68 



METALLURGY. 



Mctallur- 



gy- 



Platinum. 



. Owing to the infusibility of Platinum, it is with great 

 difficulty obtained in mass, so as to have it in a state fit 

 to be wrought into different articles. The simplest and 

 the cheapest method of working Platinum, is that prac- 

 tised in France. For this purpose, the grains of Pla- 

 tinum are mixed with an equal weight of white arsenic, 

 and one-third of pearl-ashes. This is thrown, in suc- 

 cessive portions, into a red-hot crucible, and well stir- 

 red with a platinum rod. When the whole is in a state 

 of fusion, the crucible is removed from the furnace, and 

 the mixture is allowed to cool. It is then taken from 

 the pot, and bruised, and again subjected to a similar 

 process. If after the second fusion the metallic mat- 

 ter is magnetic, it must be a third time treated in the 

 same way. 



After this it is mixed with an equal weight of white 

 arsenic and a small quantity of pearl-ashes, and again 

 fused in a flat earthern dish, in which it is allowed to 

 cool. 



It is next exposed to a heat in a muffle, sufficient to 

 expel the arsenic, but not so high as to fuse the mix- 

 ture. It is then, when hot, plunged into oil, and the 

 exposure to heat and immersion in oil repeated, till the 

 whole of the arsenic is driven off; the heat being gra- 

 dually increased as the metal becomes less fusible. 

 After the arsenic is expelled as completely as can be 

 effected in this way, and the charcoal of the oil is con- 

 sumed, it is digested in nitric acid, and then boiled in 

 water to remove impurities. Several of the pieces of 

 metal thus obtained are put together, and then exposed 

 to a high temperature ; in which state they are struck 

 so as to make them adhere. The mass is then heated 

 in a forge and beat on an anvil, by which one compact 

 piece of metal is procured. 



Platinum obtained by the above process is not pure ; 

 it contains arsenic, and the foreign ingredients of the 

 grains, by which it is not so capable of standing an 

 intense heat, or of resisting the action of chemical 

 agents. 



The other methods of obtaining platinum is by re- 

 ducing its oxide obtained by dissolving the grains in 

 nitro-muriatic acid, and precipitating by muriate of 

 ammonia. For doing this, different processes are fol- 

 lowed, though they all nearly agree with each other. 



The best of these is, perhaps, that recommended by 

 Mr. Cook. 



It consists in exposing the precipitated oxide to heat, 

 by which it is reduced, and the superfluous muriate of 

 ammonia is expelled. About half an ounce of the 

 spongy mass obtained, is then put into an iron mould, 

 and squeezed together by a wooden pestil. After this 

 another half ounce is added, and in this way the opera- 

 tion is continued, till about six ounces are squeezed into 

 the mould, which are still farther compressed by a strong 

 iron screw, by which the whole of the air is expelled. 

 It is then laid on burning charcoal, and exposed to a 

 high temperature, and when hot beat on an anvil till it 

 is of uniform .density. After this operation, it is coated 

 with a reddish crust, which is removed by covering it 

 with borax and exposing it to a white heat ; it is then 

 washed with muriatic acid, which dissolves the foreign 

 matter, and leaves the metal resplendent. 



Platinum thus obtained still retains Iridium, which 

 was precipitated from the nitro-muriatic solution ; it is 

 however sufficiently pure for the manufacture of uten- 

 sils. 



Before subjecting Platinum to any of these processes, 



the grains must be spread on a table, and a current of Mtallur- 

 air from a bellows must be passed obliquely over them. %! 

 By this the lighter particles, which consist of quartz and Vj i * ' 

 iron ore, are removed. 



Occasionally the grains, as brought to Europe, con. 

 tain a minute portion of gold. This may be got from 

 them by treating them with a small quantity of nitro- 

 muriatic acid. To the solution green sulphate of iron 

 must be added, and the precipitate thrown down, puri- 

 fied by fusion with nitre and borax. 



Copper. 



The ores of copper generally employed for yielding Copper. 

 the metal, are the sulphurets. These are wrought 

 principally in Cornwall, in Anglesea, and in Hungary. 

 In Cornwall, the ores of copper are broken into small 

 pieces, which are roasted in a furnace, somewhat simi- 

 lar to a reverberatory furnace, having a very long chim. 

 ney to increase the heat, and to carry off the sulphur 

 and arsenic with which the ore is roasted. During the 

 roasting, which continues for about twelve hours, the 

 ore is frequently stirred, so as to expose the whole of 

 it to the flame. It is then put into a small furnace of 

 the same form, and brought to a state of fusion, occa- 

 sionally mixed with a little lime, to increase the fusi- 

 bility. As the impurities collect at the top, they are 

 raked out, and put into oblong moulds, in which they 

 are allowed to cool. They then form a hard mass, 

 which is used in building. The fused copper is drawn 

 out through a hole in the lower part of the furnace, 

 which was stopped by clay, mixed with a little coal, to 

 prevent it from hardening. Fresh quantities of the 

 roasted ore are then put in, and the process is in this 

 way carried on for a considerable time. 



The fused copper is conveyed into vessels suspended 

 in a well, through which a stream of water runs. By 

 this means the metal is reduced to the granular state. 

 It is still, however, impure, being mixed with sulphur 

 and arsenic. 



To free it from these, the metal is repeatedly sub- 

 jected to heat in a reverberatory furnace, and each 

 time put into the well. During these processes, the 

 slag collects on the surface of the fused metal ; but 

 as this contains a considerable quantity of copper, it 

 is kept, and mixed with the fresh ore, previous to its 

 being put into the furnace. 



The copper after this is kept at a low red heat for 

 two days, and is then repeatedly fused, and cast into 

 moulds about 14 inches in length. It is lastly put into 

 the refining furnace, with a little charcoal, in which it 

 is again fused. If after this it bear the hammer, it is 

 fit for sale. When the fused copper is cast into the 

 moulds, the purest part of it rises to the top, and may, 

 when cold, be easily separated from the rest, by a blow 

 of a hammer. 



The copper ores of Anglesea are wrought nearly in 

 the same way. The ore there, after being reduced to 

 fragments, is put into a kiln, the flues of which termi- 

 nate in a close chamber. Heat is then applied to the 

 ore, and the sulphur, which sublimes, is carried through 

 the flue, and condenses in the chamber. Fresh quan- 

 tities of the ore are from time to time introduced, and 

 the roasting is in this way kept up for several months. 

 The poorer part of the ore only is smelted in Angle- 

 sea, the richer portion being exported. 



The smelting of the ore is carried on in a series of 

 reverberatory furnaces, having tall flues to increase the 

 draught. In these the ore mixed with a little coal- 

 dust is fused, and purified by repeated fusions. By this 



