LECT. V.] THB ROOT. SOILS. 229 



is known by the same process ; but the precipitate 

 must be washed with diluted sulphuric acid, by 

 which means the lime is formed into insoluble 

 gypsum, or sulphate of lime, and the magnesia 

 into soluble Epsom salt. These salts can be easily 

 separated by nitration and crystallization ; and 

 by knowing the quantity of each thus formed the 

 real quantity of lime and magnesia is ascertained 

 by the following rule : 



100 parts of gypsum contain 48 of aeid, 34- of Iime,andl8ofwater. 

 100 parts of Epsom salt. . . 33 19 4-8 



The organized matter, or the animal and vege- 

 table substance, is known by strongly igniting 

 what remains of the specimen, after the calcareous 

 matter is separated, in a crucible over a common 

 fire, until no blackness remains in the mass : 

 the loss of weight denotes the quantity of organic 

 matter. The clay is ascertained chiefly by sight 

 and touch ; and the ready-formed salts by the 

 evaporation of the washings of the specimen and 

 crystallization. 



Such is the method of ascertaining the prin- 

 cipal contents of any soil ; and its value may be 

 computed by the knowledge we possess from the 

 experience of agriculturists, as to the capacities 

 of the different earths for retaining water and air. 

 When the examination is completed, the products 

 should be numerically arranged, and if their 



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