Day and Shepherd — -Lime-Silica Series, of Minerals. 271 



Lime. — Calcium oxide melts at a temperature so high that 

 it is not yet possible to make a satisfactory determination of 

 its melting point. It can be fused in the electric arc under 

 favorable conditions to a clear liquid of low viscosity which 

 crystallizes readily into a well developed cubic structure. 

 Near its fusing temperature, lime either becomes quite vola- 

 tile or the carbon of the arc reduces it to the metal, which 

 volatilizes and is immediately reoxidized outside of the heated 

 zone. We are unable to offer conclusive evidence in favor of 

 the one hypothesis or the other, but the fact that pure lime at 

 2000° shows no signs of a high vapor pressure points rather 

 to the second explanation as the correct one. 



For experiments with lime fusion, we obtained some arti- 

 ficial graphite* practically free from all impurities, so that no 

 contaminating substance was introduced into the fused lime 

 from the electrodes. To further guard against possible con- 

 tamination, only that part of the cake which formed above the 

 (horizontal) arc was used in determining its physical properties. 

 Density of CaO. — The density of fused calcium oxide 

 was determined as follows : A selected portion of the crystal- 

 line mass was finely ground, ignited to drive off adsorbed 

 water, and weighed in carefully dried turpentine after the 

 method of Day and Allen. The results are not in very good 

 agreement, due probably to the difficulty of weighing out tho 

 product without its becoming superficially hydrated or absorb- 

 ing C0 2 . 



Fused CaO. H 2 at 25° = 1. 



3-313 



3-307 



3-329 



Mean density, 3*316 (25°) 



This crystallized lime is much less readily attacked by 

 water than is the amorphous oxide. It is, however, not indif- 

 ferent to water. Five grams of the crystals when ground and 

 mixed with a small quantity of water in a test tube scarcely 

 raised the temperature at all, but upon standing for some five 

 minutes, the charge exploded with considerable violence. 

 Unpowdered blocks of the crystalline oxide when placed in 

 cold water dissolved slowly without appreciable heating. Hot 

 water attacks them more rapidly, but the action of the water 

 is slow in both cases as compared with the amorphous lime. 



The hardness, according to Mohs's scale, is between 3 and 4. 



Silica. — The melting temperature of silica has been vari- 

 ously estimated at from 1200 to 2000°, but so far as known no 



* Prepared by the International Acheson Graphite Company, Niagara 

 Falls, New York. 



