354 now CKOPS feed. 



proportions, extremely important to the soil, and espe« 

 cially 50 when existing in combinations admitting of the 

 remaikable changes whicli liave come under our notice. 



That we cannot decide us to tlie precise composition of 

 the zeohtic compounds which may exist in tlie soil, is plain 

 from what lias been, stated. We have the certainty of 

 their anah)gy with the well-defined sihcates of the miner- 

 alogist, which have been termed zeolites, an analogy of 

 chemical composition and of chemical properties ; we know 

 further that they .ire likely to be numerous and to be in 

 perpetual alteration, ac, they are subjected to the influence 

 of one and another of the salts and substances that are 

 brought into contact with them ; but more than this, at 

 present, we cannot be certain of 



Physical agencies in the phenomena of absorption.— 

 While the absorption by the soil of ])otash or other base 

 is accompanied by a chemical decomposition, which Way, 

 Rautenberg, Heiden, and Knop's researches conclusively 

 connect Avith certain hydrous silicates whose j^resence in 

 the soil cannot be doubted, it has been the opinion of 

 Liebig, Brustlein, Henneberg, Stohmann and Peters, 

 that the real cause of the absorption is physical, and is 

 due to simple surface attraction (adhesion) of the jjorous 

 soil to the absorbed substance. Brustlein and Peters have 

 shown that bone and wood-charcoal, washed with acids, 

 absorb ammonia and potash from their salts to some ex- 

 tent, and after impregnation with carbonate of lime to as 

 great an extent as ordinary soil. While the reasons al- 

 ready given appear to show satisfactorily that the ab- 

 sorbent power of the soil, /or bases hi combination^ re- 

 sides in the chemical action of zeolitic silicates, the facts 

 just mentioned indicate that the pliysical properties of the 

 soil may also exert an influence. Indeed, the fixation of 

 free bases by the soil may be in all cases pai'tially due to 

 this cause, as Brustlein has made evident in case of am- 

 monia {BoyssingaulCs Agronomie, etc., T., II, p. 153). 



