COPPER 



tory furnnees having flues beneath the bed through which the flame passes before 

 coming into contact with the ore. The furnaces are sometimes supplied with inde- 

 pendent fireplaces, but more frequently a series of them is worked by gas generated 

 in Siemens's producers. A form of furnace is also employed, in some cases, in which 

 the ore is placed in a sort of muffle, between which and the outer walls of the furnaces 

 the flames are allowed to play ; in this arrangement the flame and products of com- 

 bustion do not come into contact with the ore. 



The mixture is charged into the furnaces through hoppers in the arch, and spread 

 evenly over the bed to a depth of 4 to 5 inches, a charge usually consisting of about 3 

 tons ; this is stirred and rabbled from time to time in order to expose fresh surfaces 

 to oxidation, the temperature not being allowed to exceed a dull redness. Hydro- 

 chloric acid is evolved during the roasting, and is conveyed to a condenser, from 

 which a weak acid solution is obtained, which is subsequently employed in the lixivia- 

 tion of the roasted ore. 



After the expiration of about 6 to 6J hours the whole of the copper in the ore 

 should have been converted into a soluble chloride : a sample is taken from each 

 furnace and washed twe or three times with hot water and a little dilute hydrochloric 

 acid, the residue is then treated with nitric acid, and the solution obtained rendered 

 alkaline by the addition of ammonia ; should more than a trace of blue colour be dis- 

 cernible in the solution, the sulphide of copper in the mixture has not been decomposed, 

 and the roasting must be prolonged until a satisfactory test can be obtained. The 

 charge is then drawn out on to the floor of the furnace-house and allowed to cool con- 

 siderably, after which it is transferred in iron tram-waggons to wooden lixiviating 

 vats capable of holding about 16 tons, and provided with false bottoms, over which a 

 layer of cinders is spread to serve as a filter. 



The hot roasted ore is then treated with hot water, and finally with a little hydro- 

 chloric acid ; the stronger solutions are ready for precipitation by means of metallic 

 iron, whilst the weaker are run into a reservoir, whence they are pumped back and serve 

 as washing- water to a fresh lot of furnaced ore, and so in turn become strong solutions. 



In many works the silver present in these solutions is, previously to the precipita- 

 tion of the copper, extracted by Claudet's process, which consists in mixing with them 

 a quantity of a soluble iodide, usually that of potassium, sufficient to combine with 

 the silver present, which amounts to from 3 to 4 grains per gallon. The insoluble 

 iodide of silver is allowed to subside, and the copper solution drawn off from it into 

 the precipitating vats. 



When a considerable quantity of iodide of silver has been collected, it is well washed 

 to free it from copper, and whilst suspended in water, metallic zinc in thin fragments 

 is added, and the whole kept boiling by a jet of steam. The iodide of silver is thus 

 decomposed, and metallic silver and solution of iodide of zinc produced ; the latter 

 serves to precipitate a fresh quantity of silver, whilst the former after being dried is 

 ready for the smelter. 



The copper present in the strong solutions is precipitated in large wooden vats, by 

 immersing in them scrap wrought iron ; if the solution be kept boiling by a steam jet, 

 the precipitation is completed in about 12 hours. The spent liquid; which is valueless, 

 is drawn off by a siphon from the precipitated copper, and the latter freed from iron 

 by washing through perforated plates. After being allowed to drain, the precipitate 

 is dried on a bed of fire-tiles heated by flues passing beneath, and is then ready for 

 smelting ; it contains, on the average, 70 to 75 per cent, of fine-metal. 



The material from which the copper has been washed should contain about ith per 

 cent, of that metal, and when good pyrites have been used, consists almost entirely of 

 sesquioxide of iron : it is largely employed under the name of ' Purple ore ' or ' Blue 

 Billy ' for the fettling of puddling furnaces. See PYRITES. 



Alderley Edge in Cheshire. The hydrochloric acid process is, at the present time, 

 carried on to a considerable extent at Alderley Edge in Cheshire, where the ore is in 

 many respects similar to that at Twiste, with the exception that in the last-mentioned 

 locality, mechanical agitation is dispensed with, and the acid is pumped from beneath 

 the false bottom of one tank to the top of the next, in order that the whole solvent 

 power of the acid may be utilised. The hydrochloric acid process was originally in- 

 troduced at Alderley Edge by Mr. W. Henderson, who protected his method by a pro- 

 visional Specification, dated September 30, 1857. Another specification was filed by 

 Mr. Henderson in 1859, which included the extraction of copper from pyrites by con- 

 verting the copper into chloride by calcination with common salt a process similar to 

 that originally suggested by Mr. Longmaid, and now extensively applied to the 

 treatment of burnt pyrites. The sandstone of the curious elevation above the plain 

 of Cheshire, known as Alderley Edge, is impregnated with copper existing in the state 

 of blue and green .carbonates. The bods containing this copper lie at a short 

 distance below the surface, and are therefore easily worked. 



