trical
industries. In the former it is used as dishes, crucibles, cones,
anodes, cathodes, retorts, triangles, foil, wire, etc., and as a
reagent, especially as platinic chloride (PtCl4) The finely
divided platinum known as platinum sponge or platinum black has the
property of absorbing large quantities of oxygen, especially when the
metal is heated, and of liberating this oxygen again when it is allowed
to cool. Hence platinum sponge is made use of as an oxidizing agent in
a great many chemical processes, for example, in the Schroeder-Grillo
method, for the manufacture of sulphuric acid (H2SO4), where 1 kilogram of platinum is consumed for every 10 tons ;of sulphuric anhydride produced.
In
electrical appliances platinum finds numberless uses. It is employed in
incandescent lamps, in electric furnaces, in instruments for the
measurement of electrical quantities, and as contacts and attachments
in electrical machines of almost every description. It is finding a new
and extensive use as sparking points for gas engines.
In physics it is used in thermocouples and resistance thermometers.
The
riders and small weights used with chemical and assay balances are made
of platinum alloyed with a small percentage of iridium.
Silversmiths
impart the French-gray finish, so much in vogue at present, by
electroplating the silver with a very thin coating of platinum.
Platinum,
too, has been used for coinage. In 1828 the Russian mint turned out a
considerable quantity of platinum coins; but they were not received
favorably and were soon recalled. Spain, at a time when platinum was
much cheaper than at present, is said to have debased her coinage with
this metal.
Further
uses of platinum are to be found in photography, dentistry, pyrography,
in the manufacture of surgical instruments, and in jewelry, and its
employment in other fields of industry is only precluded by its limited
supply.
As
to the uses of the other metals which usually occur intimately
associated with platinum, that is iridium, osmium, and sometimes
palladium, rodium, and ruthenium.
Iridium
is used in small percentages as an alloy to harden platinum, thus
adding to the durability of articles manufactured from that metal.
Alloys in which iridium is present in larger percentages are used in
the construction of standards of length and weight and as wire in
standard resistance coils. Iridium is also used in making knife edges
for delicate balances or other instruments where similar construction
is needed. The natural alloy of iridium with osmium, iridosmiuni, on
account of its extreme hardness, is used to point gold pens and as
bearings in watches and compasses. The cost of pure iridium is about
$30 per ounce.
Until
within a few years the presence of osmium in crude platinum was
considered a serious obstacle and interfered materially with the sale
of the product, as it was both hard to remove and in itself of no use.
The recent invention of the "Auer" or osmium lamp, which is a new
incandescent electric light using a filament of metallic osmium, has
created a considerable demand for the metal. Osmium tetrox-ide (OsO4)
is employed in staining thin sections of organic tissue in microscopic
work. Osmium compounds are also used in the precipitation of bacterial
organisms from water and other liquids.
Palladium
is employed in the construction of finely divided scales for delicate
scientific instruments and in the manufacture of chronometers and
watches. It is also used with platinum in the preparation of toning
baths in photography.
Rhodium and ruthenium are as yet of no commercial importance.
BRIEF BIBLIOGRAPHY OF PLATINUM.
The
following list comprises the most important articles on platinum which
have appeared since the issue of Bulletin No. 193 of the United States
Geological Survey on "The Geological Relations and Distribution of
Platinum and Associated Metals," by Prof. J. F. Kemp, which work
contains a complete bibliography of platinum literature up to 1903.
M R 1905—28
