On the Physical Properties of Soil. 



185 



4. Carbonate of lime exhibits great differences in its power of 

 containing water, according to the fineness of its particles ; it is 

 therefore important, in investigations of soil, to make a distinction 

 between the fine lime separated by decantation, and the earthy 

 lime as found in the form of sand in an arable land. 



5. Carbonate of magnesia, as found in arable soils, is not usually 

 in so fine a form as that artificially prepared for, and used in, 

 these experiments, but exists in a coarse-grained state in combina- 

 tion with lime or siliceous earth : when so combined, it possesses 

 in a far less degree the power of containing water, and approaches 

 in this respect to the character of the sands. 



6. Humus has usually the greatest power of containing water of 

 all the common ingredients of soil, and in a still higher degree is 

 this the case when the humic acid has not been previously dried 

 artificially, or when it is still mixed with a large proportion of 

 half-decomposed organic matters, remains of wood, leaves, roots. 

 Sec. : 100 parts of the fine earth formed by decaying wood in old 

 trees are capable of absorbing into their interstices nearly 200 

 and certain light turf-earths from 300 to 360 parts of water, even 

 when they have been previously dried artificially ; where we meet 

 with a great water-holding power, one, namely, which exceeds 90, 

 we may reckon with great probability on an abundant commixture 

 of organic matter.* 



III. Firmness and consistency of soil. — -The firmness and 

 consistency of soils is of considerable importance, in regard both 

 to the fertility and to the working of land ; the terms universally 

 adopted in husbandry, of a heavy or a light soil, rest on these 

 properties, and therefore deserve inquiry, with regard as well to 

 the dry as to the moist state of the earth. 



(a.) Firmness and consistency of a soil in its dry state. — The 

 determination of the consistence of a soil is one of the more 

 difficult problems, which in physical investigations of the earths 

 ought the less to be neglected, since we can never hope to ascer- 

 tain it by a mere chemical process. Professor Volker pro- 

 posed for this purpose, some time ago, a rather complex instru- 

 ment,! which the principal part is a kind of spade, the pressure 

 and resistance of which on the field itself is determined by 

 weight ; this method cannot, however, be applied in compara- 

 tive experiments of the consistence of individual soils, on a small 

 scale. 



Dr. Meyer (in his determination of the consistence of sandy 

 soils) applies, with this view, a plate of four square inches in 



* On this property of soils see further Note A, p. 213. 

 t In the new ' Mogelin Annals of Agriculture,' vol. iv, p. II 9, with a plate. 



