4^ E.vperhncnis on VlatiHa. 



Kition of platina would have exhibited notliing aflonifliing. 

 But as its dcoxidation conld not be afcribed to fuch a 

 caufe, it nuifi he inferred, tliat when platina is combined 

 with other nietals, it becomes oxidated uuich eafier than has 

 hitherto been ruj-'pofed. Platina, then, has this property, 

 like all other metals, in which the fiatc of combination al- 

 wavs favours oxidation. 



The followino; is the detail of an experiment made with 

 great care. Eight lumdred grains of crude wiiite platina, 

 well purified from gold, fand, and mercury, after having been 

 calcined for the fpacc of an hour, had lod only one grain. 

 Having afterwards expoied them to the a<^lion of muriatic 

 acid, they loft in the acid four grains and a half, and refamed 

 their whitenefs; by which it i? Vcqw that the oxygen of the 

 atmofphere had almuli; replaced the weight of the fulphur 

 diflinatcd. v 



The 794I grains, beinc calcined a fccond time, became 

 black, and their weight was increaled two grains, but tlie. 

 fmell of fulphur was no longer didinouilhed: "a circum'ftance 

 which renders the combination of oxviien more Urikino;. 

 Having been again expofed to the muriatic acid, they lofl 

 9' of iheir weight: they were found to be black, and'vifibly 

 corroded. i ... i- -, 



1 he 788 grains which remained were boiled k third time 

 in the fame acid, and the refult.was a new lofs ; bift that 

 which they experienced in frcfli acid, after a fourth tbulli- 

 tjon, was flow, and far inferior in the two lafl mentioned 

 boilings: it did not exceed four grains and a "half. ', ., .1 ', 



The weakened aclion of tlie acid made nie believe that I 

 ought to continue the oxidation in order to penetrate fivrther 

 into the interior of the platina, which induced, me to procccil 

 to a fourth calcination ; ,but it was ufelcfs, for the grains, ex- 

 perienced no change either'in their weight or their colour: 

 the application, therefore, of the muriatic acid was to np pur- 

 pofe. The exterior of the grains had then the appearance of 

 pure platina, having a very ftrong rcfemblance to filvcr of a 

 low alloy. 



The total lofs fuflained by thefe 8;p grains was ^']\ grains, 

 or a little more than two hundredtlis. A fri'ain of cold, not 

 perceived in purifying the crude platina, was found towards 

 the end of the operations; and this grain proved to me that; 

 the muriatic acid alone produced the eflccts I have dcfcrlbed, 

 and that nitric acid had no lliarc in ihcui. 



The metallic folutlons of which we have fpokcn contained 

 each platina, iron, and copper : they became turbid with the 

 muriale of ammonia ; from which wc may infer, that if the 



platiua 



