46 ISOMORPHISM AND THERMAL PROPERTIES OF FELDSPARS. 



portions of the work of Hautefeuille and Lenarcic, but were obliged 

 to postpone a systematic inquiry into the conditions of crystallization, 

 which involved the addition of other components or extraordinary 

 pressures, until our plant could be somewhat extended. 



Hautefeuille describes his successful preparation as a "solution" of 

 the alkaline alumino-silicate in sodium tungstate, out of which the 

 albite slowly crystallizes after long heating, but he remarks that the 

 crystallization does not take place if the mixture is heated sufficiently 

 to melt the components of the charge into a homogeneous glass. In 

 that case he obtained only a vitreous white enamel. His case does 

 not appear, therefore, to be one of simple solution, out of which the 

 same solid phase always reappears upon reproducing given conditions 

 of temperature and concentration. On the contrary, as Hautefeuille 

 describes the experiment, the components of the albite remain as inde- 

 pendent solid phases, which are then assembled in some manner 

 through the intermediary action of the melted tungstate. 



Notwithstanding the fact that our interest was confined for the 

 moment to the mere production of a small quantity of chemically pure 

 crystalline albite, we ventured to proceed along the lines of Haute- 

 feuille's unsuccessful trial. We first prepared a chemically pure 

 albite glass, i. e., we melted the components into a homogeneous mass 

 before adding tungstate. This glass was then finely powdered, thor- 

 oughly mixed with an excess of powdered sodium tungstate, and 

 maintained continuously for 8 days at noo. Upon removing from 

 the furnace at the close of the heating, both albite and tungstate were 

 found to have been completely melted and to have separated into two 

 distinct layers according to their specific gravities, the albite glass 

 being above, and showing no trace of crystallization. A second charge 

 was then prepared with equal parts of tungstate and albite, powdered 

 and mechanically mixed as before, and maintained at a temperature 

 of 900 for 1 7 days. This time we were successful. After the sodium 

 tungstate had been dissolved away with water, the albite appeared as 

 a powder of about the fineness to which it had originally been pulver- 

 ized, except that the fragments were now crystalline and apparently 

 homogeneous albite. In thin section, under the microscope, to our 

 considerable surprise, it appeared that the original glass fragments 

 were unchanged in form. The bounding surfaces were all conehoidal 

 fractures, as they came from the hammer, and evidently had not been 

 in solution with the tungstate at all. Its optical properties showed it 

 to be undoubted albite and the specific gravity was 2.620. 



The preparation of albite which we had synthesized by heating 

 with an equal weight of sodium tungstate was first purified by thor- 



