INSTRUMENTS \\i> CHEMICAL Tl.STS 577 



a. Bead reaction. - When dissolved in borax, oxides of vana- 

 dium arc yellow to yellowish green in O. F. while hot, nearly 

 colorless when cold. In R. F. a dirty green when hot and a fine 

 given when cold. The S. Ph. bead is yellow in O. F., fine green 

 in H. K. when cold. 



l>. Wet test. - The well-roasted mineral is fused with 4 parts 

 soda and 2 of niter, the fusion is dissolved in boiling water and 

 any insoluble residue filtered off; the soluble alkali vanadates will 

 be found in the filtrate ; this is acidified with acetic acid, and lead 

 acetate added, which will precipitate the vanadium as lead vana- 

 date, Pb s (VO^, yellow at first, but soon turning white ; this 

 precipitate may be tested in the S. Ph. bead as above. Molyb- 

 denum and chromium will also yield yellow precipitates with lead 

 acetate, and green beads with S. Ph. To separate vanadium 

 from these, the solution of alkali vanadate from the soda fusion 

 is not acidified with acetic acid, but solid ammonium chloride is 

 added to almost saturation, when upon standing for some time 

 ammonium metavanadate, NH 4 V0 3 , will separate as a slightly 

 yellowish crystalline precipitate ; filter and wash with ammonium 

 chloride solution. If this precipitate is heated in a porcelain 

 crucible, the ammonia is driven off, leaving a red residue, pentoxide 

 of vanadium, V 2 O 5 . If it is wished to further test this residue, 

 it may be dissolved in HC1 and reduced with zinc ; the solution, 

 yellow at first, quickly becomes green and finally blue ; the blue 

 poured off the zinc, and hydrogen peroxide added, becomes red. 



Illustration. Use oxide of vanadium. 



Thallium, Tl. Atomic weight, 204. Fusing point, 301.7 C. 



Indium, In. Atomic weight, 114.8. Fusing point, 155.3 C. 



Gallium, Ga. Atomic weight, 69.9. Fusing point, 30.15 C. 



These three very rare elements are associated in some sphalerites. 

 Of the three thallium alone occurs in large enough quantities to 

 characterize two rare minerals as thallium minerals, crookesite 

 and lorandite. 



They are best detected with the spectroscope. 



Thallium yields a bright green flame. Its salts are volatile, 

 and when in R. F. on coal it yields a white oxide coat. If mixed 

 with von Kobell's flux, it yields a lemon-yellow coat very similar 

 to lead; the bright green flame will, however, distinguish it from 

 lead. 



2p 



