:: CONTENTS. 



stances forming rocks, into silicates, metalloid compounds, salts,— explanation of 

 these terms ; chemistry of soil ; chemical notation ; the three laws of affinity 

 explained ; constitution of simple minerals composing rocks ; rocks are masses 

 of silicates ; the whole is dived into three classes only. 



CHAPTER III. 



Of the Elements of Sou, their Properties and Chemical Action 52 



The common properties of the bases of silicates ; characters of the class metal- 

 loid compounds ; particular description of silicon, or the base of flinty earth ; 

 composition of granite and the soil which it forms ; quantity of alkalies in bar- 

 ren plains; all soil contains lime, alkali, &c., — enough for any crop grown on 

 it ; action of air and moisture upon soil, produces salts ; origin of sulphate and 

 phosphate of lime in soil ; all soil contains these substances. 



CHAPTER IV. 



Of the Organic Constxtuents of Son- 64 



Number of substances forming plants ; what the organic constituents of soil are ; 

 they are formed by the action of the living plant; plants draw their inorganic 

 constituents ready formed from the soil ; two great divisions of the elements of 

 soil into the organic and inorganic ; soil composed of either division alone, bar- 

 ren ; of the laws of substitution and replacement, which affect agriculture, 

 organic matter in soil must be undergoing change ; fertility depends on chemi- 

 cally induced motion ; of decay and putrefaction ; difference of products of 

 putrefaction in free or confined air ; in free air, products are water, carbonic 

 acid, and ammonia : in confined air, besides these, various compounds of sul- 

 phur, phosphorus, and carbon, with hydrogen ; products vary according as the 

 decaying body is on the soil, in the soil, or in the subsoil ; hydrogen always in 

 excess ; importance of this principle ; decay always results in a substance 

 termed geine ; this is a generic name including several products ; at least seven 

 well-defined substances found in geine, viz. : ulmin and ulmic acid, humin and 

 humic, geic, crenic and apocrenic acids ; division of these forms of geine into 

 the hydrogen, oxygen, and neutral groups ; of the order of the products of de- 

 composition, of decaying matter in soil ; ultimate products are carbonic acid 

 and water ; crenic and apocrenic acid when pure contain no nitrogen ; no 

 ground for division of forms of geine into nitrogenous and non-nitrogenous ; all 

 forms may contain nitrogen as ammonia ; geine divided into soluble and insol- 

 uble ; characters of the two classes ; how distinguished by their relation to acids; 

 the organic acid seldom found free in soil ; several bases may be found in com- 

 bination with one acid forming soluble salts, which contribute to the growth of 

 plants ; detailed account of crenic and apocrenic acids ; two constant sources 

 of reproduction of these acids ; of the formation of nitric acid, and nitrates and 



