58 



ISOMORPHISM AND THERMAL PROPERTIES OF FELDSPARS. 



The specific gravities of the glasses and of so many of the crystalline 

 mixtures as we could obtain are tabulated below: 



Specific Gravities of Artificial Crystalline Feldspars. 



[Determinations in duplicate are braced together.] 



An. 



AbiAn 5 



(2.764 (2.734 

 (2. 765 (2.734 



0,2 . 767 



Ab,An.,. 



AbjAni. 



2.710 J2.6SO 



2.-08 : (2.680 



a _f2. 73 2 , J2.7IO 

 '2. 732 '2.710 



A2.734 



Mean 2.765 2.733 



10 



b\ 2 p 9 

 (2.677 



2.679 



Ab,An, 



(2 .660 

 2.660 

 2. 660 



U2.659 

 ( 2 . 660 



2.660 



AbaAnj. 



(2 .650 

 "< 2 . 648 



.649 



Ab. 



First de- 

 termina- 

 tion. 



' 2 . 620 



1 2.620 



.(2.614 2.601 

 (2.61.S 



'5 

 e2 . 604 



Corrected, 



2.607 



I 2.612 

 g 2 . 605 



2 605 



Specific Gravities of Feldspar Glasses. 



(2.700 (2.647 

 "( 2 . 700 { 2 . 649 



(2.648 

 "(2.647 



(2.648 

 1 2 . 649 



(2.647 

 (2.647 



(2 



"(2 



(2 

 12 



< 2 

 "(2 



593 

 594 



59i 

 59i 



590 



588 



Mean 2.700 



64S 



2-591 



( 2.533 

 (2-534 



(2.482 

 "(2.482 



<Z2 



485 



533 



2-483 



(2.458 

 (2.459 



2-383 

 2.382 



2.458 2.382 



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. 



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



g Assuming the residual tungsten to be present as WO,. 



SINTERING. 



Incidental to this work upon the relation between the feldspars, we 

 made a great many observations upon the sintering of powdered min- 

 erals, both crystalline and vitreous, of natural and artificial composi- 

 tion. While the results have not enabled us to offer positive conclu- 

 sions of importance, they are worth a note in passing. Powdered 

 glasses sinter slowly or rapidly several hundred degrees below the melt- 

 ing temperature of crystals of the same composition. When the vis- 



