T H E 



AMERICAN JOURNAL OF SCIENCE 



[FIFTH SERIES.] 



Art. I.— The Melting of Potash Feldspar; by G. W. 

 Moeey and N. L. Bowex. 



Introduction. 



While studying systems of the alkaline oxides with 

 silica, alumina, and water, the one of us (Morey) carrying 

 on the thermal and chemical work and the other (Bowen) 

 the optical examination, we succeeded in crystallizing 

 some pure artificial orthoclase in a bomb with no flux 

 other than water. Crystalline orthoclase, as hitherto pre- 

 pared artificially, has been contaminated somewhat by 

 the flux used in preparing it, and for this reason natural 

 crystals have always been used in determining the melting- 

 point of orthoclase. The natural crystals never have the 

 theoretical composition KAlSi 3 8 but always contain a 

 considerable amount of albite and sometimes other mole- 

 cules. We concluded, therefore, that the pure crystals 

 we had prepared would furnish good material for the 

 redetermination of the melting-point of orthoclase, a 

 point of much importance in the system under investi- 

 gation. 



The melting-point of orthoclase, as determined on 

 natural crystals, has been found to be in the neighborhood 

 of 1200" C. It has been found by Day and Allen to melt 

 very sluggishly. 1 We expected, therefore, that long 

 exposure to a given temperature would be necessary, 

 before assurance of the attainment of equilibrium might 

 be had. For such long exposures we have had the inesti- 

 mable advantage of the use of a furnace-temperature 

 regulator designed by our colleague, Mr. H. S. Roberts. 2 

 By means of this regulator we were enabled to maintain 



1 The isomorphism and thermal properties of the feldspars, Carnegie Insti- 

 tution of Washington, Pub. Xo. 31, pp. 51-53. 



2 J. Wash. Acad. Sei., 11, 401-409. 1921. 



Am. Jour. Sci.— Fifth Series, Vol. IV. No. 19.— July. 1922. 

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