METALS. 



467 



tries should be well cased. In the instance 

 of mercury, it has been stated by M. Dumas, 

 that the frozen metal, when brought to a much 

 lower temperature than its freezing-point, 

 undergoes a remarkable change in its molecu- 

 lar state. Cold means condensation, and no 

 doubt produces some change in the form and 

 arrangement of the ultimate particles of the 

 metal, whereby its proportions are considerably 

 modified. 



The Science of Alloys. Dr. Matthiessen, in a 

 lecture before the Royal Institution, has given 

 an interesting summary of the recent re-, 

 searches of physicists into the nature of al- 

 loys. He first demonstrated, by means of an 

 ingeniously-contrived apparatus, that the elec- 

 trical and heat-conducting powers of the 

 alloys follow the same courses. He also 

 showed that, when bars of alloys and their 

 component metals are struck, a great difference 

 will be found in the notes produced ; as, in 

 almost every case, the most sonorous alloy was 

 found to correspond in composition approxi- 

 mately with that at the turning-point of the 

 electric conducting-power curve. When wires, 

 of the same diameter, of metals and alloys are 

 broken by traction, those of the alloys will 

 require a much greater force than their com- 

 ponent metals; and it may be deduced from 

 what is known, that those alloys, the composi- 

 tion of which corresponds to the turning-point 

 of the conducting-power curve, are more te- 

 nacious than any other alloy composed of the 

 same metals. "When spirals of wires of metals 

 and their alloys are weighted to an equal ex- 

 tent, the alloys will be found, on removing the 

 weights, to possess the property of resuming 

 their original form in a much higher degree 

 than their component metals. Here, again, the 

 alloys corresponding in composition to those 

 of the turning-point of the conducting-power 

 curve are the most elastic. 



A New Mode of Toughening and Refining 

 Gold. Mr. F. B. Miller, of the Sydney Mint, 

 has introduced a new mode of treating the 

 Australian gold, which often contains a small 

 amount of antimony, rendering it brittle. Mr. 

 Miller removes the objectionable metal by the 

 following process: He first saturates a clay 

 pot with a solution of borax, to prevent any 

 absorption and loss of chloride of silver. Hav- 

 ing placed the gold in the pot, it is covered 

 with a closely-fitting but unluted lid, having a 

 hole bored in it. Through this, when the gold 

 is melted, he passes a clay pipe down to the bot- 

 tom of the pot. This pipe is in connection with 

 a chlorine generator, and by a suitable arrange- 

 ment a stream of the gas is driven through the 

 metals; after continuing the process an hour 

 or so, the crucible is allowed to cool for the 

 gold to set, and the chlorides which remain 

 liquid are poured out. A small amount of 

 gold is removed with the chlorides, but is 

 easily recovered. The plan of reducing the 

 chloride of silver, adopted by the author, was 

 to set the slab of chloride of silver between 



two plates of wrought iron, and immerse the 

 whole in dilute sulphuric acid, leaving it 

 there about 24 hours, in which time its reduc- 

 tion is usually complete. The reduced silver 

 is then dissolved in nitric acid, leaving any 

 gold that is present undissolved. The loss of 

 gold in these operations is said to be smaller 

 than in the ordinary refining process. 



Desihering Lead ly Zinc. The process of 

 desilvering lead by the use of zinc (see ANNUAL 

 CYCLOPAEDIA for 1867) is now in use in Wales, 

 in Germany, and in France. Commonly, the 

 zinc is driven off from the silver, after its ex- 

 traction from the lead, by volatilization, but 

 at Braubach they separate the metals by 

 another and ingenious method. From lead 

 drosses or chimney-fumes, they obtain chloride 

 of lead by direct treatment with dilute hydro- 

 chloric- acid, an educt of chemical works. 

 This chloride of lead is agitated in a cast-iron 

 pan with the rich silver zinc at a low red 

 heat ; chloride of zinc is formed, and the lead 

 set free, which is then separated from the 

 silver by cupellation. The pure lead again is 

 deprived of its small contents of zinc, by treat- 

 ing it in like manner with chloride of lead. 

 The chloride of zinc is treated in reverberatory 

 furnaces in order to extract any remains of 

 lead mechanically mixed with it. At the 

 works of Baron Rothschild, at Havre, the zinc, 

 in the form of a flat cylindrical ingot, is plunged 

 into the silver-lead in fusion, and caused by a 

 mechanical arrangement to revolve in it, until 

 the zinc is thoroughly fused and mixed with 

 other metals. The rich silver with the zinc 

 now rises to the top, and is skimmed off, and 

 the zinc volatilized, after which the poor lead 

 is deprived of its zinc by steam oxidation. 

 The steam oxidation process for expelling the 

 zinc from the lead is preferred by Gruner to 

 the treatment by chloride of lead, as being 

 more efficacious, less unwholesome, and less 

 expensive than the latter method. 



Reduction of Oxide of Copper ly Sugar. M. 

 A. Commaile communicates to the London 

 Chemical News the following method of re- 

 ducing oxide of copper to the metallic form 

 by means of inverted sugar. He takes a very 

 dilute solution of the oxide, and pours into it 

 sufficient caustic potash to form a precipitate ; 

 adds to this liquid a solution of inverted sugar, 

 when the precipitate will dissolve ; then boils 

 the solution, which should not be too acid; 

 and after a short time a red deposit of pro- 

 toxide is formed, which must be separated. 

 The liquid is again boiled, and a fresh precipi- 

 tate appears, which is proved to be formed of 

 metallic copper and protoxide, which latter is 

 removed by very weak chlorhydric acid ; the 

 undissolved precipitate is dried and polished 

 with some hard body, when it presents the 

 brilliant aspect of metal. On boiling the 

 mother waters, by which the second precipi- 

 tate was deposited, a third deposit is obtained, 

 consisting only of metallic copper, and as red 

 as galvanoplastic copper. This metal may also 



