62 REPORT — 1870. 



The Vftts in -wliich the burnt ores which have been roasted with salts are lixi- 

 viated, generally receive some eight or nine successive washings, either with water 

 or with water acidulated by hydrochloric acid ; and of these the first three only 

 contain a sufficient amount of silver to be worth working. 



For the purpose of removing the soluble salts, hot water is employed ; and as a 

 large proportion of the chloride of sodium used remains undecomposed, it acts as a 

 solvent for the chloride of silver produced during the process of fumacing. 



The several operations for the extraction of silver are conducted in the following 

 manner ; and as the first three washings contain Do per cent, of the total amount 

 of that metal dissolved, these alone are treated. 



These liquors are fii-st run into suitable wooden cisterns, each of the capacity of 

 about 2700 gallons, where they are allowed to settle. The yield of silver per 

 gallon is now ascertained by taking a measured quantity, to which are added hy. 

 drochloric acid, iodide of potas.sium, and a solution of acetate of lead. The precipi- 

 tate thus obtained is thrown upon a filter, and, after being dried, is fused with a 

 flux consisting of a mixture of carbonate of soda, borax, and lampblack. The 

 resulting argentiferous lead is passed to the cupel ; and fi-om the weight of the 

 button of silver obtained the amount of that metal in a gallon of the liquor is 

 estimated. 



The liquor from the settling-vat is now allowed to flow into another, whilst at 

 the same time the exact amount of a soluble iodide necessary to precipitate the 

 silver present is run into it from a gi-aduated tank, together with a quantity of 

 water equal to about one tenth of the volume of the copper-liquor. During the 

 filling of the second tank its contents are constantly stin-ed ; and when filled, a 

 little lime-water is added, and it is allowed to settle during forty-eight hours. 



The supernatant liquors are, after being assayed, run off", and the tank again 

 filled, whilst the precipitate collected at the bottom is, about once a fortnight, 

 wa.9hed 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 dilute 

 hydrochloric acid. Thus freed from salts of copper, the precipitate is decomposed 

 by metallic zinc, which reduces the iodide of silver completely, and, to a certain 

 extent, also the sulphate of lead. The result of this decomposition is : — -. 



1st. Iodide of zinc, which, after being standardized, is employed in subsequent 

 operations to precipitate further quantities of silver. 



2nd. A precipitate rich in silver, and also containing a valuable amount of gold. 



The results of six months' experience of this process at the Widnes Metal-works 

 show that i an ounce of silver and 1| grain of gold may be extracted from each 

 ton of ore worked, at a total cost, including labour, loss of iodide, &c., of 8d. per 

 ton, or Is. 4(1. per oz. of silver produced. If from this be deducted 6d., the value 

 of the 3 grains of gold in each ounce of silver, the cost of production, per oz. of 

 silver, will be IQcl, and the expense of working a ton of ore Ijcl 



On the Absorption of Hydrogen b>/ Electro-deposited Iron. 

 By "W. Chandler Egberts, Chemist of the Mint. 



The author reminded the Section of a paper read during the Meeting of the Bri- 

 tish Association at Exeter, by Dr. Jacobi of St. Petersburg, on the electro-deposi- 

 tion of iron, specimens of which were submitted for inspection. 



The well-known experiments of Mr. Graham proved that palladium occluded 900 

 times its volume of hydrogen ; and Dr. Jacobi considered that the electro-deposition 

 of iron was attended 'by a similar absorption of hydrogen, although to a less degree. 



By submitting this idea to the test of experiment, the author found that the iron 

 contained at least 15-5 times its volume of hydi-ogen. The experiments were 

 effected by heating the iron hi vaaw. 



Similar results were also obtained by Lenz and Klein. 



Mr. Graham also proved that tubes of malleable iron, when heated to redness, 

 allowed hydrogen to penetrate their walls. The experiments were then attended by 

 unavoidable errors ; but by employing a tube of iron electro-deposited on a rod of 

 wax, Mr. Roberts was enabled to confirm the results .obtained by INlr, Graham, 



