﻿966 Mr. J. Kendall on the Solubility of 



greater density of the arragonite, offering more resistance to 

 the solvent action of the water. 



The results for arragonite are, in general, less concordant 

 than those for calcite ; this is due to the instability of the 

 former. Observations with the microscope were made on 

 slides of the solid residue from each experiment • calcite was 

 always unchanged, but arragonite at 100° C. always showed 

 a few crystals of calcite, the rhombic crystals of the latter 

 being easily distinguishable among the needle-shaped crystals 

 of arragonite* The proportion of calcite present, although 

 always very small, increased regularly with the time of 

 boiling, and thus a true solubility value for arragonite was 

 never attained, but an intermediate value between the 

 solubilities of the two minerals. At 50° C. and 25° C, no 

 chnuge of arragonite to calcite was observed. 



The values obtained are in good agreement with those of 

 Kohlrausch at the ordinary temperature. The ratios of the two 

 solubilities at different temperatures are also fairly concordant 

 with the results of Foote {Zeit. phys. Chem. xxxiii. p. 740 

 (1900)). It will be seen from the diagram that the two curves 

 run almost parallel ; any transition point is obviously either far 

 above or far below the ordinary temperature, if it exists at 



all. The ratios of the solubilities are ( ( f ., ) :• — 



\ calcite / 



25° C. 50° C. 100° C. 



Observed 1-064 1-075 1-069 



Foote (by interpolation) ... 1-130 1*114 — 



Foote has concluded, from the decrease of the ratio obtained 

 with rise of temperature, that the inversion temperature is 

 above the ordinary range ; the above results, however, show 

 a Constant ratio, and hence^ since the solubility increases with 

 the temperature, greater difference of solubility with rise of 

 temperature. 



It is an interesting point that the ratio of the specific 



2"90 

 gravities of the two forms is ^^^ 1*066. The ratio of COn- 

 centration in the solid form to concentration in the solution 

 thus appears to be constant for the two varieties. 



Calcium Bicarbonate Solutions. 

 The presence of carbon dioxide increases the solubility of 

 carbonates in water to a marked degree, owing to the 

 formation of soluble bicarbonates* The equilibrium of the 

 system is determined by the partial pressure of the carbon 

 dioxide over the solution; and in the case of calcium 



