Tin is obtained from the ore by first breaking up the latter, whilst a current of water flows over it and carries off the impurities, which are lighter, and therefore more readily borne away than the heavier tin ore. After being thus freed from the admixture of other minerals, the ore is usually roasted or burned, to drive off any traces of sulphur it may contain; it is afterwards heated to redness with blind coal or culm, and a small portion of lime, when the melted metal separates from the dross, and runs into cavities prepared for its reception. It is afterwards refined by being remelted, and other impurities separated, which either sink or float on the surface. The purest metal is yielded by the ore called stream-tin, which is smelted with charcoal instead of coal. If a block of tin thus obtained is heated slightly, and then allowed to fall from a height, it separates into a number of prisms which adhere together in pyramidal masses. In this state it is termed grain-tin. Tin is a silvery-white metal possessed of a high degree of metallic lustre. It is sufficiently soft to be cut with a knife, and may be readily bent, when it gives out a peculiar crackling noise; if repeatedly bent and straightened, it becomes hot from the friction of its particles with one another, and ultimately breaks. It is inelastic and moderately ductile, but very malleable, the thickness of tin-foil being about one thousandth part of an inch. It has but little tenacity, a wire of one-tenth of an inch in diameter not being able to support a heavier weight than 49 lbs. Tin is the most easily melted of all the common metals, and it possesses the valuable property of not rusting when exposed at ordinary temperatures to the conjoined action of air and water, or even to weak vegetable acids. Tin, in a pure state, is seldom employed; but in combination with other metals it is a substance of great value. Its most important uses depend on its power of resisting the action of air and moisture; it is therefore largely employed for protecting the surfaces of copper and iron, that rust so readily.