530 



METALLURGY. (ALLOYS.) 



of the machine insures ah even distribution of 

 the sand and prevents the possibility of any 

 particle passing through without constant fric- 

 tional contact with the mercurial surface. This 

 feature prevents the finest float gold from es- 

 caping, and keeps the surfaces clean and active 

 in dealing with the more refractory ores. 



The chlorination process for the extraction of 

 gold from its ores has been greatly improved 

 within recent years, and now promises to be 

 adapted to the treatment of low-grade, non- 

 concentratable ores. The cost, relatively to the 

 production, has been brought down till it com- 

 pares favorably with the cost of the amalgama- 

 tion process. Godshall recommends as a precip- 

 itant to throw the gold from the chlorine solution, 

 precipitated sulphide of iron as far superior to 

 the sulphate, which entails waste, or to any other 

 precipitant in use, The gold solution is passed 

 through a filter containing the sulphide, using 

 two filters, one about ten feet below the other, 

 and placing the tank containing the gold solu- 

 tion about ten feet above the upper one. For 

 rapid filtration and complete action free chlo- 

 rine should be absent from the gold solution, else 

 the precipitation may be incomplete, with loss of 

 gold ; yet the solution should not be free from 

 chlorine too long before precipitation, for the 

 gold chloride might then decompose and the 

 gold settle on the bottom of the tanks. The 

 chlorine is expelled by heating, popper sul- 

 phide and lead sulphide are also efficient precipi- 

 tants ; but iron sulphide is most convenient on 

 account of the greater facility of separating gold 

 from iron. 



In Pollock's process for chlorination under 

 hydraulic pressure, the ore, crushed, roasted 

 when necessary for the removal of sulphur, and 

 partially cooled, is placed in the chlorinating 

 cylinders with about H per cent, of bleaching 

 powder and 2 per cent, of niter cake. Hydraulic 

 pressure is then applied, with more advantage if 

 the air present in the cylinder is allowed to es- 

 cape. The cylinder is then revolved. The niter 

 cake reacts with the bleaching powder, liberating 

 chlorine gas, all of which, in the absence of air, 

 passes into solution, while the strong chlorinat- 

 ing liquid is driven by the pressure into the 

 pores of the ore, all the gold of which is reached 

 and converted into chloride. 



The pyrites containing gold resulting from the 

 concentration of free milling gold ores is usually 

 treated by Plattner's process, which has been suc- 

 cessfully practiced in Grass Valley, Gal., since 

 1858. Modifications of it have, from time to 

 time, been suggested. Mears proposed to use 

 chlorine gas under pressure of from 30 to 40 

 pounds to the square inch, made in a generator 

 outside of the barrel and pumped into it, or pro- 

 duced inside of the barrel by the use of a great 

 excess of chemicals ; and while it was found that 

 more gold was dissolved, the gain was more than 

 compensated for by certain difficulties and wastes 

 in the process. Mr. A. Tbies, after four years' 

 use of the Mears process, found that he could 

 work without the pressure pumps as well as with 

 them, and having introduced other modifications 

 into the method, has perfected the barrel pro- 

 cess, which is working successfully. Its success 

 is owing, according to T. Egleston, in the " School 

 of Mines Quarterly," to the formation of nascent 



chlorine in contact with ore, which is constantly 

 being rubbed bright by the friction of the parti- 

 cles against each other and against the sides in 

 the revolving barrel. 



Considerable loss is incurred in milling the 

 gold of North Carolina on account of the fine- 

 ness of the condition in which the metal occurs. 

 It consequently escapes through the mills, ac- 

 cording to Mr. B. F. Wilson, Jr., or, according 

 to another explanation, is' wholly dissolved in 

 the mercury instead of being only* coated or per- 

 meated by it, as happens in the case of coarser 

 particles. This loss is obviated by using a solu- 

 tion of bichloride of mercury a solution which 

 has sufficient strength to act when diluted six- 

 teen thousand times. Being in the liquid state,. 

 it permeates the ground-up particles of ore and 

 amalgamates with the very fine particles of gold 

 that might otherwise escape. 



Alloys. The Japanese have been successful 

 in producing most varied and striking effects in 

 texture and color in art metal work by the use of 

 alloys, of which they have a wide range in com- 

 position. They have an alloy of silver and cop.- 

 per, sometimes with equal proportions of pre- 

 cious and base metal ; varieties of copper of 

 different degrees of purity ; several kinds of 

 brass; and a remarkable series of alloys in 

 which precious metal replaces the tin and zinc 

 of ordinary bronze. The principal alloys of the 

 last class are shaku-do and shibu-icJii. Shaku- 

 do contains about 95 per cent, of copper and 4 

 per cent, of gold ; but the proportion of gold is 

 variable, and silver and traces of other sub- 

 stances are sometimes found in it. It has been 

 used for very large works. Shibu-ichi is com- 

 posed of from about 50 to about 70 parts of 

 copper and 80 to 50 parts of silver, with traces 

 of gold and other substances. The feature of 

 interest in these alloys is the sacrifice of the pre- 

 cious metals in order to produce definite results,. 

 gold and silver, when used pure, being employed 

 sparingly to heighten the general effect. In 

 shaku-do the gold appears to enable the metal 

 to receive a beautiful rich purple coat or patina 

 when treated with certain pickling solutions, 

 while shibu-icTii possesses a peculiar silver-gray 

 tint, to which the Japanese artists are very par- 

 tial. There are several varieties of these alloys, 

 and they are combined in various proportions. 

 Thus, the composition of kiu-shibu-ichi would 

 correspond to one part of shaku-do rich in gold, 

 and two parts of shibu-whi rich in silver. The 

 most commonly employed pickling solution is 

 composed of 438 grains of verdigris and 292 

 grains of sulphate of copper in a gallon of wa- 

 ter. When boiled in a solution (No. Ill) com- 

 posed of 220 grains of verdigris and 540 grains 

 of sulphate of copper in a gallon of water, with 

 a preparation of vinegar, pure copper turns a 

 brownish red and shaku-do becomes purple. 

 The effects of small quantities of impurity in 

 the metal upon its color are strikingly exhibited 

 in using the pickles. Copper containing a small 

 quantity of antimony gives a different shade 

 from that which results from the pickling of 

 pure copper. Copper is often produced in Japan 

 from the smelting of very complex ores, while 

 the processes for purifying it are imperfect. 



The recent progress of metallurgy in the Unit- 

 ed States, according to the "Engineering and 



