﻿970 Mr. J. Kendall on the Solubility of 



The specific gravity of the precipitated crystals was found, 

 however, by the Westphal balance to be identical with that 

 of arragonite, 2' 89. 



The higher values obtained at the lower temperatures of 

 25° C. and 50° 0. are clearly to be accounted for by the 

 obstinate retention of the last trace of carbon dioxide by the 

 solution, equilibrium never being attained in the time of 

 experiment. This was found to be also the case at 100° C. 

 When the experiments were conducted as before until a 

 precipitate had formed, and then all the liquid decanted off, 

 fresh water added to the crystals remaining, and the experi- 

 ment continued as before, the following solubility values 

 were obtained. 



25° C. 50° C. 



4 days -018791 '01958 i 



6 days -01868/ -01976/ 



100° C. 



60 mins. -02271 



120inins -02238 



These are still, it will be seen, much higher than those 

 previously found for calcite and arragonite ; the value at 

 100° C. is scarcely lowered at all. The curve of the solubility 

 has now, however, become approximately parallel to those 

 given by the two crystalline varieties. 



Further investigation showed that decantation is in- 

 sufficient to remove the final trace of carbon dioxide. It is 

 necessary to shake up thoroughly the crystals that remain 

 with successive quantities of water, before proceeding with 

 the experiment ; and by this means constant results were 

 finally obtained, comparable with those previously found for 

 the mineral calcite and arragonite. 



*> ^J- Mean result. 



2 days -01450 I — 



5 days -01464/ -01466 -01460 



50° C. 



2 days -015541 '01549 



5 days '01536/ — '01546 



100° C. 



60 mins '01909 '01917 



120 mins '01899 '01911 '01909 



It will be seen that the results of the experiments at 

 25° C. are substantially the same as those for mineral calcite 

 at that temperature ; those at 50° C. lie between the values 



