1865.] CHEMISTRY OF NATURAL WATERS. 3 



strata destitute of neutral soluble salts may be first examined. 

 Between such sedimentary strata and the waters charged with 

 organic and mineral matters from decaying vegetation, there 

 are important reactions. The composition of these waters is 

 peculiar. They contain, relatively to the sodium, a large amount of 

 potassium salts, besides notable quantities of silica and phosphates, 

 in addition to the dissolved organic matters and the earthy carbo- 

 nates, and in some cases ammoniacal salts and nitrates or nitrites. 

 The sulphuric acid and chlorine are moreover not sufficient to 

 neutralize the alkalies, which are perhaps in part combined with 

 silica or with an organic acid. 



§ 5. The experiments of Way, Voelcker, and others have shown 

 that when such waters are brought into contact with argillaceous 

 sediments, they part with their potash, ammonia, silica, and 

 phosphoric acid and organic matter, which remain in combination 

 with the soil ; while, under ordinary conditions at least, neither 

 soda, lime, magnesia, sulphuric acid, nor chlorine are retained. 

 This power of the soil appears from the experiments of Eichhorn 

 to be in part due to the action of hydrated double aluminous 

 silicates ; and the process is one of double exchange, an equivalent 

 of lime or soda being given up for the potash and ammonia 

 retained. The phosphates are probably retained in combination 

 with alumina or peroxyd of iron ; and the silica and organic 

 matters also enter into insoluble combinations. It follows from 

 these reactions that the surface-waters charged with the 

 products of vegetable decay, after having been brought in 

 contact with argillaceous sediments, retain little else than sul- 

 phates, chlorids, or carbonates of soda, lime, and magnesia. 

 In this way the mineral matters required for the growth of 

 plants, and by them removed from the soil, are again restored 

 to it; and from this reaction results the small proportion 

 of potash salts in the waters of Ordinary springs and wells as 

 compared with river-waters. From the waters of rivers, lakes, 

 and seas, aquatic plants again take up the dissolved potash, phos- 

 phates, and silica ; and the subsequent decay of these plants in 

 contact with the ooze of the bottom, or on the shores, again restores 

 these elements to the earth. See a remarkable essay by Forch- 

 hammer on the composition of fucoids, and their geological rela- 

 tions, Jour, fur Prakt. Chem., xxxvi, 388. 



§ 6. The observations of Eichhorn upon the reaction between 

 solutions of chlorids and pulverized chabazite, which, as a hydrated 



