imilar compound. On ignition the
double chloride is decomposed, leaving the platinum as a spongy metallic
mass, which is melted in an electric furnace and rolled or hammered into
the desired shape.

~Physical properties.~ Platinum is a grayish-white metal of high luster,
and is very malleable and ductile. It melts in the oxyhydrogen blowpipe
and in the electric furnace; it is harder than gold and is a good
conductor of electricity. In finely divided form it has the ability to
absorb or occlude gases, especially oxygen and hydrogen. These gases,
when occluded, are in a very active condition resembling the nascent
state, and can combine with each other at ordinary temperatures. A jet
of hydrogen or coal gas directed upon spongy platinum is at once
ignited.

~Platinum as a catalytic agent.~ Platinum is remarkable for its
property of acting as a catalytic agent in a large number of
chemical reactions, and mention has been made of this use of
the metal in connection with the manufacture of sulphuric acid.
When desired for this purpose some porous or fibrous substance,
such as asbestos, is soaked in a solution of platinic chloride
and then ignited. The platinum compound is decomposed and the
platinum deposited in very finely divided form. Asbestos
prepared in this way is called platinized asbestos. The
catalytic action seems to be in part connected with the
property of absorbing gases and rendering them nascent. Some
other metals possess this same power, notably palladium, which
is remarkable for its ability to absorb hydrogen.

~Chemical properties.~ Platinum is a very inactive element chemically, and
is not attacked by any of the common acids. Aqua regia slowly dissolves
it, forming platinic chloride (PtCl_{4}), which in turn unites with the
hydrochloric acid present in the aqua regia, forming the compound
chloroplatinic acid (H_{2}PtCl_{6}). Platinum is attacked by fused
alkalis. It combines at higher temperatures with carbon and phosphorus
and alloys with many metals. It is readily attacked by chlorine but not
by oxidizing agents.

~Applications.~ Platinum is very valuable as a material for the
manufacture of chemical utensils which are required to stand a high
temperature or the action of strong reagents. Platinum crucibles,
dishes, forceps, electrodes, and similar articles are indispensable in
the chemical laboratory. In the industries it is used for