Polytechnic Association Proceedings. 835 



rily complicated, and the tube, this favorite monster of English 

 engineering, is not forgotten. 



CRYOLITE AND ITS USES. 



BT DR. ADOLPH OTT. 



The mineral cryolite was first discovered in 1825, by Giescke, at 

 Arksutfiord, in West Greenland, where it occurs in veins of gneiss. 

 It is found associated with pachuolite, iron pyrites, spathic iron, and 

 galena. According to Bischof it is one of those secondary fluorides; 

 from which it is probable that it originated from decomposed glim- 

 mer. It consists of 54.5 per cent Fl.; 32.5 per cent Na.; and 13 

 per cent Al.; and its chemical formula is expressed by 3 Na F1+ 

 AL Flc- Cryolite belongs to the trimetric system, like chiolite (of 

 the form: 3 Va F1+2A1, FI3), chodneffite (2 Na FI+AI2 FI3), and 

 pachnolite (51.15 p. c. Fl, 17.44 p. c. Ca, 12.04 Na, 10.37 Al, 8.63 

 HO.), minerals very similar to it in its chemical composition. It is of a 

 vitreous luster, a snow-white color, translucent and brittle; fusible in 

 the flame of a candle, and before the blowpipe it is decomposed, fluate 

 of soda being absorbed b}^ the charcoal, while the crust of alumina 

 remains behind. Its specific gravity varies from 2.816 to2.943. 



Henry Rose, in Berlin, was the first who recommended the use 

 of cryolite for the manufacture of aluminium, for which purpose it 

 was then exported to a large extent, but only a few years since a 

 variety of diaspor, called bauxite, was substituted for it, which is 

 found in almost inexhaustible beds in Southern France. Cryolite 

 is now chiefly employed for the manufacture of caustic, carbonate, 

 aluminate, and bicarbonate of soda, and sulphate of alumina. In 

 fusing the cryolite together with a certain proportion of silica, it 

 forms what is called hot cast porcelain, a product recently intro- 

 duced into market by the Atlantic Quartz Company, in West Phila- 

 delphia. In the Patent Record of the United States, we find also 

 a mixture consisting of cryolite, silica, and borax, claimed for the 

 welding of iron and steel. 



For the production of carbonate of so<la, cryolite is treated in 

 the drj^, but for the production of caustic soda in the wet wa}-. 

 Both processes are carried on to a large extent by the Penns}^- 

 vania Salt Manufacturing Company, in Natrona, on the Alleghany 

 river. Thereby aluminate of soda results as an intermediary, and 

 hydrate of alumina as a secondary product. The latter is generally 

 converted into sulphate of alumina, a salt largely used as a mordant 

 in dyeing and calico printing. 



