Thus chemists seemed obliged to imagine a something in addition to the gross or ponderable matter of which bodies are composed, in order to account for the properties of these bodies. As Science has advanced she has been able to define what this something is; at least, she has defined it more clearly than the older workers could do.
I have said, as Science has advanced she has defined the unknown something; but it should be remembered that that wonderful book, which contains—according to the greatest authorities—the germs of all our modern advances, was written sixty years before Lavoisier's time. Sixty years before the apparent overthrow of the theory of phlogiston, Newton had laid the foundations of the science which was to reveal the true lineaments of that Unknown whom the phlogisteans ignorantly worshiped.
We have learned to extend the meaning of the word thing—we speak of "the power of doing work" as a measurable and definite thing—although not as matter: and we know that when a body burns it loses a certain amount of this power of doing work, or, as it is more shortly put, of energy. As usual, it is a question of words. The older workers could not define phlogiston; we are able to define energy, and therefore we can see clearly where they saw but darkly. Chemistry now acknowledges that the properties of a compound are not only determined by the composition of the matter of that compound, but by the amount of energy associated with that collocation of matter. She has been able to point out many instances of compounds composed of the same matter, but possessed of different amounts of energy, and, at the same time, of very different properties. And, moreover, chemistry aided by physics has concluded that the properties of a body "are dependent on the variations of the energy of the body, and not on its total value," and therefore that "it is unnecessary, even if it were possible, to form any estimate of the energy of the body in its standard state." (I quote from that remarkable little book of the late Professor Clerk Maxwell, "Matter and Motion.")
Whenever Science made the advance from the vague conception of "principles" and "imponderable matter" to the definite conception of "mass," "motion," and "energy," she was able to recognize the truth which lurked under the cumbersome and inexact nomenclature of the phlogistean chemists.
I have said that, as usual, the dispute between the phlogisteans and their opponents was proved to be a question of meaning of words: as usual, also, subsequent research showed that, while both were wrong, both also were right.
Composition is important, but composition is not all. The burned body has properties differing from those of the unburned body, because it has lost a certain amount of "the power of doing work"; but it has a less power of doing work because it is possessed of a structure different from that which it possessed before. Composition and properties,
