METALS. 



487 



:uv \\ -irliin reach, the wont of sulphuric acid 

 \\ li.-u necessary, bo made up by tho uso 

 in- iitlu-r substance, such as green vitriol, 

 ur copperas. Ores containing from 80 to 100 

 ounces of silver to the ton should bo mixed 

 wi;h 10 per cent, of salt. Rich ore is often 

 roasted with 20 per cent, of salt. If ull tho 

 chlorine of tho salt could bo transferred to the 

 sil\vr, an insignificant amount of salt only 

 would bo required for ores containing 100 

 ounces of silver not more than 3J- pounds to 

 tho ton; but, in consequence of tho different 

 way in which tlm chlorine decomposes and 

 unites with base metals and gases, tho escape 

 of chlorine from tho surface of the ore without 

 coming in contact with tho silver, etc., a great 

 deal more of the salt must be applied. Per- 

 manent stirring is not essential, and Mr. Kus- 

 tel remarks that a good chloridizing roasting 

 should give over 90 per cent, of the silver con- 

 verted into chloride of silver, and show as lit- 

 tle as possible of base metal chlorides, which 

 are formed under the action of chlorine and 

 hydrochloric acid. 



Reducing Silver with Zinc. In refining gold 

 bullion by Miller's now chlorine process, the sil- 

 ver contained in tho alloy is separated in the 

 state of argentic chlorides. Mr. Leibus, assayer 

 of the mint at Sydney, reduces this chloride to 

 the metallic fonn on the large scale by a simple 

 application of galvanism. A weak solution of 

 common salt, or water alone, forms the ex- 

 citing liqnor, and the silver chloride and strips 

 of zinc placed therein supply the galvanic ele- 

 ments. After about twenty-four hours, the 

 action has nearly ceased, and the chloride is 

 found to be changed to metallic silver, with a 

 loss in the zinc of 24 or 25 per cent, of the 

 weight of the chloride reduced. Mr. Leibus 

 remarks that, by using a part of the resulting 

 liquor from a previous reduction of argentic 

 chloride, and which contains chloride of zinc, 

 it has been found that the galvanic action sets 

 in very rapidly, and accelerates thereby the 

 completion of the reduction. No acid is used, 

 and, therefore, the amount of zinc used in each 

 reduction has invariably been found to be 

 almost the theoretical quantity required to 

 combine the chlorine of the argentic chloride 

 treated with tho metallic zinc, in order to form 

 chloride of zinc. 



The reduced silver is boiled out in acidulated 

 water, in order to remove the basic oxy-chlo- 

 rides, and finally in pure water. As soon as it 

 is taken off the last boiling, it is immediately 

 ready for tho melting-pot, since the heat from 

 the boiling water dries tho porous mass of 

 silver sufficiently to allow of its immediate 

 melting. 



Claude? s Silver Process. Tho ingenious 

 process invented by M. F. Clandet, for the 

 separation of the small amount of silver found 

 in ordinary copper liquors, illustrates tho 

 economy of modern chemistry, by which waste 

 products are turned into sources of profit. The 

 ores treated were iron pyrites imported into 



Groat Britain from Ppain and Portugal, for the 

 manufacture of sulphuric acid. These were 

 found to contain 1- tu.cn four and five per 

 cent, of topper, and this copper carried silver, 

 which tests showed to exist in the ore to tho 

 value of about 18 dwt. per ton. Clandct's pro- 

 cess saves tho silver by first concentrating tho 

 copper liquors by repeated washings of tho 

 ore, and then treating them as follows: Tho 

 liquors are run into wooden cisterns, each of 

 tho capacity of about 2,700 gallons, where they 

 are allowed to settle. Tho yield of silver, per 

 gallon, is then ascertained by taking a meas- 

 ured quantity, to which are added hydrochloric 

 acid, iodide of potassium, and a solution of 

 acetate of lead. The precipitate thus obtained 

 is thrown upon a filter, and, after being dried, 

 is fused with a flux, consisting ojf A mixture of 

 carbonate of soda, borax, and lampblack. Tho 

 resulting argentiferous lead is passed to tho 

 cupel, and, from tho weight of the button of 

 silver obtained, tho amount of that metal in a 

 gallon of the liquor is estimated. The liquor 

 from tho settling-vat is now allowed to flow 

 into another of slightly larger capacity, while, 

 at the same time, the exact amount of a solu- 

 ble iodide, necessary to precipitate the silver 

 present, is run into it from a graduated tank, 

 together with a quantity of water equal to 

 about one-tenth the volume of the copper 

 liquor. During the filling of the second tank 

 its contents are constantly stirred, and, when 

 filled, a little lime-water is added, and it is al- 

 lowed to settle during forty-eight hours. The 

 supernatant liquors are, after being assayed, 

 run off, and the tank again filled, when the 

 precipitate collected at the bottom is, about 

 once a fortnight, washed into a vessel prepared 

 for its reception. This precipitate is chiefly 

 composed of sulphate of lead, iodide of silver, 

 and salts of copper, from which the latter are 

 readily removed by washing with water acidu- 

 lated by hydrochloric acid. Thus freed from 

 salts of copper, tho precipitate is decomposed 

 by metallic zinc, which reduces the iodide of 

 silver completely, and, to a certain extent, sul- 

 phate of lead. The result of the decompo- 

 sition is iodide of zinc, which can be employed 

 to precipitate further quantities of silver, and 

 a precipitate rich in silver and also containing 

 a valuable amount of gold. The result of 

 nearly six months' experience of this process 

 at the Widnes Metal Works sh6w that J an 

 ounce of silver and 1| grain of gold may bo 

 extracted from each ton of ore worked, at a 

 total cost, including labor, loss of iodide, etc., 

 of 8d. per ton, or Is. 4d. per ounce of silver 

 produced. If from this amount bo deducted 

 6d., the value of the three grains of gold con- 

 tained in each ounce of silver, the cost of pro- 

 duction, per ounce of silver, will be reduced 

 to 10d., and the expense of working a ton of 

 ore to 5d. This leaves a profit of about 2s. on 

 each ton of ore worked. 



Economical Gold-Working. The Mining 

 Journal has a paper on the cheap and effective 



