226. _PLATINA, the most ponderous of all the metals with which we are acquainted, is, when purified, about twenty times heavier than water. It is also one of the hardest and most difficult to be melted, is of white colour, but darker and not so bright as silver, and is found only in small blunted and angular grains or scales in the sands of some of the rivers in South America._ If platina could be obtained in sufficient quantity, it would perhaps be the most valuable of all metals. The important uses to which it is applicable may easily be imagined when we state that it is nearly as hard as iron, and that the most intense fire and most powerful acids have scarcely any effect upon it. Platina is not fusible by the heat of a forge, but requires either the concentrated rays of the sun in a burning mirror, the galvanic electricity, or a flame produced by the agency of oxygen gas. It is admirably adapted for the uses of the philosophical chemist: although vessels made of it must always be found expensive, from its being necessary to solder them with gold; and although it has the disadvantage of being subject to corrosion by the application or use of caustic alkalies. Vessels made of it are not liable to be broken, and are as indestructible as those made of gold. When properly refined, its colour is somewhat betwixt that of silver and iron. Not being liable to tarnish like silver, platina is manufactured into several kinds of trinkets. Its ductility is so great that it may be rolled into plates, or drawn into wire; and platina wire, for strength and tenacity, is considered much preferable to that either of gold or silver of equal thickness. Platina is also made into mirrors for reflecting telescopes, into mathematical instruments, pendulums, and clock─work; particularly where it is requisite that the construction of these should be more than usually correct, as platina is not only free from liability to rust, but is likewise subject to very little dilatation by heat. It is sometimes beaten into leaves and applied to porcelain, in the same manner as leaf gold; and its oxide (21) is used in enamel painting, and might be used, with great advantage, in the painting and ornamenting of porcelain. The platina employed for all these purposes is repeatedly melted with arsenic, as without the aid of this it could only be obtained in very small masses, owing to the intense heat that is required for its fusion. This extraordinary metal was unknown in Europe until about the year 1735, when it was first brought from South America by Don Antonio Ulloa. 227. _GOLD is a metal distinguished by its yellow colour; by its being next in weight to platina, softer than silver, but considerably more hard than tin; and being more easily melted than copper._