578 JV. L. Bowen — Melting Phenomena of 'the 



sened by the fact that the writer was able to use in the present 

 investigation the same artificial mixtures prepared by Day and 

 Allen. 



Experimental Part. 



Method of Working. 



An idea of the principle involved in quenching may be con- 

 veyed by a brief description of the method as practised. A 

 charge of a given composition is held at a measured temperature 

 for a definite period of time and is then quenched by allowing it 

 to fall into a dish of mercury at room temperature. The instan- 

 taneous chilling precludes any possibility of physical or chem- 

 ical readjustment in the charge ; any portion that was liquid 

 at the furnace temperature appears as glass, and any crystalline 

 portion remains, in general, unchanged in crystal form. Exam- 

 ination of the quenched charge under the microscope, then, 

 reveals those phases which were present at the furnace temper- 

 ature. The time of holding the charge at constant temperature 

 may be lengthened at will and equilibrium assured even in 

 extremely viscous materials. 



The furnace used in the present work was a platinum 

 resistance furnace, kept at constant temperature by regula- 

 ting a resistance in series with it. By constant watching, the 

 temperature could be held within one degree of the temper- 

 ature desired. The furnace thus becomes a high-temperature 

 thermostat. The junction of the thermoelement was within 

 seven or eight millimeters of the charge, which offered abun- 

 dant accuracy in a thermostat arrangement. 



This system (furnace and thermoelement) was calibrated by 

 quenching charges of substances of known melting points, lith- 

 ium metasilicate, diopside and anorthite, under like conditions. 

 The results of this calibration are tabulated below. In each 

 individual case the initial material was completely crystalline. 







Table I. 







Composition 



Temperature 

 microvolts 



Time 



Eesult 



Date 



Li,SiO s .... 

 Li 8 Si0 3 ___. 

 Li 2 SiO,.... 

 Li,Si0 3 .... 



._ 11820 

 . 11920 



.. 11950 

 . 11950 



1/2 hr. 

 1/2 hr. 



1/2 hr. 

 • 1/4 hr. 



cryst. 

 cryst. 



glass 

 glass 



Jan. 10, 1913 

 Jan. 10, 1913 

 Jan. 10, 1913 

 Jan. 10, 1913 



The melting-point therefore lies between 11920 and 11950 

 microvolts; value by standard element 11953 microvolts. Cor- 

 rection to be applied to quenching system is therefore, for 

 the present purpose, negligible. 



