mineralogy. 
SECT. CXXV. 
•C. Vitriolic acid united with phlogifton, Acidum 
vitrioli phlogifto comhinatum. The ^fulphu^ 
Jdndj Sulphur a. See Seft, clL 
SECT. CXXVL 
D, Vitriolic acid faturated with alcaline fait, 
Acidum mtrioli alcali minerali faturatum. 
.ns in general is underwood by that expreffion, viz. that the 
hecerogetieous particles are not very obvious, npr of any 
great confequence. 
The phlogidon winch is contained in the black* alum 
fUates, may perhaps .during the calcination difpofe the iron 
to be eaiier diflolved j and it may aifo occalion the black 
-colour in fome of them, that even contain but very little of 
iron, as moil likely in part of thofe from Nas (r. 2.). 
It is not eafily determined, whether the earth in the alum 
.Hates is argillaceous or quartzofe, or whether it is a black in- 
durated humus, or mould, becaufe all thofe three earths, 
-when dilTolved in the vitriolic acid, produce alum. The Co- 
Jogne pipe-clay is a plain proof of the firft ; the quartzofe 
earth, in liquor filicum, of the fecond ; and aluminous foffil- 
woods are actually employed for making alum in Bohemia 
and HelTe. Thefe earths may, or may not, contain iron ; 
however, they prevent, in the former cafe, the phlogidon, 
together v/ith the vitriolic acid, from mineralizing ail the 
iron, and making a marcafite of it, excepting here and there, 
in fome inhgnihcant quantity, as in cracks, or when it meets 
.with fome heterogeneous bodies, as Ihells, infefls, Sec. in the 
laid earths. There is a remarkable progrelHon from the 
black alum Hates to the pit-coal, in proportion as the quan- 
tity of the phlogiftou encreafes, and the quantity of the 
;€ar!h decreafes (Sed. clix.). It is this phlogidon which 
makes this alum (late capable of burning by itfelf, when it is 
once lighted ; wherein it differs from the alum ores of Lumini, 
which, in order to be brought to moulder, require the being 
lexpofed to the heat of the fun, and to be fprinkied with water : 
the former has alfo within itfelf fufficient matter to fponta- 
^leoufly flame upon certain occafioas, according to what the 
K 4 celebrated 
