218 



TENACITY OF SOIL. 



M. Schiibler finds, from his experiments, that a dry soil is very 

 easily worked vi^hen its tenacity does not exceed 10, that of pure 

 clay being 100 in the moist state. Soils are further worked with 

 ease when their adherence to a surface 3.937 inches square is re- 

 presented by a weight of from 0.15 to 0.30 kil. ; i. e. from 0.380 to 

 0.760, or nearly ^d to |ths of a lb. avoird. ; the latter term passed, 

 the difliculty of working increases rapidly, and a very considerable 

 force is required when the adherence to the same surface amounts 

 to 0.70 kil. or 1 840 lbs. avoird. 



The tenacity of a wet soil is not, however, in the direct ratio of 

 its faculty of imbibition. Loams and loose calcareous soils, which 

 absorb much more water than clay, are nevertheless much less tena- 

 cious ; and then water actually makes sandy soils stiffer than they 

 are when dry. 



Every practical farmer knows how much more friable stiff wet 

 soils become from the effects of frost. The water in expanding as 

 it becomes solid pushes apart the molecules of the soil, and it is to 

 this action that the advantages of autumn ploughing are with justice 

 ascribed. M. Schiibler found that the cohesion of a stiff clay which 

 was equal to 68 fell to 45, when before it was tried the clay was 

 exposed to the frost. 



Disposition of the soil to become dry. The faculty of throwing 

 off by evaporation any excess of water with which it may be charg- 

 ed, is as essential to constitute a good soil as is that of retaining 

 moisture in due proportions. Those soils which throw off too slow 

 ly the excess of moisture they have acquired during the winter 

 occasion much trouble to the husbandman. They are perfect]y un- 

 workable in the spring, and consequently can only be sown veiy 

 4ate. M. Schiibler tried the retentive powers of the soil by the 

 following method. A metallic disc, furnished with a narrow rim. 

 was suspended to the «m of a balance. Over this disc, the soil tc 



* The abbreviate kil. In the above table signifies killogramme, a weight equal to 2.S 

 lbs. avoirdupois. As the weights are principally interesting in their relations lo 90* 

 aootber, it has not been thought necessary to reduce them to English weights. 



