CONSISTENCY OF SOIL. 217 



pure clay ; while the calcareous sand retained 41 per cent. less. 

 This fact proves how much the state of suhdivision must influence 

 the physical properties of soils ; and it is easily to be understood 

 that in noting the presence of calcareous matter in an arable soil 

 we are carefully to indicate the form and degree of subdivision in 

 which it occurs ; humus, however, is the substance wbich shows 

 itself most greedy of moisture, and we perceive from this fact where- 

 fore soils rich in this principle have so strong an affinity for water. 



Consistence, tenacity, friability of soils. The consistence or 

 tenacity of soils is an important property which agriculturists indi- 

 cate when they speak of soils being strong or stiff, and light, tiie 

 amount of power expended in ploughing being taken as a measure 

 of these qualities. To compare different soils under the point of 

 view of their tenacity in the dry state, M. Schiibler moulded various 

 kinds, duly moistened, into equal and similar parallelepipeds. 

 When these solids were completely dry, he placed either extremity 

 upon a fixed support, and by means of the scale of a balance hung 

 exactly from the middle of the prisms, he added weights gradually 

 until they gave way ; the weight, supported by each parallelepiped 

 immediately before it broke, expressed its tenacity. 



In working a damp soil we have not only to overcome its force of 

 cohesion, but further and principally to get the better of its adhesion 

 to our implements. This consideration led M. Schiibler to estimate, 

 always comparatively, the power w^hich it is necessary to expend in 

 working soils of different descriptions. As the material which 

 enters into the construction of agricultural instruments is in general 

 iron and wood, he did no more than ascertain the disposition of the 

 soil tj adhere to these two substances. In the experiments, the 

 results of which we shall immediately detail, two discs were employ- 

 ed, one of iron, the other of beech-wood, having equal surfaces. 

 The disc was connected with the extremity of the arm of a very 

 delicate balance ; it was then brought into perfect contact with the 

 moist soil, and when it adhered, the opposite scale of the balance was 

 loaded until the adhesion was overcome. In experiments of this 

 kind it is obviously indispensable that the soil in each instance should 

 have the same degree of humidity ; they were tried, consequently, 

 at the point of saturation with water. 



Pure dry clay possessed the greatest tenacity, and its power was 

 expressed by the number 100 ; the tenacity possessed by other mat- 

 ters was then compared to that of pure clay. The following table 

 exhibits the results of the two series of experiments, viz. those 

 having reference to the tenacity and those having reference to the 

 f^rce of cohesion. 



19 



