W. Gibhs on the Platinum metals. 353 



a basic compound under these circumstances. The cTilorid oNH,, 

 RhaClg. is then to be further purified by crystallization. 



Rhodium from ruthenium. — The separation of rhodium from 

 ruthenium is best effected by means of nitrite of potash. The 

 mixed sohition of the two metals is to be boiled for a short time 

 with an excess of the nitrite together with a little carbonate of 

 potash to keep the solution neutral or slightly alkaline. The 

 yellow or orange-yellow solution is then to be evaporated to dry- 

 ness upon a water bath, the dry mass rubbed to fine powder and 

 then treated in a flask with absolute alcohol in the manner 

 pointed out for the separation of platinum from ruthenium. 

 After filtration and washing with absolute alcohol, the rhodium 

 remains undissolved in the form of a mixture of the two double 

 nitrites of rhodium and potassium. These may be ignited with 

 a large excess of sal-ammoniac so as to yield, after washing, me- 

 talHc rhodium, or the nitrites may be dissolved in hot chlorhydric 

 acid, ammonia added, and the rhodium precipitated as sulphid, 

 which is then treated in the manner already pointed out, so as 

 to convert the rhodium into the double chlorid of rhodium and 

 ammouium. To remove the last traces of ruthenium the rho- 

 dium salt may be a second time treated with nitrite of potash, as 

 above, and again washed with alcohol. The presence of the least 

 trace of ruthenium is easily detected by adding a drop of color- 

 less sulphid of ammonium to the alcoholic solution. The method 

 *5| obtaining pure ruthenium from the double nitrite of ruthe- 

 nium and potassium has already been given. 



For the separation of osmium from the other metals of the 

 ?^oup I have no better method to offer than that which is uni- 

 Y'fsally employed, namely, the volatilization of the osmium in 

 tl"-^ form of osmic acid. The separation of palladium is m all 

 cfi-^es al::o best effected by the processes commonly employed, 

 -i'Of'ially by takinf^ advantage of the solubility of the double 

 -^'^^■■s of protochlorid of palladium in solutions of the alkaline 



,^^^ith these prehminary and general statements the method 

 "nich I emplov in separating the different metals of the plati- 

 ■■'-^'^'^ group from each other will be intelligible. The mass of 

 'I'^'ible chlorids, obtained as already mentioned, is to be rubbed 

 ':;;i tine powder; introduced into a deep porcelain evaporating 

 •ii^ii and mixed with four or five times its volume ot boiling 

 '^■''^ter. A solution of nitrite of soda is then to be added in small 

 T'^:intities at a time, the solution being continually stirred and 

 ?;(Msionally neutralized by addition of carbonate of soda. Ihe 

 V.'l'iid soon becomes olive-green and the greater part of the mass 

 ^'^'^olves: it is advantageous, when the quantity ot the mixed 

 chlorids is large, to pour" off the liquid as soon as it appears sat- 

 ''irated and to°repeat the operation with a fresh quantity of water. 



