Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/361

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351
Mr. William Phillips on the Oxyd of Tin.
Electricity—the coloured portions, when placed in communication with an electrified conductor, emit bright sparks on the approach of the finger. Haüy.
Colour—whitish, either translucent or opake; it is sometimes of a resin yellow, but more often of a deep brown somewhat reddish, more frequently blackish, or black; occasionally brick-red, but in that case generally bears in some respect marks of having been exposed to the action of fire.
Transparency—the-more colourless crystals are generally somewhat transparent, in which respect they sometimes almost equal common quartz.
Lustre—resinous or vitreous.
Dust—of a dull ash grey.
Analysis—77,5 tin, 21,5 oxygen, 0,25 oxide of iron, 0,75 silex. Under the blowpipe it decrepitates; becomes pale and opake; is reducible in part to a metallic state, but with difficulty. When heated and melted with glass, it imparts to it a milk white colour.—Brongniart.
Primitive Crystal.

The Abbé Haüy in his “Traité de Minéralogie” assigned the cube to the oxyd of tin as its primitive form, because he thought he “ perceived the natural joints parallel with the faces of that solid, although they were not sufficiently determinate to remove all doubt.” This opinion was combated by Mr. Day in a paper on this substance, published in an early volume of the Philosophical Magazine, in which he assumed as its primitive crystal an octahedron composed of the two quadrilateral pyramids commonly seen