“There are few subjects, perhaps none, that have occasioned more perplexity to chemists than that of _phlogiston_, or, as it is sometimes called, the principle _of inflammability_. It was the great discovery of Stahl that this principle, whatever it be, is transferable from one substance to another, how different soever in their other properties, such as sulphur, wood, and all the metals, and therefore is the same thing in them all. But what has given an air of mystery to this subject has been that it was imagined that this principle, or substance, could not be exhibited except in combination with other substances, and could not be made to assume separately either a fluid or solid form. It was also asserted by some that phlogiston was so far from adding to the weight of bodies that the addition of it made them really lighter than they were before; on which account they chose to call it _the principle of levity_. This opinion had great patrons. “Of late it has been the opinion of many celebrated chemists, Mr Lavoisier among others, that the whole doctrine of phlogiston has been founded on mistake, and that in all cases in which it was thought that bodies parted with the principle of phlogiston, they in fact lost nothing, but on the contrary acquired something; and in most cases an addition of some kind of air; that a _metal_, for instance, was not a combination of two things, viz., an _earth_ and _phlogiston_, but was probably a simple substance in its metallic state; and that the calx is produced not by the loss of phlogiston, or of anything else, but by the acquisition of air.”