80 GEATES. 



alumina, are universal constituents of soil, and the two first 

 are constantly present in plants. In their relation to geine, 

 these all combine with that, they all form soluVjle compounds 

 in the moist state, but after' having been thoroughly dried, 

 these geates are insoluble, even sun baking diminishes their 

 solubility. In this dried state, they are earthy powders, and 

 have long been mistaken for earthy portions of soil. The 

 fact that lime and magnesia form super-salts (120), may 

 help to explain why the free use of lime may often require 

 a long time to develop any beneficial effects. At first, its 

 action renders the geine insoluble ; and it is only when, by 

 exposure, the lime is changed in part to a carbonate, and 

 thus rendered inert, that a super-geate of lime, which is very 

 soluble, forms and begins to show its effects upon vegetation. 

 The easy decomposition of geate of lime, by alkaline car- 

 bonates, teaches also, that if to geate of lime is added an 

 alkaline carbonate, the geine may be dissoluble, and brought 

 into use. It is probable, that when land has been over- 

 limed, the evil can be corrected only by the use of ashes. 

 The carbonate of lime will act on the silicates, as will be 

 hereafter shown. 



125. The properties and relations of geine with water, are 

 also of the highest agricultural value (116). The great in- 

 solubility shows at once how small must be the amount of 

 this portion of soil, which can be ever removed by drainage 

 or filtration, by flood, or rain, and that, in the practice of 

 irrigation, very little effect can be due to the solvent power 

 of w^ater on geine. Its almost total insolubility, seems a 

 wise provision of a far-reaching Providence, that an element 

 of soil, which has been and can be produced by the decay 

 of organic bodies only, and chiefly by plants on the earth's 

 surface, should not be borne away by the first falling 

 shower, * 



