gions of the mysterious and the unknown. When we look for an advance in precision of ideas, for a logical development of a satisfactory theory, or for generalizations which shall help us better to classify chemical phenomena in terms of force and energy, we are compelled to admit that the years have not brought the theory of affinity to a state of active growth; rather it is like that strange counterpart of a living tree, the branching coral, whose many busy workers do indeed each for themselves add their mites to the accretions of past generations, but who have failed with all their toil to infuse that mysterious principle which would make of their labors a living organism ruled by an internal law of growth. Affinity, under its own name, is no longer presented in recent manuals. Chemists have more and more turned their attention to details, to accumulating methods of analysis and synthesis, to questions of the constitution of salts, to discussions about graphic and structural formulæ, and to hypotheses about the number and arrangement of atoms in a molecule; but they have not, until quite recently, made systematic attempts to measure the energies involved in reactions. Why? I believe the answer can be found mainly in two reasons. First, the word affinity is in bad odor; it dates back to the time when men mistook wild guesses for ascertained facts; when they knew not the distinction between physics and metaphysics, and when a plausible but flexible occult cause was a more welcome guest to a philosopher's brain than a stiff, hard fact. We see how enormously complicated the phenomena of chemical action have become, and we have lost all faith in hypotheses which can be evolved by the mere force of metaphysical introspection. Therefore, we are afraid to retain a name which once belonged to an idea now long buried in the limbo where so much scholastic rubbish has been consigned, and hence all the facts belonging to affinity are given under separate heads, and thus they lose the great advantage of being bound together under one title.

Secondly, there is a more important reason arising from what has hitherto been the traditional scope of our science.

Natural philosophy early sought the aid of Mathematics, and so laid the foundation for the comprehensive physics of to-day. Astronomy has always dealt with number, and hence stands as the best type of an exact science. Mechanics, in its analytical form is little else than a material embodiment of algebra and geome

try. Chemistry alone of the physical sciences has offered no foothold to mathematics, and yet all her transformations are governed by the numbers which we call atomic weights. What is it which causes Chemistry, so preeminently the analytic science of material things, to be the only one of her group which does not invite the aid of Mathematics, the great analytic science of immaterial things?

It is because three fundamental conceptions underlie physics, while only two serve the needs of the chemist.

If I may borrow an analogy from geometry, I would say that physics is a science of three dimensions, while chemistry is a science of two dimensions. In the first, nearly every transformation is followed by its equation of energy and this involves the concepts space, mass, time; while in the second, an ordinary chemical equation gives us the changes of matter in terms of space and mass only; that is to say, in units of atomic weight and atomic volume.

Imagine for a moment what physics would be to-day without those grand generalizations, Newton's theory of gravitation, Young's undulatory theory of light, the dynamic theory of heat, the kinetic theory of gases, the conservation of energy and Ohm's law in electricity! Every one of these, except the last, is a dynamic hypothesis and involves velocity, that is, time, as one of its essential parts. In comparison with the above, all ordinary chemical work may be termed the registration of successive static states of matter. The analyst pulls to pieces, the synthetic chemist builds up; each records his work as so many atoms transferred from one condition to another, and he is satisfied to exhibit the body produced quietly resting in the bottom of a beaker motionless, static. The electrolytic cell tells us the stress of chemism for specified conditions as electromotive force; the splendid work done in thermochemistry enables us to know the whole energy involved when A unites with B, or when A B goes through any transformation however intricate, but it does not inform us of the dynamical equation which accompanies them, and which should account for the interval between the static states.

Whenever we look outside of chemistry we find that the lines of the great theories, along which progress is making, are those of dynamic hypotheses; if we go to our biological brethren we see them, too, moving with the current; the geologist studies upheavals, denudation, rate of subsidence, glacial action and all

