462 Proceedings of Philosophical Societies. [June, 



Tlie chromium is next to be separated. For tliis purpose the 

 liquid is evaporated, the residue dissolved in water, and filtered, to 

 separate the silica that may be present. Pronitrate of mercury is 

 then poured in, whith occasions a precipitate of chromate of mer- 

 cury, which, being dried and heated, gives the green oxide of 

 chromium. There remains for examination the first precipitate of 

 iridium, titanium, iron, chromium, and alumina. There is like- 

 wise a little osmium, which is removed by digesting in muriatic 

 acid, distilling, and precipitating by zinc as before. If there 

 remain portions undissolved, they must be triturated with nitre, as 

 at fir;t ; and we observe that the oftener this operation is repeated 

 the more blue do the muriatic acid solutions become, because they 

 contain less and less iron and titanium, vvliich, as more easily dis- 

 solved, are first acted upon by the acid, and leave behind them a 

 greater proportion of iridium. 



Now iridium has this property : when in that state of oxidation 

 that it forms red solutions in acids, it is only precipitated by sal- 

 ammoniac, and that in the state of a triple salt. It is therefore 

 brought to this state by boiling its muriatic solution with nitric acid. 

 The liquid is neutralized by ammonia. By boiling, the iron and 

 titanium are thrown down. The iridium is then precipitated by sal- 

 ammoniac ; and the triple salt obtained, when exposed to a red 

 heat, leaves iridium in a state of purity. 



This metal, so difficult to separate from the singular alloy which 

 concealed it from all eyes, possesses remarkable properties. Its 

 colour and lustre are very similar to those of platinum. It is more 

 difficultly fusible. It is insoluble in the simple acids, difficultly 

 soluble in nitro-muriatic acid ; but potash and nitre oxidize it, and 

 combine with it into black powder, which gives a blue-coloured 

 solution. With boiling nitro-muriatic acid, it forms a red solution. 

 Its blue solutions themselves become red when boiled ; but both the 

 blue and the red solutions are discoloured by sulphate of iron, sul- 

 phureted hydrogen, iron, zinc, and tin. Oxymuriatic acid causes 

 them to resume their colour. It is iridium which gives a red colour 

 to the last precipitates of the triple salt of platinum, while the first 

 precipitates, into which it does not enter, are yellow. 



The properties of osmium are not so easily determined, in con- 

 sequence of the ease with which it is oxidated and volatilized. Its 

 oxide is white, and very caustic. It exhales an unsupportable odour. 

 It is flexible and fusible, like wax ; and as soon as it touches an 

 animal matter, it blackens it. Its solution in water becomes blue 

 by nutgalls, &c. 



M. Mongez, member of the Clr.ss of Ancient Literature, has 

 read a memoir on the bronze of the ancients, in which he shows, 

 from experiments made by M. Darcet, that it is not by immersion 

 in cold water that bronze becomes hard, as is the case with steel ; 

 but that it acqui.'-es its hardness by being heated red-hot, and then 

 allowed to cool slowly in the air. M. Darcet has taken advantage 

 of this property to make symbals, instruments hitherto made only in 



