434 
Journal of Agricultural Research 
Vol. XI, No. 9 
iodin caused by aspirating through it large quantities of air. Turbidity 
with silver nitrate was reached with about 120 c, c. of air from the 
standard hydrocyanic-acid gas solution when 450 c. c. of air at the same 
concentration of gas would neutralize 1 c. c. of N/100 iodin. 
These experiments, made in loose soil, emphasize the slow rate of 
diffusion of hydrocyanic-acid gas in the soil, which rate would neces¬ 
sarily be very much slower, and perhaps would be checked entirely* 
in field conditions. Diffusion seems to be accomplished to a large 
extent by at least a partial saturation of the soil body through which 
it is moving (Table X). In experiment 1 the concentration of the gas 
seemed quite uniform throughout the tube, but in experiment ia, after 
standing 48 hours, a decided decrease is shown in the last section of the 
tube, indicating that the outer part was not saturated to the same 
extent as the sections through which the air was drawn. Solubility of 
the gas in water is indicated in experiment 2 (wet soil), the outer end 
of the tube not having a trace of gas, while the concentration in the 
first three sections is very high. The chemical reaction or adsorption 
of the dry gas by the clay soil over a period of time is also shown in 
experiments 1 and ia, where the quantity of air required for turbidity 
increases from 160 c. c. immediately after charging the tube to 1,200 
c. c., 48 hours afterwards. The most striking difference in the retention 
of hydrocyanic-acid gas is shown between sand and clay soils. In 
experiment 1, 108 liters of air from the hydrocyanic-acid gas solution were 
aspirated through the tube and in experiment 3 only 66 liters of air 
from the hydrocyanic-acid gas solution were used, yet an equal amount of 
hydrocyanic-acid gas was recovered from each. 
The absence of chemical reaction or of adsorption on the soil parti¬ 
cles in pure sand is shown in experiments 4 and 4a. Here the gas remains 
in the tube for five days without any decrease in the total amount 
present. The difference between a wet and dry soil is again shown in ex¬ 
periments 4 and 5. 
Table X. —Summary of experiments with a soil tube 
Experi¬ 
ment 
No. 
Kind of soil. 
Quan¬ 
tity of 
air aspi¬ 
rated 
through 
tube. 
Inter¬ 
val 
before 
testing. 
Moisture. 
Amount of air required to cause turbidity with 
silver nitrate. 
1 st 
section. 
2d 
section. 
3d 
section. 
4th 
section. 
5 th 
section. 
6th 
section. 
I. 
Clay. 
Liters. 
108 
108 
30 
66 
66 
30 
3 ° 
30 
Hours. 
Moist. 
C.c. 
120 
330 
120 
io 5 
(«) 
75 
200 
390 
C. c. 
120 
240 
130 
*05 
C.c. 
120 
420 
145 
105 
C.c. 
135 
450 
1, 080 
140 
C.c. 
145 
820 
C.c. 
160 
I, 200 
ia.... 
2 . 
...do. 
...do. 
48 
...do. 
Wet. 
-2. 
Sand.... 
...do. 
Moist. 
140 
210 
0. 
sa*... 
16 
...do. 
4*.. *. 
...do. 
Dry_ 
75 
170 
380 
130 
210 
380 
130 
200 
310 
220 
I90 
310 
5 00 
180 
300 
1 
...do. 
120 
,,, do. 
1 1 * * * • • 
...do. 
Wet. 
0 . 
a No trace HCN. 
