PLA 'TINA, or PLATINUM, is an important metal, which was first made known in Europe by Mr. Wood, assay-master in Jamaica, who met with its ore in 1741. Platina is separated from the sand and other matters with which it is mixed, by washing with a great quantity of water, from which the heavier parts of course subside, and the ore in question. The ore of platina is composed of irregular rounded grains, which are sometimes flattened; they are of various sizes, often very small, and occasionally they exhibit traces of crystallisa tion; but these are probably derived from the presence of some other metal. The ore, which has a specific gravity of 17.33, contains traces of six or seven other metals ; and the process of separation is one of great compli cation. The pure platinum has a grayish white colour, intermediate between silver and tin. When it is free from iridium, it is so very ductile that it may be drawn into very fine wire, not exceeding the 2000th part of an inch in diameter; it is also very malleable, and may be beaten into thin leaves. When perfectly pure, it is softer than silver, and it is susceptible of receiving a fine polish. Of all
metals it is the least expansible. Its density varies from 19i to 211 times that of water. It suffers no change by exposure to the air, nor is it oxidized when heated in it. It does not under any circumstances decompose water.
It is infusible in the strongest heat of a smith's forge, but it may be melted by voltaic electri city or by tho oxyhydrogen blowpipe. Of all metals, except iron and copper, it is the most tenacious: a wire of the diameter of -Nth of an inch,' is capable of sustaining a weight of 274 pounds. Like iron, platina possesses the very valuable property of welding at a high temperature, and this enables us to form it into chemical vessels of great and daily use.
The uses of platina are numerous and im portant; but it is especially employed for forming vessels, not merely for chemical operations on a small scale, but for the con centration of sulphuric acid by manufactures. Some years ago as much as 1000/. was paid for a platina still for making certain acrid chemicals ; the price being about a guinea an ounce; but it is now lower in value.