Studies in Soil Physics, IV. 171 



physicists, has been applied by Mitsclierlich to the soil. Using 

 a Bunsen ice calorimeter and very ingenious devices for intro- 

 ducing and wetting the dried soil he is able to obtain values 

 which are concordant and reproducible for any one soil and 

 which vary from soil to soil with variations in the physical 

 character. Of course the correlation of the heat of wetting with 

 the general physical properties is just as empirical as was the 

 correlation of the mechanical analysis therewith, but this as before 

 is comparatively unimportant. The heat of wetting is a single 

 quantity expressible in a single unit; it is free from the shape 

 error and the group error that beset the mechanical analysis; 

 and it is probably closely and rigidly related to the fundamnetal 

 physical character(as distinguished from ])hysical condition) 

 of the soil. As a soil constant however, it is open to two 

 errors; (i) the elTects due to tlie heats of solution and dilution 

 of the soluble material present in the soil; and (2) the effects 

 of the organic residues, largely the remains of plants. The 

 former is probably unimportant. In all ordinary soils the soluble 

 salts are so small in total quantity and so nearly the same in 

 nature and amount that their effect on the heat of wetting is 

 probably almost constant, especially if the same relative amounts 

 of soil and water be employed in each case. The effect of theor- 

 gani: material , is less easilypredicted. They may behave similarly 

 to the inorganic materials, or they may not. They are known 

 to effect both the general physical behavior of the soil and the 

 heat of wetting. If they affect both in the same way and ratio, 

 the exact forms of the relations are unimportant — the heat of 

 w etting is nevertheless a true representation of physical character. 

 If the effects on physical character and on heat of wetting 

 are diverse the latter will fail to properly indicate the former 

 when much organic matter is present. More complete eluci- 

 dation of this matter must aw ait further experiment. In any event 

 the heat of wetting seems to ofi'er much promise as a substitute 

 for, complement to, mechanical analysis, and it has actually 

 been so used by Mitscherlich and his co-workers, apparently 

 with satisfactory results. 



*ror details see his Bodenkunde fiii Land und Forstwirte. 1905. P. 51-70 



