ASSAY OF TIN ORE.--Tin-stone will yield up its metal if mixed with charcoal, borax and soda, and heated on the hearth of a furnace or before a blow-pipe. The presence of tin may be tested by dissolving the metal thus roasted out, in aqua regia and adding a decoction of Brazil-wood: if the metal was tin, the liquid will be colored a beautiful crimson. ASSAY OF LEAD ORE.--Both galena and cerussite are rich ores, and when abundant pay well. They are easily reduced by heat, the former being usually mixed with charcoal and iron filings. If a western backwoodsman wants shot or bullets, he kindles a fire in a hollow tree or an old stump, puts some galena on the charred wood, and melts it down. After cooling, he finds the metal at the bottom. The smelting of a ton of lead costs about $6. The average price per ton of galena is $30. When galena is dissolved in warm nitric acid, a clean plate of zinc placed in it will be coated with brilliant blades of lead; if the galena contains silver, a plate of copper will be served in the same way. A solution of chromate of potash poured into a solution of lead ore in nitric acid will throw down a yellow powder. TO TEST THE PURITY OF GRAPHITE.--Its value depends upon the amount of its carbon. Pulverize and then dry at a heat of about 350 degrees, twenty grains of it; then place it in a tube of hard glass four or five inches long, half an inch wide and closed at one end. Add twenty times as much well dried oxide of lead and well mix. Weigh the tube and contents, and afterwards heat before a blow-pipe till the contents are completely fused and no longer evolve gases. Ten minutes will suffice for this. Allow the tube to cool and weigh it. The loss in weight is carbonic acid. For every twenty-eight parts of loss there must have been twelve of carbon. CHAPTER VI. MINERAL SPRINGS. WHAT ARE MINERAL SPRINGS--GENERAL LOCATION--GAS SPRINGS--IRON SPRINGS--SULPHUR SPRINGS--ALUM SPRINGS--EPSOM SPRINGS--SALT SPRINGS--WARM SPRINGS--ARTESIAN WELLS AND OIL WELLS, AND WHERE TO BORE FOR THEM. Any spring which contains a large amount of foreign matter, as gas, salts and earthy ingredients, is called _mineral water_. The special prominence of any ingredient gives it its particular name. Many iron springs contain salt, salt springs contain iron, and both may contain gas; the name is derived from the most prominent ingredient. Our country is rich in mineral springs; there is not a State without one. But in general they are most numerous in hilly or mountainous regions, especially where the rocks are much deranged in position, or “faulted,” as the miners say. As for example, in Eastern New York and in the valley between the Blue Ridge and the Alleghany from Harper’s Ferry to the Natural Bridge. The Pacific States, also, are as remarkable for the number and variety of their mineral springs as for their metallic ores.