Platinum
is used for pins in artificial teeth. Vessels of copper, brass, etc.,
may be plated with platinum by welding the platinum foil to the other
metals. Dishes made in this way withstand the action of acids even when
the coating is very thin, but they are apt to scale when heated highly.
They have not come into use because of the care necessary in making
them. Tips of lightning rods are frequently plated with platinum.
Finely divided platinum is used as a luster in porcelain painting.
Eeflecting surfaces on glass have been made quite successfully with a
thin coating of platinum. By polishing a surface of glass and using a
coating on this for direct reflection, mirrors can be made even when
the glass is somewhat imperfect; such mirrors in certain physical
instruments have the advantage of transmitting just enough light to
enable observations to be made conveniently through the mirror.
As
an addition to other metals platinum has never been markedly useful. It
is itself rendered more suitable for instruments of measurement by the
addition of iridium, usually in the proportion of nine parts of
platinum and one part of iridium. This alloy is harder and less
fusible than pure platinum, and compares with steel in elasticity. If
the proportion of iridium reaches 20 per cent., the alloy is scarcely
attacked by nitro-hydrochloric acid.
These
uses, though numerous, do not consume a large amount of platinum, and
the extension of the industry must be looked for in new uses sufficient
to consume the quantity of the metal which the known sources can
furnish. Lately the use of incandescent electric lights and also gas
jets made luminous by a heated platinum spiral have caused an increased
demand for the metal, and the steady rise in price during the last two
years may be referred to this cause.
