On Changes of Physical Constants which take place in certain Minerals and Igneous Rocks, on the Passage from the Crystalline to the Glassy State; with a short Note on Eutectic Mixtures

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Abstract
The effect of high temperatures on minerals and igneous rocks has long been a subject of geological research. De Saussure, in 1779, was the first to remark the fact that igneous rocks diminished in density on fusion, and became converted into a glassy substance. Further investigations as to these phenomena were made by Dolomieu in 1788, Sir James Hall in 1790, Magnus in 1831, and Bischof in 1841. The work of these early observers inspired Delesse in 1846 to publish an important paper on the glasses formed by the fusion of igneous rocks. This paper gives a good idea of the methods employed, at a time when electrical heating was an unknown factor in scientific research. With the improved appliances of modern science, the number of investigators has so greatly increased that it is only possible to mention the more recent researches of Barus, Dœlter, Joly, Teall, Cusack, Bakhuis Roozeboom, Vogt, Åkerman, Allen, and Day. At the present time, every well-appointed laboratory has its electrical installation, and high temperatures may thereby be easily attained. As I had a strong current at my disposal. Prof. Sollas suggested that I should melt certain minerals and igneous rocks by means of a simple platinum-resistance, and endeavour to redetermine the change of specific gravity which accompanies their fusion. In the following paper I have given a brief account of some experiments on the fusion of igneous rocks, and the determination of their specific gravities in the glassy state; I have also added a few

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