428 
Journal of Agricultural Research 
Vol. XI, No. 9 
The minimum dosage for killing all the lettuce seedlings, the most 
susceptible plants experimented with, was, in the case of gas applied to 
the leaves only, a dilution 0.5871 gm. of sodium cyanid per liter (equiva¬ 
lent to 0.176 per cent of hydrocyanic acid gas over the solution), and at 
this concentration each of the plants tested showed a death rate of from 
50 to 80 per cent when the solutions were applied to the roots. From 
this it will be seen that the gas alone is almost as toxic when applied to 
the leaves as the hydrocyanic-acid gas solution is when applied to the 
roots. 
Table V .—Minimum dosages toxic to insects experimented upon a 
Insect. 
Sodium 
cyanid per 
liter. 
Approximate 
concentration 
of gas. 
Phylloxera. 
Gm. 
0. 0078 
. 0156 
. 12 < 
Per cent. 
O. 0023 
. 0046 
Houseflies. 
Beetles. 
• J 
a Maximum dosage harmless to all plants experimented with both in the gaseous and solution form of 
the add was 0.0366 gm. of sodium cyanid per liter, approximately 0.0109 per cent of hydrocyanic-add gas 
Over the solution. 
These experiments indicate that a dosage toxic to flies and phylloxera— 
viz, 0.0156 gm. of sodium cyanid per liter (equivalent to 0.0046 per cent 
of hydrocyanic-acid gas over the solution)—would be safe for all the plants 
experimented upon; but for the beetles used so much stronger dosage is 
required that it would be extremely injurious, if not fatal, to every plant 
experimented upon. Before planted areas could be treated it would be 
necessary to determine experimentally the minimum dosage fatal to the 
insects present and compare that with plants growing thereon, besides 
considering reactions of the gas and the soil. There would probably be a 
considerable margin of safety on some soils between the killing strengths 
necessary for an insect, such as the phylloxera, and injury to more hardy 
plants, especially in the dormant season. 
B. PHYSICAL-CHEMICAL ACTION OF HYDROCYANIC-ACID GAS IN THE 
SOIL 
If hydrocyanic-acid gas is used as a soil fumigant, it will be necessary 
to fill the soil with gas, either from sodium cyanid placed in the soil and 
decomposed into hydrocyanic-acid gas, or by generating the gas at the 
surface and forcing it into the soil. Tubes sunk into the soil to various 
depths make it possible to draw out the gas for measurement. The con¬ 
centrations thus determined, compared with the data given above on the 
toxicity of the gas to insects, would indicate the probabilities of the 
presence of a killing strength of hydrocyanic-acid gas in the soil. 
For drawing gas out of the soil %-inch gas pipe cut into 36-inch lengths 
was used. The tubes may be sunk to any depth, up to 30 inches, at which 
a determination is desired. To operate, the tube is sunk into the ground 
a short piece of rubber tubing is drawn over the end projecting out of the 
