PLATINA. 
489 
being greater than that of gold. It is so refractory 
in the tire, that the greatest degree of heat which 
can possibly be obtained with the assistance of 
oxygen gas is scarcely sufficient to melt it ; though 
the solar rays, when concentrated by the most 
powerful means, fuse it in less than two minutes. 
What we have here said must be understood of 
pure platina ; for when mixed with other metals 
and semi-metals, especially with arsenic, it melts 
very easily. 
Don Antonio de Ulloa, who, in concert with the 
French astronomers, was sent to Peru in order to 
measure a degree of the meridian at the equator, is 
the first person who has mentioned platina. It ap- 
pears, however, from the manner in which he has 
spoken of it, that he never saw the metal, since he 
describes it as tc a stone of such resistance, that it is 
not easily broken by a blow upon an anvil. It is not 
subdued by calcination ; and it is very difficult to 
extract the metal it contains, even with much labour 
and expense.” 
As platina is capable of receiving a very high 
polish, not so subject to tarnish as mixed metals, 
nor, like glass, to give a double image, the French 
government have consigned a quantity to the mem- 
bers of the Institute, for the purpose of construct- 
ing a telescope of such a magnitude and excel- 
lence, as (they hope) shall exceed the best of Dr. 
Herschel’s. 
One of the properties which renders this metal 
of great utility to practical mathematicians, is the 
