62 Dv Davy on Carbonic Acid 



generally admitted. But, whilst the effect of its decompo- 

 sition, under the influence of light, has been carefully stu- 

 died, comparatively little or no attention, to the best of my 

 knowledge, has been paid to the solvent power of this acid 

 in the physiology of vegetables. 



When we examine the ashes of plants, we find in the ma- 

 jority of them, besides certain salts soluble in vi^ater, certain 

 other compounds of little or no solubility in this fluid, such 

 as carbonate of lime, phosphate of lime, and silica; and the 

 two latter, in many of the grasses, especially in ti'opical 

 species, in proportions exciting our surprise. Tliat these 

 inorganic elements, as they are commonly called, are derived 

 from the soil, can hardly be doubted, judging from well-esta- 

 blished facts ; but, it is a question of some interest how they 

 are derived, what tlie menstruum is by which ihey are con- 

 veyed and distributed, and whether the acid mentioned— 

 the carbonic acid — is mainly concerned in the function. 



To endeavour to answer this question, at least in part, I 

 have instituted some experiments, which I shall now de- 

 scribe, with their results. The subjects of the first trials I 

 made were phosphate of lime, silica, and alumine. Portions 

 of these (all with the exception of the sulphate of lime) were 

 used in a moist state, freshly precipitated, after having been 

 well washed on a filter. They were introduced into bottles, 

 such as are used for holding soda-water, and were filled with 

 water strongly impregnated with carbonic acid gas by means 

 of the apparatus commonly employed in the manufacture of 

 of soda-water, and were corked and wired in the usual man- 

 ner. The degree of the compression of the gas was not 

 ascertained : that it was considerable was evident from the 

 explosive manner in which the corks were expelled on re- 

 moving the binding wire for the purpose of examining the 

 effects. In each instance, on the removal of the cork, the 

 water was filtered as soon as possible, using three or four 

 filters ; and, generally, I may remark, there was no appear- 

 ance of any turbidness or precipitation on the escape of the 

 highly-compressed gas, seeming to indicate, as might have 

 been expected, that no solvent power was exercised by the 

 compressed air. In each instance the filtered fluid was 



