86 
A SYSTEM OP 
Moreover, there are fome of this order which 
grow fofc in Water, and, when only moiflened, 
become dudile and tenacious : thefe are commonly 
called clays. Some crack in the water, after hav- 
ing imbibed a fufficient quantity of it, but do 
not grow fofter in it, and are therefore in the firft 
degree of induration : fome imbibe the water^ 
but do not crack or fall to pieces •, thefe are yet 
piore indurated : and finally, fome there are, in 
which the water has no ingrefs at all. Thus, by 
following the fuccefiive gradation of induration 
of a fubftance, which throughout all thefe cir- 
cumftances is eafiiy difcovered to be the fame, 
one may with great reafon conclude, that the 
hardnefs of the jafper may perhaps be the laft 
degree of hardnefs, and that this ftone confe- 
quently confifts of an argillaceous fubllance, 
(Seft. Ixv.) that already pofiefles a quality which 
the other clays cannot acquire but in the fire ; 
having, befides, the fame effedt as the boles (Sed. 
Ixxxvi.) when melted in the fire together with 
oajc^reous or other earths. 
SECT, LXXVIII, 
A, Porcellain Clay, "Terra PorceUaneay vulgo. 
Argilla Apyra, 
Is very refraclory in the fire, and cannot in 
any common ftrong fire be brought into fufion 
any farther than to acquire a tenacious foftnefs, 
without lofing its form : it becomes then of a 
dim fliining appearance and Tolid texture, when 
it is broke ; firikes fire with fteel ; and has con- 
fequently the beft qualities required, as a fub- 
lichee whereof veffels capable of refilling a melt- 
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