as a solvent in the process of Vegetation. G3 



carefully examined, subjected to such trials as were requi- 

 site to determine whether and to what extent the substance 

 introduced had been acted on by the acid. I shall briefly 

 notice the results individually. 



Phosphate of Lime. — After having been kept eleven days, 

 the carbonic acid water, in which a portion of this compound 

 had been introduced, was examined. The water, immedi- 

 ately after filtration, was clear. The whole was divided into 

 two portions ; to one ammonia was added, the other was left 

 exposed to the air. The volatile alkali instantly rendered 

 the water turbid; six cubic inches of the water yielded a 

 precipitate, which, collected and weighed, after having been 

 dried and heated nearly to redness, was found equal to -64 

 of a grain. It had the properties of phosphate of lime. The 

 other portion exposed to the air, about 85 cubic inches, ex- 

 amined after two hours, was found to have on its surface a 

 fine continuous pellicle, not unlike that which forms on lime- 

 water similarly exposed. Examined again after fourteen 

 hours, the pellicle had become more conspicuous, and a de- 

 position was observable on the inside of the glass vessel, 

 diminishing downwards. The pellicle examined under the 

 microscope with a high power (one-eighth of an inch focal 

 distance) appeared finely granular, portions of it with well- 

 defined bi'oken edges, other portions with a delicate arbo- 

 rescent outline. The pellicle foimaed on the surface, and the 

 deposit on the sides of the vessel collected on a filter, after 

 thirty-eight hours' exposure, and thoroughly dried, weighed 

 •7 of a grain. Still the water held carbonic acid and phos- 

 phate of lime in solution, for, on addition of ammonia to the 

 filtered fluid, it was rendered turbid, and yielded "S of a grain 

 more of phosphate of lime. These results appear to sliew 

 that 20,000 parts by weight of water saturated with carbonic 

 acid gas arc capable of dissolving 1 part by weight of phos- 

 phate of lime. The readiness with which phosphate of lime 

 is dissolved by means of carbonic acid is most easily shewn 

 by adding a portion of freshly-precipitated phosphate, well 

 washed, to water merely satui'ated with carbonic acid gas 

 by agitation. In a few minutes, if the portion be small, it 

 will disappear, and will be precipitated distinctly by the ad- 



