Prof. R. Bunsen on Rhodium. 261 



through a tube just projecting below a perforated cork, and 

 emerges through a delivery-tube which is just over the layer of 

 liquid. When the air has been completely expelled the exit- 

 tube is closed, and the flask filled with hydrogen is connected, 

 by means of a piece of thick caoutchouc tubing, with the Do- 

 bereiner's apparatus for the whole duration of the reduction. 

 The temperature of the flask is kept just below 100° C. by placing 

 it in a large iron pot which is heated by a small flame day and 

 night. A water-bath at a constant level is better. The re- 

 duction begins at once, and is completed in five or six days if 

 the quantity of metal amounts to about 100 grms. The first 

 deposit consists principally of platinum and palladium ; in the 

 succeeding one rhodium preponderates; and the last parts are par- 

 ticularly rich in iridium. It is best to stop the reduction as soon 

 as the liquid has assumed a greenish-yellow colour. The last 

 traces of iridium which it still contains are obtained by evapo- 

 rating the contents of the flask, igniting them with carbonate of 

 soda, and afterwards exhausting the fused mass with aqua regia, 

 so as afterwards to add them to another operation with chloride 

 of barium. The reduction may be still more accelerated, if the 

 liberated hydrochloric acid is removed from time to time by 

 evaporation, care being taken to displace each time the hydrogen 

 by aqueous vapour or carbonic acid before allowing air to enter, 

 so as to avoid dangerous explosions. The palladium-metals se- 

 parated consist of lustrous spangles, foil, and dendrites. Pla- 

 tinum and palladium are extracted by aqua regia, and, after 

 treatment with soda, separated by chloride of potassium and 

 iodide of potassium in the manner indicated above. The mother- 

 liquor still contains some rhodium and traces of iridium, which 

 are precipitated as iodide by repeated boiling with solution of 

 iodide of potassium. These are dissolved in aqua regia and 

 added to the subsequent separation of these metals. 



The metals thus treated with aqua regia, and partially oxi- 

 dized, are reduced by hydrogen at a temperature just below red- 

 ness, and again converted into chlorides by being treated with 

 chloride of barium in a current of chlorine. If from the solution 

 of these metals the last traces of platinum and palladium are 

 also removed by boiling with soda, and precipitation with chlo- 

 ride and iodide of potassium, there only remains the separation 

 of iridium and rhodium. For this purpose the reddish-brown 

 liquid is evaporated with hydrochloric acid, filtered, mixed with a 

 great excess of bisulphite of soda, and left to stand in the cold for 

 several days. Rhodium slowly deposits as an amorphous lemon- 

 yellow soda double sulphite, while the solution becomes yellow 

 and finally decolorized. With this change of colour, the rhodium 

 precipitate also becomes brighter. The precipitate, well washed 



