By carefully comparing the physical properties of these two acids (composition, odor, color, decomposition products, solubility, boiling point, crystal form and angles of silver and barium salts) the authors conclude that these differently named substances are the same acid. On the subject of nomenclature they then say:

In fact in going from formic or acetic acid to the fatty acids proper this is the first among the acids to display the fatty character; it is the first that separates from its solution in the form of an oily layer; it is the first to give, with alkalis, salts that are unctuous to the touch, like alkaline soaps.

These characters have led us to designate this acid by the name propionic acid, which recalls its position in the series of fatty acids: it is the first among them. One cannot be surprised that we are making it the object of detailed investigations.