Experimmts on Thitlna, 4^ 



elfe than the mineralization or fulphuret of that metal which 

 it has been thought proper, in the modern nomenclature of 

 metallic fubftances, to call platina. 



V. On the Oxidation of crude Platina, 



When native platina is brought to- a red heat in open vef-^ 

 fels, it afliimes the appearance of the oxidated iron of a sun 

 barrel ; but with this difference, that the oxidation effedled 

 at the furface is found at its viaximum \ for by rubbina; it on 

 paper, or triturating it with water in a porcelain mortar, a 

 red powder is detached from it. Another proof of this is ob- 

 tained by digefting over it muriatic acid, which entirely dif- 

 fblves this powder, and with alkalies gives a precipitate of 

 oxidated iron of 48 per cent. The platina which remains 

 has recovered its vvhltenefs. 



I (hall here give an account of an experiment made a good 

 many years ago by C. Darcct, and at which I was prefent. 

 That chemift put into a crucible, placed in the porcelain fur- 

 nace of Serres,fome ounces of crude platina: when taken from 

 the furnace the platina was triturated with water, and fepa- 

 rated by thefe means from all the powder it contained. After 

 this firft fubtiance was removed from it, it was put again into 

 the furnace, and purified a fecond time in the fame manner; 

 and this operation, being repeated, gave a new quantity of 

 powder. After palling through the furnace in this manner, 

 as far as I can remember, feven or eight times, the platina 

 was totally changed into an oxide of a very dark brown co- 

 lour. I was prevented, by particular circumftances, from 

 learning of Darcet what was the refult of his laft experiments. 



An account of experiments made on platina in the porce- 

 lain furnace of Fiirftemburg may be fecn in the Journal de 

 Pbyjique; but as the author did not take care to remove the 

 oxide as it was fortned, he concl'^ded, as Macquer, Baumc, 

 and other chemifts had done that platina was mdeftruilible. 

 But let. us return to the oxidation in quertion. 



The muriatic acid, of which we have fpoken, had taken 

 from the calcined platina three oxides, viz. that of iron, that 

 of copper, and that of platina. This folulion, united with the 

 jpolution of muriate of ammonia, gave the yellow precipitate 

 which is peculiar to platina. 



Poiafli being employed to complete the precipitation from 

 the liquor, the refult was a fecond precipitate of red oxide of 

 iron, mixed with a little copper, which immediately mani- 

 ftded itfcif by muriate of amnicnia. 



If in this folution there had been found only a little oxide, 

 which the muriatic acid mi^ht have fur-o;cygcnatcd, the fo- 

 lution 



