20 



chemical composition is apparently similar, that is to say, that the nu- 

 merical results obtained by analysis show the like quantities of silica y 

 lime, magnesia, soda, potash, phosphoric acid, &c., and yet a certain 

 crop, clover for instance, will flourish on the one and not on the other. 

 The physical nature of such soils, their depth, character of subsoil, as- 

 pect, texture, climatic conditions, &c., have likewise to be taken into 

 account. Thus the many problems that enter into the study of soils 

 are so various that chemical analysis alone does not afford, in most cases, 

 a sufficient guide to an estimate of their agricultural capabilities, nor to 

 point out the particular manure that is adapted for the special crops 

 intended to be grown. 



The most detailed chemical analysis usually gives only the proportion 

 of the different constituents, and without any reference to their state 

 of combination in which they exist in the soil or to their absorptive and 

 retentive powers. 



GREAT CARE NECESSARY IN OBTAINING THE SAMPLK FOR ANALYSIS. 



On the care with which the soil is sampled, of course, depends the value 

 of the analytical results, and too much stress cannot be laid on the neces- 

 sity that exists to obtain a fair average sample, representing, as far as 

 possible, both the good and bad qualities of the soil that is to be submitted 

 to analysis. As the chemical analysis of a soil is a very long, tedious, 

 and delicate operation, and the difference of a one thousandth of 1 per 

 cent, in any one constituent is equivalent to 20 or 30 pounds to the acre 

 lost or gained in that element, the importance of the sample truly rep- 

 resenting the soil is apparent. 



THE CHEMICAL COMPOSITION OF SOILS. 



Soil consists of an organic and of an inorganic or mineral part ; the 

 former derived from the decay of plant life for many ages, together with 

 the dung and remains of animals, and the latter arising from the weather- 

 ing of the rocks. 



THE ORGANIC MATTER. 



This varies in different soils, being most deficient in sandy soils and 

 poor clays, and even in very fertile lands occurring only in small quan- 

 tities. In the famous black soil of Russia, which is found in the prov- 

 inces of the Ural Mountains and in those that border them, it varies 

 from 5 to 12 per cent. In some of our own prairie soils the amount is 

 nearly as high. In leaf mold it occurs considerably higher and in peat 

 more than 50 per cent, very often. From its dark color it is a good ab- 

 sorbent of heat, its own specific heat being much above that of the soil 

 generally. It is hygroscopic and greatly increases the water-holding 

 power of sandy soil; besides, it has the power of absorbing and retain- 

 ing am rnoniacal salts. By its decomposition it forms a source of carbonic 



