which the vegetable body contains. The oil, the acid, &c., extracted by distilling vegetable bodies did not exist in them, but are formed during the mutual action of the constituents upon each other, promoted as their action is by the heat. These views were quite new and perfectly just, and threw a new light on the nature of vegetable substances and on the products obtained by distilling them. It showed the futility of all the pretended analyses of vegetable substances, which chemists had performed by simply subjecting them to distillation, and the error of drawing any conclusions respecting the constituents of vegetable substances from the results of their distillation, except indeed with respect to their elementary constituents. Thus when by distilling a vegetable substance we obtain water, oil, acetic acid, carbonic acid, and carburetted hydrogen, we must not conclude that these principles existed in the substance, but merely that it contained carbon, hydrogen, and oxygen, in such proportions as to yield all these principles by decompositions. As nitric acid acts upon metals in a very different way from sulphuric and muriatic acids, and as it is a much better solvent of metals in general than any other, it was an object of great importance towards completing the antiphlogistic theory to obtain an accurate knowledge of its constituents. Though Lavoisier did not succeed in this, yet he made at least a certain progress, which enabled him to explain the phenomena, at that time known, with considerable clearness, and to answer all the objections to the antiphlogistic theory from the action of nitric acid on metals. His first paper on the subject was published in the Memoirs of the Academy, for 1776. He put a quantity of nitric acid and mercury into a retort with a long beak, which he plunged into the water-trough. An effervescence took place and gas passed over in abundance, and was collected in a glass jar; the mercury being dissolved the retort was still further heated, till every thing liquid passed over into the receiver, and a dry yellow salt remained. The beak of the retort was now again plunged into the water-trough, and the salt heated till all the nitric acid which it contained was decomposed, and nothing remained in the retort but red oxide of mercury. During this last process much more gas was collected. All the gas obtained during the solution of the mercury and the decomposition of the salt was nitrous gas. The red oxide of mercury was now heated to redness, oxygen gas was emitted in abundance, and the mercury was reduced to the metallic state: its weight was found the very same as at first. It is clear, therefore, that the nitrous gas and the oxygen gas were derived, not from the mercury but from the nitric acid, and that the nitric acid had been decomposed into nitrous gas and oxygen: the nitrous gas had made its escape in the form of gas, and the oxygen had remained united to the metal.