128 A POPULAR TREATISE ON GEMS
glass,
fine emerald-green when cold, though when hot often yellowish or
reddish. Its solutions are usually green, and the metal is thrown down
by potassa as a bluish-green by-, drate, again dissolved in excess of
the alkali. The chrome in many minerals is very certainly discovered by
melting the assay with three times its bulk of saltpetre, which,
dissolved in water, gives with acetate of lead a yellow precipitate.
Vanadium, melted
on platinum wire with borax or salt of phosjshorus, gives a fine green
glass in the reducing flame, which becomes yellow or brown in the
oxidating flame, distinguishing it from chrome.
Uranium, with
salt of phosphorus, forms in the oxidating flame a clear yellow; in the
reducing flame a fine green glass. With borax its reaction'is similar
to that of iron.
Molybdenum forms in the reducing flame, with salt of phosphorus, a green ; with borax, a brown, glass. .
Tungsten or Wolfram forms,
with salt of phosphorus, in the oxidating flame, a colorless or yellow,
in the reducing flame, a very beautiful blue glass, which appears green
when warm. "When accompanied by iron, the glass is blood-red, not blue.
Or melt the assay with five times as much soda in a platinum spoon,
dissolve it in water, filter, and decompose the result with
hydrochloric acid, which throws down the tungstic acid, which is white
when cold, but citron-yellow when heated.
Tantalium, as tantalic acid, is readily dissolved by salt of phosphorus, and in large quantity into a colorless glass, " which does not become opaque in cooling, and does not acquire
a blue color from solution of cobalt. Or fuse the assay with two times
as much saltpetre, and three times as much soda, in a platinum spoon;
dissolve this, filter, and decompose the fluid by hydrochloric acid:
the tantalic acid separates as a white powder, which does not become yellow when heated.
