COPPER 919 



by assays taken in succession. The grain of the copper becomes finer by degrees, 

 and its colour gradually brightens. Wheu the grain is extremely fine, or close, 

 when the trial-pieces, half cut, through and then broken, present a silky fracture, 

 and the copper is of a fine light red, the refiner considers the operation to be com- 

 pleted ; but lie verifies still further the purity of the copper, by trying its malleability. 

 For this purpose, he takes out a sample in a small ladle, and pours it into a mould. 

 When the copper is solidified, but still red-hot, he forges it. If it is soft under the 

 hammer, and does not crack on the edges, the refiner is satisfied with its ductility, 

 and pronounces it to be in its proper state. He then orders the workmen to mould 

 it : they lift the copper out of the furnace in large iron ladles lined with clay, and 

 pour it into moulds of a size suitable to the demands of commerce. The ordinary 

 dimensions of the ingots or pigs are 12 inches broad, 18 long, and from 2 to 2 thick. 



The period of the refining process is 20 hours. In the first six, the metal heats 

 and suffers a kind of roasting ; at the end of this time it melts. It takes four hours 

 to reach the point at which the refining, properly speaking, begins ; and this last part 

 of the process lasts about four hours. Finally, six hours are required to arrange the 

 moulds, cast the ingots, and allow the furnace to cool. 



The charge of copper in the refining process depends upon the dimensions of the 

 furnace. In different works the charge varies from 3 to 5 tons. 



When the copper offers difficulties in refining, a few pounds of lead are added to 

 it. This metal, by the facility with which it scorifies, acts as a purifier, aiding the 

 oxidation of the iron and other metals that may be present. The lead ought to bo 

 added immediately after removing the door to skim the surface. The copper should 

 be constantly stirred to expose the greatest possible surface to the action of the air. 

 and to produce the complete oxidation of the lead ; since the smallest quantity of 

 this metal in copper causes a difficulty in the lamination ; i. e., the scale of oxide 

 does not come clean from the surface of the sheets. 



The operation of refining copper is delicate, and requires, upon the part of the 

 workmen, great skill and attention to give the metal its proper ductility. Its surface 

 ought to be entirely covered with wood-charcoal ; without this precaution, the refining 

 of the metal would go back, as the workmen say, during the long interval which 

 elapses in moulding ; whenever this accident happens, it must be stirred anew with 

 the wooden pole. 



Too long employment of the pole causes the copper to become more brittle than it 

 was prior to the commencement of the refining ; that is, when it was dry. Its colour 

 is now of a very brilliant yellowish red, and its fracture fibrous. When this occurs, 

 the refining, as the workmen say, has gone too far, and the refiner removes the char- 

 coal from the top of the melted metal ; he opens the side door, to expose the copper 

 to the action of the air, and it then resumes its malleable condition. 



The theory of refining may be thus explained : We may conclude that the copper 

 in the dry state before refining, is combined with a small portion of oxygen, or, in 

 other words, that a small portion of sub-oxide of copper is diffused through the mass, 

 combined with it ; and that this proportion of oxygen is expelled by the deoxidising 

 action of the wood and charcoal, whereby the metal becomes malleable. 2. That 

 when the refining process is carried too far, the copper gets combined with a little 

 carbon. Thus copper, like iron, is brittle when combined with oxygen or carbon ; 

 and becomes malleable only when freed entirely from these substances. 



It is remarkable, that copper, in the dry state, has a strong action upon iron ; and 

 that the tools employed in stirring the liquid metal become glistening, like those 

 used in a farrier's forge. The iron of the tools consumes more rapidly at this 

 time than when the copper has acquired its malleable state. The metal requires 

 also, when dry, more time to become solid, or cool, than when it is refined ; a circum- 

 stance depending, probably, upon the difference in fusibility of the copper in the two 

 states, and which seems to indicate the presence of oxygen. 



When the proper refining point has been passed, another very remarkable circum- 

 stance has been observed ; namely, that the surface of the copper oxidises less easily, 

 and that it is uncommonly brilliant, reflecting clearly the bricks of the furnace vault. 

 This fact is favourable to the idea suggested above, that the metal is in that case com- 

 bined with a small quantity of carbon ; which absorbs the oxygen of tie air, and 

 thus protects the metal from its action. 



Copper is brought into the market in different forms, according to the purposes 

 which it is to serve. That which is to be employed in the manufacture of brass is 

 granulated. In this condition it presents more surface to the action of zinc, and com- 

 bines with it more readily. To produce this granulation, the metal is poured into a 

 large ladle, pierced with holes and placed above, a cistern filled with water, which 

 must be hot or cold, according to the form of the grains required. When it is hot 

 round grains are obtained analogous to lead shot ; and the copper in this state is called 



