e case of preparing the pure metal or
its salts for pharmaceutical or chemical purposes. The basic nitrate
is the salt generally prepared, and, in general outline, the process
consists in dissolving the metal in nitric acid, adding water to the
solution, boiling the precipitated basic nitrate with an alkali to
remove the arsenic and lead, dissolving the residue in nitric acid,
and reprecipitating as basic nitrate with water. J.F.W. Hampe prepared
chemically pure bismuth by fusing the metal with sodium carbonate and
sulphur, dissolving the bismuth sulphide so formed in nitric acid,
precipitating the bismuth as the basic nitrate, re-dissolving this
salt in nitric acid, and then precipitating with ammonia. The bismuth
hydroxide so obtained is finally reduced by hydrogen.

_Properties._--Bismuth is a very brittle metal with a white
crystalline fracture and a characteristic reddish-white colour. It
crystallizes in rhombohedra belonging to the hexagonal system, having
interfacial angles of 87 deg. 40'. According to G.W.A. Kahlbaum, Roth
and Siedler (_Ziet. Anorg. Chem. 29_, p. 294), its specific gravity is
9.78143; Roberts and Wrightson give the specific gravity of solid
bismuth as 9.82, and of molten bismuth as 10.035. It therefore expands
on solidification; and as it retains this property in a number of
alloys, the metal receives extensive application in forming
type-metals. Its melting-point is variously given as 268.3 deg. (F.
Rudberg and A.D. von Riemsdijk) and 270.5 deg. (C.C. Person);
commercial bismuth melts at 260 deg. (Ledebur), and electrolytic
bismuth at 264 deg. (Classen). It vaporizes in a vacuum at 292 deg.,
and its boiling-point, under atmospheric pressure, is between 1090
deg. and 1450 deg. (T. Carnelley and W.C. Williams). Regnault
determined its specific heat between 0 deg. and 100 deg. to be 0.0308;
Kahlbaum, Roth and Siedler (_loc. cit._) give the value 0.03055. Its
thermal conductivity is the lowest of all metals, being 18 as compared
with silver as 1000; its coefficient of expansion between 0 deg. and
100 deg. is 0.001341. Its electrical conductivity is approximately
1.2, silver at 0 deg. being taken as 100; it is the most diamagnetic
substance known, and its thermoelectric properties render it
especially valuable for the construction of thermopiles.

The metal oxidizes very slowly in dry air at ordinary temperatures,
but somewhat