HYDROCYANIC-ACID GAS AS A SOIL FUMIGANT 
By E. Ralph Ong, 
Instructor in Entomology , Agricultural Experiment Station of the University of 
California 
INTRODUCTION 
Though much has been written on soil fumigation, it can not be said 
that we have a satisfactory method for treatment against soil insects. 
Most of such work has been done in France with carbon disulphid against 
phylloxera, but no reliable data on soil work exist regarding the avail¬ 
ability of hydrocyanic-acid gas, the most efficient fumigant known in 
orchard and house work; hence, the following study was made of the 
action of hydrocyanic-acid gas in the soil and its effect on germinating 
seeds and plants. 
Any extensive treatment of the soil must be considered in relation to 
crops grown thereon, especially those occupying the ground for a period 
of one year or more. Operations possible while the ground is occupied 
by a crop are much to be preferred, although knowledge of the treat¬ 
ment of unplanted areas is very desirable. The experiments to be 
described in this paper were made largely with the idea of the treatment 
of occupied ground, for it follows as a matter of course that treatment 
which is safe for planted areas is also safe for bare land. 
Two distinct lines of work are necessary for the study of this subject: 
(a) Establishing a definite ratio between the minimum point of tox¬ 
icity to insects and the maximum dosage which is safe to germinating 
seeds and plants. 
(b) A study of the physical and chemical action of the gas in the soil; 
the rate and extent of diffusion and absorption by soil water; the adsorp¬ 
tion of the gas by soil particles and its decomposition by certain soil 
constituents. 
A. RELATION OF POINT OF TOXICITY OF INSECTS AND PLANTS 
Many data have been accumulated by the various Experiment Sta¬ 
tions, and particularly by the California Station, regarding the toxicity 
of hydrocyanic-acid gas to insects. Likewise there are many data 
(i~8) 1 available on the effects of the gas on plants, but practically all 
of them are based on house experiments where the actual concentration 
of the gas is not accurately known. Therefore it was necessary to make 
a few tests to establish a basis of comparison. 
A method elaborated by Prof. C. W. Woodworth, of the California 
Station, in the investigation of the action of hydrocyanic-acid gas on 
the eggs of certain insects, makes use of the vapor-tension laws of gases. 
1 Reference is made by number (italic) to “ Literature cited,” p. 436. 
Journal of Agricultural Research. 
Washington, D. C. 
ku 
Vol. XI, No. 9 
Nov. 26,1917 
Key No. Cal.— 12 
