462 



METALLURGY. 



tion has not begun. The ores unadapted to the 

 cyanide process are especially those containing 

 coarse gold, those containing copper, which con- 

 sumes the expensive chemical potassium, and for 

 the same reason those containing ferrous sulphate 

 or acid soluble salts. With respect to telluride ores, 

 the question is not yet satisfactorily settled. As to 

 the comparative cost of cyanide lixiviation and 

 chlorination, there are not yet sufficient data for 

 speaking dogmatically, even where ores are equally 

 adapted to the two processes. Both are valuable 

 contributions to the metallurgy of gold, and are as- 

 sisting immensely in increasing the production of 

 that metal. 



W. Mietzchke has observed that auriferous py- 

 rites, whether in solid rock or in a loose condition, 

 display the peculiar behavior that the gold uni- 

 formly distributed in the mass in the state of sul- 

 phide, in proportion as it is converted into an 

 oxidized product, moves toward the middle of the 

 mass. Hence the pyritic nucleus of a half-weath- 

 ered crystal shows double the proportion of gold 

 that does the average mineral before decomposition. 

 In a fully weathered specimen the author found a 

 granule of gold with crystalline surfaces. The con- 

 firmatory specimens were obtained from the Oren- 

 burg government, Russia. 



The Cassel-Hinman gold and bromine process is 

 applied for the extraction of gold from low-gnu k> 

 ores, and from those which will not give up their 

 gold to amalgamation. The expensiveness of bro- 

 mine, making its use without recovery impracti- 

 cable, has prevented its employment in many casrs 

 in which it would otherwise be preferable. Stating 

 its advantages, Mr. Parker C. Mcllhiney observes 

 in the "Journal of the American Chemical Society" 

 that it is a much less powerful oxidizing agent 

 than chlorine, so that oxidizable materials like py- 

 rites are much less acted upon by it than by chlo- 

 rine. In fact, it is impossible to treat with bromine 

 water pyrites containing gold, and to extract most 

 of the gold as bromide without attacking much 

 pyrites, which it is not possible to do with chlorine 

 water. Further, bromine dissolves gold much more 

 easily than does chlorine. These facts make it evi- 

 dent that if some means can be devised for recover- 

 ing the bromine which has been used in the treat- 

 ment of the ore, much better results can be obtained 

 than by chlorination. The Cassel-Hinman process 

 consists in adding to the liquor which has acted 

 upon the ore, and which still contains a large excess 

 of bromine as well as some bromides, sufficient chlo- 

 rine or oxidizing agent and acid to liberate the 

 bromine from the bromides and then to distill off 

 the bromine by steam. The amount of liquid 

 which it is necessary to distill off for this purpose is 

 surprisingly small. The liquid thus freed from 

 bromine is in an ideal condition for the precipita- 

 tion of gold, and this may be accomplished by any 

 convenient method. 



Experiments described by Parker C. Mcllhiney 

 go to show that hydrochloric acid in presence o'f 

 air is without action on metallic gold, and that fer- 

 ric chloride is without action on gold unless oxygen 

 is present, but that ferric chloride acts as a very 

 efficient carrier of chlorine in the presence of hy- 

 drogen and oxygen. This fact, the author remarks, 

 ' helps to account for the solubility of gold in mine 

 waters and in other waters containing iron, acid, 

 and common salt. 



Difficulties met in assaying gold extracted by 

 certain processes and containing base metals, nota- 

 bly lead and zinc, have been investigated by Mr. 

 Edward Matthey, who finds that in such alloys the 

 gold is concentrated toward the center and lower 

 portions, whence it is impossible by the usual pro- 

 cesses to ascertain their true value from the assay 



of specimen pieces with even an approximation to 

 accuracy. When silver is also present, however, 

 these irregularities are greatly modified. The 

 method of obtaining " cooling curves " of the alloys 

 shows that the freezing points are very different 

 when silver is present in the alloy and when it is 

 absent from it. This fact leads the author to be- 

 lieve that if the base metal present does not exceed 

 30 per cent., silver will dissolve and form a uni- 

 form alloy with gold. His conclusion is sustained 

 by experiments which he cites, and which, in fact, 

 lead up to it. 



A method of separation of silver from gold by 

 volatilization is proposed by Dr. Joseph W. Rich- 

 ards. He has found that on heating to a bright- 

 yellow heat (not to whiteness) upon charcoal an 

 alloy of gold and silver, before a sharp-pointed oxi- 

 dizing flame, the silver volatilizes easily and stead- 

 ily until less than 3 per cent, of that metal remains 

 in the gold. The volatilization is estimated to 

 take place a little above the melting point of cop- 

 per, say at from 1,100 to 1,200 C. To remove 

 the remainder of the silver, the heat is raised 

 nearly to whiteness, to about the melting point of 

 steel (1,500" (.'.). When the silver is entirely elimi- 

 nated, the gold begins to volatilize also ; in fact, a 

 trace of gold will be carried off with the last of the 

 silver. The author has tested this method of sepa- 

 ration in many different ways, and has found the 

 separation to be absolute when the conditions he 

 describes in detail are observed. It was suggested 

 in the discussion of his paper at the Franklin In- 

 stitute that the method might be practicable in 

 the ordinary assay of gold and silver at assay 

 offices if an electrically heated furnace could be de- 

 vised in which the buttons could be placed on suit- 

 able supports and kept at the proper temperature 

 to volatilize silver, with a current of air passing 

 over them. 



The principle on which the process of D. Tom- 

 masi for the electrolytic dcsilverization of argen- 

 tiferous lead is founded consists in electrolyzing a 

 lead solution which not merely possesses an ex- 

 tremely weak electric resistance, but does not give 

 rise to lead peroxide (Pb0 2 ), and, in taking the 

 argentiferous alloy itself as anode and cathode, a 

 metallic disk which can not be attacked by the 

 bath. Under the action of the current the lead of 

 the anodes enters into solution and is transferred, 

 in the state of spongy crystals, upon the disk which 

 serves as cathode ; while all the silver contained in 

 the lead, being insoluble in the bath, is deposited 

 in the bottom of the vat in a perforated receiver 

 destined for its collection. 



In the extraction of the precious metals by lead 

 at A in ad or City, the mineral is reduced to a powder 

 of suitable fineness and is then roasted to drive 

 away sulphur, arsenic, and antimony. While it is 

 still hot it is drawn into the bottom of a receiver 

 containing melted lead and supplied with a series of 

 grates placed one above another, between which 

 the shakers turn. The mineral is thus brought 

 into close contact with the melted lead, and when 

 it comes out contains no gold or silver. 



Copper and Nickel. The processes of treating 

 copper ores are divided by Dr. J. E. Mackenzie into 

 3 classes: 1, Of ores free from sulphur; 2, of ores 

 containing sulphur; 3, of ores containing very 

 small percentages of copper (3 per cent, and under). 

 The minerals worked by processes of the first class 

 are cuprite, malachite, and azurite. The metal is 

 run from them by fusion with charcoal in a small 

 blast furnace, and the impure metal is refined by 

 melting in a small furnace with a hemispherical 

 bed, a blast of air being directed upon the metal to 

 oxidize the impurities. The minerals treated by 

 methods of the second class are copper pyrites (or 



