Properties of the Feldspars. 



123 



The black portions are glass. It is interesting to observe that 

 while the crystal has melted completely across, there has been 

 no displacement of the cleavage plane. 



The preceding 

 experiments gave a 

 clear idea of the phe- 

 nomena attending 

 the melting of albite 

 and orthoclase, and 

 convinced us that the 

 absorption of heat 

 accompanying fu- 

 sion, which we had 

 searched for in vain 

 upon the heating 

 curves in the earlier 

 experiments, had 

 eluded us merely 

 because it was ex- 

 tended over so long 

 a stretch of the curve 

 as not to be notice- 

 able. Some very 

 exact measurements 

 of the temperature 

 change from minute 

 to minute were 

 therefore made in 

 the hope that a more 

 intelligent search 

 might be more suc- 

 cessful. Separate 

 charges of glass and 

 of crystals of the 

 same composition 

 and of equal weight 

 were prepared and 

 successively heated 

 in the same furnace 

 with the same cur- 

 rent. The specific 

 heat is of course not 

 identical in the two 

 cases, but the curves were comparable in form. Above 1100° 

 we felt sure that one of the curves must contain an absorp- 

 tion of heat which would be absent from the other. Such 



1 













1 























1 















I 



































1 

























13000^ 

 (1290°) 













/ 



































/ 













/ 























/ 











/ 



/ 

























II 











/ 

























i 











f 





I 



/ 



/ 









12500 





















/ 







/ 





























; 



/ 





/ 























/ 













/ 

























/ 









1 







































/ 













/ 





1 9 000 









/ 











1 



/ 











/ 















/ 



f 



















/ 

















I 







1 



i 



l 



I 









// 



/ 



m 















\\ 







: 



1 









' 



'/ 



















!j 







' 



/ 





















11500 













1 





/ 











































'/ 



























i 



ii 









/ 





























I 



i 





1 



t 



























/ 



/ 







I 



















11000 



(1135°) 











/ 









I 



























/ 







/ 





























/ 



1 





/ 































i 







/ 





























i 





























10500 











/ 





























































, 









I 



/ 



I 



































/ 



























s 





































3 10000 









' 































1 





i 





1 

























3 







/ 





| 



























9500 



r 









/ 



























































:■ 





























c 



(1000°) 20 40 



Time (minutes). 



SO 



Fig. 10. 



100 120 140 160 



