as a solvent in the process of Vegetation. 67 



the precipitate obtained by adding ammonia to the filtered 

 water, and also by evaporating to dryness the same water 

 after the addition of ammonia and filtration. 



These latter results appear to shew, that water impreg- 

 nated with carbonic acid has the power of dissolving, at the 

 same time, several compounds, as carbonate of lime, carbo- 

 nate of magnesia, phosphate of lime and silica, besides what 

 water alone is capable of taking up. 



The application of these results to the physiology of vege- 

 table growth appears to be pretty obvious, and, in some par- 

 ticulars, in admirable harmony with previously ascertained 

 facts. For instance, how admirable it is, that the acid from 

 which vegetables derive their carbonaceous elements, chiefly 

 by the action of light and oxygen, is restored to the atmo- 

 sphere by its decomposition, should, in passing from the soil, 

 be the bearer of so many elements derived from the soil, and 

 insoluble in water alone, to be deposited, it may be taken for 

 granted, where required, partly owing to the decomposition 

 of the acid, when the process of vegetation is most active 

 tinder the influence of light, and partly owing to evapora- 

 tion under the influence of heat, and of other causes promot- 

 ing it. 



Perhaps the careful study of the manner and the influ- 

 ences under which the several substances admitting of solu- 

 tion in water, and in water holding carbonic acid in solution, 

 are deposited, may throw some light on the composition of 

 plants, as regards their inorganic elements. For instance, 

 as sulphate of lime does not appear to have its solubility in- 

 creased by the addition of carbonic acid to water, it does not 

 seem incongruous that it should seldom be found excepting 

 in minute quantities in vegetables. As alumine, insoluble in 

 water, does not appear to be rendei'ed soluble by the same 

 acid, the remark just made is a fortiori applicable to it, as a 

 constituent of plants ; indeed, it seems questionable, that this 

 earth, which performs so important a part in the soil, physi- 

 cally considered, is ever abstracted from the soil to enter 

 into the composition of any vegetable. Phosphate of lime, 

 judging from the experiments I liave made, appears to part 

 with its solvent carbonic acid on exposure to the atmosphere 



