revealing itself by its effects when it came into contact with material bodies. There was some doubt whether it possessed the attribute of weight at all; but its properties were supposed to be quiescent when it became united with a substance which thereby became phlogisticated. It needed to be excited in some special way before it could be brought again into activity. When combined it was in a passive condition.
The amusing features of the phlogiston theory only developed when it came to be realised that when the phlogiston was driven out of a body, as in the case of the calcination of a metal, the calx remaining was heavier than the metal with the phlogiston had been. The first explanation of this phenomenon was that phlogiston not only possessed no heaviness, but was actually endowed with a faculty of lightness. This hypothesis was, however, a little too far-fetched for even the seventeenth century. Boerhaave thereupon discovered that as the phlogiston escaped it attacked the vessel in which the metal was calcined, and combined some of that with the metal. This notion would not stand experiment, but Baume's explanation of what happened was singularly ingenious. He insisted that phlogiston was appreciably ponderable. But, he said, when it is absorbed into a metal or other substance it does not combine with that substance, but is constantly in motion in the interstices of the molecules. So that as a bird in a cage does not add to the weight of the cage so long as it is flying about, no more does phlogiston add to the weight of the metal in which it is similarly flying about. But when the calcination takes place the dead phlogiston, as it may be called, does actually combine with the metal, and thus the increase of weight is accounted for.
