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Some years after the cessation of the physical research work of Hallock and Barus for the U.S. Geological Survey, which had been inaugurated by Clarence King, and which had been discontinued because of insufficient appropriations by Congress, similar work was resumed by Arthur L. Day under the direction of George Becker in a small laboratory in the Survey building. One of the first problems attacked was that of the soda-lime-feldspars as products of dry fusion of their chemical components. It was proposed to demonstrate the correctness of Tschermak's theory of isomorphous mixtures of albite and anorthite molecules in the formation of a continuous series of soda-lime-feldspars (Tschermak, 1865), an assumption long since accepted as a fact by students of the microscopical characters of zonal plagioclases in rocks. It was proposed also to determine the physical constants of definite mixtures of the end molecules of the series.

One of the first obstacles encountered, as I recollect it, was the impossibility of producing crystals of pure albite from a dry melt by any process at Day's command, and the doubt in that physicist's mind whether albite ever occurred in nature as a crystallization from an igneous magma, assuming that molten rock magmas were dry molten liquids. Subsequently, the high viscosity of albite substance at the conversion point from crystal to amorphous glass was demonstrated, the effects of admixture of other substances upon melting point and viscosity were taken into account, and the doubts of pyrogenetic albite were

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