4 THE CANADIAN NATURALIST. [Feb. 



silicate of alumina and lime, may perhaps be taken as a represen- 

 tative of the hydrous double silicates in the soil, show that these 

 substitutions of protoxyd bases are neither complete nor absolute. 

 It would appear, on the contrary, that there takes place a partial 

 exchange or a partition of bases according to their respective affini- 

 ties. Thus the normal chabazite, in presence of a solution of 

 chlorid of sodium exchanges a large portion of its lime for soda ; but 

 if the resulting soda-compound be placed in a solution of chlorid 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 chlorid of potassium, 

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

 In like manner, chabazite, in which, by the action of a solu- 

 tion of sal-ammoniac, a part of the lime has been replaced by 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 chlorids of potassium and sodium, but even 

 to chlorid of calcium. It results from these mutual decom- 

 positions that there is a point where a chabazite containing 

 both lime and soda, or lime and ammonia, would remain un- 

 changed in mixed solutions of the corresponding chlorids, 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 soil, 

 the result of these affinities is an almost complete elimination of 

 the ammonia and potash from infiltrating waters. 



§ 7. That the replacement of one base by another in this way is 

 not complete is shown moreover by the experiments of Liebig, De- 

 herain and others, who have observed that a solution of gypsum 

 removes from soils a certain amount of potash-salt, which was insol- 

 uble in pure water. In this way gypseous waters may also acquire 

 portions of sulphate of soda, and perhaps of sulphate of magnesia, 

 from silicates. 



It is not certain that all the above reactions observed for chaba- 

 zite are applicable without modification to the double hydro-alu- 

 minous silicates of sedimentary strata. Were such the case, impor- 

 tant changes might, in certain conditions, be effected in the com- 

 position of saline waters. Thus in presence of a great amount 

 of a hydrous silicate of lime and alumina, solutions of chlorid of 



* Silliman's Journal [2] xxviii, 12. 



