Bowen and Andersen — Binary System MyO-SiO v 489 



instantaneously to room temperature by allowing the charge 

 to fall into a dish of mercury, and examining the charge under 

 the microscope to determine the phases present. In this man- 

 ner the phases present at all attainable temperatures, in all 

 compositions, can be definitely fixed. The thermoelement of 

 Pt-Pt : Rh, used to measure the temperature, is frequently 

 calibrated by quenching charges of pure, artificial minerals of 

 known melting point, usually diopside and anorthite. As will 

 appear from an examination of the tabulated results, the actual 

 procedure with any given mixture is to locate by quenching, 

 between as narrow limits as possible, the tenrperature at which 

 a phase appears or disappears. 



To reach some of the higher temperatures an iridium 

 furnace was used and the temperatures were measured optically. 



Results. 



The completed results are now presented in tabular and 

 diagrammatic form before proceeding to their discussion. 



Table I. 



Quenching Results. Platinum Resistance Furnace. Tempera- 

 ture Measured with Thermoelement. 



(a) Liquidus of Forsterite. 



Composition Tempera- 



Oxides Compounds tare Time Result 



MgO Si0 2 j Mg 2 Si0 4 11 '7 ) 1625° 1 hr. glass and minute amount 



42 



58 



I MgSi0 3 88-3 f 







forsterite 



40-1 



59-9 



MgSi0 3 100 



1576° 



1578° 



1 hr. 

 1 hr. 



glass and forsterite 

 glass only 







(b) Temperature of Invariant Point, Forsterite- 

 Clino-enstatite-Liquid. 



50 



50 



1 Mg 2 Si0 4 58-5 | 

 (MgSiOs 41-5) 



1555° 

 1559° 



1 hr. 

 1 hr. 



elino-enstatite and for- 

 sterite 

 glass and forsterite 



42 



58 



(Mg,Si0 4 11-7 ) 

 ( MgSi0 3 88-3 ) 



1555° 

 1559° 



1 hr. 

 1 hr. 



clino-enstatite and for- 

 sterite 

 forsterite and glass 



40-1 



599 



MgSi0 3 100 



1556° 



1558° 



1 hr. 

 1 hr. 



clino-enstatite 

 glass and forsterite 







Temperature = 



1557° ± 



2° 



(c) Composition of Invariant Point, Forsterite- 

 Clino-enstatite-Liquid. 



Composition Tempera- 



Oxides Compounds ture Time Result 



MgO Si0 2 j MgSi0 3 97 ) 1557° 1 hr. glass only 



38-8 61-2 "j Si0 2 3 J 1555° 1 hr. glass and clino-enstatite 



