42 Memoir upon Palladhun and Rhodium. 



taken from it an excess of acid favourable to its solution and 

 crystallization. 



The solution of the muriate of rhodium separated from the 

 copper and from the iron, and from the traces of palladium 

 which mi;^ht still exist in it, forms with ammonia a precipi- 

 tate of a fa'.vn colour and nearly insoluble, which is an ammo- 

 niacal submuriate of rhodium, as evinced by the vapours of sal 

 ammonia which it gives on being heated *. The liquor from 

 which this suhmuriate has Jjeen separated preserves a deep fawn 

 colour, notwithstanding the excess of ammonia ; but upon heat- 

 ing it even without ebullition, it furnishes" a new quantity of 

 flaky precipitate of a clearer yellow than the first. Lastly, the 

 hquor evaporated to dryness, and its residue taken up with wa- 

 ter, still left a small quantity of matter similar to the foregoing. 

 All these precipitates were ammoniacal submuriate of rhodium ; 

 which proves that this salt is a little, soluble in water, and that 

 an excess of ammonia seems to favour this solubility. 



SoJubility. — The ammoniacal muriate of rhodium is dissolved 

 very ea<*ily in cold water ; its solution is of a purjde red colour, 

 nearly like that of cochineal or recent strawberry juice: but this 

 colour becomes brown upon the application of heat, and even 

 6j)ontaneously after some time. 



This salt is in grains, crystalline, and very brilliant: it is not 

 soft to the touch like the ammoniacal submuriate of palladium. 



§ IX. Decnmpnsitimi of the ammoniacal Muriate of Rho- 

 dium ly Potash. — Two grammes of this salt dissolved in water, 

 having been mixed with a solution of potash, produced a red 

 precipitate, and emitted ammonia. In a few minutes the (|uan- 

 tity of precipitate was diminished, and the supernatant liquor 

 assumed a greenish-yellow coloiu-. By the aid of heat, the pre- 

 cipitate which I have mentioned was speedily dissolved, the li- 

 quor became deeper in colour, and plenty of ammonia was given 

 off: there was an excess of potash in the liquor. 



The solution of muriate of rhodium in potash exposed to the 

 _^ir for some days produced yellow crystals : this is probably a 

 triple salt of muriate of rhodium at the minimum of acid, and 

 muriate of potash dissolved by an excess of alkali : at least it 

 seems to be proved by tins ; viz. that by the excess of potash 

 saturated by the muriatic acid, a yellowish white precipitate in- 

 soluble in water is formed: this is neutral muriate of potash 

 and rhodium. 



§ X. Reduction of the ammoniacal Muriate of Rhodium. — 



* This name suits it better, as this snit furnishes 50 per cent, of metal 

 on tlip application of heat, whereas before having been piecij)itated by 

 aiiiinunia it gives onlv 28. 



Fifteen 



