22 Rankin and Wright — Ternary System CaO-Al 2 0-Si0 2 . 



grams are easy to manipulate and are usually sufficient for both 

 the optical and thermal study. 



The amount of a charge required for each of the three meth- 

 ods is as follows : (1) For the determination of energy changes, 

 we have found that in order to obtain the sharpest break (which 

 is the record, on a heating curve, of an energy change) a charge 

 of 2 5 to 5 grams should be used. (2) For baking in order to 

 grow crystals, the charge varies from 1 to 100 grams. (3) For 

 quenching, a charge of 0*1 to 0*5 gram is sufficient for the 

 microscopical examination, and such a charge is easily main- 

 tained at constant temperature. 



All experiments were performed in an oxidizing atmosphere 

 (air) ; the furnaces used were of platinum or iridium. The 

 platinum furnace consists of a coil of platinum wire (wire l-2 mni 

 diameter ; coil 2^ inches diameter, 9 inches long, six turns to 

 the inch) wound on the inside of a cylinder of impure magne- 

 site which is insulated with MgO powder and a fire clay cylin- 

 der. Temperatures within the platinum furnace are measured 

 with a platinum-rhodium thermoelement, in connection with a 

 potentiometer and galvanometer.* It is heated by the current 

 from a storage battery (voltage 110, capacity 300 amp. hrs.) } 

 and the temperature within the furnace can be maintained con- 

 stant (± 2°) at 1550° for a period of 12 hours ; for lower tem- 

 peratures the temperature can be maintained constant for much 

 longer periods of time. 



The iridium furnace consists of a straight iridium tube about 

 18 cm long and 4 cm in diameter and is heated by a low voltage 

 alternating current. Temperatures within this furnace are 

 measured with an optical pyrometer, f This furnace is used 

 only for the determination of melting-points of substances which 

 melt completely at a definite temperature within the range 

 1600°-2100°. 



EXPERIMENTAL INVESTIGATION. 



GENERAL RELATIONS OF THE BINARY COMPOUNDS IN THE 

 TERNARY SYSTEM. 



The investigation of the three binary systems showed that 

 in the ternary system, in addition to the components them- 

 selves, the following binary compounds would occur, viz : — 

 CaO.Si0 2 ; 3Ca0.2Si0 2 ; 2CaO.Si0 2 ; 3CaO . A1 2 3 ; 5CaO. 

 3A1 2 3 ; CaO.Al 2 3 ; 3Ca(J.5Al 2 3 ; Al 2 3 .Si0 2 ; 3CaO.Si0 2 . 



In fig. 5 the compositions of the binary compounds and 

 quadruple points are given as points on the sides of the tern- 



* Walter P. White: Potentiometer Installation, especially for high temper- 

 ature and thermo-electric work, Phys. Rev. xxv, 334-352 (1907). 



f Day, Shepherd and Wright: Lime-Silica Series of Minerals, this Journal, 

 (4), xxii, 286, 1906. 



