Tin is an essential ingredient in _bell─metal_, _bronze_, _pewter_, and various other compounds. It may be combined with lead, in any proportion, by fusion; and this alloy is harder, and possesses much more tenacity than tin. The hardest alloy is a composition of three parts of tin and one of lead. The presence of the tin destroys, in a great measure, the noxious qualities of the lead. It is sometimes customary to tin copper vessels with this mixture, and it has been ascertained that such vessels are in no respects injurious. There are three kinds of _pewter_ in common use. These are called _plate_, _trifle_, and _ley pewter_. The first, which is made into plates and dishes, is formed of tin, with a small proportion of lead and antimony (245). The second, or _trifle pewter_, which is made in somewhat different proportions, is used for the quart and pint pots of the publicans: and the _ley pewter_, which is formed of three parts of tin and one of lead, is manufactured into wine and spirit measures. Tin may be beaten into leaves or plates that are much thinner than paper. But, when it is thus worked, several leaves must be joined together. They then support each other, and yield to the hammer without tearing. These leaves are used for the silvering of glass globes, and the plating of other metals. Those that are used for the silvering of looking─glasses are much thicker. The article called _tin─foil_ is an alloy, consisting generally of two parts of tin and one of lead; and capable of being beaten to less than the thousandth part of an inch in thickness. 239. _LEAD is a heavy metal, of pale and livid grey colour when broken, not sonorous when pure, very flexible, and so soft that it may be marked with the nail. It stains paper or the fingers of a bluish colour, and is about eleven times heavier than water._ T_he most common state in which lead is found is in combination with sulphur and a small portion of silver. This ore is known by the name of_ galena, _and is frequently in the form of blackish cubical crystals. Lead is also found in union with arsenic (242) and many acids._ Great Britain possesses the most important lead─mines in the world; and those that are best known are in the counties of Flint and Derby. The latter are supposed to have been worked even in the time of the Romans. Lead mines are entered sometimes by perpendicular shafts, and sometimes (when in the sides of hills) by levels. In some of the Derbyshire mines, where the depth of the veins will admit of it, the men work, at different heights, of from four to six feet above each other, along what are called stoops; the uppermost men being two or three yards before those next in succession, and thus forming a kind of steps. The implements used are picks, hammers, and strong iron wedges; and the rocks are also frequently loosened by means of gunpowder.