Prof. 11. Bunsen on Rhodium. 259 



given off under the same circumstances after the addition of 

 potassiochloride of iridium. 



I. II. III. 



Palladium . . . . 00 1-5 



Copper 0-0 18-4 



Lead 23-5 58-0 



Nickel 70-8 242-4 



Tin 80-0 9200 



Cadmium .... 9*1 10400 



The metallic mass separated from the zinc regulus, and alter- 

 nately digested with hydrochloric acid and water, forms a fine 

 dusty black powder, and, together with some admixed grains of 

 sand arising from the crucible, weighed 65 grms*. It has the 

 property of softly exploding with the appearance of fire when 

 gently heated. The ignited and cooled powder, w r hen brought 

 in contact with cold unexploded powder, at once explodes the 

 latter. If the explosion is effected by heating in an hermeti- 

 cally closed tube, either exhausted or filled with carbonic acid, 

 neither hydrogen, nor chlorine, nor nitrogen, nor oxygen, nor 

 aqueous vapour is liberated. From the method of preparation, 

 these are the only bodies which could be present absorbed or in 

 combination ; it must therefore be assumed that all, or part, of 

 the metals separated from the zinc are in a peculiar allotropic 

 condition, which by heating, or by contact w r ith non-allotropic 

 metals, is got rid of with development of heat. The black powder 

 which exhibits these explosive properties consists essentially of 

 rhodium and iridium, with more or less considerable quantities 

 of the platinum-metals originally present, as well as traces of 

 lead, copper, iron, and zinc. 



It is most intimately mixed with three to four times its 

 weight of finely powdered perfectly dehydrated chloride of barium, 

 and heated in a current of chlorine at a temperature which effects 

 no disengagement of the gas. 



The apparatus used for this purpose was arranged as follows. 

 In the sheet-copper capsules, c, c, Plate II., provided with slides, 

 d, and of which five or six could be arranged in a series, flasks 

 of from 160 to 250 cubic centims. capacity were placed half 

 full of the above mixture, and surrounded on all sides by ignited 

 magnesia. Each flask is provided with a double-bored caout- 

 chouc stopper, e e, and w 7 ith two glass tubes ; one of these tubes, 

 through which the gas enters, passes to the bottom of the 

 flask, the other, by which the gas emerges to enter the next 

 flask, terminates just below the cork. The glass tubes are con- 

 nected by india-rubber tubes, and are provided with bulbs 

 * A kilogramme of residues from other parts of the Petersburg stocks 

 gave more than 120 grammes of this powder. 



S2 



