The
combination of iron and sulphur, for example, may easily be performed by
fusion; but, by aqueous solution, this particular combination is again
resolved, and forms an acido-metallic, that is, a vitriolic substance,
after the phlogiston (by means of which it is insoluble in water) has
been separated from the composition, by the assistance of vital air.
The variety of these sulphureo-metallic substances, in point of
composition, is almost indefinite; but, unless they were all soluble in
water, this could not have happened by the action of that solvent. If we
shall allow any one of those bodies to have been formed by the fluidity
of heat, they must all have been formed in the same manner; for there is
such a chain of connection among those bodies in the mineral regions,
that they must all have been composed, either, on the one hand, by
aqueous solution, or, on the other, by means of heat and fusion.
Here, for example, are crystallised together in one mass, 1_st,
Pyrites_, containing sulphur, iron, copper; 2_dly, Blend_, a composition
of iron, sulphur, and calamine; 3_dly, Galena_, consisting of lead
and sulphur; 4_thly, Marmor metallicum_, being the terra ponderosa,
saturated with the vitriolic acid; a substance insoluble in water;
5_thly, Fluor_, a saturation of calcareous earth, with a peculiar acid,
called the _acid of spar_, also insoluble in water; 6_thly, Calcareous
spar_, of different kinds, being calcareous earth saturated with fixed
air, and something besides, which forms a variety in this substance;
_lastly, Siliceous substance_, or _Quartz crystals_.
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