1 86 Bijhop of Landaff’s Obfervattons on 
The fhale from which alum is made, when it is firfl dug out 
of the earth, gives no impregnation to water; but by expofure 
to air and moifture its principles are loofened, it fhivers into 
pieces, and finally moulders into a kind of clay, which has an 
aluminous tafte. Alum is an earthy fait refulting from an 
union of the acid of fulphur with pure clay; and hence we 
are fure, that fhale, when decompofed by the air, contains the 
acid of fulphur ; and from its oily black appearance, and efpe- 
dally from its being inflammable, we are equally certain that it 
contains phlogifton, the other conftituent part of fulphur. 
And indeed pyritous fubftances, or combinations of fulphur 
and iron, enter into the compofition of many, probably of ail 
forts of fhale, though the particles of the pyrites may not be 
large enough to be feen in fome of them ; and if this be ad- 
mitted, then we need be at no lofs to account for the bits of ful- 
phur, which are fublimed to the top of the heaps of fhale, 
when they calcine large quantities of it for the purpofe of 
making alum : nor need we have any difficulty in admitting,, 
that a phlogiftic vapour muff be difcharged from fhale, when 
it is decompofed by the air. Dr. Short fays, that he burned 
a piece of aluminous fhale for half an hour in an open fire; 
he then powdered and infufed it in common water, and the 
water fent forth a moft intolerable fulphureous fmell, the very 
fame with Harrogate water. He burned feveral other pieces 
of fhale, but none of them flunk fo flrong as the firft. This 
difference may be attributed, either to the different qua- 
lities of the different pieces of fhale which he tried, or 
to the calcination of the firft being pufhed to a certain 
definite degree ; for the combination of the principles on 
which the fmell depends may be produced by one degree 
of heat, and deftroyed by another. I have mentioned, 
briefly, 
