16 
CHEMISTRY: FERGUSON AND MERWIN 
6 Grassi, B., and Foa, A., R. C. R. Acad. Lincei, Rome, (See. 5), 13, 1904, (241-253), 17 
figs, in text. 
6 Janicki, C, Zs. wiss. Zool., Leipzig, 95, 1910 (243-315), pis. 6-9. 
^ Grassi, B., and Sandias, A., Galatola, Catania, 1893, (1-151), pis. 1-5. 
8 Zulueta, A. de., Trah. Nac. Cienc. Nat., Madrid, 23, 1915, 25 pp., 1 pi. 6 figs, in text. 
9 Hartmann, M. Hertwig's Festsch., 1, 1910 (349-392), pis. 27-30, 3 figs, in text. 
THE TERNARY SYSTEM CaO-MgO-SiOa 
By J. B. Ferguson and H. E. Merwin 
Geophysical Laboratory, Carnegie Institution of Washington 
Communicated by A. L. Day, November 25, 1918 
A number of investigations dealing with one or more of the four oxides, 
lime, alumina, magnesia and sihca, have in recent years been carried out at 
the Geophysical Laboratory of the Carnegie Institution of Washington, as a 
preliminary step in the study of the rocks and minerals of the earth's crust. 
These studies^ include all of the possible binary systems and three of the four 
possible ternary systems which may be constructed from these oxides. The 
fourth ternary system has been studied only in part. We desire in this 
paper to present a summary of the results we have obtained in a study of the 
remainder of this fourth ternary system, and also to correlate these results 
with the results previously obtained. 
The experimental methods employed are similar to the methods used in the 
previous investigations at this laboratory. Samples of known compositions 
were prepared by fusing together in platinum crucibles weighed amounts of 
chemically pure calcium carbonate, magnesia and silica and subsequently 
reducing the samples to fine powders. The production of homogeneous 
samples usually necessitated the repeating of this process once or twice. The 
investigation of a sample was conducted as follows: a small quantity of the 
sample was wrapped in a piece of platinum foil which was about 1 sq. cm. in 
area and this charge was tied by a fine platinum v/ire to a small ring of mar- 
quardt porcelain. The porcelain ring was hung on a fine platinum wire, the 
ends of which were connected to two stout platinum leads. A marquardt 
porcelain tube carried these leads and also a platinum-platinrhodium ther- 
moelement the junction of which was not more than a few millimeters from 
the charge. The charge, thermoelement, etc., were inserted into a hot plat- 
inum resistance furnace and the furnace temperature was regulated in such a 
manner as to maintain the charge at a predetermined temperature for a suffi- 
cient time to allow an equilibrium condition to be attained (usually from fif- 
teen to thirty minutes but sometimes as long as forty-eight hours). The wire 
supporting the ring and the charge was then fused by passing an electric cur- 
