1879.] Group of Metals known as the Platinum Series. 465 



baskets such, as are used in the manufacture of chlorine gas for holding 

 the oxide of manganese. When the first charge of acid is sufficiently 

 saturated, a fresh quantity should be added until no more action is 

 apparent ; at this stage the greater part of the lead will have been 

 dissolved out together with a portion of any copper, iron, palladium, 

 or rhodium that may have been present. These metals are subsequently 

 extracted from the mother-liquors y the nitrate of lead by crystallization, 

 and the remaining metals by well-known methods. 



The metallic residue now obtained will be found in the state of an 

 amorphous black powder (a form most suitable for further treatment), 

 consisting of platinum, lead, and small proportions of the other metals 

 originally present — the iridium existing as a brilliant crystalline sub- 

 stance insoluble in nitric acid. After digesting this compound in 

 weak aqua regia, an immediate dissolution takes place of the platinum 

 and lead, leaving the iridium still impure, but effecting a complete 

 separation of the platinum. 



To the chloride of platinum and lead after evaporation is added 

 sufficient sulphuric acid to effect the precipitation of the whole of the 

 lead as a sulphate, and the chloride of platinum after dissolution in 

 distilled water is treated with an excess of chloride of ammonium and 

 sodium, the excess- being necessary in order that the precipitated 

 yellow double salt may remain in a saturated solution of the pre- 

 cipitant. The whole is then heated to about 80° y and allowed to stand 

 for some days ; the ammonio-chloride of platinum will settle down as 

 a firm deposit at the bottom of the vessel, whilst if any rhodium, as is 

 generally the case, is present, the surface liquor will be coloured a 

 rose tint, occasioned by a combination of the salts of the two metals. 



The precipitate must be repeatedly washed with a saturated solu- 

 tion of chloride of ammonium and subsequently with distilled water 

 charged with pure hydrochloric acid. This is necessary for its puri- 

 fication. The small quantity of the double salt which will be taken 

 up and held in solution is of course recovered afterwards. Rhodium 

 may still exist in the washed precipitate, which must therefore not be 

 reduced to the metallic state until its separation is completed, and 

 this is best effected by mixing with the dried compound, salts of 

 chloro-platinate and chloro-rhodiate of ammonia, bi-sulphate of potash 

 with a small proportion of bi-sulphate of ammonia, and subjecting to 

 a gradual heat brought by degrees up to a dull red in a platinum 

 capsule, over which is placed an inverted glass funnel. The platinum 

 is thus slowly reduced to a black spongy porous condition freed from 

 water, nitrogen, sulphate of ammonia, and hydrochloric acid, the 

 rhodium remaining in a soluble state as bi-sulphate of rhodium and 

 potash, which can be dissolved out completely by digesting in boiling 

 distilled water ; a small quantity of platinum will have been taken up 

 in a state of sulphate, but is regained by heating the residue (obtained 



