Experiments on Plat'ina. 49 



piatina be diflblved in the muriatic acid^ that it may be pre- 

 cipitated by that fait. 



Let us now return to the crude piatina. When treated 

 with dulcified muriate of mercury, it is found at the bottom 

 of the retort with all the iigns of corrofion. The water im- 

 mediately takes from it alight efHorefcence of a yellowifh 

 white colour; and potafh, pouied into the liquor^ feparates 

 from it a red oxide of iron and of copper. In regard to pia- 

 tina, none is found in it; from which we may conclude that 

 the iron and copper only had received from the muriate of 

 mercury a fufficient quantity of oxygen to efteft their folu- 

 tion. The lofs of the ore was 12 per cent. We are there- 

 fore obli"-ed to acknowled<'e three metals in piatina ore. We 

 fliall (how hereaftL'r, that bcfides fulphur it contains alfo two 

 other coinbuftibles *. 



VI. Experimenls lu'ilb the Nttr'ic Acid on Piatina. 



Nitric acid of 35 degrees, in which crude piatina, purified 

 from fand, iron, and copper, was boiled, did not even alter 

 the pulifli of the grains : it only fcparated ihe mercury from 

 the cold. The fame acid had as little aftion on the piatina 

 grains blackened bv calcination, and fubjecSled to the fame 

 ebullition : thcv retained their cruft, and the (late of the acid 

 was in no manner changed. Margraf and Lewis, however, 

 aflert that nitric acid has foiiie kind of an atfion on them. 

 But their acid cither contained muriatic acid, or the grains 

 on which they operated were more ferruginous. This is very 

 poflible; fur there are fome kinds of crude piatina which have 

 a great many incruded grains, and others cavernous, which 

 contain red t)xide. The black coloured crude piatina in my 

 pofleflion, and which belonged to Don Pedro d'Avila, is in 

 that (late. I can now entertain no doubt that black kinds 

 of piatina are fometimes brought to us. That lent a few 

 years ago to the king's cabinet, of which I have a fpecimen 

 given me by our tranflator of Buffon, is of this kind. It 

 may be whitened by means of the muriatic acid, but not 



'" The author of the Mineralogy of Spain, Don Chriftian H-ngen, 

 expreflcs hinifelf thus in the fcventii number of the Annnlfs d' drncias 

 Vaturalei: " After liavin^ read the memoir pubi (hed Ij- L Piouft in 

 the firft volume of this colleiStion, one is ol)li<;cd to acknowk-dge th;u piatina 

 is never found pure m a native ft:ite; it always exhibits a real mineral- 

 izjlion, as tliis meinoir proves. It is much to be rcgr;ited that we have 

 not yet the leaft geogniirtic notice rcfpcding this valuable fubftancc. Pon 

 Herrgen indicates at the fame time the places where piatina is found, 

 which are, Cbo,:o, Pol>aya)i, Suho, Rio del Pmto in the province of Peru, 

 Cart^in.ienc. and Barbiida in New Giei ada. 



Vol. XI. D fufficiently 



