688 IRIDIUM AND OSMIUM. 



Nitrate of palladium, Pd O, NO 5 , is formed by dissolving 

 the metal in nitric acid ; the solution dries up into a dark red 

 saline mass. When an excess of ammonia is added to this salt, 

 and the solution evaporated by a gentle heat, a colourless am- 

 moniacal nitrate is deposited in rectangular tables. 



Peroxide of palladium, Palladic oxide, Pd O 2 , 865.9 or 69.36. 

 To prepare this oxide, Berzelius recommends a solution of the 

 hydrate or carbonate of potash to be added, by small quantities 

 at a time, to the dry bichloride of palladium and potassium, 

 mixing well after each addition. A yellowish brown powder 

 separates, which is the hydrated peroxide, retaining a little al- 

 kali. Washed with boiling water, it loses the greater part of its 

 combined water and becomes black. This oxide dissolves with 

 difficulty in acids ; the solutions are yellow. The corresponding 

 bisulphuret of palladium has not been formed. 



Bichloride of palladium, Pd C1 2 , is obtained in solution, 

 when protochloride is dissolved in concentrated aqua regia, and 

 the solution only slightly heated. It forms a solution of so dark 

 a brown as to appear black, which gives a red precipitate with 

 chloride of potassium. When the solution is diluted or heated, 

 chlorine gas is evolved, and protochloride of palladium repro- 

 duced. The double salt of this chloride and chloride of potas- 

 sium is obtained by treating the double protochloride of palla- 

 dium and potassium in fine powder with aqua regia, and eva- 

 porating the supernatant fluid to dryness. It forms a cinnabar 

 red powder, in which little octohedral crystals can be perceived, 

 both the palladic and palladous double chlorides being isomor- 

 phous with the corresponding compounds of platinum. When 

 treated with hot water, this double salt emits chlorine, and is in 

 a great measure decomposed. The salts of the peroxide of pal- 

 ladium are scarcely known. 



SECTION III. 

 IRIDIUM AND OSMIUM. 



Eg. 1233.5 or 98.84 ; Ir. 



The black scales which remain when native platinum is dis- 

 solved in aqua regia, were discovered by Mr. Smithson Ten- 



