/ 
1920-21.] Relation of Soil Colloids to Conductivity of Soil. 61 
VII. — The Relation of the Soil Colloids to the Thermal Con- 
ductivity of the Soil By Capt. T. Bedford Franklin, B.A. 
(Cantab.). 
(MS. received December 28, 1920. Read February 7, 1921.) 
SUMMARY. 
SECTION 
I. Introduction ......... 
II. Scope of the Investigation and Effect of Change of Period on Values 
r 4 
of 
R. 
Rr 
III. Evidences of Changes in Values of 
Temperature of Soil 
(а) In sand .... 
(б) In clay loam 
(c) In clay loam, ignited clay loam, and sand 
IV. Conclusions .... 
with Changes in Mean Surface 
page 
61 
62 
63 
63 
64 
64 
67 
I. Introduction. 
Early investigators regarded the soil as an inert framework of soil grains 
of various sizes covered with a continuous film of water, and the properties 
which in theory it should possess under such a hypothesis were found 
not to accord too well with the results of experiment. But when the 
existence of soil colloids was understood, the differences between theory 
and experiment tended to disappear one by one, as shown by the work of 
Bouyoncos in America in 1915 and of Keen in England in 1914, 1919, 
and 1920.* 
These and other investigators have shown that it is essential to take 
into account the colloidal properties of the soil before its physical pro- 
perties can be understood properly, and in doing so have cleared up many 
of the points of difference between experiment and the old theory which 
was based on a hypothesis that disregarded these soil colloids. 
In a previous paper on soil temperature I have discussed the effect of 
* “ The Effect of Temperature on the most important Physical Processes in Soils.” 
G. J. Bouyoncos, Technical Bulletin No. 22, Michigan Experimental Station , 1915. 
“The Evaporation of Water from Soil,” B. A. Keen, Journal of Agricultural Science, 
vol. vi, part iv, Dec. 1914. 
“ A Quantitative Relation between Soil and the Soil Solution,” B. A. Keen, ibid., 
vol. ix, part iv, Oct. 1919. 
“The Relations existing between the Soil and its Water Content,” B. A. Keen, ibid., 
vol. x, part i, Jan. 1920. 
