Nov. 26 ,1917 
Hydrocyanic-Acid Gas as a Soil Fumigant 
435 
SUMMARY 
(1) The toxicity of hydrocyanic-acid-gas solutions varied with the 
insects experimented upon, from the minimum for houseflies of 0.0156 gm. 
of sodium cyanid per liter (equivalent to 0.0046 per cent of hydrocyanic- 
acid gas over the solution) to the maximum for beetles of 0.125 gm. 
sodium cyanid per liter (equivalent to 0.0365 per cent of hydrocyanic- 
acid gas over the solution), the latter being the most resistant of any 
insect experimented upon. 
(2) Gas from a solution of approximately the same strength as that 
used above on houseflies retarded the germination total of lettuce seed 
11.3 percent. 
(3) Lettuce seed is not killed by two days' exposure to hydrocyanic- 
acid gas as strong as 0.0366 gm. of sodium cyanid per liter (equivalent to 
0.0109 per cent of hydrocyanic acid gas over the solution) and will give 
a good germination percentage if removed at the end of this time. 
(4) Stimulation was greatest at a point one sixteenth of that causing 
retardation—viz, 0.0011 gm. of sodium cyanid per liter (approximately 
0.00033 per cent of hydrocyanic-acid gas over the solution). 
(5) Solutions of hydrocyanic-acid gas approximately 256 times as 
strong as that necessary to produce gas having the minimum killing 
strength for flies were fatal to all seedlings tested and to 50 per cent of 
the cuttings placed in the solution, while a solution approximately twice 
as strong as that required to produce a gas concentration fatal to flies 
had no effect even upon seedlings. 
(6) Sodium-cyanid solutions introduced into the soil failed to give a 
trace of hydrocyanic-acid gas in air drawn from the soil. 
(7) The use of pressure in forcing gas into the soil did not materially 
increase the rate at which it could be introduced. 
(8) Soil and water are both strong absorbents of hydrocyanic-acid gas. 
Retention of hydrocyanic-acid gas by the soil is dependent upon the 
character of the soil, while that of water remains constant under uniform 
conditions of pressure and temperature. 
(9) The variability of gas absorption by the soil makes it practically 
impossible in field work to estimate the dosage of sodium cyanid re¬ 
quired to give a toxic effect on insects and at the same time to be within 
the margin of safety to plants. 
(10) In small amounts of soil of a uniform character it is possible to 
determine experimentally the margin of safety between certain insects 
and plants. 
(11) A heavy damp or a very wet sandy soil is almost impervious to 
hydrocyanic-acid gas. 
(12) A pure sandy soil when wet will take up hydrocyanic-acid gas 
only in proportion to the amount of water present and this may again 
be given off, but gas in contact with a clay soil either enters into a 
chemical combination with some of the soil constituents or is adsorbed 
by the soil particles. 
