AGRICULTURAL CHEMISTRY. 175 



By acting on cbabazite with dilute chlorid of ammonium for ten days 

 the mineral was altered, and contained 3*33 per cent, of ammonia. 

 Digested twenty-one days, the mineral yielded 6*94 per cent, of 

 ammonia, and also had lost water. 



Eichhorn found that the artificial soda-chabazite re-exchanged soda 

 for lime when digested in a solution of chlorid of calcium; in solution 

 of chlorid of potassium both soda and lime were separated from it and 

 replaced by potash. So, the ammonia-chabazite in solution of chlorid 

 of calcium exchanged ammonia for lime, and in solutions of chlorids of 

 potassium and sodium both ammonia and lime passed into the liquid. 

 The ammonia-chabazite in solution of sulphate of magnesia lost 

 ammonia but not lime, though doubtless the latter base would have 

 been found in the liquid had the digestion been continued longer. 



It thus appears that in the case of chabazite all the protoxyd bases 

 may mutually replace each other, time being the only element of 

 differences in the exchanges. 



In experimenting on natrolite, however, Eichhorn found that it was 

 not affected by solution of chlorid of calcium, owing perhaps to some 

 peculiarity in the constitution of this mineral, its soda being probably 

 more firmly combined than that of chabazite. 



These valuable researches, though serving but as an introduction 

 to the study of a highly-complicated subject, present so close an 

 analogy to what is observed in case of the soil, no matter whether it 

 be fertile or barren, clay or sand, that we are fully warranted in 

 assuming the presence in all soils of hydrous double silicates which 

 determine the absorption and retention of potash, ammonia, &c, from 

 solutions of their salts. 



As regards the fixation of the acids, we know that oxyd of iron and 

 alumina, as well as lime and magnesia under certain conditions, form 

 insoluble phosphates and silicates; we are also acquainted with an 

 insoluble chlorine compound, viz: chloro-phosphate of lime, which 

 occurs abundantly as the mineral apatite, while sulphuric acid forms 

 insoluble combinations with excess of peroxyd of iron anda lumina. 

 We know, however, no insoluble compounds of nitric acid with any of 

 the bases found in the soil, excepting oxyd of iron and alumina, and 

 these require a high temperature for their formation. 



The fixation of the bases in the circumstances described, both in the 

 soil and with hydrate cl aluminous silicates, is influenced by a variety 

 of conditions, physical and chemical. The only points which further 

 require notice are : 1st. That an ordinary soil is capable of fixing a 

 vastly larger quantity of ammonia, potash, or phosphoric a$id — the 

 three generally most rare, and therefore most precious forms of plant 

 food — than is ever likely to be brought into the soil either by natural 

 or artificial means. 2d. That the soil never completely removes any of 

 these bodies from even the most dilute solution. 3d. The soil which 

 has saturated itself from a solution of these bodies restores them again 

 sloivly to pure water or to a weaker solution. 



Way, Russell, and Liebig, from a partial apprehension of the nature 

 of this absorption, drew the premature inference that land plants do 

 not receive their food from solutions, but themselves attack and solve 



