as a solvent in the process of Vegetation. 65 



could any trace of alumine be detected in the minute residue 

 obtained by evaporating this portion to dryness. 



Silica. — A portion of gelatinous silica obtained from liquor 

 silicum, by means of an acid, was exposed to the action of 

 the aerated water eight days. The filtered fluid was not 

 distinctly precipitated by ammonia ; nor did a pellicle form 

 on a portion of it e.xposed to the atmosphere ; but, from both 

 portions, — that to which ammonia had been added, and that 

 to which no addition had been made, a minute quantity of 

 silica was obtained by evaporation to dryness. It adhered 

 to the platina capsule, forming delicate circles ; the deposit 

 was opaque and white ; was not dissolved by nitric acid : 

 under the microscope it had the appearance of small thin 

 plates, transparent, without any regularity of form, as to 

 outline. From six cubic inches of aerated water, I infer 

 that about -01 of a grain of silica was deposited. In another 

 experiment, in which some silica that had been obtained from 

 a mineral water in fine powder, had been exposed, after hav- 

 ing been dried, to the action of the water containing cai'bonic 

 acid gas compressed, for nineteen days, the results obtained 

 were very similar to the preceding. In this instance, there 

 was a slight appearance of turbidness produced on the addi- 

 tion of ammonia to the filtered water, and a very slight de- 

 position on the inside of the glass vessel, in which a portion 

 of the water was exposed to the atmosphere, and that of 

 matter not dissolved by an acid ; and, farther, the proportion 

 of white matter having the character of silica, obtained by 

 the evaporation of the water, was greater than in the first 

 instance, — from 6 cubic inches -06 of a grain was procured. 

 In a third experiment, in which a white powder, consisting 

 chiefly of the silicious skeletons of infusoria, had been exposed 

 to the action of water saturated with carbonic acid, without 

 condensation, for fifteen days, a similar result was witnessed 

 on evaporation, viz., a minute residue of silica. 



Besides the foregoing, I have made many other trials of 

 tlie action of water impregnated with carbonic acid gas, both 

 compressed and without compression, the results of which 

 have been in accordance with the preceding. I shall briefly 



VOL. XLV. NO. LXXXIX.— JULY 1848. E 



