122 Ferguson and Merwin — The Ternary System. 



In conclusion, thanks are due Dr. N. L. Bowen for his 

 friendly criticisms and Mr. Gr. A. Rankin for certain pre- 

 liminary results which he generously placed at our dis- 

 posal at the commencement of the investigation. 



Summary. 



The ternary system lime-magnesia-silica has proved to 

 be the most complicated of the four possible ternary 

 systems which may be constructed from the four oxides, 

 lime, magnesia, alumina, and silica. The crystalline 

 phases which are definite compounds and which appear 

 as primary phases are as follows : 



Lime; magnesia; silica (tridymite and cristobalite) ; 

 aCaO.Si0 2 (pseudowollastonite); 3Ca0.2Si0 2 ; a and /? 

 2CaO.Si0 2 ; MgO.SiOo (clino-enstatite) ; 2MgO.Si0 2 (for- 

 sterite) ; CaO.Mg0.2Si0 2 (diopside) ; 5CaO.2MgO.6SiO. 

 and 2CaO.Mg0.2Si0 2 . The melting point of 2CaO.MgO. 

 2Si0 2 is 1458° ± 5°C and the decomposition temperature 

 of 5Ca0.2Mg0.6Si0 2 is 1365° ± 5°C. 



In addition to these, crystals representing several solid 

 solutions also appear as primary phases. The solid solu- 

 tions are : 



1. A complete series with clino-enstatite and diopside 

 as end members, generally known as pyroxenes. 



2. The pseudowollastonite solid solutions whose com- 

 positions form an area bounded by the following lines: 

 (1) the CaO.Si0 2 -CaO.Mg0.2Si0 2 line; (2) a line run- 

 ning from the composition CaO, 44-4, MgO 3-1, Si0 2 52-5 

 on the above-mentioned line across to the composition 

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

 2Si0 2 line; (3) then either the last-mentioned line back 

 to CaO.Si0 2 , or, more probably, an approximate continua- 

 tion of line (2) to about the composition CaO 50, Si0 2 

 50, on the side line. 



3. The wollastonite solid solutions ; these extend to 

 about 17 percent diopside or 3-2 percent MgO at the 

 higher . temperatures. The most concentrated of these 

 solid solutions along the diopside line (the 17 per cent) 

 decomposes at 1340° ± 5°C, and this solid solution is the 

 only one represented on the liquidus. 



4. The 5CaO.2MgO.6SiO, solid solutions. Only a few 

 of these solid solutions which are decomposed at the 

 higher temperatures near the decomposition-temperature 



