316 



SCIENCE. 



the modified medium-sized dynamo-machine, capable 

 of producing 36 webers of current with an expenditure 

 of 4 horse-power, and which, if used for illuminating- 

 purposes, produces a light equal to 6000 candles, I find 

 that a crucible of about 20 centimetres in depth, immersed 

 in a non-conductive material, is raised up to white heat 

 in less than a quarter of an hour, and the fusion of one 

 kilometre of steel is effected within, say, another quarter 

 of an hour, successive fusions being made in somewhat 

 diminishing intervals of time. It is quite feasible to 

 carry on this process upon a still larger scale by increas- 

 ing the power of the dynamo-elec ric machine and the 

 size of the crucibles. 



By the use of a pole of dense carbon, the otherwise 

 purely chemical reaction intended to be carried into effect 

 may be interfered with through the detachment of parti- 

 cles of carbon from the same ; and although the con- 

 sumption of the negative pole in a neutral atmosphere is 

 exceedingly slow, it may become necessary to substitute 

 for the same a negative pole so constituted as not to 

 yield any substance to the arc. I have used for this pur- 

 pose (as also in the construction of electric lamps) a 

 water pole or tube of copper, through which a cooling 

 current of water is made to circulate. It consists simply 

 of a stout copper cylinder closed at the lower end, having 

 an inner tube penetrating to near the bottom for the 

 passage of a current of water into the cylinder, which 

 water enters and is discharged by means of flexible india- 

 rubber tubing. This tubiug being of non-conductive 

 material, and of small sectional area, the escape of cur- 

 rent from the pole to the reservoir is so slight that it may 

 be entirely neglected. On the other hand, some loss of 

 heat is incurred through conduction in the use of the 

 water pole, but this loss diminishes with the increasing 

 heat of the furnace, inasmuch as the arc becomes longer, 

 and the pole is retired more and more into the crucible 

 cover. 



To melt a gram of steel in the electric furnace takes, 

 it is calculated, 8100 heat units, which is within a frac- 

 tion the heat actually contained in a gram of pure carbon. 

 It results from this calculation that, through the use of 

 the dynamo-electric machine, worked by a steam engine, 

 when considered theoretically, 1 lb. of coal is capable of 

 melting nearly 1 lb. of mild steel. To melt a ton of steel 

 in crucibles in the ordinary air furnace used at Sheffield, 

 from zy z to 3 tons of best Durham coke are consumed ; 

 the same effect is produced with 1 ton of coal when the 

 crucibles are heated in the Regenerative Gas Furnace, 

 whilst to produce mild steel in large masses on the open 

 hearth of this furnace, 12 cwts. of coal suffice to produce 

 1 ton of steel. The electric furnace may be therefore 

 considered as being more economical than the ordinary 

 air furnace, and would, barring some incidental losses 

 not included in the calculation, be as regards economy 

 of fuel nearly equal to the Regenerative Gas Furnace, 



It has, however, the following advantages in its fauor: 

 is'. That the degree of temperature attainable is theo- 

 retically unlimited. 2d. That fusion is effected in a per- 

 tectly neutral atmosphere. 3d. That the operation can 

 be carried on in a laboratory without much preparation, 

 and under the eye of the operator. 4th. That the limit 

 OJ lint practically attainable with the use of ordinary re- 

 fractory materials is very high, because in the electric 

 furnac: the fusing material is at a higher temperature 

 nan the crucible, whereas in ordinary fusion the tempt 1- 

 o( the crucible exceeds that of the material fused 

 within it. 



Without wishing to pretend that the electric lui naee 



t( d is in a condition to supersede other 

 furnac s for ordinary purposes, the advantages above in- 

 di< .te I will make it a useful agent, 1 believe, for carrying 

 on chemical reactions of various kinds at temperatures 

 and under conditions which it has hitherto been impos- 

 sible to secure. 



DESILVER1ZATION OF LEAD BY THE ZINC 

 PROCESS.* 



By J. E. Stoddart. 



