Mr. William Phillips on the Oxyd of Tin, 351 



Electricity — the coloured portions, when placed in communication 

 with an electrified conductor, emit bright sparks on the approach 

 of the finger. Haiiy. 



Colour — whitish, either translucent or opake ; it is sometimes of a 

 resin yellow, but more often of a deep brown somewhat reddish, 

 more frecpently 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 com- 

 mon 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 Abbe Haiiy in his " Traite de Mineralogie" 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 octo- 

 hedron composed of the two quadrilateral pyramids commonly seen 



