DEGREE OF TEMPERATURE TO WHICH SOILS CAN BE 

 COOLED WITHOUT FREEZING 



By George Buoyoucos 

 Michigan Agricultural Experiment Station 



The general impression seems to be that when the temperature of soils 

 falls slightly below the freezing point (o° C. or 32 F.) they freeze, that 

 is, the soil moisture is converted into ice. This is hardly the case, how- 

 ever. In conducting investigations to study and measure the different 

 forms of water in the soil by means of the dilatometer method l and to 

 study and measure the concentration of the soil solution directly in the 

 soil by means of the freezing-point method, 2 it was discovered that it is 

 almost impossible to freeze the soils when they are cooled only slightly 

 below the freezing point. This is true even when the concentration of 

 the soil solution is exceedingly small and the freezing-point depression 

 consequently negligible. Indeed, it was found that it is difficult 

 to start solidification in the soils unless they are supercooled at 

 about i° C. below their true freezing point. Even at this degree of 

 undercooling freezing begins only with vigorous agitation. If the soil 

 is not vigorously agitated or disturbed it will remain at this temperature 

 indefinitely without freezing. As the degree of undercooling is increased, 

 however, the ease with which solidification is induced is also increased. 

 Finally a temperature is reached where freezing starts automatically 

 without agitation of the soil mass. This critical temperature is sur- 

 prisingly low for all soils, as will be observed from the experimental data 

 presented in Table I. This table shows the amount of cooling which 

 the soils are able to withstand without freezing. The procedure by which 

 these experimental results were obtained consisted in placing a i-inch 

 column of wet soil in a freezing-point tube, inserting the bulb of a Beck- 

 mann thermometer into this column of soil, and cooling the soil in 

 different low temperatures until a temperature was reached where 

 freezing would readily take place automatically. The figures rep- 

 resent approximately the limit of supercooling which these soils can 

 resist without freezing. At this maximum degree of supercooling 

 the soils can be maintained indefinitely if they are not disturbed or 

 agitated. With a slight disturbance or agitation, however, they will 



1 Bouyoucos, George J. measurement of the inactive or unfree moisture in the son. by means 

 of THE dilatometer method. In Jour. Agr. Research, v. 8, no. 6, p. 195-217, 1 fig. 1917. 



classification measurement of the different forms of water in the soil by means op the 



dilatometer method. Mich. Agr. Exp. Sta. Tech. Bui. 36, 48 p., s fig. 1917. 



2 — and McCool, M. M. further studies on the freezing point lowering op soils. Mich. 



Agr. Exp. Sta. Tech. Bui. 31, 51 p. 1916. 



Journal of Agricultural Research, Vol. XX, No. 4 



Washington, D. C. Nov. 15. 1920 



vm Key No. Mich. -11 



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