1826.] the Ore of Iridium. 19 



This black deposit was light and bulky. When exposed to 

 the heat of & spirit-lamp in a small porcelain crucible, it took 

 fire, and burnt for an instant, owing, I suspect, to some small 

 vegetable matter from the filter being mixed with it. It retained 

 its black colour after having been exposed to a strong red heat, 

 but the weight was reduced to 4-765 grains. When this powder 

 was digested in nitro-muriatic acid, a red solution was obtained, 

 which became colourless by the addition of gallic acid, and 

 could not be precipitated by the action of any reagent tried. 

 Hence it was iridium. A complete solution of the black powder 

 could not be effected by nitro-muriatic acid, showing that the 

 iridium was in the metallic state. 



The muriatic acid solutions being collected together and 

 evaporated to dryness, left a black matter weighing 3'3 grains ; 

 but reduced by exposure to a strong red heat to 1*89 grain. 

 This portion had been united to the 4*765 grains of iridium 

 obtained from the potash, and the whole was digested for a 

 week on the sand-bath in muriatic acid. The red coloured 

 liquid became colourless when ammonia was added to it in 

 excess ; but a slight flocky precipitate fell which had a browu 

 colour, and weighed, after being dried in a red heat, 0'33 grain. 

 This matter dissolved in muriatic acid. The solution was 

 reddish yellow, and struck a deep blue with prussiate of potash. 

 Hence the flocks were peroxide of iron, equivalent to 0'23 grain 

 of metallic iron. The colourless solution thus freed from iron 

 being evaporated to dryness, and redissolved, assumed its 

 original red colour. 



Thus from 8*82 grains of ore of iridium were obtained, 



Iridium 6"43 or 7*5 



Iron..... 0-23 0-277 



Loss (obviously osmium) 2-16 2-51 



8-82 



I have shown in a late work that the atomic weight of iridium 

 is 3-75. We see from the preceding analysis, which I had the 

 patience to perform twice, notwithstanding the tediousness of 

 the manipulations, that the ore of iridium (abstracting the iron, 

 which is probably only accidentally present) is composed of three 

 parts iridium and one part osmium. If we consider it as a 

 compound of two atoms iridium and one atom osmium, the atom 

 of osmium will be 2*5. If it be a compound of one atom of each 

 constituent, the atom of osmium will be 1-25, or the same as the 

 atom of fluoric acid. We have not data at present to determine 

 which of these suppositions is the true one. I shall, therefore, 

 make choice of the first number provisionally till we have it in 

 our power to determine the point with more accuracy. 



c2 



