"[A]ll the substances which may reasonably be considered as earthy... possess much greater weight, hardness, fixity, and infusibility, than any other element; for these qualities are insensible, or do dot exist, in the element of fire; they are in an exceedingly small degree in the air, and are more sensible and considerable in water; but are infinitely less than in any thing which can be considered as earth. Hence... the qualities above-mentioned are the distinguishing and characteristic essential properties of the earthy element. But these qualities are not so eminently united in any of those [earthy] substances... as in... vitrifiable earth. ...[T]hen ...this earth is the heaviest, hardest, most fixed, and most infusible, and even the most apyrous of all earths, when it is very pure; and also... the most homogeneous, the most simple, and elementary earth, as we shall prove by a more particular examination of its properties, and by a companion of these with the properties of the other earthy substances."