30 FUMIGATION INVESTIGATIONS IN CALIFORNIA. 
The measurement around the bottom of the tent can be obtained 
by the use of a tapeline 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. T\ Tiile 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- 
fulness 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 
emplo} T ed 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 
