumigation of citrus trees with liquid hydrocy- 

 anic acid. 



Liquid hydrocyanid acid is by no means new, having been known to 

 chemists for many years. In its pure state it is a colorless liquid with 

 a specific gravity of .70 at 65° F. The high volatility of this substance 

 (it boils at 80° F.) produces easy gasification at the ordinary tem- 

 peratures of fumigation. If impure it decomposes rapidly. 



The application of this gas to the tented tree is extremely simple. A 

 tank, suitably vented, holding about two gallons, is mounted on a 

 platform with a measuring device and a pump (PL 4, Fig. 1). The 

 Uquid hydrocyanic acid, after measurement into storage coils, is forci- 

 bly discharged through a short rod fitted with a mist type of spray 

 nozzle, and quickly disappears as an invisible gas. 



During the season of 1917 approximately 540,000 pounds of solid 

 sodium cyanid were converted into liquid hydrocyanic acid for the use 

 of thirty fumigation outfits .^ So far this year more than one million 

 pounds of sodium cyanid have been similarly treated for the use of 

 ninety-four fumigation crews.^ A very much greater amount would 

 have been used could it have been produced. 



Gas Distkibution 



It has been the writer's belief for many years that gas distribution is 

 influenced by the method of application or generation and in 1908 this 

 led to the invention of a cover device^ for deflecting the rise of gas from 

 a generating vessel. In pot fumigation a dense column of gas rises 

 rapidly from the generator until deflected by the branches, foliage and 

 ultimately the tent. The spreading of the gas through the lower part 

 of the tree follows the forcing downward of the diffused column after 



1 South Africa Jl. Sci., v. 12, No. 3. 



2 Data obtained from the concern that liquifies hydrocyanic acid. 



3 U. S. Dept. Agr. Bur. Ent. Bull. No. 79, p. 58. 



