(_c_) _General Industrial Uses._—Copper as metal is also employed to a considerable extent in certain important industries, as in textile manufacture, where it is used for the rollers in calico-printing; and it is in general industrial use in the form of copper heaters, vats, coils, pans, and the like, and occasionally also for roofing and sheathing. =Uses of Copper Alloys.=—Between 20 and 30 per cent. of the copper produced is employed in the form of alloys. The more important of these are:— =Brasses=; alloys of copper and zinc. =Bronzes=; chiefly alloys of copper and tin. =Coinage Alloys=; of gold and silver with copper. =German Silver=; alloys of copper, nickel, and zinc. =Special Bronzes=; alloys of copper with such metals as aluminium and manganese. It is further not unlikely that several classes of ternary alloys, at present still under investigation, may have important industrial application in the future. Among such alloys may be mentioned the copper-aluminium series alloyed with other metals, Monel metal and the Monel steel series, etc. Of the above alloys, the brasses are by far the most widely used. It may be recalled that the advantages possessed by alloys of copper and zinc are in large measure due to their increased strength and hardness; to the fact that they are more fusible, and more fluid when melted, and so give good castings; that they are characterised by a good colour and high lustre, as well as by the factor of cheapness resulting from the addition of a less costly metal—zinc—in their manufacture. The uses of the copper alloys may also be arranged in two classes—(_a_) engineering uses, and (_b_) general uses. Of the brasses, those containing upwards of 70 per cent. of copper may be rolled cold, whilst the alloys with less than 70 per cent. are hot-rolled. In the engineering industry large quantities of 70/30 brass are utilised in the form of condenser tubes, whilst for the multifarious requirements of general engineering work, very considerable amounts of brass of lower tenor are employed in the forms of taps, pipes, fittings, etc. Muntz metal, the 60/40 brass, finds extended application for the sheathing of ships, whilst the employment of brass and of the other alloys for all manner of articles of general utility is a matter of common knowledge.