 Caloric figures in Lavoisier’s list of elements as the “element of heat or fire” (Lavoisier 1789, p. 175), “becom[ing] fixed in bodies … [and] act[ing] upon them with a repulsive force, from which, or from its accumulation in bodies to a greater or lesser degree, the transformation of solids into fluids, and of fluids to aeriform elasticity, is entirely owing” (1789, p. 183). He goes on to define ‘gas’ as “this aeriform state of bodies produced by a sufficient accumulation of caloric.” Under the list of binary compounds formed with hydrogen, caloric is said to yield hydrogen gas (1789, p. 198). Similarly, under the list of binary compounds formed with phosphorus, caloric yields phosphorus gas (1789, p. 204). The Lavoisian element base of oxygen combines with the Lavoisian element caloric to form the compound oxygen gas. The compound of base of oxygen with a smaller amount of caloric is oxygen liquid (known only in principle to Lavoisier). What we would call the phase change of liquid to gaseous oxygen is thus for him a change of substance. Light also figures in his list of elements, and is said “to have a great affinity with oxygen, … and contributes along with caloric to change it into the state of gas” (1789, p. 185).