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JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
version from a potassium to a sodium basis in 1910-1913 when the price 
of potash products increased. Since 1914, sodium cyanide has domi¬ 
nated the field in all lines of fumigation. 
In 1912, William Dingle, a practical fumigator, invented a portable 
machine for generating gas outside the tent from cyanide in solution. 
Subsequently a modified type of generating machine known as the 
cyanofumer was developed in Los Angeles and displaced the pot system 
very largely in California in 1915-17. Although this new method did 
not appear superior to the pot method in scale control, it was an im¬ 
provement in several ways over the more cumbersome pot method from 
the standpoint of the fumigation manager. 
One of the greatest forward steps in fumigation was the development 
of liquid hydrocyanic acid by William Dingle in 1916. Mally, in South 
Africa was experimenting in a small way with the same chemical almost 
simultaneously but entirely independently. The simplicity of the 
“liquid gas” method, as commonly termed, led to its immediate adop¬ 
tion in California. A combined attack on the problem by entomologists, 
chemists, manufacturers and fumigators quickly led to the development 
of a standardized system of liquid gas fumigation with a uniformly 
high grade product. Today fully 90 per cent of the 2]/ 2 million dollar 
annual fumigation campaign in California comes under the liquid sys¬ 
tem, the remaining 10 per cent being divided between cyanofumer and 
pots. Three large manufacturing concerns are now in the field, one 
making the liquefied product from sodium cyanide, one from calcium 
cyanide and the other synthetically. 
Methods of application have undergone repeated changes and no less 
than 12 different types of generating machines have been developed 
and used since the method originated. Some of these machines have 
been adapted for atomization of the liquid through a mist nozzle while 
others convert the liquid to gas by heat. A very large amount of 
valuable data bearing on the limitations of liquid hydrocyanic acid for 
orchard fumigations has been accumulated. One reflection of this 
information is the greatly increased practice of daylight fumigation, a 
decidedly hazardous operation in former days with pot or cyanofumer. 
The most recent development in fumigation has been the use of 
calcium cyanide as a dust. Quavle was the first to use this material 
for fumigating beneath a tent. At the present time calcium cyanide dust 
as an orchard fumigant is merely in the experimental stage. Preliminary 
work appears to have shown it very effective against scale insects but 
more damaging to plants under certain conditions than cyanide gas 