The treatment of argentiferous leads with zinc, for the 

 purpose of extracting the silver and refining the lead, is by 

 no means a novel process. About twenty years ago a 

 metallurgist named Parks took out patents for desilverizing 

 rich leads by means of zinc, and a manufacturing firm 

 adopted his process. They were, however, subsequently 

 obliged to abandon it, in consequence of the difficulty ex- 

 perienced in the separation of the zinc from the concen- 

 trated silver, to admit of the cupellation of the latter metal. 

 A German chemist named Flach afterwards took up the 

 subject, and by running the alloy of zinc, silver, and lead 

 along with iron slag, through a peculiarly constructed 

 blast-furnace, was enabled to free the concentrated silver- 

 lead from zinc. He also proposed the use of this furnace 

 for removing of traces of zinc from the desilverized lead, 

 but this was abandoned in favor of the ordinary im- 

 proving or calcining pan.' The operation with the blast- 

 furnace was found to be very troublesome, and as the 

 greater portion of the zinc was entirely lost, was by no 

 means economical. M. Manes, of Messrs. Guillem & Co., 

 Marseilles, who were the first to work Flach's process, 

 found out and patented a simple means of treating the 

 alloy, and recovering the zinc by distillation. This is the 

 process now in use and known as the Flach-Guillem pro- 

 cess, and which is carried on in the following manner : — 

 About 18 tons of "rich lead," containinggenerally from 60 

 to 70 ounces of silver per ton, are melted in a large cast-iron 

 pot, to which 1 per cent, by weight of zinc is added, and the 

 whole well stirred for twenty minutes. The fires are drawn, 

 and the contents allowed to settle and cool until the zinc 

 rises to the surface, and forms a solid ring or crust con- 

 taining the silver and other foreign metals. This alloy is 

 removed to a small pot at hand, where part of the lead is 

 sweated out, and the alloy thoroughly dried. The large pot 

 with the lead now partially desilverized is again heated up, 

 and treated in the same way as before, but with the addition 

 of only a half per cent, of zinc, which when it has risen to 

 the top is removed as before, and dried. A third addition 

 of a quarter of per cent, of zinc is found necessary to take 

 out the remainder of the silver, care being taken, on the 

 cooling "of this zincing, that all the crystals are cleanly 

 skimmed off. The lead in the large pot is assayed, and 

 found almost always to contain less than 5 dwts. of silver to 

 the ton of lead ; if it should happen to contain more, it is 

 due to carelessness on the part of the workmen. The pot 

 is now tapped, and the lead run down into an improving 

 pan, where it is kept at a high heat for nearly eight hours, 

 for the purpose of oxidising or burning off the small per- 

 centage of zinc which is left in it from the zincing process ; 

 after seven or eight hours' firing in this pan it should con- 

 tain no trace of zinc. It is then tapped and run into moulds 

 for market lead, or for the manufacture of lead products. 

 The old improving pans were made of cast-iron, placed on a 

 bed of sand, with a groove in the upper sides, which groove 

 was filled with bone-ash to prevent the action of oxide of 

 lead on the iron. These pans, from the giving way of the 

 bone-ash, and the great wear and tear on the iron from the 

 high heats necessary, were found to be both troublesome 

 and expensive ; they were very often under repair, and 

 seldom lasted more than six or eight months. They have 

 been superseded by an improving pan of cast-iron lined 

 with brick inside. This pan, instead of being placed on a 

 bed of sand, as was the case with the old improving pan, 

 is hung on brick walls, and is quite open both below and 

 round the outside. This new pan lias been working in 

 the patentee's works, Marseilles, for some years without 

 any break down. It burns no more coal, and can be as 

 economically worked in every way as the old pans. The 

 zinc and silver alloy, after being dried, is melted in a 

 plumbago crucible, covered on the top, well luted with 

 fire clay, connected with a small cast iron receiver by 

 means of a plumbago pipe, and fired up with coke. The 

 zinc, disiils over, and is condensed in the iron receiver. 

 All< 1 all the zinc has been distilled, the pipe is discou- 

 nt ted, the cover removed, and the lead and silver, left in 



* Read before the Philosophical Society of Glasgow, Nov. 8, 1880. 



