[ 281 ] 
of a pale yellow colour, as if it had been gilded. 3. 
When exhaled almoft to a drynefs, it emitted vapours 
of the fmell of burning brimftone. 
And laftly, befides all thefe, I have frequently re- 
marked of feveral other waters, here and there men- 
tioned in this work, that their fediments, obtained by 
evaporation, did manifeft fome pittance of this mine- 
ral, by the fetor they acquired on being rubbed with 
fait of Tartar; which, in the language of our author 
above-mentioned, being attracted by the acid, the 
phlogifton is let loofe. 
I have above recommended the farther inveftiga- 
tion of fulphur as a defideratum in the hiftory of mi- 
neral waters ; and (hall now beg leave to conclude 
this paper with the mention of two or three more 
articles, which greatly want further elucidation. 
The firfl: is alum, which, although hitherto found 
but in extremely few waters, and chiefly in thofe of 
Nevil Holt, Ballycaftle acid water, and perhaps in the 
Hartfell water in Scotland, above-mentioned, accord- 
ing to fome late experiments ; yet the genuine cryf- 
tals of alum have not as yet been fatisfadlorily de- 
monftrated in any of thefe. 
The fecond is the volatile mineral alcali, which 
the nitre of the ancients contained; and fome of our 
mineral waters here and there give ftrong fufpicions 
of, by the experiments with a mixture of quick-lime, 
and of the folution of mercury fublimate corrofive : 
but this matter greatly merits farther inquiry, and 
feveral difficulties attending it remain neceflary to be 
explained. 
Thirdly, the hint lately given in the 49th Vol. 
Part. II. of the Tranfaflions, of the efficacy of the 
Vol. LI. Oo Ca- 
