162 DESCRIPTIONS OF MINERALS. 



Tin is also used extensively as tinfoil ; but most tinfoil consists be* 

 neath tbe surface of lead, and is made by rolling out plates of lead coated 

 with, tin. Witb quicksilver it is used to cover glass in tbe manufac- 

 ture of mirrors. Tin oxide (dioxide), obtained by cbemical processes, 

 is employed, on account of its bardness, in making a paste for sharp- 

 ening fine cutting instruments, and also to some extent in tbe prepara- 

 tion of enamels. Tbe chlorides of tin are important in tbe precipita- 

 tion of many colors as lakes, and in fixing and cbanging colors in dye- 

 ing and calico-printing. Tbe bisulphide bas a golden lustre, and was 

 termed aurum musivum, or mosaic gold, by tbe alchemists. It is much 

 used for ornamental painting, for paper-hangings and other purposes, 

 under the name of bronze powder. 



TITANIUM. 



Titanium occurs in nature combined with, oxygen, form- 

 ing titanium dioxide or titanic acid, and also in oxygen com- 

 binations with iron and calcium, and in some silicates. It 

 has not been met with native. 



The ores are infusible alone before the blowpipe, or nearly 

 so. Their specific gravity is between 3-0 and 4*5. 



Rutile. 



Dimetric. In prisms of four, eight, or more sides, with 

 pyramidal terminations, and often bent as in 

 the figure; 1a1 = 123°7£\ Crystals often 

 acicular, and penetrating quartz. Some- 

 times massive. Cleavage lateral, somewhat 

 distinct. 



Color reddish-brown to nearly red ; streak 

 very pale brown. Lustre submetallic-ada- 

 mantine. Transparent to opaque. Brittle. 

 H. =6-6-5. G. =4-15-4 -25. 



Composition. Ti 2 = Oxygen 39, titanium 61 = 100. 

 Sometimes contains iron, ancf has nearly a black color ; this 

 variety is called Nigrine. B. B. alone unaltered ; with salt 

 of phosphorus a colorless bead, which in the reducing flame 

 becomes violet on cooling. 



Diff. The peculiar subdamantine lustre of rutile, and 

 brownish-red color, much lighter red in splinters, are striking 

 characters. It differs from tourmaline, idocrase, and augite, 

 by being unaltered when heated alone before the blowpipe ; 

 and from tin ore, in not affording tin with soda ; from 

 sphene in its crystals. 



