Prof. R. Bunsen on Rhodium. 2G3 



second time by the method already described. The green solu- 

 tion free from rhodium, but containing all the iridium, is freed 

 from sulphuric acid by heating it, first in a platinum dish over 

 the open fire, and then at a gradually increasing temperature in 

 a porcelain crucible in a sand-bath; the porcelain crucible with its 

 contents is finally strongly heated in a charcoal fire, by which 

 neutral sulphate of soda and sesquioxide of iridium are formed. 

 The latter remains as a black powder, after boiling out the 

 fused mass, and is easily washed by decantation. It weighed 

 9*1 grms. 



According to these experiments, there were thus obtained 

 from a kilogramme of residue : — 



grms. 

 Chloride of potassium and platinum . . 117*5 



Iodide of palladium 77 



Chloride of potassium and palladium . . 19*0 

 Sulphate of rhodic oxide and soda . . . 332 



Sesquioxide of iridium 9*1 



Iridium containing ruthenium .... 4*5 



The whole of the mother-liquors and residues from these pre- 

 parations gave, when tested by zinc, inconsiderable traces only of 

 platinum-metals. 



In a subsequent memoir I shall recur to the constitution of 

 the new compounds on which the method described is based, as 

 well as to the atomic weight and properties of the chemically 

 pure metal and some of its compounds. I will merely remark 

 that working up 5 or 6 kilogrammes of crude material requires 

 very little time, especially if all the filtrations are effected by a 

 method which I introduced some time ago into my labora- 

 tory, and which consists in filtering in ordinary glass funnels 

 with ordinary filter-paper under the pressure of a column of 

 water of 25 to 30 feet. This pressure is produced by means of 

 a water air-pump, on Spren gel's principle, which works day and 

 night with a jet of water scarcely as thick as a straw, when by 

 simply opening a tap it is connected with the water supply of 

 the laboratory. The length of time required for washing preci- 

 pitates is diminished to \ or \, especially in quantitative work, 

 and the quantity of wash-water required is not more than from 

 1*0 to I ; immediately after filtering, the paper can be removed 

 (even from gelatinous precipitates) like the skin of a boiled potato, 

 so clean and completely, that the same filter may be used a second 

 time ; and the precipitates are obtained in such a form that they 

 may be directly ignited without any further drying. 



A minute description of this method, which, as regards cer- 

 tainty, precision, and rapidity, brings analysis by weight very 

 near volumetric methods, I must defer to another communication. 



