When calamine is employed, 1⁄2 cwt. of copper, 3⁄4 cwt. of calamine, and 1⁄3 the volume of both of charcoal mixed, are put into 7 crucibles, and exposed to heat during 11 or 12 hours; the product being from 70 to 72 lbs. of brass.
Brass-plate rolling.—At Hegermühl there are two re-heating or annealing furnaces, one larger, 18 feet long, and another smaller, 81⁄2; the hot chamber is separated from the fire place by iron beams, in such a way that the brass castings are played upon by the flames on both their sides. After each passage through the laminating press (rolls) they are heated anew, then cooled and laminated afresh, till they have reached the proper length. The plates are besmeared with grease before rolling.
[Fig. 166.] shows the ground plan of the furnace and its railway; [fig. 167.] the cross section; and [fig. 168.] the section lengthwise; a a, the iron way bars or rails upon the floor of the foundry, for enabling the wheels of the waggon-frame to move readily backwards and forwards; b b, the two grates; c c, the ash pits; d d, the fire beams; e e e, vents in the roof of the hot chamber f; g g, two plates for shutting the hot chamber; h, the flue; i, the chimney. After the rolling, the sheets covered with a black oxide of copper, are plunged into a mother water of the alum works for a few minutes, then washed in clean water, and lastly, smeared with oil and scraped with a blunt knife.
In rough brass and brass wares, no less than 16,240 cwts. were manufactured in the Prussian States in the year 1832.
For musical purposes, the brass wire made in Berlin, has acquired great and merited celebrity; but that of Birmingham is now preferred even by foreigners.
Brass Colour, for staining glass, is prepared by exposing for several days thin plates of brass upon tiles in the leer or annealing arch of the glass-house, till it be oxidized into a black powder, aggregated in lumps. This being pulverized and sifted, is to be again well calcined for several days more, till no particles remain in the metallic state; when it will form a fine powder of a russet brown colour. A third calcination must now be given, with a carefully regulated heat; its quality being tested from time to time by fusion with some glass. If it makes the glass swell, and intumesce, it is properly prepared; if not, it must be still farther calcined. Such a powder communicates to glass, greens of various tints, passing into turquoise.
When thin narrow strips of brass are stratified with sulphur in a crucible, and calcined at a red heat, they become friable, and may be reduced to powder. This being sifted and exposed upon tiles in a reverberatory furnace for ten or twelve days, becomes fit for use, and is capable of imparting a calcedony, red or yellow tinge to glass by fusion, according to the mode and proportion of using it.
The glass-makers’ red colour may be prepared by exposing small plates of brass to a moderate heat in a reverberatory furnace, till they are thoroughly calcined, when the substance becomes pulverulent, and assumes a red colour. It is then ready for immediate use.