57 



attributed to the great affinity of the nitrous acid to phlogiston, part of the 

 acid laying hold of the phlogis. of the metals, & thereby preparing them 

 for dissolution, whilst the remainder dissolves them. In general the nitrous 

 acid dissolves metals with great effervescence, produces a considerable heat, 

 & the vapours produced thereby are of a deeper colour, more pungent, & 

 more elastic, than those of the simple nitrous acid, or than those produced 

 by dissolving alcalies and earths in it, which I think can be owing only to 

 their union with the phlogiston. 



As the precipitates from the solution of mercury & the perfect metals in 

 acids are reducible without the help of inflammable matters, it has been 

 thought that those metallic substances are not deprived of their phlogiston 

 by acids ; but yet the vol. sulphureous acid produced in dissolving mercury 

 in oil of vitr. seems a strong proof that mercury is deprived of its phlogiston 

 by solution in that acid ; & yet (as you tell me you have tried yourself) the 

 mercury may be revived from thence without the addition of any matter 

 usually called inflammable ; I have found too that the same vol. sulph. acid 

 is produced by dissolving silver in concentrated oil of vitriol : I should 

 imagine therefore that mercury and the perfect metals were deprived of their 

 phlogiston by solution in acids, as well as the imperfect ones, but that by 

 reason of their great affinity to phlogiston they acquired it again from the 

 matter which must be added to separate the acid from them, since there 

 seems no reason to think that the purest f. alk., or even lime, is intirely free 

 from phlogiston. The effervescence & elastic vapours produced during their 

 solution in aq. fort, or aq. regia, seemingly much of the same nature as those 

 attending the solution of the imperfect metals in these acids, very well agree 

 with this hypoth. Whereas it seems likely that if they were not deprived of 

 their phlogiston thereby, they would dissolve quietly without efferv., as arsen. 

 does in the vitr. & marine acids. If this hypoth. is true, it may serve to 

 account for gold not being soluble in any simple acid, but only in aq. regia. 

 Gold, I imagine, has little or no affinity to the nitrous acid, but only to spt of 

 salt ; but its affinity to that acid alone is not sufficient to deprive it of its 

 phlogist. : it therefore requires the united efforts of the nitrous & marine 

 acids, the nitrous to absorb the phlogist., & the marine to dissolve the 

 metal. That gold has little or no affinity to the nitrous acid, seems likely, 

 from what Dr. Lewis says, — that gold when by particular management made 

 to dissolve in the nitrous acid is precipitated again only by exposure to the 

 air, & that upon committing a solution of gold in aqua regia to distilla- 

 tion, the nitrous acid flies off leaving the gold united to the spt of salt. 



Miscellaneous Experiments on the Arsen. Acid. 



P. 22. 3-4 of arsen. acid was put in a small vial covered & intirely im- 

 mersed in sand in a crucible, so as to shut off all communication with the 

 air : it was calcined in this manner for a good while with a heat raised high 

 enough to make the glass red hot & soft, as appeared from its having received 

 the impression of the sand : no arsenical fumes were perceived; the arsen. 

 acid was not melted, & lost but 6 gra. of its weight, which very likely were 

 only water. 



