114: Ferguson and Merwin — The Ternary System. 



The liquidus-solidus temperature relations have now, as 

 far as possible, been determined over the entire ternary 

 system and they may be represented by a solid model 

 constructed by properly filling in the model shown in fig. 

 9. A photograph of this solid model is shown in fig. 11. 

 These relations may also be indicated by means of a tri- 

 angular concentration diagram similar to the one shown 

 in fig. 8, upon which isotherms have been drawn and the 

 temperature of the fixed points given. In figs. 12 and 13 

 are such diagrams, 12 given in weight percent and 13 in 

 mol percent. 



Discussion of the Fields. 



A complete discussion of the wollastonite, of the 

 pseudowollastonite and of the 5Ca0.2Mg0.6Si0 2 solid 

 solutions and their respective fields will appear in a 

 subsequent paper. The general conclusions only will be 

 indicated at this time. 



The pseudowollastonite field. — This field belongs to 

 solid solutions whose compositions form an area bounded 

 by the CaO.$i0 2 -CaO side line, the CaO.Si0 2 -diopside 

 line and a line extending from the compositions CaO 444, 

 MgO 3-1, Si(X 52-5, on the CaO.Si0 9 -diopside line to the 

 composition CaO 46-7, MgO 3-5, Si0 2 49-8, on the CaO. 

 Si0 2 -2CaO.Mg0.2Si0 2 line and probably to the composi- 

 tion CaO 50, Si0 2 50 on the side line. 



The wollastonite field. — The evidence does no more 

 than establish the existence of this tiny field which 

 belongs to the most concentrated solid solution of diop- 

 side in wollastonite which decomposes at the highest tem- 

 perature. This solid solution containing between 3-1 and 

 3-5 percent MgO or approximately 17 percent of diopside 

 has the highest decomposition temperature, 1340 ±5°C, 

 the pure wollastonite inverting to pseudowollastonite at 

 1200°a The limit of 3-1 to 3-5 percent MgO agrees with 

 the limit of 3-15 MgO (17 percent diopside) found by 

 Allen and White as does the decomposition temperature 

 of 1340 °C with their observations. 42 



The 5Ca0.2Mg0.68i0 2 field.— This field belongs to a 

 series of solid solutions which are not stable at their melt- 

 ing points and which lie on or near the 5Ca0.2Mg0.6Si0 2 

 composition. The fact that the decomposition tempera- 

 tures of these and other solid solutions rise sharply as 



42 This Journal, 27, 1, 1909. 



