"It might be objected that the lost air is still contained in the residuum of air which could not farther be united with the phlogiston; for finding that kind of air lighter than common air, it might be supposed that the phlogiston when united with this air made it less ponderous, which circumstance is already known from other experiments. However, since phlogiston is a substance, (which always supposes some weight,) I very much doubt whether this hypothesis be founded on truth."