210 
Journal of Agricultural Research 
Vol. VIII, No. 6 
CONDITION OF THE UNFREE WATER IN THE SOILS 
It has been seen, therefore, that there is a certain amount of water 
in soils which refuses to freeze, the exact amount varying with the degree 
of supercooling, number of times the soil is frozen, and degree of moisture 
present. Under certain empirical conditions—25 gm. of air-dry soil 
mixed with 5 c. c. of water supercooled to 3 0 C. in a temperature of 
— 4 0 —the percentage of water, on the absolute dry basis, that remains 
unfrozen corresponds remarkably closely to the moisture content known 
as the wilting coefficient, to the water content at which solidification can 
not be induced, etc. In order to distinguish this water from the free 
water which freezes easily, is readily available to plants, etc., it is desig¬ 
nated as “unfree” water. 
The question now is, How does this unfree water exist in the soil? 
Does it exist as capillary water, physically adsorbed water, loosely 
chemically combined water, or in all forms? 
It must be stated in advance that it is not definitely known in which 
form or forms this unfree water exists. The problem is very complex 
and exceedingly difficult of definite solution. It is, however, under 
special investigation, and it is hoped that a definite solution of it may 
be presented at a later date. However, it may be stated at this time that 
there are many evidences, both direct and indirect, which indicate quite 
strongly that most of this unfree water exists as physically adsorbed and 
loosely chemically combined, with the latter probably predominating. 
Capillary water, as ordinarily understood, is present in small quantities. 
It probably abounds mainly in the initial region of the unfree water. 
The physically adsorbed and loosely chemically combined water probably 
exists in the solid phase or as solid solution. 
The following are some of the evidences which go to indicate that most 
of the unfree water exists in a physically adsorbed and loosely chemi¬ 
cally combined condition and consequently in the solid phase or as solid 
solution: 
(1) As it has already been stated, the studies on the lowering of the 
freezing point of soils showed that this value increased in all soils with 
the exception of quartz sand and some extreme types of sand at a far 
greater rate than the percentage of water decreased. In other words, 
the ratio of the freezing-point lowering and the percentage of water 
were not inversely proportional (approximately) as might be expected, 
save only in the quartz sand and some of the sands. Thus, a clay at 
92.76 per cent of moisture gave a depression of 0.039° C. and at 39.28 
per cent, 1.075; the ratio of the percentage of water at the two moisture 
contents is only 2.37, while that of the depression is 27.56. 
This phenomenon was explained on the supposition that some of the 
water contained by the soils was either physically adsorbed or loosely 
chemically combined or both, in which event this portion of the water 
