more rapidly in moist air or when heated. In the last
case it becomes coated with a greyish-black layer of an oxide (dioxide
(?)), at a red heat the layer consists of the trioxide (Bi2O3); and is
yellow or green in the case of pure bismuth, and violet or blue if
impure; at a bright red heat it burns with a bluish flame to the
trioxide. Bismuth combines directly with the halogens, and the
elements of the sulphur group. It readily dissolves in nitric acid,
_aqua regia_ and hot sulphuric acid, but tardily in hot hydrochloric
acid. It is precipitated as the metal from solutions of its salts by
the metals of the alkalis and alkaline earths, zinc, iron, copper, &c.
In its chemical affinities it resembles arsenic and antimony; an
important distinction is that it forms no hydrogen compound analogous
to arsine and stibine.

_Alloys_.--Bismuth readily forms alloys with other metals. Treated
with sodammonium it yields a bluish-black mass, BiNa3, which takes
fire in the air and decomposes water. A brittle potassium alloy of
silver-white colour and lamellar fracture is obtained by calcining 20
parts of bismuth with 16 of cream of tartar at a strong red heat. When
present in other metals, even in very small quantity, bismuth renders
them brittle and impairs their electrical conductivity. With mercury
it forms amalgams. Bismuth is a component of many ternary alloys
characterized by their low fusibility and expansion in solidification;
many of them are used in the arts (see FUSIBLE METAL).

_Compounds_.--Bismuth forms four oxides, of which the trioxide, Bi2O3,
is the most important. This compound occurs in nature as bismuth
ochre, and may be prepared artificially by oxidizing the metal at a
red heat, or by heating the carbonate, nitrate or hydrate. Thus
obtained it is a yellow powder, soluble in the mineral acids to form
soluble salts, which are readily precipitated as basic salts when the
solution is diluted. It melts to a reddish-brown liquid, which
solidifies to a yellow crystalline mass on cooling. The Hydrate,
Bi(OH)3, is obtained as a white powder by adding potash to a solution
of a bismuth salt. Bismuth dioxide, BiO or Bi2O2, is said to be formed
by the limited oxidation of the metal, and as a brown precipitate by
adding mixed solutions of bismuth and stannous chlorides to a solution
of caustic potash. Bismuth tetroxide, Bi2O4, sometimes termed bismuth
bism