ery of bismuth" or "subnitrate of bismuth" of
pharmacy, and under the name of pearl white, _blanc d'Espagne_ or
_blanc de fard_ has long been used as a cosmetic.

_Sulphides_.--Bismuth combines directly with sulphur to form a,
disulphide, Bi2S2, and a trisulphide, Bi2S3, the latter compound being
formed when the sulphur is in excess. A hydrated disulphide,
Bi2S2.2H2O, is obtained by passing sulphuretted hydrogen into a
solution of bismuth nitrate and stannous chloride. Bismuth disulphide
is a grey metallic substance, which is decomposed by hydrochloric acid
with the separation of metallic bismuth and the formation of bismuth
trichloride. Bismuth trisulphide, Bi2S3, constitutes the mineral
bismuthite, and may be prepared by direct union of its constituents,
or as a brown precipitate by passing sulphuretted hydrogen into a
solution of a bismuth salt. It is easily soluble in nitric acid. When
heated to 200 deg. it assumes the crystalline form of bismuthite.
Bismuth forms several oxysulphides: Bi4O3S constitutes the mineral
karelinite found at the Zavodinski mine in the Altai; Bi6O3S4 and
Bi2O3S have been prepared artificially. Bismuth also forms the
sulphohaloids, BiSCl, BiSBr, BiSI, analogous to the oyxhaloids.

Bismuth sulphate, Bi2(SO4)3, is obtained as a white powder by
dissolving the metal or sulphide in concentrated sulphuric acid. Water
decomposes it, giving a basic salt, Bi2(SO4)(OH)4, which on heating
gives (BiO)2SO4. Other basic salts are known.

Bismuth forms compounds similar to the trisulphide with the elements
selenium and tellurium. The tritelluride constitutes the mineral
tetradymite, Bi2Te3.

_Analysis_.--Traces of bismuth may be detected by treating the
solution with excess of tartaric acid, potash and stannous chloride, a
precipitate or dark coloration of bismuth oxide being formed even when
only one part of bismuth is present in 20,000 of water. The blackish
brown sulphide precipitated from bismuth salts by sulphuretted
hydrogen is insoluble in ammonium sulphide, but is readily dissolved
by nitric acid. The metal can be reduced by magnesium, zinc, cadmium,
iron, tin, copper and substances like hypophosphorous acid from acid
solutions or from alkaline ones by formaldehyde. In quantitative
estimations it is generally weighed as oxide, after precipitation as
sulphide or carbonate, or in the metallic form, reduced as above.

_Pha