96 CHEMISTRY OF NATURAL WATERS. IX.] 



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, phosphates, 

 and silica ; and the subsequent decay of these plants in con- 

 tact with the ooze of the bottom, or on the shores, again 

 restores these elements to the earth. See a remarkable essay, 

 by Forchhammer, on the composition of fucoids, and their 

 geological relations, Jour, fur Prakt. Chem., XXXVI. 388. 



6. The observations of Eichhorn upon the reaction be- 

 tween solutions of chlorides and pulverized chabazite, which, 

 as a hydrated silicate of alumina and lime, may perhaps be 

 taken as a representative of the hydrous double silicates in 

 the soil, show that these substitutions of protoxide bases are 

 neither complete nor absolute. It would appear, on the con- 

 trary, that there takes place a partial exchange or a partition 

 of bases according to their respective affinities. Thus the nor- 

 mal chabazite, in presence of a solution of chloride of sodium, 

 exchanges a large portion of its lime for soda ; but if the re- 

 sulting soda-compound be placed in a solution of chloride of 

 calcium, an inverse substitution takes place, and a portion 

 of lime enters again into the silicate, replacing an equivalent 

 of soda ; while, by the action of a solution of chloride of potas- 

 sium, both lime and soda are, to a large extent, replaced by 

 potash. In like manner, chabazite, in which, by the action 

 of a solution of sal-ammoniac, a part of the lime has been 

 replaced by ammonia, will give up a portion of the ammonia, 

 not only to solutions of chlorides of potassium and sodium, but 

 even to chloride of calcium. It results from these mutual de- 

 compositions that there is a point where a chabazite contain- 

 ing both lime and soda, or lime and ammonia, would remain 

 unchanged in mixed solutions of the corresponding chlorides, 

 the affinities of the rival bases being balanced.* Inasmuch, 

 however, as the proportions of ammonia and potash in natural 

 waters are usually small when compared with the amounts of 

 lime and soda existing in the form of hydro-silicates in the 



* Amer. Jour. Science (2), XXVIII. 72. 



