SOSMAN, HOSTETTER, MERWIN : CALCIUM CARBONATE 565 



The result of the dissociation pressure measurements, so far 

 as their original purpose is concerned, was disappointing. The 

 cause lies probably in the slow rate of dissociation of the dry ma- 

 terials at 400°. A number of interesting facts were obtained, 

 however, which have been thought worth present publication, 

 as we have had to discontinue the work for the present. 



Forms of lime. CaO is obtainable in two distinct physical 

 states. That made by heating Iceland spar at 700° in the 

 vacuum furnace, and pumping out the last traces of CO2, is very 

 fine grained and porous, with a faint double-refraction. The 

 refractive index seems to be quite variable, but on account of 

 the porosity of the material accurate measurements of the 

 index could not be made. The oxide is very reactive, absorbing 

 water from the air even when confined in a desiccator in the 

 presence of calcium chloride. After being reheated to 1200°, 

 the index rose, and gave values varying from 1.725 to 1.77; the 

 oxide was then much more stable in air, and did not take up 

 moisture while the microscopic examination was being made, 

 as did the first sample. As in the first case, however, the porosity 

 interferes with accurate measurement. Again reheated, to 1400°, 

 the oxide showed a prevailing refractive index of 1.81, with some 

 grains as low as 1.79. It still showed double-refraction. 



On account of its fineness, it is impossible to say conclusively 

 whether this variety is crystalline or am.orphous. The double- 

 refraction may be the result simply of strains within an amorphous 

 solid. 



The reactivity of this porous lime was shown by another ex- 

 periment. 452.5 m.g. of 200 mesh Kahlbaum calcite was heated 

 and evacuated at 750° in the vacuum furnace, in presence of 

 P2O5, for about 30 minutes. When it had cooled to 110°, 15 

 mg. dry CO2 was admitted. (The gas had been drawn from a 

 cylinder of liquid CO2, passed over hot copper and copper oxide, 

 dried over P2O5 and stored over mercury.) The reaction began 

 immediately with a rise of temperature; as the charge cooled 

 to room temperature the absorption still continued, but at a 

 decreasing rate. Even at room temperature the absorption 

 continued slowly, 0.48 m.g. being taken up in 21^ hours. About 



