194 



On the Physical Properties of Soil. 



further drying, we measure the dimensions of the cube by means 

 of a rule on which the tenths of lines can be distinguished, and 

 may thus calculate easily the volume of the earth, and conse- 

 quently find the diminution in bulk which has been caused by 

 the drying. 



The experiments I made with the simpler earths, exhibited on 

 this point the following differences : — 



Kinds of Earth. 



XOOO cubic lines 

 became diminished 

 in volume to 



1000 parts there- 

 fore diminished in 

 volume by 



Sandy clay •.»«•.. 

 Stiff clay, or brick earth • • • 

 Carbonate of magnesia , • • 



(no change) 



f 950 cubic 1 

 1 lines J 



940 



911 



886 

 817 

 846 

 800 

 851 

 880 

 965 



50 parts 



60 

 89 

 114 



183 ,, 

 154 

 200 

 149 

 120 

 35 



General remarks. — 1. Gypsum, in this respect, is seen to be 

 very similar to the sands, and diminishes its volume in a very in- 

 considerable degree. 



2. Fine carbonate of lime, notwithstanding its great power of 

 containing water, gives on drying only a very small diminution of 

 bulk, not by any means so great as that of clay ; this property of 

 the earths does not stand, therefore, in the same proportion 

 with their power of containing water, and in as little with the firm- 

 ness and consistency of the soil ; humus, notwithstanding its little 

 consistency, exhibits on drying a remarkable degree of con- 

 traction. 



3. Among those earths which are free from humus, clay is the 

 one which gives the greatest diminution of bulk on drying ; an 

 addition, however, of sand, or of carbonate of lime, diminishes this 

 property considerably. 



4. The tendency of many kinds of marl to fall into numerous 

 small pieces on drying may be explained from this great difference 

 which clay and lime, the elements of marl, experience in their 

 diminution of bulk on drying . after having been moistened ; these 

 individual parts changing their volume in a different degree, and 

 thus occasioning a more easy disintegration of the natural com- 

 poun(J we call marl. 



5. Humus, of all the usual ingredients of soil, experiences on 



