MELTING POINTS AND MELTING INTERVALS 



15' 



amine the distribution of heat in a crucible containing a pure mineral 

 whose melting point requires to be determined. In a cylindrical furnace 

 in which heat is supplied to the charge from the sides (the usual case, 

 figure 3) its outermost layer will be the first to receive heat, and through 

 this layer heat will be transmitted to the inner layers somewhat slowly, for 

 most minerals conduct heat but poorly when compared with familiar 

 metals. The same analysis shows that heat leaves the crucible for the 

















< 











c 



^ 



-1/ 

























c 

 < 





J2 

 < 



i 



4~ 

























/ 

































/ 





/ 





























/ 





/ 































/ 





/ 























J 







c/ 







/ 



























y 



/ 





y 





r 



c 





> 



-' 









>> 

















y 



-^ 







/ 











5, 



3 















/ 









/ 









1 

















/ 









/ 









1 



f\ 





> 

 5 











/I 











/ 







/ 



1 



' 





s 











/ 









/ 









/ 



1 







. 



















/ 









/ 



/ 







E 



















/ 







1 





/ 







7 

















1 









/ 





/ 







3 

























/ 





/ 







^ 









ja 

















/ 



1 









e 







1 











a 







a 





a 



































/ 



































/ 































1 





/ 



































































i 



































/ 



































_/_ 











Time - I division = 5 minutes 



Figure 2. — Melting Curves of the Feldspars 



Taken from Day and Allen : "The Isomorphism and Thermal Properties of the Feld- 

 spars." Publications of the Carnegie Institution of Washington, No. 31. The melting 

 intervals are (roughly) included between the letters a c of each curve. A typical metal 

 melting curve (silver) is included for comparison. 



most part through the top and bottom layers in the same order. iVt the 

 beginning of melting around the periphery, therefore, the center of the 

 charge has a lower temperature, and has not begun to melt. The exposed 

 upper surface is colder still. If the material has a very high melting point 

 these gradients may be steep. Suppose that we have decided not to depend 



XII— Burx. Geol. Soc. Am., Vol. 21, 1900 



