14 Allen , etc. — Diopside and its delations 



Cal. for 



CaSi0 3 , 



Found MgSi0 3 



SiO„ _ 55-59 55*62 



CaO . 25-73 25-83 



MgO 18-61 18-55 



Fe 2 3 etc. -18 



CI trace 



100-11 100-00 



Several products made in this way were united and tested 

 in a mixture of methylene iodide and benzene to see if all was 

 of uniform specific gravity. A small fraction, containing some 

 of the larger crystals, floated, while the rest sank. These crys- 

 tals seemed to differ from the rest only in porosity. The 

 remainder were then divided into two fractions of only slightly 

 different density and the specific gravity of each was deter- 

 mined by the pycnometer. 



■ ._. . , . Sp. gr. at 25° 



1. Lighter traction ' ° 



Jti \j at 25 



= 3-270 



2. Heavier " " 



3-275 



3. Natural diopside 





from Ham Island, 





Alaska, 



3-268 



An idea of the expansion of the diopside in the process of 

 melting may be obtained by comparing this constant with the 

 specific gravity of the glass of the same composition : 



2-830. 



HO at 25 c 



The description and angular measurements of these crystals 

 are to be found in Part II of this paper. 



Melting Point Curve from J^6'3 — 100 per cent MgSiO s . — 

 Referring again to fig. 1, it is seen that beyond 46*3 per 

 cent xvIgSi0 3 , the addition of it lowers the melting point 

 gradually but very slightly, until about 68 per cent has been 

 reached. Near this point there is an abrupt rise, the curve 

 finally terminating at 1524°, the melting point of magnesium 

 silicate. On the first branch of the curve (46*3-68 per 

 cent) mix crystals of magnesium silicate in diopside sepa- 

 rate. This conclusion was tentatively reached in the prelimin- 

 ary thermal work when it was found that the addition of a 

 large percentage of magnesium silicate lowered the melting 

 point of diopside very little, while the mixtures continued to 

 show but one absorption of heat. The thermal evidence was 

 subsequently confirmed by the specific volume curve, and by a 

 very elaborate microscopic study. 



