Experhnents on Platina^ 53 



fingers, breaks, and ftill gives a pretty large qnahtity of black 

 powder. It is therefore neeeflary to again take from the bottom 

 of the water the mineral found there; to rub it ftrongly be- 

 tween the hands; to feparate the powder from it; and to 

 unite it to the former. It is evident, from what has been 

 here faid, that the friclioa and flioeks experienced by the 

 mineral, agitated bv ebullition, and corroded by the acids, 

 effecl the feparation of the black powder. 



If thefe grain?, inftead of being pounded, are left whole, 

 and if thev are examined with a magnifying glafs, it is feeu 

 that they have retained their form, that they are eafily broken, 

 and that they are hollow, and covered with brilliant laminae. 

 The aperture through which the folvent has penetrated into 

 the interior is often difcovered ; and as their colour is la 

 nothing different from that of the powder, there can be no 

 doubt that the latter is the refiduum of the crofion of the 

 grains of the platina. In a word, thefe phsenomena are 

 more remarkable in black platina ore than in white, becaufe 

 the principle which produces this powder appears to nie to 

 be more abundant in the former. 



XII. Experiments on the Black Fowder. 



Two hundred grains of this powder, well prefled together, 

 being calcined in a wide crucible, exhaled fulphuric acid 

 fumes. Towards the end of the calcination I thought I per- 

 ceived that the fumes, though dill acid, had no longer a ful- 

 phurous charafter. The refiduum was pretty black, and 

 beean to be agglutinated together: it had loll 23 parts. The 

 177 which remained were diflblved in nitro-muriatic acid j 

 and the folution being precipitated by muriate-of ammonia, 

 the refult was an ammoniacal muriate fimiiar to others, of 

 which I fhall fpeak hereafter. The remaining liquor was 

 found much lefs coloured than ufual. I treated it with pot- 

 alh, which, to my great aftonifliment, precipitated a white 

 phofphate of iron. I call it white, becaufe it is that which 

 all iron oxidated to its maxirtnim produces. We have here, 

 therefore, on the one hand fulphur, and on the other phol- 

 phorus, combined in the refiduum of our crude platina in 

 greater quantity than in the metal itfelf. 



As the remainder of the black powder weighed no more 

 than 42 grains, it is evident that the acid had diflblved 135 

 of the 177 grains of black powder calcined. 



Thefe 43"grains of powder were flill very black: they no 

 longer emitted any odour by the flame of the blowpipe. 

 They were not attacked by the nitro-muriatic acid. They 

 were aothini;, elfe but plumbago or graphite very pure. To 



1^ 3 aicertaia 



