316 Shepherd, Rankin, Wright — Binary Systems of 



The most interesting fact with respect to the lime which has 

 come to light in the coarse of this investigation is the evident 

 growth of the grains at temperatures above 1300°. Fine 

 impalpable powder resulting from the calcination of calcite 

 was heated for a week in the electric resistance furnace at 

 1300°-1400° and found at the end of that time to consist of 

 rounded grains of lime measuring as high as , 01- , 02 mm in 

 diameter in place of the submicroscopic material which went 

 into the furnace. This temperature is 1000° or more below 

 the melting temperature of crystallized calcium oxide, 

 and yet at ordinary atmospheric pressure and in the dry state 

 crystals of calcium oxide grow rapidly at 1400° and resemble 

 in all respects those formed out of melts of different composi- 

 tions. This principle of causing crystal growth many degrees 

 below the melting point and in the dry state is being 

 applied constantly in this laboratory to render fine microscopic 

 preparations suitable for optical examination. Experience 

 thus far gained has shown that not all compounds grow with 

 equal rapidity under these conditions, and in fact free alumina 

 seems to be little affected by this treatment. The growth of 

 calcium oxide crystals under these conditions is, however, 

 definitely established, and is an important fact to be taken 

 into consideration in connection with crystal formation and 

 growth. 



The 3CaO.Al,0 3 compound: CaO 6M<B, Al 2 O a 37-78.— 

 Preparations of this composition have never been obtained per- 

 fectly homogeneous and free from grains of free lime and also 

 of the lower refracting 3Ca0.5Al 2 3 compound. The amounts 

 of the latter, however, are not large and their presence has 

 been shown to be due to dissociation. Optically this compound 

 is simple in its properties. It crystallizes in the isometric 

 system and exhibits no pronounced cleavage. Indications of 

 cleavage after (111) or (110) were observed here and there, but 

 only imperfectly developed. The fracture is conchoidal ; the 

 hardness is about 6. Although no separate crystals for gonio- 

 metric measurement could be obtained, the frequent hexagonal 

 and rectangular outlines of the grains in the thin section 

 indicate the rhombic dodecahedron (110) or octahedron as the 

 predominating form. The grains are colorless, of glassy 

 luster, and isotropic, with refractive index ?z Na =l*710±'001 

 measured on the Abbe total refractometer. Occasionally faint 

 gray interference colors were observed on certain grains and 

 were evidently due to strain. No definite arrangement of 

 inclusions or zonal growth was noticeable, even on the largest 

 grains, measuring 0'l mm in diameter. 



The 5Ca0.3Alfi % compound: CaO 4.7-78, Al,0,5°2-22.— 

 Separate crystals of this compound were not obtained and no 



