Obtaining Osmium and Iridium from the Platinum residue. 375 



Mr. Booth of Philadelphia, who is at present engaged in my labora- 

 tory, and who rendered me much assistance in these experiments, dis- 

 covered at the same time a cyanid of iridium and potassium. He ob- 

 tained it according to the method given by Gmelin for the correspond- 

 ing platinum salt, viz., by gentle long continued ignition of a mixture 

 of dry protocyanide of iron and potassium (prussiate of potassa) with 

 iridium in powder. This must be performed apart from the air, for 

 otherwise, when heated to a certain degree, the mass undergoes 

 combustion. The coagulated mass is powdered and dissolved in 

 water. Upon evaporation of the almost colorless solution, a portion 

 of undecomposed iron and potassium-cyanid crystallizes and at length 

 the salt of iridium. 



Cyanide of iridium and potassium (probably protocyanide) crystalli- 

 zes in long four prisms, generally in twin-crystals similar to selenite, 

 to judge from the angle on their terminating planes. They are 

 perfectly colorless and clear, and have not that blue and yellow opa- 

 lescence, peculiar to the corresponding salt of platinum. They are 

 soluble in water and not in alcohol, and their solution is not precipi- 

 tated by sulphuretted hydrogen. They contain no water; — decrep- 

 itate strongly on being heated and become black ; — by stronger heat 

 they fuse and iridium separates, often covering the glass with a me- 

 tallic mirror. 



The excess of iridium, which had been added to the potassium 



iron-cyanide, and which remained after dissolving the ignited mass in 



water, has taken up much iron and carbon. It has now become so 



combustible that when ignited in one point, it continues the ignition 



of itself throughout the whole mass, like a pyrophorus. The iron 



may afterward be easily separated by digestion with hydrochloric 

 acid. 



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