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molecular combinations, without saturation, and solidification takes 

 the form of Van t'Hoff's "solid solution," namely an amorphous glass. 

 Rhyolite and trachyte magmas, with the A1 2 3 percentage vary- 

 ng from 6 to 20, were fused in large masses under varying conditions, 

 of cooling and for periods of a fortnight or more, solidifying invari- 

 ably as structureless glass; the same magmas, it will be remembered, 

 with an excess of alumina, developed the minerals of the corundum 

 group with the greatest ease. The attempts were repeated with fluorides 

 and phosphates added, but again without result. Finally success was 

 obtained by adding 1 per cent, of tungstic acid to a rhyolite mixture 

 of the following composition : 



A completely homogeneous glass was formed by the first fusion in 

 the hottest part of the furnace, and partial crystallization was obtained 

 by leaving the crucible at the inner mouth of the entrance chamber for 

 fourteen days — a temperature estimated to vary between 800 ° and 

 iooo C. A heterogeneous mass showing flow structures resulted, 

 yellow and white streaks alternating with bands of gray glass. In the 

 microscope the white zones proved to be aggregates of myriads of 

 bipyramidal quartz microlites, of hexagonal form, extinguishing 

 parallel to the vertical axis, and optically positive. The yellowish 

 streaks were much more abundant than the white, and proved to be 

 composed of hexagonal plates of biotite of very perfect form and show- 

 ing the truncated edges of the combination: (001) (in) (111) (o 11 ). 

 The absorption scheme, pleochroism, color, extinction and double 

 refraction all agree with the properties of biotite. Many of the crystals 

 show corrosion phenomena. Finally abundant aggregates of transparent 

 prisms were observed, sometimes in spherulitic grouping, with extinc- 

 tion usually parallel and occasional twinning. These were believed to 

 be sanidine. There were some other indeterminate colored grains and 

 spicular crystals. The groundmass was essentially an isotropic glass, 

 but showed a spicular microfelsitic structure. There had thus been 

 reproduced by " dry fusion," with the aid of tungstic acid, an association 



