602 STATE BOARD OF AGRICULTURE. 



osmotic pressure that tlie depressions of the freezing point represent 

 at the opposite extreme moist uro contents, the values of both of these 

 factors liave been calculated and are presented together with their re- 

 spective depressions of the freezing point. The concentration is ex- 

 pressed in parts per million of solution and was calculated directly from 

 soil water extracts and not from any particular pure chemical com- 

 pound or combinations therefrom. The procedure for accomplishing 

 this consisted of mixing a large amount of soil with a small quantity 

 of water, allowing the mixture to stand for about two days with oc- 

 casional stirring, and then filtering the solution through a filter paper. 

 A portion of this solution was used to measure its lowering of the freez- 

 ing point and the remainder was employed to determine its total solid 

 matter by evaporating a definite volume of it to dryness and weighing the 

 residue. From the freezing point depression of the extract and its cor- 

 responding amount of solid material present, the concentration in p. 

 p. m. of solution that might be represented by the values of the lowering 

 of the freezing point of each soil was calculated. There were three 

 difi'erent types of soil from which water extracts were made; namely, 

 clay, loam and peat. It was found by calculation that 100 p. p. m. of 

 solid material in the soil water extract gave the following values 

 of the lowering of the freezing point; clay, .0038°, loam .0030°, and 

 peat .0031 °C. Evidently equal concentration of the water extracts of 

 these three diff'erent types of soil caused about the same lowering of 

 the freezing point. This is extremely interesting in view of the fact that 

 on account of the marked difference in the physical and chemical com- 

 position of these soil types entirely difi'erent results might have been 

 expected. On account of this remarkable closeness of the lowering of 

 the freezing point for all three soil extracts, an average was taken in 

 the com.putation of the concentration of the soil solution of the various 

 soils as represented by their lowering of the freezing point. 



It is readily realized that the foregoing procedure of estimating the 

 magnitude of concentration that the various values of the freezing 

 point depression might represent is open to many objections, but it is 

 believed that it is perhaps the best way of obtaining an idea as to the 

 magnitude of this value. 



The osmotic xjressure was calculated from a table of osmotic pressures 

 as worked out by Harris and Gortner, (9), from the formula ^^ = 

 12.06 A — 0.021 A ^, where "^ is the osmotic pressure in atmospheres, 

 and A is the lowering of the freezing point in centigrade degrees. For 

 convenience and usefulness this table is reproduced herewith. 



(») Am. Jour. Bot. 1, 75-78, 1914. 



