In the laboratory, brass may be made very well in the small way in a short time. Put into a crucible a mixture of calamine and charcoal, bury it in the requisite pro portion of copper shot, cover the whole with charcoal powder, lute on a cover to the crucible, and heat,slowly in a wind furnace for half an hour, till the zit* be gins to burn off in a blue flame round the top of the crucible : then raise the fire, and heat briskly for half an hour longer. This process of cementation is also shown by the following management. Put the mixture of calamine and charcoal into a crucible, cover it with a thin layer of clay, over which, when dry, lay a thin plate of copper, cover the whole with fine charcoal powder, and lute on a co ver to the crucible. Apply heat gradu ally, and the vapour of the reduced saint will rise through the floor of clay, pene trate the red hot copper plate above it, and gradually convert it into brass, which at the end of the operation will be found lying melted on the stratum of clay. The increase of weight gained by the topper in this operation will afford a good prac tical test of the goodness of the calamine, and its fitness for brass-making in the great way. The most important proper ties of brass, compared with copper, are the following: the colour of brass is much brighter, and more approaching to that of gold ; it is more fitsible than cop per ; less subject to rust, and to be acted upon by the vast variety of substances which corrode copper with so much ease ; and it is equally malleable when cold, and more extensible than either cop per or iron, and hence is well fitted for fine wire. Brass, however, is only mal leable when cold. Hammering is found to give a magnetic property to brass, perhaps, however, only arising from the minute particles of iron beaten off the hammer during the process, and forced into the surface of the brass ; hut this cir cumstance makes it necessary to employ unhammered brass for compass-boxes, and similar apparatus. The expansion of brass has been very accurately determin ed, as this metal is most commonly used for mathematical and astronomical instru ments, where the utmost precision is re quired. Mr Smeaton found that twelve
inches in length of cast brass, at 32°, ex panded by 180 degrees of heat (or the interval from freezing to boiling water) 225 ten thousandth parts of an inch. Brass wire under the same circumstances expanded 232 parts ; an alloy Of 16 of brass with one of tin expanded 229 parts. The expansion of hammered copper is only 204 such parts ; but that of zinc is 253 : so that brass holds a middle place in this respect between its two compo nent metals.
Analysis shows a vast variety in the proportions of the different species of brass used in commerce. In general, the extremes of the highest and lowest pro portions of zinc are from 12 to 25 per cent. of the brass. Even with so much as 25 per cent of zinc, brass, if well manu factured, is perfectly malleable, though zinc itself scarcely yields to the hammer. Mr. Diz6 analyzed a specimen of remark ably fine brass made at Geneva, for the purpose of escapement wheels, and the nicer parts of watch-making, the perfect bars of which bear a very high price. This metal unites great beauty of colour to a very superior degree of ductility. It was found to consist of 75 of copper with 25 of zinc, and probably too the copper was Swedish, or some of the finer sorts. The common brass of Paris seems to con tain about 13 per cent. of zinc, the Eng lish probably more. The uses of brass are very numerous. It is applicable to a great variety of purpose s,i s easily wrought by casting and hammering, and by the lathe ; its wire is eminently useful, and it takes a high and very beautiful polish. The appearance of brass is given to other metals, by washing them with a yellow laquer or varnish, a substitution often very much to the detriment of the manu factured article. Many other yellow alloys of copper are used, such as bronze, bell-metal, &c. most of which are triple compounds, and will be noticed under the article COPPER.