On the Physical Properties of Soil 



193 





Water evapo- 



Power of con- 



Kinds of Earth. 



rated in 4 



taining water of 





days. 



the earths. 





Grains. 



Per cent. 





1 AC 



140 



OQ 



Light gavden-mould • . . • 



1 /I Q 

 14.3 



oJ 





loo 



LI 





132 



366 





131 



34 





131 



60 





129 



256 



Black turf-soil, not so light . . 



128 



179 



123 



70 





123 



87 



Whence follows, that the different degree of looseness or consist- 

 ency of the ground has a considerable influence on the more or 

 less easy drying of deep soils ; the garden-mould employed in these 

 experiments, notwithstanding its great power of containing water^ 

 in which it stands near to pure clay, gave off again to the air far 

 more moisture in the same time than the clays ; likewise the turf- 

 soils and magnesia, notwithstanding their great power of contain- 

 ing water, became di'y again at a quicker rate than the clays ; the 

 fine grey clay, after fourteen days, exhibited in these experiments 

 still a damp surface, while the surfaces of the turf-soils and mag- 

 nesia became perfectly dry many days earlier : since the consist- 

 ency of a soil, and its tendency to become contracted into a 

 narrower space, exerts so great an influence on the drying of a 

 stratum only one inch deep, this must, of course, be the case in a 

 far higher degree with beds of soil having a depth of several 

 inches. 



V. Diminution of bulk on drying. — The greater number of soils 

 become contracted into a narrower space on drying ; and in con- 

 sequence of this circumstance, cracks and fissures frequently occur 

 in land, and have an injurious effect on the vegetation, as the finer 

 roots, which often ramify horizontally, and not unfrequently supply 

 to the plants the greater part of their means of nourishment, are, 

 by such contractions, either laid bare of soil or torn asunder. In 

 order to subject soils to comparative experiments on this point, 

 the following plan may be adopted : we either form of the earths, 

 in their wet state, large cubic pieces of equal size, being at least 

 ten lines (or ten-twelfths of an inch) in height, breadth, and 

 length, and therefore 1000 cubic lines (or a little more than half 

 a cubic inch) in content, or we let such earths be fitted and dried, 

 one after the other, in an accurately-w^orked cubic inch ; after some 

 time, when the weight of these cubes of earth ceases to change by 



VOL. I. o 



