Nitrogen Thermometer from. Zinc to Palladium. 153 



ignited in a large porcelain crucible. The resulting metal was 

 dissolved in aqua regia and freed of nitric acid. This solution 

 was diluted and precipitated by potassium iodide, and the fil- 

 trate — 6k solution B " — removed as above. 



From solutions A and B, separately, the platinum metals 

 were first removed by long boiling with ammonium formate. 

 The metal — 1 to 2 g. in weight, mostly palladium — was filtered 

 and the filtrate and washings were examined further for other 

 heavy metals by the usual methods. 



Separation of the P alladium from the Platinum Metals. — 

 Considering now the ammonium formate precipitate, Erdmann 

 and Makowka* have obtained satisfactory separations of palla- 

 dium from platinum and iridium by treating the solution of 

 the mixed chlorides with acetylene. Palladium comes down as 

 acetylide and the other metals are un precipitated. I found 

 also that rhodium solutions even on heating were not precipi- 

 tated by acetylene. As for osmium, the ease with which it 

 oxidizes and the high volatility of its oxide makes its elimina- 

 tion, in the process of preparing the palladium, fairly certain. 

 Ruthenium, the rarest element among the platinum metals, 

 need hardly be looked for; still it was sought for in the iri- 

 dium found. The acetylene method was used, for lack of 

 a safer one, though very tedious. In solutions at all con- 

 centrated, I find the palladium ceases to precipitate long 

 before it is entirely removed from solution. Perhaps this 

 is due to the accumulation of acid liberated in the process. 

 At least, when the solution is separated from the acetylide, 

 evaporated and diluted again, acetylene brings down another 

 portion. After five or six operations, a residual solution was 

 obtained on which acetylene had no further action. The acety- 

 lide was now carefully ignited with a little ammonium nitrate, 

 the metal redissolved, and the whole process repeated. The 

 residual solution was then added to the first and from it .NH 4 C1 

 brought down platinum. In the chlor-platinate no iridium 

 was found. It was ignited and the metal was entirely soluble 

 in a few drops of aqua regia. It was again precipitated with 

 NH 4 C1 and finally weighed as platinum — Pt = 1*6 mg. = 0'007 

 per cent. No rhodium was found in the filtrate. In the 

 attempt to dissolve in aqua regia the several portions of metal 

 formed by igniting the acetylide, tiny insoluble residues accu- 

 mulated. These were fused with KHS0 4 , which, as is well 

 known, dissolves palladium and rhodium but not iridium or 

 platinum if the temperature is kept low. The soluble portion 

 was dissolved in water and precipitated with ammonium for- 

 mate. It turned out to be palladium, since it w T as precipitated 

 by potassium iodide and no trace of rhodium was found. 



* Zeitschr. anal. Chemie, xlvi, 146, 147, 1907. 



