COPPER 



915 



505, 506 



Melting furnaces are sometimes also used for calcination. Some of those near 

 Swansea serve this double purpose ; they are composed of 3 floors (fig. 507). The 

 floor A, is destined for melting the calcined ore ; the 

 other two, B, c, serve for calcination. The heat being 

 less powerful upon the upper sole c, the ore gets dried 

 upon it, and begins to be calcined : a process completed 

 on the next floor. Square holes, d, left in the hearths B 

 and c, put them in communication with each other, and 

 with the lower one A ; these perforations are shut during 

 the operation by a sheet of iron, removable at pleasure. 



The hearths B and c, are made of bricks ; these are 

 horizontal at the top and slightly vaulted beneath ; they 

 are two bricks thick, and their dimensions larger than 

 those of the inferior hearth, as they extend above the 

 fire-place. On the floors destined for calcination the 

 furnace has two doors on one of its sides : on the lower 

 story there are also two ; but they are differently placed. 

 The first, being in the front of the furnace, serves for 

 drawing off the scoriae, for working the metal, &c. ; and 

 the second, upon the side, admits the workmen to make 

 necessary repairs. Below this door is placed the dis- 

 charge or tap-hole, which communicates by a cast-iron 

 gutter with a pit filled with water. The dimensions of 

 this furnace in length and breadth are nearly the same 

 as those of the melting furnace above described; the 

 total height is nearly 12 feet. It is charged by means 

 of either one or two hoppers. 



3. Boasting Furnace. The furnaces employed for this 

 purpose are in general similar to the calciners ; but in the 

 smelting-works of Messrs. Vivian, the furnaces above 

 alluded to present a peculiar construction; this is for 

 the purpose of introducing a continuous current of air 



upon the metal, in order to facilitate its oxidation. This process was originally in- 

 vented by Mr. Sheffield, who disposed of his patent right to Messrs. Vivian. 



The air is admitted by a channel through the middle of the fire-bridge, which 

 extends all its length ; it communicates with the atmosphere at its two extremities, 

 whilst square holes, left at right angles to this channel, conduct the air into the 

 furnace. This very simple construction produces a powerful effect in the roasting. 

 It not only promotes the oxidation of the metals, but burns the smoke,. and assists in 

 the vaporisation of the sulphur ; while by keeping the bridge cool it preserves it from 

 wasting, and secures uniformity of temperature to the hearth. 



4. Refining Furnace. In this, as in the melting furnace, the side slopes towards 

 the front door instead of the side doors, because in the refining furnace the copper 

 collects in a cavity formed in the hearth near the front door, from which it is lifted 

 out by ladles ; whereas, in the melting furnaces, the metal is run out by a tap-hole 

 in the side. The sole is laid with sand ; but the roof is higher than in the melting 

 furnace, being from 32 to 36 inches in height. If the top arch were too much 

 depressed, there might be produced upon the surface of the metal a layer of oxide very 

 prejudicial to the quality of the copper. In that case, when the metal is run out, its 

 surface solidifies and cracks, while the melted copper beneath breaks through and 

 spreads irregularly over the cake. This accident, called the rising of the copper, pre- 

 vents it from being laminated, and requires it to be exposed to a fresh refining 

 process, when lead must be added to remove the oxide of copper. This is the only 

 occasion upon which the addition of lead is proper in refining copper. When the metal 

 to be refined is mixed with others, particularly with tin, as in extracting copper from 

 old bells, then very wide furnaces must be employed, to expose the metallic bath on 

 a great surface, and in a thin stratum, to the oxidising action of the air. 



The door, on the side of the refining furnace, is very large, and shuts with a framed 

 brick door, balanced by a counter-weight. 



5. Heating Furnaces, being destined to heat the pigs or bars of copper to be lami- 

 nated, as well as the copper sheets themselves, are made much longer in proportion 

 to their breadth. Their hearth is horizontal, the vault not much depressed ; they 

 have only one door, placed apon the side, but which extends nearly the whole length 

 of the furnace ; this door may be raised by means of a counter-weight, in the same 

 way as in the furnaces for the fabrication of sheet-iron and brass. 



Series of Operations to which the Ore is subjected. The ores which are smelted in the 

 Swansea works are chiefly copper pyrites, more or less mingled with gangue (vein-stone). 



SN 2 



