1870.] BROOME — ON CANADIAN PHOSPHATES. 253 



stitucnts from the soil, there is still some degree of uncer- 

 tainty ; whether they imbibe those salts already existing in a 

 state of solution, and thus obtain the matter required for 

 their groAvth ; or whether they dissolve out certain elements 

 from the soil, by the solvent action of their own juices. 



Eichhorn's results demonstrate that pure distilled ivater 

 can dissolve from the soil much more of mineral ynatter than 

 tvould he requisite for the supply of an ordinary crop* The 

 solvent powers of waters are also in almost every case, much 

 augmented by the presence of carbonic acid, and occasion- 

 ally, doubtless, by the existence in them of dissolved organic 

 acids, t These acids do not, in all probability, exert any 

 very important influence in dissolving food for the plant, so 

 long as they exist in growing vegetation, but only on their 

 being eliminated by processes of natural decay. When thus 

 released, they are probably very active in dissolving com- 

 pounds of sesquioxide of iron, and alumina ; as is, indeed, 

 abundantly proved by the occurrence in nature of such 

 minerals as beauxite, mellite, pigotite and oxalite, com- 

 pounds in which sesquioxide of iron or alumina, exist, com- 

 bined with water and an organic acid.f 



The utility of decaying vegetable matters as a manure, 

 may, consequently, be due as well to the solvent action of 

 certain products of their decomposition, as to the fertilizing 

 properties of their several mineral constituents. 



The absorptive powers of soils tend, moreover, to con- 

 centrate within their mass certain mineral constituents, 

 derived from small proportional quantities of them existing in 

 infiltrating waters ; and this absorption is very marked 

 between phosphoric-acid compounds and soils of a clayey 

 character, which seem especially adapted for their retention. 



For the sake of demonstrating this fact, an experiment 



* Poggendorf Annalen, Xo. 9, 1858, etc. ; also Johnson, in Silliman's 

 .Journal, [2] sxviii., 1869, 



+ Tide Chemistiy of Xatural Waters, bj Dr. T. Steny Hunt, in 

 Sillimans Journal, 1865. 



\ Ibid. 



