9. Preparation of crude copper by roasting and fusion of regulus.

10. Refining and toughening of crude copper, producing fine metal.

For the purpose of showing clearly the character and objects of these 10 operations, considered in detail, the following statement of analysis of the constituents of the more common ores is necessary:-Copper Antimony Sulphur Arsenic. Lead Silica.

The separation of the copper in a state of pority is, of course, the object of all the operations just enumerated. As a simple chemical question, it can be comparatively easily done on the scale of ordinary laboratory operations; but for practical purposes, the same means cannot be adopted, principally on account of the too great cost of the agents required, but also because of the too great nicety of process for the ordinary labour employed in such extensive operations.

The First Operation has for its object the separation of all the substances capable of being volatilized by heat. This is etfected by exposing the ore, in a ruoghly pulverized condition, to the joint action of heat and atmosphere in a reverberatory furnace shown in plan and section in Figs. S and 9. The furnace consists of a fireplace a, for the production of the heat, and of a, sole b, on which the crude ore is subjected to Its action. They are divided from each other by the bridge c, which is so constructed as to admit heated air to the gases produced in the fireplace, which, for the regular distribution of the heat over the whole of the sole of the furnace, requires to be ignited, not within the fireplace, but at the back of the bridge, so entering into full combustion, and producing streams of flame over the whole surface of the sole. As the production of an oxidizing flame should be the object in this furnace, the proper arrangement of the bridge for controlling the admission of air is of the greatest importance. The regular distribution of the heat over the whole of the furnace is effected by having the arch 3 ft. high over the bridge, gradually diminishing to 1 ft. over the back bridge.

The sole of the furnace is usually 16 to 24 ft. square, having 2 doors d on each side, through which the workman rakes over (rabbles) the charge of ore at intervals of 1 1/2 to 2 hours, so as to expose fresh surfaces to the action of the heated air passing over it. The charge is introduced through hoppers e fixed in the arch of the furnace; and when the calcination is completed, it is drawn through holes / in the bed or sole of the furnace into an arched recess g below. The bed of the furnace may with advantage be extended to 60 ft. by 16 ft., being divided into 4 different parts, each 3 in. higher than the other. The consumption of coals in this operation need be but very small, as when the ore is first introduced, the assistance of heated air alone is sufficient to maintain the combustion of the sulphur of the ore, the heat from which causes the evolution of arsenious acid from the arsenic. The gradual increase of heat in the charge is very necessary to be provided for, as with too much heat the charge, while still holding much sulphur and arsenic in combination, is very liable to be fused; and in this condition the evolution of the sulphur and arsenic is very much impeded, as is also the oxidation of the other metals present.

When the charge is drawn, it still contains some sulphides and sulphates; most of the sulphur, arsenic, antimony, and zinc, will have been evolved; the copper and iron, not remaining in combination with sulphur, will have been converted into oxides; and the siliceous or earthy matters will remain unchanged. Unless a very large quantity of arsenic and other volatile metals shall have been driven off, the charge, when drawn, will not differ much in weight from the charge put into the furnace, as the sulphur evolved will have been to a considerable extent replaced by the oxygen of the air, which will have combined with the other metals, producing oxides. The volatile products pass off into the flues, where a portion is deposited; but the remainder, consisting principally of sulphurous and sulphuric acids, together with the carbonic acid, water, and nitrogen, the products of the combustion of the fuel, are diffused from the top of the chimney h through the surrounding atmosphere. By the adoption of means hereafter noticed, a very large proportion of this sulphur is rendered available, in the form of sulphuric acid, for the numerous manufacturing purposes for which this important chemical agent is required; and thus, while a valuable product is obtained, the deleterious effects on the surrounding country are confined to a much more limited extent.

Fig. 8.

Copper Part 4 30011

The reverberatory furnace may be built of copper slag-blocks, cast in moulds 18 in. by 9 in., faced internally with firebrick, and externally with fire-brick or common brick; the whole laid with fireclay; the fronts and sides covered with plates of cast iron, bound together with cast-iron studs and wrought-iron braces. The products of combustion pass off over the back bridge into a descending flue, or into underground flues, communicate ing with the main shaft or chimney.

A still further economy of fuel may be effected by constructing the back beds of the furnace of cast-iron plates, causing the heated air and gases to circulate in flues below the plate before finally passing away through the descending flue. The cast-iron soles are more durable than the fire-brick usually employed; and the labour for rabbling or turning over the charges may be applied with much greater effect. Lengthened experience has shown that the cast-iron plates are not affected by the united action of heat and sulphur, as might have been anticipated. Second Operation. - The reverberstory furnace employed in this operation is about J the capacity of that employed for calcining the raw ore, supposing it to be a single furnace. Its construe-tion is shown in Fig. 10. It is built also of the same materials; hut as a very much greater heat is produced within it, much more core is necessary in its construction. It in charged through the hopper a with about 20 cwt. of material, consisting of calcined ore from the first operation, a small proportion of crude ore, a small quantity of fluor-spar as a flux, some of the scoria of the same operation, and fusible scoria from the fourth, fifth, and seventh operations.