XXXVI.
BLACK.
498.
Black is not exhibited in so elementary a state as white. We meet with it in the vegetable kingdom in semi-combustion; and charcoal, a substance especially worthy of attention on other accounts, exhibits a black colour. Again, if woods—for example, boards, owing to the action of light, air, and moisture, are deprived in part of their combustibility, there appears first the grey then the black colour. So again, we can convert even portions of animal substance to charcoal by semi-combustion.
499.
In the same manner we often find that a sub-oxydation takes place in metals when the black colour is to be produced. Various metals, particularly