188 



On the Physical Properties of Soil. 



(b.) Consistence of soil in the moist state, and its attachment 

 or adhesion to agricidtural implements. — When land is worked 

 in a wet state^ we have not only to overcome the cohesiveness of 

 the particles among themselves, but at the same time their attach- 

 ment and adhesion also to the agricultural implements employed. 

 If we wish to subject this property to a comparative trial, we may 

 effect it in the following manner. We fasten large round plates, 

 equal in size, made of iron and wood (as the two materials com- 

 monly used for agricultural implements), underneath the scale-pan 

 of a balance, and put weights into the other scale until both are 

 equally balanced ; we now bring the plate into exact contact with 

 a moistened earth lying beneath it, and put weights into the other 

 scale-pan until the plate is draw^n away from the earth ; the amount 

 of such weights corresponds to the degree of adhesion, or to the 

 difficulty of working the earth in its wet state ; the degree of this 

 adhesion is often more considerable than would have been 

 expected — an adhesion plate of three or four square inches required 

 upwards of two ounces of counter-weight in order to draw it 

 away from the surface of garden-mould : in the case of the heavier 

 clays, the weight required was as much as five or six ounces. 

 From the size of the plate employed in this experiment, it 

 is of course easy to calculate the amount of adhesion for larger or 

 smaller surfaces. 



The following table contains the results derived from experi- 

 ments made according to the foregoing plans, on the firmness and 

 consistence of earths ; the amount of adhesion in the wet state is 

 calculated in pounds on a surface of one square foot. 



Kinds of Earth. 



In the Dry State. 



Firmness, that of 

 Clay being 100. 



In the Wet State. 



Adhesion to Agricultural 

 Implements, on a surface of 

 1 Square foot ; with 



Iron. 



Wood. 



Siliceous Sand . . 

 Calcareous Sand . . 

 Fine Lime . 

 Gypsum Powder . 

 Humus .... 

 Magnesia .... 

 Sandy Clay , 

 Loamy Claj'' . . • 

 Stiff Clay or Brick-earth 

 Grey pure Clay . 

 Garden- mould 

 Arable Soil . . 

 Slaty Marl . . . 



0 

 0 



5-0 

 7.3 

 8.7 

 11.5 

 57.3 

 68'8 

 83.3 

 100.0 

 7.6 

 33.0 

 23.0 



3.8 

 4.1 

 14.3 

 10.7 

 8.8 

 5.8 

 7.9 

 10.6 

 17.2 

 27.0 

 6.4 

 5.8 

 4.9 



pounds 



4.3 pounds 



4.4 

 15.6 

 11.8 , 



9.4 



7.1 



8.9 

 11.4 

 18.9 

 29.2 



7.5 



6.4 



5.5 



(c.) General results from these experiments.— l. If we com- 

 pare the different consistency of the earths with their different 



