128 Day and Allen — Isomorphism and Thermal 



Specific Gravities of Artificial, Crystalline Feldspars. 



An AbjAn 5 AbiAn 2 AbjAih Ab 2 An 1 Ab 3 Aiii Ab Ab 



(First Deter- (Cor- 



mination) rected) 



j 2'764 I 2*734 j 2'710 j 2-680 ( 2'660 j 2'650 j 2-620 2*607 

 (2-765 "j 2-734 (2-708 (2*680 \ 2*660 ( 2'648 C ( 2-620 



( 2-660 



a 2-767 j 2-732 , j 2-710 , j 2*679 , j2'659 ,j 2614 2-601 

 a ) 2-732 °\ 2-710 °\ 2-677 ( 2'660 a (2-615 



/ 2-612 



a 2-734 e 2*604 #2*605 



Mean 2-765 2-733 2-710 2-679 2*660 2*649 2*605 



Specific Gravities of Feldspar Glasses. 



j 2'700 j 2*647 j 2-593 j 2'533 j 2*482 j 2* 



( 2-700 ( 2-649 ( 2-594 ( 2*534 ( 2*482 ( 2* 



j 2-648 j 



( 2-647 ( 



j 2-648 j 



( 2-649 \ 



458 j 2-383 



459 / 2-382 

 2-591 a 2-485 

 2-591 

 2590 

 2-588 



( 2-647 

 "j 2-647 



Mean 2*700 2-648 2*591 2-533 2'483 2-458 2*382 



Determinations in duplicate are enclosed in brackets. 



a. Another preparation. 



b. Same material reheated for several days at temperatures 

 about 150° below the melting point. 



c. Contained about 0-8 per cent of sodium tungstate. 



d. Purified by warming with dilute hydrochloric acid, then 

 with water, and afterwards with ammonia. 



e. Purified by fusion with acid sodium sulphate. 



f. Assuming the residual tungsten to be present as Na 2 W0 4 . 



g. Assuming the residual tungsten to be present as W0 3 . 



Sintering. — Incidental to this work upon the relation 

 between the feldspars, we made a great many observations 

 npon the sintering of powdered minerals, both crystalline and 

 vitreous, of natural and artificial composition. While the 

 results have not enabled us to offer positive conclusions of 

 importance, they are worth a note in passing, 



Powdered glasses sinter slowly or rapidly several hundred 

 degrees below the melting temperature of crystals of the same 

 composition. When the viscosity is relatively slight (anorth- 

 ite) crystallization begins at a low temperature and proceeds 

 very rapidly, the sintering probably being due to the inter- 

 weaving of the crystal fibers during their formation. In vis- 

 cous glasses (albite) sintering also begins at low temperatures, — 



