50 



AGRICULTURAL CHEMISTRY". 



then are these substances? They may 

 easily be detected by the examination of a 

 soil, which is always^ fertile in given cosmi- 

 cal and atmospheric conditions; for it is 

 evident, that the knowledge of its state and 

 composition must enable us to discover the 

 circumstances under which a sterile soil 

 may be rendered fertile. It is the duty of 

 the chemist to explain the composition of a 

 fertile soil,, but the discovery of its proper 

 state or condition belongs to the agricultu- 

 rist ; our present business lies only with the 

 former. 



Arable land is originally formed by the 

 crumbling of rocks, and its properties de- 

 pend on the nature of their principal com- 

 ponent parts. Sand, clay, and lime, are the 

 names given to the principal constituents of 

 the different kinds of soil/ 



Pure sand and pure limestones, in which 

 there are no other inorganic substances ex- 

 cept siliceous earth, carbonate or silicate of 

 lime, form absolutely barren soils. But ar- 

 gillaceous earths form always a part of fer- 

 tile soils. Now from whence come the 

 argillaceous earths in arable land, what are 

 their constituents, and what part do they 

 play in favouring vegetation? They are 

 produced by the disintegration of aluminous 

 minerals by the action of the weather ; the 

 common potash and soda felspars, Labrador 

 spar, mica, and the zeolites, are the most 

 common aluminous earths, which undergo 

 this change. These minerals are found 

 mixed with other substances in granite, 

 gneiss, mica-slate, porphyry, clay-slate, 

 grauwacke, and the volcanic rocks, basalt, 

 clinkstone, and lava. In the grauwacke, 

 we have pure quartz, clay-slate, and lime ; 

 in the sandstones, quartz and loam. The 

 transition limestone and the dolomites con- 

 tain an intermixture of clay, felspar, por- 

 phyry, and clay-slate; and the mountain 

 limestone is remarkable for the quantity of 

 argillaceous earths which it contains. Jura 

 limestone contains 3 20, that of the Wur- 

 temberg Alps 45 50 per cent, of these 

 earths. And in the muschelkalk and the 

 calcaire grossier they exist in greater or less 

 quantity. 



It is known, that the aluminous minerals 

 are the most widely diffused on the surface 

 of the earth, and as we have already men- 

 tioned, all fertile soils, or soils capable of 

 culture, contain alumina as an invariable 

 constituent. There must, therefore, be 

 something in aluminous earth which ena- 

 bles it to exercise an influence on the life of 

 plants, srd to assist in their developement. 

 The p ; rrvwerty on whica this depends is that 

 of its invariably containing potash and soda. 



Alumina exercises only an indirect influ- 

 ence on vegetation, by its power of attract- 

 ing and retaining water and ammonia; it is 

 itself very rarely found in the ashes of 

 plants,* but silica is always present, having 



* Alumina is generally supposed to be a com- 

 mon ingredient of the ashes of plants, and it is 



in most places entered the plants by means 

 of alkalies. In order to form a distinct con- 

 ception of the quantities of alkalies in alu- 

 minous minerals, it must be remembered 

 that felspar contains 17| per cent, of potash, 

 albite 1 1-43 per cent, of soda, and mica 3 5 

 per cent.; and that zeolite contains 13 16 

 per cent, of both alkalies taken together. 

 The late analyses of Ch. Gmelin, Lowe, 

 Fricke, Meyer, and Redtenbacher, have also 

 shown, that basalt contains from | to 3 per 

 cent, of potash, and from 5 7 per cent, of 

 soda, that clay slate contains from 2-75 3-31 

 per cent, of potash, and loam froml ^4 per 

 cent, of potash. 



If, now, we calculate from these data, and 

 from the specific weights of the different 

 substances, how much potash must be con- 

 tained in a layer of soil, which has been 

 formed by the disintegration of 26,910 square 

 feet (1 Hessian acre^ of one of these rocks 

 to the depth of 20 inches, we find that a 

 soil of 



Felspar contains 1,675,000 Ibs. 



Clink-stone " from 220,000 to 440,000 " 



Basalt " " 52,300 " 82,600 " 



Clay-slate " " 110,000 " 220,000 " 



Loam, " " 95,000 " 330,000 " 



Potash is present in all clays ; according to 

 Fuchs, it is contained even in marl ; it has 

 been found in all the argillaceous earths in 

 which it has been sought. The fact that 

 they contain potash may be proved in the 

 clays of the transition and stratified moun- 

 tains, as well as in the recent formations 

 surrounding Berlin, by simply digesting 

 them with sulphuric acid, by which process 

 alum is formed. (Mitscherlich.) It is well 

 known also to all manufacturers of alum, 

 that the leys contain a certain quantity of 

 this salt ready formed, the potash, of which 

 has its origin from the ashes of the stone 

 and brown coal, which contain much argil- 

 laceous earth. 



When we consider this extraordinary dis- 

 tribution of potash over the surface of the 

 earth, is it reasonable to have recourse to 

 the idea, that the presence of this alkali in 

 plants is due to the generation of a metallic 

 oxide by a peculiar organic process from the 

 component parts of the atmosphere ? This 

 opinion found adherents even after the 

 method of detecting potash in soils was 

 known, and suppositions of the same kind 

 may be found even in the writings of some 

 physiologists of the present day. Such 

 opinions belong properly to the time when 

 flint was conceived to be a product of chalk, 

 and when every thing which appeared in- 

 comprehensible on account of not having 

 been investigated, was explained by assump- 

 tions far more incomprehensible. 



very frequently stated in the results of their 

 analyses ; but in most cases it has been mistaken 

 for phosphate of magnesia, or phosphate of alu- 

 mina, with which it has many properties in com- 

 mon, and from which it cannot be distinguished 

 without much care and attention. ED. 



