204 Messrs. Stodart and Faraday on [Maech, 



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

 solution of oxide of osmium, will have the peculiar smell belong- 

 ing to that substance, and will give a blue precipitate with tinc- 

 ture 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 experinced eye will frequently perceive, 

 on the first action of the acid, the presence of the alloying metal. 

 When this is platina, gold, or silver, a film of the metal is 

 quickly formed on the surface of the acid. 



Of alloys of platina, 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 judgment 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, cromium alloy, silver alloy, gold 

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

 palladium alloy, platina 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 platina alloy in most abundance. 



In connection 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 than 

 those last referred to. When the alloys are immersed in diluted 

 acid, the peculiar properties which some of them exhibit, not 

 only mark and distinguish them from common steel, and from 

 each other, but also give rise to some considerations on the 

 state of particles of matter of different kinds when in intimate 

 mixture or in combination, which may lead to clearer and more 

 perfect ideas on this subject. 



If two pieces, one of steel, and one steel alloyed with platina, 

 be immersed in weak sulphuric acid, the alloy will be imme- 

 diately acted on with great rapidity and the evolution of much 

 gas, and will shortly be dissolved, while the steel will be 

 scarcely at all affected. In this case, it is hardly possible to 

 compare the strength of the two actions. If the gas be collected 

 from the alloy and from the steel for equal intervals of time, the 

 first portions will surpass the second some hundreds of times. 



A very small quantity of platina alloyed with steel confers this 

 property on it: T ^ increased the action considerably; with 

 •5^ and -j-^ it was powerful ; with 10 per cent of platina it 



