Properties of the Feldspars. 99 



Mitchell Co., North Carolina, a quantity of which was placed 

 at our disposal by the U. S. National Museum. The material 

 was powdered so as to pass readily through a 100-mesh 

 sieve, and placed in 100 cc or 125 cc platinum crucibles, some- 

 times open and sometimes covered, in charges of from 100 to 

 150 grams. These charges were heated slowly in the electric 

 furnace from 600° to above 1100° C, but, although the thermal 

 apparatus was sufficiently sensitive to detect an unsteadiness of 

 a tenth of a degree with certainty, not the slightest trace of an 

 absorption or release of heat was found. The charge at the 

 beginning of the heating was a dry crystalline powder, which 

 was prodded from time to time with a stout platinum wire to 

 ascertain its condition as the heating progressed. At about 

 1000° traces of sintering were evident, at 1075° it had formed 

 a solid cake which resisted the wire, at 1150° this cake had 

 softened sufficiently to yield to continued pressure and at 1300° 

 it had become a viscous liquid which could be drawn out in 

 glassy, almost opaque threads by the wire. Under the micro- 

 scope the opacity was seen to be clue to fine, included bubbles, 

 the material being entirely vitreous. The cooling was equally 

 uninstructive ; the vitreous mass solidified gradually without 

 recrystallization or the appearance of any thermal phenomenon. 

 Frequent repetition with fresh charges and varied conditions 

 added nothing to our knowledge of the melting temperature, 

 and the matter began to look very unpromising. 



We also reheated charges of the resulting glass which was 

 sometimes repowdered and sometimes in the cake as it had 

 cooled. But except to Observe that the glass powder began to 

 sinter earlier (800°), no new facts appeared.* 



Then we tried by various means to recrystallize the melted 

 orthoclase. We mixed crystalline powder with the glass, we 

 applied successive quick shocks to the cooling liquid for several 

 hours with an electric hammer below the crucible, we varied 

 the rate of cooling and even tried rapid see-sawing between 

 800° and 1300°. We circulated air, water vapor, and car- 

 bonic dioxide through the charge throughout the heat- 

 ing, and finally introduced a rapid alternating current sent 

 directly through the substance while cooling, but no trace of 

 crystallization resulted. An extremely viscous, inert mass 

 always remained which gradually hardened into a more or less 

 opaque glass. It appeared somewhat translucent if very high 

 temperatures had been reached, but was never clear. 



Following orthoclase, a number of specimens of natural 

 albite were tried under similar conditions and with entirely 

 similar results. 



* These sintering temperatures varied within considerable limits with the 

 fineness of the material and therefore serve only in a very rough way to 

 define the state of the charges. 



