Properties of the Feldspars. 115 



heating merely acts to change the general inclination of the 

 curve but not to emphasize the absorption of heat. 



By way of conveying a concrete impression, it may be added 

 that Ab 3 An a just above its melting temperature resists the intro- 

 duction of a stout platinum wire (l*5 mm diameter) unless the 

 cold wire is thrust in very quickly and vigorously. If the wire 

 is first allowed to become hot in the furnace, it will give 

 way itself instead. No acceleration of the melting process 

 tending to sharpen the break in the curve appears to be possi- 

 ble without the introduction of new substances or new con- 

 ditions (water vapor under pressure for example) which would 

 take the experiment outside the definition of a " dry melt." 

 We have undertaken some preliminary experiments in these 

 directions, but they belong to another phase of the subject. 



A number of efforts were made to locate the melting tem- 

 perature of AbgAiij, which are given in the list below. 

 Although two days were required to crystallize each charge of 

 the material sufficiently for a determination, the recorded 

 numbers possess but little significance, as will be clear from 

 the foregoing. 



AB3AN1 



First Preparation. 







Electromotive Temper- 



Date. 



Element. 



Force in MV. attire. Kemarks. 



Nov. 23, 1903 



A 





1325° 



" 25, " 



A 





13415 1336 



" 28, " 



A 





13698 1359 



Dec. 26, " 



A 





13319 1328 



Jan. 14, 1904 



No. 3 





13893 1370 





Mean 1344° 





Second 



Preparation. 



Mch. 11, 1904 



A 





13218 1320 



" 14, " 



No. 3 





13469 1335 



1329° 

 Approximate melting temperature 1340°. 



Ab i An 1 . — With Ab 4 An 1 a third proof of the identity of 

 composition of the first crystals to separate and the vitreous 

 residue was obtained. The optical identification of this feld- 

 spar is absolute. If we could obtain crystals at all in a melt 

 of this chemical composition, therefore, it would offer a crucial 

 test of the relation of the solid and liquid phases in a part of 

 the curve where no melting point or specific gravity determi- 

 nation upon crystals was possible. After some days of nearly 

 continuous heating at a temperature somewhat below its 

 assumed melting point, a few crystals of Ab 4 An x were obtained 

 and identified. 



