576 MINERALOGY 



is red while hot, yellow while cooling, finally smoky-brown when 

 cold. There are many oxides which interfere with the bead reac- 

 tion for iron, and there are other elements which yield nearly the 

 same colors. The table of bead reactions on page 594 must be 

 consulted. Bead reactions in combination with the magnetic 

 test below will serve to identify the presence of iron. 



b. Magnetism. Compounds of iron when ground finely and 

 treated on coal in R. F. become magnetic ; this is especially so if 

 fused with soda on coal, the fusion washed in the mortar, when 

 the black residue will be magnetic. It must be remembered that 

 cobalt and nickel become magnetic also ; however, these, if present, 

 can easily be detected by their bead reactions. In testing the 

 residue after reduction it should be cold and in fine powder ; spread 

 out on a white paper, the magnet is passed carefully over it; if 

 magnetic, particles should move to the magnet. Particles may 

 stick to the magnet from moisture or other causes and still not 

 be magnetic. 



Illustration. For the above tests use hematite, Fe 2 3 . 



Uranium, U. Atomic weight, 238.5. 



a. Bead reaction. The colors of uranium oxides in borax are 

 like iron ; in S. Ph. uranium oxide is yellow while hot, yellowish 

 green on cooling in O. F. ; in R. F. the bead is a fine green when 

 cold. Chromium, vanadium, and molybdenum also give green 

 beads in R. F. 



6. Wet test. Dissolve the powdered mineral in HC1, or if 

 insoluble first fuse with soda, nearly neutralize the free acid with 

 ammonia, then add a solution of sodium carbonate until a precipitate 

 ceases to form, then half as much more, let stand. Uranium at 

 first precipitated is redissolved in the excess of sodium carbonate 

 and will be found on filtering in the filtrate. Acidify the filtrate 

 with HC1, boil to expel CO 2 , add an excess of ammonia, when 

 yellow ammonium urinate, (NH 4 ) 2 U 2 07, will precipitate. This is 

 filtered and tested for the bead reaction as above, or dissolved 'in 

 1 cc. of dilute H 2 SO 4 , a small scrap of zinc added, which reduces 

 the uranium, yielding at first blue, turning finally to green. If 

 the green solution is poured off the zinc, in another test tube, and 

 hydrogen peroxide added, then sodium carbonate in excess, the 

 solution will assume a cherry-red color ; this is a very delicate test 

 for uranium. 



Illustration. Use powdered uraninite. 



Vanadium, V. Atomic weight, 51. Fusing point, 1680 C. 



