by washing, and the dried oxide mixed with about one-third its weight of coal or charcoal, and introduced into crucibles with alternate layers of granulated copper.

The crucibles employed were made of fire-clay, 12 inches deep, 8 inches wide at the top, and 63 inches wide at the middle, inside measure. The king-pot, as the middle pot was termed, was 13 inches deep, and would hold 120 lbs. of metal, while the smaller ones would only hold 84 lbs. The charge consisted of 100 lbs. calcined ore and 40 lbs. coal, to every 66 lbs. of bean-shot copper.

1 The furnace used, Figs. 5 and 6, consisted of a circular chamber m, lined with fire-brick; it was contracted above to a circular opening, in which was fixed a cast-iron collar ee; it was closed at the bottom by a cast-iron bed-plate aa, in which were twelve holes symmetrically arranged round one larger hole in the centre k, through which the ashes and clinkers could be withdrawn from time to time. Below this plate was the ash-pit n, communicating in front by means of an air-way c, with a vault i, through which air was admitted, and access gained by the workmen to the ash-pit. In the small holes in the bed-plate were placed cast-iron twyers f, tapering upwards. The space between the twyers was filled up with fire-bricks to form a solid bed. The air for the combustion of the fuel entered through these twyers. Several furnaces were constructed in a row, and the whole covered with a large cone like that of a glasshouse.

The crucibles were placed in the furnace so that the large or king-crucible occupied the central position. Each pot was loosely covered with a piece of coal, and smaller pieces of fuel were packed between the pots. When the operation was completed the king-pot was first removed, and the contents well stirred with an iron rod. Each of the side pots were then removed in succession, well stirred, and when the brass in each case had subsided to the bottom the contents were poured into the king-pot. The dross was 1 Percy's Metallurgy, p. 613.

then skimmed from the surface, and the metal poured into suitable moulds.

In this process oxide of zinc is reduced at a temperature below the melting point of copper, which, being exposed to the action of the vapour of zinc, becomes permeated with this metal and converted into brass. If the temperature be raised too high at an early stage of the process the copper would melt, sink to the bottom of the crucible, and much of the zinc escape without alloying with the copper.

When the metal obtained by the above process was not of the desired quality, it was necessary to undergo a fresh fusion with calamine and charcoal, or with copper, according as the copper or zinc was in excess.

DIRECT PREPARATION OF BRASS

§ 51. This method consists of melting copper and zinc together in the desired proportions, either in a crucible, or in a reverberatory furnace, the latter being used chiefly for Muntz's or yellow metal, where large ingots are required. Many attempts have been made to do away with crucibles for the manufacture of brass, and to substitute special furnaces of the reverberatory type; but the loss of zinc is so great, and the composition of the brass so liable to be uncertain, that even for yellow metal many manufacturers have discarded the reverberatory, and gone back to the old crucible method.

A crucible furnace is generally a rectangular chamber 12 to 16 inches square and 3 to 4 feet deep, lined inside with fire-brick, and connected near the top with a chimney by means of a flue, which is generally horizontal at the part adjoining the furnace, then inclining upwards into the chimney. This is especially the case when several furnaces open into one chimney. The proper construction of the furnace and disposition of the flues is a matter of the first importance, as a slight difference in the arrangement of the flues will considerably affect the draught and prevent the

Scale % of an inch to a foot Vertical Section

FIG. 7.

Scale 1⁄2 of an inch to a foot
Plan

FIG. 8.

attainment of that high temperature necessary in melting copper, brass, bronze, and similar metals. The section of the flue has a great influence on the working of a furnace,

oboo

Scale 34 of an inch to a foot

Front Elevation

FIG. 9.

for if too narrow the friction will be great and the draught too sluggish. For an active and strong draught the flue must be wide and the chimney large and high. The section

K