548 ON THE MANUFACTURE of edge TOOLS. with 0.015 of chromium. These, he says, both forged well, the first better than cast-steel. A knife and a razor were made from them, and both proved very good; their edges were hard and solid, but their most remarkable character was the fine damask they took, when washed over with sulphuric acid. This damask was composed of white silvery veins, and nearly resembled that given by the alloy of steel and silver. The white parts are probably pure chromium, on which acids have no action. This chromic steel was prepared by fusing together cast-steel and the alloy of chromium and 108 Quarterly Journal of Science, vol. xii. page 174. Annales de Chimie et de Physique, tome xvii. page 55. ESSAY XVI. ON THE MANUFACTURE OF TIN-PLATE. [First printed in the MEMOIRS OF THE LITERARY AND PHILOSOPHICAL SOCIETY OF MANCHESTER, Vol. III. New Series, and copied from thence into the Annales de Chimie et de Physique, tome xii. for the year 1819, page 153.] As the processes in this manufacture are more numerous and complicated than is generally imagined, it may be advisable to preface the account with an enumeration of some of those properties of tin which will be most likely to explain the rationale of the principal operations. Tin has a great affinity for several of the other metals-particularly for zinc, mercury, copper, antimony, lead and iron; and owing to these affinities, its employment in the arts is very considerable. Tin, with zinc, forms a metal of close grain, very useful for many purposes, especially for the forma tion of pewter. The zinc is found to impart great hardness to the tin, without lessening its ductility. The combination of mercury and tin, in which the tin is dissolved by the mercury into a very soft amalgam, is largely employed, as is well known, in silvering the backs of mirrors, and for other purposes in the arts. An amalgam of tin of greater consistence was formerly in use in the museums of Paris for closing the mouths of glass-bottles containing sundry curious and valuable preparations. Copper is also alloyed with tin for various purposes of manufacture. This metallic mixture is employed in making what are called bronze statues; for casting bells, and pieces of artillery, and also for the fabrication of medals and medallions. In some of these cases the tin is mixed with copper, on account of its property of rendering the copper more fusible; and this was probably the reason why the ancient Romans used that metal in the greater part of their brass coinage. It is owing to the affinity of tin for copper, that vessels of capacity, made with the latter metal, for culinary and other purposes, are so readily covered with a coating of tin, to preserve them from the action of substances which would not fail to erode copper, unprotected by some such covering. The affinity of tin for copper is further exemplified by the process of whitening pins, which is effected by boiling if |