wells: solubility of calcite in water 617 



previously made by others: Monomethyl red, a-naphthylamine red, 

 dimethyl-a-naphthylamine red and diphenylamine red. The well 

 known methyl red had been previously investigated by Palitzsch. Of 

 these indicators the most satisfactory are those containing two sub- 

 stituent alkyls. 



Several new indicators of the sulphonephthalein type were prepared ; 

 namely, thymolsulphone-phthalein, a-naphtholsulphone-phthalein, and 

 bromthymol-sulphone-phthalein. An improved method of preparation 

 for the sulphone-phthaleins is described. 



The hydrogen-ion concentrations at which the color changes of the 

 above indicators occur was determined. 



The authors will shortly publish the result of their investigations 

 on the utility of the most satisfactory of the new indicators with par- 

 ticular reference to their salt and protein errors and to their applica- 

 bility in biochemical investigations, 



PHYSICAL CHEMISTRY.— T/ie solubility of calcite in water 

 in contact with the atmosphere, and its variation with tempera- 

 ture. Roger C. Wells, Geological Survey.^ 



It is well known that even the small amount of carbon dioxide 

 in the atmosphere is sufficient greatly to increase the solubility 

 of calcite in water. Direct experiments on this point at tempera- 

 tures above 25°C. were made by Kendall,- who found the solution 

 to contain calcium equivalent to 46 parts of calcium carbonate 

 per million at 25° and 29 parts at 50°. The partial pressure of 

 carbon dioxide in Kendall's experiments was found by him to be 

 3.69 X 10~^ atmospheres. 



Recently all the data on the solubility of calcite in carbonic 

 acid water have been critically examined by Johnston,^ and he 

 has calculated the solubility of calcite in water at 16°, in con- 

 tact with air containing certain small pressures of carbon dioxide, 

 with the results given below. 



When Kendall's results are compared with those calculated by 

 Johnston, under similar conditions, the agreement is not as good 

 as one could wish. Moreover, in a paper by Dubois* on the 



1 Published with the permission of the Director of the U. S. Geological 

 Survey. 



2 Philos. Mag. Ser. 6, 23: 973. 1912. 



3 Jour. Am. Chem. Soc. 37: 2001. 1915. 



^ Proc. Sec. Sci., Amsterdam Academy, 3: 46. 1901. 



