Intelligence and Miscellaneous Articles. 153 



production of oxide of zinc and osinic acid, we must conclude that 

 at about 300 c the substance undergoes a change of state accom- 

 panied by a large disengagement of heat. In air the change of 

 state is immediately followed by combustion, which augments the 

 evolution of heat. 



The residue is only partially attacked by concentrated nitric acid 

 or aqua regia. It is quickly and completely oxidized when 

 thrown into a mixture of fused potass and potassium nitrate ; 

 ir must even be thrown in in small portions, the mixture being 

 but little heated, to avoid too strong a deflagration when the divided 

 material touches the surface of the oxidizing liquid. If one wishes 

 to make use of this residue either for the analysis of the osmide or 

 to extract the metals which it contains, it is better to mix it with 

 anhydrous baryta and barium nitrate : one can then heat it with- 

 out fear of losing the substance, which is then attacked totally and 

 easily. 



This substance is evidently a complex mixture of various alloys 

 which zinc is capable of forming with the platinum metals ; we 

 were therefore induced to examine more closely those different 

 combinations. 



II. Osmium simply dissolves iu zinc. When the fused button 

 of this metal with osmium in a state of division is acted upon by 

 hydrochloric acid, there remains pure osmium with a crystalline 

 appearance. 



Palladium and platinum, treated in the same manner, leave a 

 residue consisting of alloys which undergo no isomeric modification 

 when heated in vacuo. Rhodium, on the contrary, and iridium and 

 ruthenium especially, as one of us has already proved *, combine 

 with zinc with much liberation of heat : and when the zinc button 

 is dissolved in hydrochloric acid, residues are obtained which are 

 susceptible of undergoing a true isomeric modification accompanied 

 by a brisk liberation of heat, without loss of gas, when heated in a 

 vacuum above 300 \ Before the liberation of heat, the blackish 

 residues would be more or less readily attached by aqua regia. 

 They lose this property after the liberation of heat, and then take 

 the metallic appearance. 



The thermal phenomenon which accompanies the change of state 

 of the iridium residue is so marked that it may serve for the 

 recognition of the presence of small quantities of iridium in 

 platinum (1 or 2 per cent, for example). The metal to be assayed 

 is dissolved in a large excess of zinc ; and the button is acted upon 

 by dilute hydrochoric acid ; the residue, well dried, raised to a 

 temperature above 300° in a platinum capsule becomes incan- 

 descent at various points. Ruthenium and rhodium produce 

 similar effects. 



TTT . In brief, osmium is the only platinum metal which does 

 not retain zinc when its alloy with a large excess of zinc is treated 

 with an acid capable of dissolving that metal. The other metals 

 obstinately retain a notable proportion of it (on the average 10 to 



* Comptes Rendus, t. xc. p. 1150. 



