THE NONMETALLIC MINERALS. 387 



?Zsvw. — The rare oloments coriuni, zircoiiium, thorium, yttrium, 

 lanthanium, etc., which are as a rule associated with eacii other in the 

 minerals cerite, zircon, monazite, samarskite, etc., as described, find 

 their commercial use not in the form of metals, l)ut as oxides only; 

 and it is only since the introduction of the Welshach incandescent 

 system of lighting that their use in this form has assumed aii}^ com- 

 mercial importance. 



This Welsbach light consists of a cap or hood to gas or other l)urners, 

 to increase- their illuminating powers. The cap is made of cotton or 

 other suitable material, impregnated with the oxides in proportions 60 

 per cent zirconia, 20 per cent 3'ttria, and 20 per cent lanthanum. The 

 fabric is strengthened and supported with fine platinum wire and 

 suspended in the fiame. On igniting in the flame the fabric is quickly 

 reduced to ash, the cotton being burnt away and the earthy matter 

 still retaining the form of a cap or hood.^ 



The drawback to the use of these oxides has been, it is said,'^ the 

 great difficulty in obtaining them in a pure condition. Several methods 

 have been used, but usually with poor results, especially when the 

 mineral contains iron. 



The demand for the minerals of this group being so limited there is 

 no regular market price. The Mineral Industry for 1893 quotes zir- 

 con at 10 cents a pound, monazite 25 cents, and samarskite 50 cents. 

 It is stated that 1 ton of zircon will }deld sufficient zirconia for half a 

 million Welsbach burners. 



BIBLIOGRAPHY. 



See paper on Monazite, by H. B. C. Nitze, in Mineral Resources of the United States, 

 Part. 4, of the Sixteenth Annual Report U. S. Geological Survey, 1894-95, pp. 667-693. 

 This contains a very satisfactory bibliography down to date of publication. Also 

 see Les Terres Rares Mineralogie- Properties Analyse, by P. Truchot. Carre et Naud. 

 Paris, 1898. 



3. Vanadinite. 



This is a vanadinate and chloride of lead of the formula (PbCl) 

 Pb^VjOi.,, = Vanadium pentoxide 19. -1 per cent; lead protoxide 78. 7 per 

 cent; chlorine 2.5. In nature often more or less impure through the 

 presence of arsenic and traces of iron, manganese, zinc, and lime. 

 Color deep red to brown and straw-yellow % resinous luster; translucent 

 to opaque. Hardness 2.75 to 3. Gravity 6.66 to 7.23. When a drop 

 of nitric acid is applied to a particle of a crystal there is soon formed 

 a yellow^ coating of vanadic oxide. This reaction is quite characteristic 

 and furnishes an easy and convenient means of determination. 



Localities and mode of occurrence. — Occurs in prismatic crystals with 

 smooth faces and sharp edges; crystals sometimes cavernous at the top, 



' .Tdui-nal of the Society of Chemical Industry, V, 1886, p. .522. 

 -Mineral Resources of the United States, 1885, p. 393. 



