40 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



place in many other districts in southern California. In short, the 

 experience with this new method of fumigation has been so success- 

 ful throughout the southern fruit-growing sections that it is only a 

 matter of time when it necessarily must entirely supplant the old 

 methods. 



THE CHEMICALS IN FUMIGATION. 



For the generation of hydrocyanic-acid gas in fumigation potas- 

 sium cyanid, 1 sulphuric acid, and water are necessary. The hydro- 

 cyanic-acid gas is produced by the action of the sulphuric acid on 

 the cyanid of potassium. Under the early methods of generating 

 hydrocyanic-acid gas the cyanid was dissolved in water before being 

 used. At the present time cyanid is used entirely in the crystal 

 form. The water is first measured and poured into the generating 

 vessel. The required amount of acid is then added to the water, 

 producing a great increase of the temperature of the mixture. While 

 the mixture is hot it should be placed beneath the tree and the 

 cyanid added. If permitted to cool before the cyanid is added, 

 the generation of gas will not only be slower than with the heated 

 mixture, but the amount of available gas will be decreased, thus 

 making the operation more expensive, and necessarily less efficient. 



POTASSIUM CYANID (KCN). 



An imported potassium cyanid designated as 98 to 99 per cent 

 pure is used almost exclusively for fumigation purposes in southern 

 California. This imported potassium cyanid has been employed 

 throughout the field investigations of this bureau and is referred to 

 in this bulletin whenever cyanid is mentioned, unless specific men- 

 tion of another grade is given. Analyses of seven samples taken 

 promiscuously in the field during this investigation averaged 98.1 

 per cent pure, the poorest sample being 97.28 per cent. The gen- 

 eral fumigation experience with such a high grade of potassium 

 cyanid has been very satisfactory. This cyanid is purchased in 

 cases containing approximately 200 pounds. 



The potassium cyanid most frequently used in California for 

 fumigation purposes is commonly spoken of as u German" cyanid, it 

 being generally known that this chemical is imported from Ger- 

 many. This term "German" has been used in distinguishing the 

 regular potassium cyanid from another kind popularly known as 

 "American" cyanid, which has had a very limited and unsatisfactory 

 usage for a number of years. This " American" cyanid was known 

 to be of a generally much harder composition and slower in gener- 

 ation. Because this latter cyanid is made in America the general 

 belief has prevailed among fumigators that it is impossible to manu- 



1 For the use of sodium cyanid. see Part II of this Bulletin. 



