74 On the Alloys of Steel [1822. 



of rhodium was formed, distinguishable by its colour, and by 

 the triple salt it formed with muriate of soda. 



To analyse the compound of steel with iridium and osmium, 

 the alloy should be acted on by dilute sulphuric acid, and the 

 residuum boiled in the acid ; the powder left is to be collected 

 and heated with caustic soda in a silver crucible to dull redness 

 for a quarter of an hour, the whole to be mixed with water, 

 and having had excess of sulphuric acid added, it is to be di- 

 stilled, and that which passes over condensed in a flask : it will 

 be a solution of oxide of osmium, will have the peculiar smell 

 belonging to that substance, and will give a blue precipitate 

 with tincture of galls. The portion in the retort being then 

 poured out, the insoluble part is to be washed in repeated 

 portions of water, and then being first slightly acted on by 

 muriatic acid to remove the iron, is to be treated with nitro- 

 muriatic acid, which will give a muriate of iridium. 



In these analyses, an experienced eye will frequently per- 

 ceive, on the first action of the acid, the presence of the 

 alloying metal, When this is platinum, gold, or silver, a film 

 of the metal is quickly formed on the surface of the acid. 



Of alloys of platinum, palladium, rhodium, and iridium and 

 osmium, a ready test is offered when the point is not to ascer- 

 tain what the metal is, but merely whether it be present or not. 

 For this purpose we have only to compare the action of the 

 same acid on the alloy and on a piece of steel; the increased 

 action on the alloy immediately indicates the presence of the 

 metal ; and by the difference of action, which on experience 

 is found to be produced with the different metals, a judgement 

 may be formed even of the particular one present. 



The order in which the different alloys stand with regard 

 to this action is as follows : steel, chromium alloy, silver alloy, 

 gold alloy, nickel alloy, rhodium alloy, iridium and osmium 

 alloy, palladium alloy, platinum alloy. With similar acid the 

 action on the pure steel was scarcely perceptible ; the silver 

 alloy gave very little gas, nor was the gold much acted on. 

 All the others gave gas copiously, but the platinum alloy in 

 most abundance. 



In connexion with the analysis of these alloys, there are 

 some very interesting facts to be observed during the action 

 of acids on them, and perhaps none of these are more striking 



