METALLURGY. 



preventing or diminishing this loss a scale col- 

 lector is placed within the pickling tank in any 

 convenient position, and is connected by means 

 of terminals to a depositing or electric-lighting 

 dynamo. In the case of large baths two or more 

 collectors can be employed, or only one may be 

 used which is moved about to different parts of 

 the bath at suitable intervals. From time to 

 time the scale collector is taken out and the 

 adhcriii" scale is removed either by breaking 

 the circuit or by means of a suitable brush or 

 scrai>cr. It is claimed in behalf of this apparatus 

 that a great saving of acid is effected when it is 

 used: that it can be attached without any diffi- 

 culty to any ordinary lead-lined pickling vat, and 

 docs" not require skilled labor to look after it; 

 that all the magnetic oxide or scale on the plate 

 is collected almost as soon as it leaves the iron 

 or steel, instead of being allowed to remain in 

 the solution and be acted upon by the acid as at 

 present: and that it opens the way to consider- 

 able economy in large works where much acid is 

 Used. 



Gold and Silver. An electrolytic apparatus 

 recently introduced for the extraction of gold 

 may U- used, it is claimed, for freeing the metal 

 from any auriferous material by direct chlorina- 

 tion and* the simultaneous generation of sodium 

 amalgam, or it may be employed as a separate 

 generator of chlorine gas and sodium, to be used 

 afterward in connection with gold extraction or 

 for the electro-deposit of gold from solution. 



In the assay of gold bullion at the United 

 States Mint, as described by Alexander E. Outer- 

 bridge, the bullion is first weighed in the " de- 

 posit weigh room," and is then sent to the " de- 

 posit melting room." Here it is put into a cru- 

 cible, which has been previously heated in the 

 melting furnace, and is covered with a thin coat- 

 ing of borax, which forms a sort of fluid glass, 

 and acts as a screen to protect the metal when 

 it is molten from the oxidizing influence of the 

 air. The fluid mass is actively stirred for the 

 purpose of rendering it thoroughly homogeneous, 

 and the metal is then cast into an iron mold, 

 called a " shoe," and plunged into water to cool 

 and to dissolve off any part of the borax glass 

 which may have adhered to its surface. A slight 

 loss of weight usually occurs during this process, 

 in consequence of a partial refining out of the 

 base metals, and the new weight is that with 

 which the depositor is credited. In the assay or 

 analysis the assayer first determines approxi- 

 mately the relative proportions of the metals 

 existing in the alloy, and from this bases his 

 more careful determinations. A half gramme of 

 the alloy is weighed off and wrapped in an en- 

 velope of pure lead in the form of a bullet. The 

 bullet is placed in a small cup made of calcined 

 bone dust, which has been brought to a white 

 heat. The mass melts immediately, and the 

 lead, oxidizing rapidly by absorbing oxygen 

 from the heated air that passes over its surface, 

 sinks by virtue of the extreme fluidity of the 

 oxide into the pores of the cupel, where it is ab- 

 sorbed rapidly, carrying with it also all the base 

 metals that may have been originally combined 

 ith the allov, while the precious metals, not 

 being oxidizable, simply melt, and are not so fluid 

 to be capable of sinking into the cupel. A 

 separation thus takes place, and at the moment 

 the base metal is removed a beautiful 

 flash" is observed to take place on the surface 

 the metal. The "button" of purified gold 

 ilver resulting from this operation is next 

 The loss indicates the proportion of 

 metal. Another weighing of the sample is 



then made, pure silver in the form of fine granules 

 is added in the proportion of about 2 parts of 

 silver to 1 of gold, the alloy is inclosed in a sheet 

 of lead and cupelled as before. The silver button 

 remaining is laminated, coiled into a roll called 

 a " cornet," and boiled in nitric acid. The acid 

 dissolves the silver, leaving a little roll of nearly 

 pure gold. This gold cornet is then annealed in 

 the furnace to give it toughness, and is finally 

 weighed. The weight represents the proportion 

 of pure gold. The proportion of silver is ascer- 

 tained by subtracting the weight of pure gold 

 plus the weight of the base metal from the origi- 

 nal weight of the assay sample. 



Charcoal is used in Australia to precipitate 

 gold on a large scale from cyanide solutions; but 

 it appears from a paper read by Mr. J. J. Lowles 

 at the Institute of Mining and Metallurgy, giv- 

 ing the details and results of the process, that 

 the expense and inconvenience are considerably 

 greater than in zinc or electrotype precipitation. 

 The chemical interaction involved in the precipi- 

 tation is not understood. 



The accepted theory of the chemical reactions 

 w r hich occur in the pan amalgamation of silver 

 has been since the experiments of Hague that 

 cuprous chloride is formed by the interaction of 

 common salt, bluestone, and metallic iron, and 

 is instrumental in reducing sulphide of silver. 

 From a series of experiments performed by him, 

 however, Mr. H. F. Collins finds that a chloride 

 ore is readily treated in an iron pan without blue- 

 stone or metallic copper, the silver compounds 

 being directly reduced by the iron. In the case 

 of sulphide ore treatment is facilitated by the 

 addition of sulphate of copper, which is readily 

 reduced to metallic copper by the iron. The cop- 

 per, whether amalgamated or not, acts on sul- 

 phide of silver, reducing it to metal and enabling 

 it to be taken up by the mercury. On the other 

 hand, cuprous chloride, a still more energetic 

 agent in reducing sulphide of silver, never exists 

 in the pan. In this way the comparatively bad 

 results obtained in the treatment of sulphide ores 

 in the presence of metallic iron are explained. The 

 use of copper-bottomed vessels in the treatment 

 of sulphide ores has been practiced for more than 

 a century. In such vessels cuprous chloride is 

 formed in considerable quantities. 



Specimens of native silver accompanying matte 

 and artificial galena, exhibited by Prof. Liver- 

 sidge at the Royal Society of New South Wales, 

 were obtained from between two courses of brick- 

 work in the arch over the vault of an old reverber- 

 atory furnace; the upper course had been raised 

 bodily but remained intact, and the space be- 

 tween became filled to a thickness of about 4 

 inches with a layer of clean matte. The metallic 

 silver occurred on the surfaces in the cracks and 

 crevices of the matte and bricks. 



Among experiments reported by Mr. Breakell 

 to the Institution of Mining Engineers as bearing 

 upon the value of Russell's modification of the 

 hyposulphite process is one proving that the pres- 

 ence of copper increases the volatilization loss of 

 silver in chloridizing roasting. On the other hand, 

 metallic silver and sulphide of silver, which are 

 always present, especially in badly roasted 

 charges, are readily dissolved by hyposulphite 

 solutions containing copper, though not readily 

 acted on in its absence. It follows that the pres- 

 ence of copper should be avoided in the furnace 

 charges, and that it may be added with advan- 

 tage in the later stages of the process. 



As a cheap, simple, and practical method of 

 desilverizing copper Preparator Joseph Girard, of 

 the Faculty of Sciences of Paris, recommends 