kinds of changes in reference to their velocity; the physiologist is actively registering the time element in vital phenomena through the rate of nervous transmission, the rate of muscular contraction, the duration of optical and auditory impressions, etc.; and we cannot ignore the fact that all the great living theories of the present contain the time element as an essential part. Now, I cannot but ask whether one reason why chemistry has evolved no great dynamical theory, that the word affinity has disappeared from our books, that we go on accumulating facts in all directions but one, and fail to draw any large generalization which shall include them all, may not be just because we have made so little use of the fundamental concept, time. To expect to draw a theory of chemical phenomena from the study of electrical decompositions and of thermochemical data, or from even millions of the customary static chemical equations would be like hoping to learn the nature of gravitation by laboriously weighing every moving object on the earth's surface and recording the foot-pounds of energy given out when it fell. The simplest quantitative measure of gravity is, as every one knows, to determine it as the acceleration of a velocity; when we know the value of g we are forever relieved, in the problem of falling bodies, from the necessity of weighing heterogeneous objects at the earth's surface, for they will all experience the same acceleration! May there not be something like this grand simplification to be discovered for chemical changes also?

The study of the speed of reaction has but just begun; it is a line of work surrounded with unusual difficulties, but I confidently believe it contains a rich store of promise; all other means for measuring the energies of chemism seem to have been tried except this. Is it not therefore an encouraging fact that to us, the chemists of the nineteenth century, is left for exploration the fruitful field of the true dynamics of the atom, the discovery of a time rate for the attractions due to affinity? I like to think so, and let us hope that the Newton of Chemistry may come in our day and while we yet have voices to honor him.

6.

7.

Torbern Bergman. De Attractionibus Electivis, 1775. Also in the 3rd vol. of his Opuscula Torberini Bergman Physica at Chemica, 1783.

H. Debus. loc. cit.

8. Chas. Daubeny. Introduction to the Atomic Theory, 2nd ed., p. 55.

9.

10.

C. L. Berthollet. Essai de Statique Chimique, 1803.

Sir H. Davy. Phil. Trans., 1807. Ditto, 1826.

11. Wurtz Dict. loc. cit.

12.

13.

Amadeo Avogadro. Journal de Physique, lxxiii, p. 58.

B. C. Brodie. Quar. Jour. Chem. Soc. iv, 194.

14. D. Mendelejeff. Zeitschrift fur Chemie, 1869, 405 and Annalen der Chemie, 8 suppl., 133.

15. Lothar Meyer. Ann. der Chem., 7 suppl., 356.

16. J. Newlands. Chem. News, x, 59-94.

18. A. W. Williamson. A Theory of Etherification. Quar. Jour. Chem. Soc. iv, 106.

19. J. B. Richter. Anfangsgrunde der Stockiometrie, Breslau, 1792. 20. William Higgins. A comparative view of the Phlogistic and Antiphlogistic Theories, 1789.

21. Wurtz Dict., art. Affinite, p. 72.

22.

F. Guthrie. Phil. Mag. (4) xlix, 1-20. The first of several papers by him on Cryohydrates.

23. Thomas Andrews. Phil. Trans., 1844. Also Phil. Mag. xxxii, 392, followed by a series of papers on the same subject.

24. Thos. Wood. On the heat of Chemical Combination. The first of the series is in Phil. Mag. (4) ii, 268.

25. Favre and Silbermann. Ann. Ch. Phys. (3) xxxiv, 385 and in succeeding volumes.

26.

27.

J. Thomsen. Pogg. Ann. lxxxviii, 349, and in following volumes.
Alex. Naumann. Lehr- and Handbuch der Thermochemie, 1882.

28. H. St. Claire Deville. Compt. rend. xlv, 857.

Also in the Leçons

de Chimie of the Paris Chemical Society, on Dissociation, 1864;

and on Affinity, 1867.

29. Wurtz Dict. loc. cit.

30. Gladstone and Tribe. A law in chemical dynamics. Proc. Roy.

Soc. xix, 498.

31. R. B. Warder. Suggestions for computing the speed of chemical reactions. Proc. A. A. A. S., xxxii, 156.

32. J. H. Gladstone. Chemical Affinity as existing among substances in solution. Phil. Trans., March, 1854.

33. J. W. Draper.

Chemical Action of Light, Jour. Frank. Inst., xix, 469, 1837. Also many others on the same subject in Phil. Mag. from 1842 to 1857.

34. H. E. Roscoe. Measurement of the Chemical Action of light. Proc. Roy. Soc., 1857, 326. Also in conjunction with Bunsen till 1862. Edm. Becquerel. Chemical rays which accompany Light. Compt. rend., xiii, 198, 1841.

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