6Q T>r Davy on Carbonic Acid 



notice such of them as are likely to be useful in connection 

 with vegetable physiology. 



A portion of calcareous marl in fine powder, acted on for 

 fourteen days by water containing carbonic acid gas con- 

 densed, yielded, after filtration, on exposure to the air and 

 evaporation to dryness, some carbonate of lime, a little cai'- 

 bonate of magnesia and phosphate of lime, and a trace of 

 silica, and a minute portion of carbonate of potash. 



In a similar experiment, continued for the same time, on a 

 portion of the ashes of the sugar-cane, the carbonic acid 

 water yielded a considerable portion of phosphate of lime, 

 and of carbonate of potash, and a small proportion of carbo- 

 nate of magnesia, with a little silica, and a trace of carbo- 

 nate of lime, — results in harmony with the composition of 

 this ash, as ascertained by analysis. 



A portion of a subsoil from the island of Tinnidad was 

 similarly acted on for eighteen days. The aerated water then 

 yielded a little cai'bonate of lime, a very little carbonate of 

 magnesia and phosphate of lime, and a trace of silica and of 

 carbonate of soda. 



A mixture of two grains of bi-carbonate of potash and of 

 four grains of a ehall<-like matter, of which there are exten- 

 sive deposits in Barbadoes, consisting chiefly of the silicious 

 skeletons of infusoria, was acted on by water containing cai*- 

 bonic acid gas compressed, for eleven days. This water, 

 then filtered and evaporated, yielded, besides the alkaline 

 salt, a trace of carbonate of lime and magnesia, and of phos- 

 phate of lime and silica ; and it may be worthy of remark, 

 that the silica obtained in this instance, notwithstanding the 

 presence of a large proportion of tlie vegetable alkali, was 

 not more in quantity than when no alkali had been intro- 

 duced. 



A mixture of four grains of di'ied phosphate of lime, and 

 of the same quantity of carbonate of lime, and of the chalk- 

 like matter above mentioned, all in the state of fine powder, 

 was similarly acted on during fifteen days. This examined, 

 the aerated water was found to yield some carbonate of lime, 

 a minute portion of phosphate of lime and of carbonate of 

 magnesia, and a trace of silica. Silica was detected both in 



