This will seem the more probable, if
we consider these Particulars.
First, That the pure parts of Metals are of themselves very _flexible_ and
_tuff_; that is, will indure bending and hammering, and yet retain their
continuity.
Next, That the Parts of all vitrified Substances, as all kinds of Glass,
the _Scoria_ of Metals, &c. are very hard, and also very brittle, being
neither _flexible_ nor _malleable_, but may by hammering or beating be
broken into small parts or powders.
Thirdly, That all Metals (excepting Gold and Silver, which do not so much
with the bare fire, unless assisted by other saline Bodies) do more or less
_vitrifie_ by the strength of fire, that is, are corroded by a saline
Substance, which I elsewhere shew to be the true cause of fire; and are
thereby, as by several other _Menstruums_ converted into _Scoria_; And this
is called, _calcining_ of them, by Chimists. Thus Iron and Copper by
heating and quenching do turn all of them by degrees into _Scoria_, which
are evidently _vitrified_ Substances, and unite with Glass, and are easily
_fusible_; and when cold, very hard, and very brittle.
Fourthly, That most kind of _Vitrifications_ or _Calcinations_ are made by
Salts, uniting and incorporating with the metalline Particles. Nor do I
know any one _calcination_ wherein a _Saline_ body may not, with very great
probability, be said to be an agent or coadjutor.
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