Prof. It. Bun sen on Rhodium. 255 



62 grammes. The filtrate is introduced into a large stoppered 

 flask, which must not be more than half full ; if chlorine is passed 

 into the flask which is shaken from time to time until no more 

 absorption of the gas in the space above the liquid ensues, all 

 the palladium is separated as a vermilion-red precipitate con- 

 sisting of bichloride of palladium and potassium contaminated 

 by platinum and some rhodium and iridium. This weighed 

 157 grammes. The liquid from which these precipitates are 

 obtained is evaporated with hydrochloric acid not quite to dry- 

 ness. On the addition of as much water as was necessary, by 

 rubbing with a pestle, just to dissolve the chloride of potassium 

 and the other soluble salts, a dirty chamois-yellow precipitate 

 was left; this was separated by filtration, boiled for a short time 

 with soda-lye and a i'cw drops of alcohol, then mixed with hy- 

 drochloric acid until the precipitate at first formed was redis- 

 solved. After saturating the filtered solution with chloride of 

 potassium, 13*5 grammes of chemically pure bichloride of plati- 

 num and potassium were obtained. The mother-liquor from 

 which all these metals were separated, when tested with zinc and 

 hydrochloric acid, indicated the presence of copper, but no pla- 

 tinum-metals. The separation of the vermilion-red palladium 

 precipitate was effected as follows : — It was dissolved in boiling- 

 water, by which part of the bichloride of palladium was reduced 

 to protochloride with disengagement of chlorine. After evapo- 

 rating the solution with 60 grammes of oxalic acid and redissol- 

 ving it in solution of chloride of potassium, 42 grammes of bi- 

 chloride of platinum and potassium remained, which were yellow, 

 and almost completely free from foreign admixtures. The wash- 

 ing was effected as before. The brown filtered liquid, which was 

 somewhat evaporated in the water-bath, deposited on cooling 19 

 grammes of large and very beautifully formed transparent pea- 

 green crystals of protochloride of palladium and potassium, which 

 contained an admixture of chloride of potassium, but were found, 

 on testing, to be free from other platinum-metals. 



The liquid poured off from these crystals, carefully neutralized 

 with soda, gave a slight precipitate of sesquioxide of iron and 

 oxide of copper, which was removed. On the addition of iodide 

 of potassium in the cold, all the palladium was separated as iodide. 

 As iodide of palladium is soluble in iodide of potassium, an excess 

 of the precipitant must be carefully avoided. This is readily 

 effected if from time to time a little drop is taken from the outer 

 edge of the liquid by means of a capillary tube"* : as long as the 

 precipitation is not complete, the drops brought against a white 

 ground appear brown; when the precipitation is just complete, 



* By this little device almost every constituent of a liquid which gives 

 an insoluble precipitate may be volumctiically determined in a short time. 



