1920-21.] Relation of Soil Colloids to Conductivity of Soil. 
63 
observations were made only when the soils had more or less the same 
R 
water content, we could find the values of p- 4 for each soil corresponding 
K 0 
to various values of the period T. 
These values are given in Table I alongside some observed values of 
r 4 . 
R n 
*4 
in clay loam for those periods. 
Table I. — Change of — J with Change of Period. 
XVn 
Interval 
Min. 
to 
Max. 
Period 
T 
in Hrs. 
R 0 
Sand. 
5t 
R 0 
Clay Loam. 
| 
Observed Value 
of 
R 
-i in Clay Loam 
R 0 
Mean 
Surface 
Temperature 
for Period. 
in Hrs. 
for that Period. 
6 
12 
•41 
•30 
•26 
2-5° C. 
8 
16 
•44 
•33 
•30 
5-0° C. 
9 
18 
•46 
•35 
•32 
3-0° C. 
10 
20 
•475 
•375 
12 
24 
•52 
•42 
•42 
100°’ c. 
24 
48 
•54 
•50 
•52 
5-0° C. 
5*0° C. 
36 
72 
•60 
•60 
•61 
8-5° C. 
9*0° C. 
It will be seen that good agreement was obtained between the calculated 
R 
and observed values of p^ in clay loam when the mean surface temperature 
R 0 
during the period was about 10° C. — the temperature at which the standard 
R 
observation was made, — but that ^ fell considerably below the calculated 
rt 0 
value when the mean surface temperature was below 10° C. 
R 
This suggested plotting the values of at various temperatures but 
K 0 
the same period against the corresponding mean surface temperatures ; the 
results for sand and clay loam are given in the next section. 
R 
III. Evidences of Changes in Values of ^- 4 with Changes in 
JLvq 
Mean Surface Temperature of Soil. 
(a) In Sand. 
Owing to the strict conditions under which observations were made for 
R 
this investigation, only about sixty values of in each soil were recorded 
