268 



Journal of Agricultural Research 



Vol. XX, No. 4 



readily freeze. Again, if the temperature of cooling is only slightly 

 lowered the soils will immediately freeze. These numerical data, there- 

 fore, represent just about the maximum cooling which the soils can 

 withstand indefinitely without freezing when they are kept quiet. 



For the sake of an interesting comparison, Table I also presents the 

 limit of supercooling without freezing of several artificial materials. 



Table I. — The degree of cooling which soils and artificial materials can witlistand without 

 freezing when they are kept quiet and with the water content at about the saturation 

 point 



Material. 



Degree 



of 

 super- 

 cooling 

 without 

 freezing. 



Quartz sand... 



Coarse sand 



Fine sand 



Very fine sand 

 Stony loam 



Loam 



Silt loam 



Clay loam 



Humus loam. . 



Clay 



Red clay 



Dark clay 



Brick clay 



Clay subsoil... 



Peat 



Muck 



Water 



Silica 



Carbon black. . 



Gelatin 



Agar 



°C. 



-4.2 

 -4.2 



-4.2 

 -4. 2 

 -4.2 

 -4.2 

 -4. 2 

 -4.2 

 -4. 2 

 -4. 2 

 -4.2 

 -4. 2 

 -4. 2 

 -4.2 



-5-o 



-5-.o 



-6.0 

 -6.0 

 -6.0 

 -6.0 

 -6.0 



An examination of the foregoing experimental results reveals at once 

 the fact that the amount of cooling which the soils are able to withstand 

 without freezing is considerable, being about -4.2 C. (7.56^.) for the 

 mineral soils and about -5 C. (9 F.) for the peats and mucks. 



It is of interest to observe that the maximum supercooling is still 

 greater for the water and for the artificial materials, amounting in all 

 cases to about -6° C. (10.8 F.). Since water freezes at about the same 

 degree of supercooling as the artificial materials, it would logically seem 

 that it is the water which limits the degree of supercooling of those 

 materials and that they themselves have no influence on the degree of 

 supercooling of water in one way or the other. 



The question now rises, why do the soils withstand a smaller degree of 

 supercooling than the artificial materials? 



