METALS. 
57 
and consisting of a double fluoride of aluminium and sodium, 
which, when heated with metallic sodium and common salt, 
yields aluminium. Another source of the metal is found in 
Bauxite , a mineral orginally obtained from Beaux, in the south 
of France, and composed chiefly of alumina and peroxide of iron. 
A series illustrating the preparation of aluminium from bauxite, 
as formerly carried on at the Washington Aluminium Works, is 
here exhibited. By heating a mixture of bauxite and soda-ash 
an aluminate of soda is obtained, and from a solution of this salt, 
alumina in the state of hydrate may be precipitated by an acid. 
A mixture of this precipitated alumina with common salt and 
charcoal is treated with chlorine, and from the double chloride 
of aluminium and sodium thus formed, metallic aluminium is 
obtained by the reducing action of sodium. 
At the present time aluminium is largely obtained by various 
electrical processes. In Cowle’s method, a mixture of alumina, 
carbon and copper is subjected to the current of a powerful 
dynamo, whereby an alloy of aluminium and copper is obtained, 
forming the well-known aluminium bronze , which has been 
rather extensively used for ornamental purposes. 
Magnesium is a metal which may be prepared by the action 
of sodium, at a red heat, on chloride of magnesium ; and it has 
also been obtained by the electrolysis of the chloride. Its 
specific gravity is 1*74, that of aluminium being about 2*6. 
Cadmium is a somewhat rare metal, extracted from the zinc 
smelted from cadmiferous blende. Specimens of metallic 
cadmium are shown in the form of ingot. An amalgam of 
cadmium is used in dentistry. The sulphide, known as cadmium 
yellow , is employed by artists, while the iodide is used in 
photography. 
Bismuth is a metal which occurs mostly in a native state. 
The ready fusibility renders its metallurgical treatment exceed- 
ingly simple, the metal being readily separated from any foreign 
matters by fusion. Some singularly beautiful examples of 
bismuth, crystallised artificially, are introduced. The iridescence 
is said to be given to the surface by the regulated action of 
heat. Bismuth is used in the formation of type metal, pewter , 
solder, and fusible .metal. An alloy of bismuth 8, lead 5, and 
tin 3, will melt at a temperature lower than that of boiling- 
water. 
Antimony is a brilliant crystalline metal, extremely brittle, 
obtained mostly from the sulphide, known as stibnite. The 
crystalline structure is well shown by the fern-frond pattern on 
the surface of a cake of “ star antimony.” 
A curious old antimony cup is here exhibited. When wine 
was allowed to stand in such cups, tartarised antimony ( tartar 
emetic) was formed and dissolved, and consequently when the 
wine was drunk it produced sickness. 
A gilt copper cup obtained from the copper mine of Herrn- 
grund in Hungary, by alteration of an iron cup, is also shown 
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