Mr. Cock on Palladium. 17 



troy, with its own weight of silver and a certain quantity of 

 nitrate of potash ; the effect of this fusion is to remove all 

 earthy matter, and the greater part of the base metals con- 

 tained in the gold dust and in the silver melted with it. The 

 fused mixture is cast into ingot moulds, and when cooled, the 

 flux or scoria (containing the oxides of the base metals and 

 the earthy matter, combined with the potash of the nitre) is 

 detached. Two of the bars thus obtained are then remelted 

 in a plumbago crucible, with such an addition of silver as will 

 afford an alloy containing one-fourth its weight of pure gold, 

 and which being first well-stirred to insure a complete mix- 

 ture, is poured through a perforated iron ladle into cold water, 

 and thus very finely granulated ; it is then ready for the pro- 

 cess of parting. For this purpose about 25 lbs. of the granu- 

 lated alloy is placed in a porcelain jar, upon a heated sand-bath, 

 and subjected to the action of about 25 lbs. of pure nitric acid, 

 diluted with its own bulk of water: after the action of this quan- 

 tity of acid, the parting of the gold is very nearly effected ; 

 but to remove the last portions of silver, &c, about 9 or 10 lbs. 

 of strong nitric acid is boiled upon the gold for two hours. 

 It is then completely refined, and after being washed with 

 hot water is dried and melted into bars containing 15 lbs. 

 each. 



The nitrous acid gas, and the vapour of nitric acid arising 

 during the above process, are conducted by glass pipes (con- 

 nected with the covers of the jars) into a long stone-ware 

 pipe, one end of which slopes downwards into a receiver for 

 the condensed acid, the other end being inserted into the flue 

 for the purpose of carrying off the uncondensed gas. 



The nitrate of silver and palladium obtained as above is 

 carefully decanted into large pans, containing a sufficient 

 quantity of solution of common salt to effect the precipitation 

 (as a chloride) of the whole of the silver, the palladium and 

 copper remaining in solution in the mother liquor, which is 

 drawn offj and when clear is run off, together with the sub- 

 sequent washings from the chloride of silver, into wooden 

 vessels, and the metallic contents are then separated in the 

 form of a black powder, by precipitation with sheet zinc, as- 

 sisted by sulphuric acid. 



The chloride of silver, when washed clean, is reduced by 

 the addition of granulated zinc Washed on the filter with 

 boiling water, dried and melted in plumbago crucibles, with- 

 out the addition of any flux. 



From the black powder obtained as above, the palladium is 

 extracted by resolution in nitric acid and super-saturation 

 with ammonia, by which the oxides of palladium and copper 



Phil. Mag. S. 3. Vol. 23. No. 149. July 1843. C 



