ON PLATINA. 121 



muriate of ammonia, and the colour of the precipitate is more 

 orlefs intenfe, according to the quantity of powder contained ■ 

 in the folution. 



From what has been fo far ftated, it appears, that this black The black pow- 

 powder is the caufeof the ditTerent colours which the different of cdour in"the 

 precipitates or triple falts of platina exhibit, under different precipitates, 

 circumftances. 



In order to learn the nature of this fuhftance, I fliall detail Enquiry into 

 the experiments which were undertaken for that purpofe. The this"ubftance. 

 precipitates or falts I made ufe of were, the triple ammoniacal 

 muriate of platina, and the triple muriate of platina and foda; 

 the former fait I preferred on account of its eafy decompofibi- 

 lity, and the latter on account of being very Ibluble, 



Erperiments on the tripk anwioniacal Muriate of Platina. 



Equal quantities of the before-obtained yellow and dark red Aqueous folu- 

 precipitate, being feparately difTolved in equal quantites off'°"^°^. .^ 'J 

 water, the firft fait furnifhed a folution of a gold yellow colour, precipitates; the 

 whereas that of the latter was orange red. On adding to the firft gold. yeiiow, 

 latter folution a minute quantity of green fulphate of iron, or red. 

 fulphureous acid, it became infiantly of a gold yellow colour; The latter was 

 the fameeffecl was produced, though flowly, by the addition o^\y ^^^^^ port^^ 

 alcohol. of gr. fuiph. of 



It was natural to fuppofe that the colour of the red ralt^'^*J^"j,°'' ''y ^^- 



might be owing to the higher degree of oxidizement of the The red colour 



diflblved platina. In order to convince myfelf of this conjee- ^^^ not owing 

 » . to greater oxi* 



ture, I attempted to transfer oxigen to the yellow fait, by means dizement, 



of nitric and oxiginized muriatic acids. This however failed; 

 the colour of the fait remained yellow as before. On repeating 

 the aj^plication of nitric and oxiginized muriatic acids alter- 

 nately, the refult was only a very pale red coloured precipitate. 



Equal parts of the yellow and red precipitate, deficcated at The yellow and 

 equal temperatures, and under the fame circumftances, when ''^'^ precipitates 

 decompofed by heat, yield alfo unequal quantities of fixed re- equal refi^ues 

 fidue. That of the firft, amounted to 0,44' of the weight of w'^s" ^ecom- 

 the fait employed, and that of the latter was 0,4- and 5. ^°^^^ ^^ ^''^• 



If yellow precipitate be reduced by heat, the platina ob- The yellow 

 tained is imcommonly fnluhle \n a comparatively fmall quan- Precipitate if re. 

 tity of nitro-muriatic acid, and the folution yield a yellow 'i>T^-\'^^fMuh\e^ 

 cipitate with muriate of ammonia. " platina ; which 



J /-again affords a 

 yellow preci^. 



