30 FUMIGATION INVESTIGATIONS IN CALIFORNIA. 



The measurement around the bottom of the tent can be obtained 

 by the use of a tapeUne or by pacing. Under this system the work 

 is facilitated by having a chart or table of figures showing the cubic 

 contents corresponding to different dimensions. 



THE CHEMICALS REQUIRED IN FUMIGATION. 



For the generation of hydrocyanic-acid gas in fumigating, potas- 

 sium cyanid, 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 hydro- 

 cyanic-acid gas the cyanid was dissolved in water before being used. 

 At the present time cyanid is used in the crystal form entirely'. The 

 water is first measured out and poured into the generating vessel. 

 The required amount of acid is then added to the water, producing a 

 great increase in 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. 



An imported cyanid designated as 98 to 99 per cent pure is used 

 almost exclusively for fumigation purposes in southern California, 

 under the popular belief that it is superior to American cyanids for 

 this purpose. There seems to be no real basis for this common belief, 

 and, in fact, experiments conducted by Prof. Wilmon Newell while 

 State entomologist of Georgia demonstrated that certain brands of 

 American cyanid met all the requirements necessary for fumigating 

 nursery stock, and it seems reasonable to believe that these will also 

 be equally available for citrus-orchard fumigation. A series of 

 laboratory and field tests has been planned to demonstrate the use- 

 fidness of all the available brands of potassium cyanid. 



In the field investigation reported in this bulletin the 98 to 99 per 

 cent imported cyanid commonly used in southern California has been 

 employed throughout and, although no chemical analysis was made, 

 the results proved entirely satisfactory. 



SULPHURIC ACID. 



Too much stress can not be placed upon the quality of sulphuric 

 acid used in fumigation. Operators have repeatedly informed the 

 writer of much burning of fruit and foliage which occurred during 

 the season of 1905, owing to the use of a grade of acid differing from 

 that ordinarily employed. An analysis of the acid used that season 



