THE kind tone of the first part of the notice, in your issue of December 15 (vol. xxv. p. 150), of my work on Inorganic Chemistry leads me, with your permission, to reply to some questions asked by the reviewer in the latter portion of his remarks. He first inquires “Why should he (the student) begin his chemical career by learning that ‘combining weight’ is synonymous with ‘atomic weight’?” To this I answer, Because in our best standard works on chemistry these terms are applied indifferently to the same series of numbers; and further that the combining weight, a number deduced from experiment, is according to the atomic theory the relative weight of the atom of that particular element. To the query “Why should he draw from the statement of Avogadro's law the erroneous conclusion that the molecules of all gases are of the same size?” I reply by pointing out that Frankland states that the bulk of any elementary molecule, in the gaseous condition, is the same as that of hydrogen; and that Roscoe, Miller, and Tilden affirm that all gaseous molecules occupy the same volume. The phrase “are of the same size” is simply intended to convey, the same meaning as the term “occupy the same volume.” I have not deemed it necessary in such a work as that under review to point out that the volume occupied by a molecule consists in part of intermolecular space; neither do the works of the chemists quoted when explaining the same law.