54 Experiments on Plathia. 



afcertain with more certainty the nature of this powder, I 

 thought proper to make the following experiment 



I diirolved aoo grains of black povvdcr well dried, but not 

 calcined, in nitro-muriatic acid of the fame ftrength. Having 

 wailied and weighed the refiduum, it indicated that the fol- 

 vent had taken up onlv 24 grains. The folution i)eing then 

 treated with muriate of ammonia gave me common muriate 

 of ammonia; and the lad liquor produced, by the addition 

 of potafh, phofphate of iron, which gave me no new inform- 

 ation. 



But, if it be recollefted that 200 grains of the black pow- 

 der, which had loft 23 grains of fulphur and phofphorus, 

 afterwards fuffered to be taken up by the fame folvent even 

 ^3f) grains of platina, one will certainly be aftonilhed to find 

 that 200 grains of the fame powder, which ftill retained its 



23 grains of combuftible matter, Ihould have refiftcd the 

 aftion of the folvent to fuch a degree as to give up to it only 



24 grains of metal. This refiftance muft n^celfarily find its 

 meafure in the difference between the numbers 135 and 24, 

 which here reprefent to us the quantities taken from the black 

 powder during the firft and fecond experiments. 



I then fufpefted that the union of the combuftibles accu- 

 mulated in the platina, formed, perhaps, the greateft obftacle 

 to the folution, both in thefe experiments and in thofe made 

 on platina on a large fcale. Several fa6ls, which I had already 

 obferved in regard to the folution of metallic fulphurets, com- 

 pared \yith that of their refpeftive metals, confirmed me in 

 this opinion, at leaft until other obfervations had enabled 

 me to rectify what might not be founded on that conjefture, 



I therefore" colle6led"the powder, after the fmall lofs it had 

 experienced in the nitro-muriatic acid, and expofed it to the 

 flarne of the blowpipe. At the fame inftant it exhaled fumes 

 of fulphur, and perhaps even of fulphuric acid, as dcnfe as 

 that which it had produced before being fubjefted to the 

 aftion of the folvent. If we fuj-pofe, then, that the black; 

 powder gives up to the folvent 135 parts inftead of 24, at the 

 moment when it is feparated from the combuftibles by tor- 

 refadtion, there remains no doubt that thefe combuftibles, 

 on the one hand, oppofe a ftroug refiftance to the aftion of 

 acids, and defend the platina from it; and, on the other, 

 that oeconomy requires, in operations on a large fcale, that 

 the blacky powder ftiould be preferved feparate, to b^ calcined 

 before it is treated with nitro-muriatic acid. 



If we refledthat the fulphurets and phofphurcts of iron, 

 which are the only ores found in fmall quantity in the mi- 

 neral, are incapable qf oppofing fuch a refinance to the aftion 



of 



