Fusibility, ductility and the hammer

Meaning

I.8.4 contrasts metals capable of fusion and of yielding under the hammer with stones that resist those behaviours. Ductility describes how a body responds to working, not simply how hard it is. The account relates these properties to salt, sulphur, mercury, impurity and the degree of vitrifying action, all within the author's historical theory. In stones, corrupting sulphur’s adustion is said to overcome the salt. Metals are formed through salt and mercury yet still undergo hardening; their greater or lesser resistance follows the amount of impurity and combustible earthiness present during thickening. In the closing triad glass hardens, salt supplies matter, and mercury or water joins and condenses.

The hammer is an ordinary material image with argumentative force: resistance to it helps distinguish kinds of solidity that a visual surface alone cannot reveal. The text does not make every hard body a metal or every fusible body a fully perfected metal. These behavioural distinctions qualify the broader discussion of glass and vitrification and should not be replaced by an anachronistic table of modern material properties.