88 Ferguson and Merwin — The Ternary System. 



The two systems Si0 2 -CaO.Mg0.2Si0 2 and CaO.MgO. 

 2Si0 2 -2MgO.Si0 2 have been studied by Bowen 31 as part 

 of the ternary system diopside-forsterite-silica. They 

 show simple eutectics, as may be seen in the diagrams 

 given in figs. 4 and 5. 



But in his ternary system Bowen found that there 

 existed a complete series of solid solutions having diop- 

 side and clino-enstatite as end members. 32 Most of these 

 solutions, like clino-enstatite, are unstable at their melt- 

 ing points. The rather complicated relations which 

 obtain as a result of this someAvhat unusual condition 

 will not be discussed here but may be found in the orig- 

 inal paper. 



The concentration relations in these systems in so far 

 as they affect the ternary system CaO-MgO-Si0 2 are 

 collectively shown on the triangular diagram given in fig. 

 6 and form the starting point of the present investiga- 

 tion. 



General Procedure. 



The initial step in a research of this character is the 

 preparation of charges of known composition, and for 

 this purpose chemically pure calcium carbonate, magne- 

 sium carbonate and silica were used. The magnesium 

 carbonate was not used directly in this process but was 

 first calcined in a platinum crucible in a Fletcher gas- 

 blast furnace. After the ingredients were weighed out 

 and thoroughly mixed in a mortar, the mixtures were 

 fused in platinum crucibles and then reduced to a fine 

 powder. This process was repeated two or three times 

 to ensure complete homogeneity in the final product. 

 Mixtures which fused completely at temperatures below 

 1500 °C were heated in a platinum-resistance furnace; 

 those melting at higher temperatures, in a Fletcher gas- 

 blast furnace. "When possible the compositions were 

 finally prepared as glasses, since this form of material 

 is necessary in many experiments and in addition may 

 be easily tested under the microscope for homogeneity. 



A few peculiarities were noted during the preparation 

 of the compositions. Those lying within the silica field, 

 unless they rapidly cooled, gave either milky or porce- 

 lain-like glasses. In the porcelain-like glasses in which 

 the crystallization was further advanced, crystals of 



31 This Journal (4), 38, 207, 1914. 



32 See p. 92. 



