Triumphs and Wonders of the 19th Century: The True Mirror of a Phenomenal Era / A volume of original, entertaining and instructive historic and descriptive writings, showing the many and marvellous achievements which distinguish an hundred years of material, intellectual, social and moral progress

by James P. Boyd

II. PHYSICAL CHEMISTRY.

In strictly physical chemistry the relations of electricity and heat to chemical action have been extensively developed during the century. The specific heats of the elements and of most of their compounds have been carefully determined, and thermo and physical chemistry under the leadership of such master minds as Berthollet, Thompson, Van’t Hoff, and Ostwald have been brought to the highest degree of perfection.

The chemist now does not consider that he knows any body until he knows thoroughly its relations to heat and to electricity. The action of light must also be included, but this subject will be more thoroughly discussed under graphic chemistry.

The nature of solutions has also been developed by the studies of Ostwald and Van’t Hoff, and as a result of these studies, a flood of light has been thrown upon the constitution of compound bodies.

In the development of physical chemistry, attention should be directed to the help afforded by Newlands (1864) and Mendelejeff (1869) and others, showing that the elements form groups which tend to recur with a periodicity which is sufficiently definite to enable the investigator to foretell to some extent the properties of the elements which have never yet been discovered, and whose existence is necessary in order to fill up the gaps in existing groups.

By this method the existence, atomic weight and properties of scandium, gallium, and germanium were foretold years before their discovery. Such actual realization of a scientific-prophetic method is one of the strongest indications of the basis of fact upon which it rests. Although a rigid application of the principles of the periodic law is not possible, yet its discovery and elaboration mark one of the great forward steps of chemical philosophy.

If we regard any material system by itself, i.e., independently of any other system or influence by which it may be surrounded, we recognize it as consisting of essentially two things,—matter and energy. A precise definition of either matter or energy is difficult, if not impossible; but what is connoted by these names is sufficiently well understood by their well-known properties. Both energy and matter are essential to each and every system. They are coexistent. In the light of human experience, we cannot conceive of one existing without the other; and in the study of any material system, consideration of one of these components without the other can only be regarded as incomplete. But, for the sake of convenience, this has been the practice, and, generally speaking, chemists have concerned themselves with matter changes of equilibria, while physicists have more especially directed their attention to energy equilibria. The object of the physical chemist is to follow equilibria changes in given systems, having due regard for both the matter and energy involved.

Berthollet may be regarded as the first true physical chemist, on account of his classical views on mass action. Largely because the time was not ripe for it, his views were not generally adopted.

A quarter of a century later (1867), Guldberg and Waage gave a precise mathematical expression of the law, but still it attracted very little attention from investigators. A tremendous impetus was given to the subject by the electrolytic dissociation theory of Arrhenius (1887), and the extension of the additive laws of gases to dilute solutions, by Van’t Hoff (1885). This was but a comparatively small field in the subject, but it stimulated activity along the whole line, the wonderful increase of our knowledge concerning the velocity or rates of reaction, the heat changes involved, and the marvelous development of electrolytic chemistry being pertinent instances.

The generalization of Gibbs, known as the phase rule (1876), which accurately states the condition for equilibrium in the system, and the Theorem of Le Chatelier (1884), that any change in the factors of equilibrium from outside is followed by a reverse change within the system, together with the mass law, now give us a consistent theoretical foundation for the subject. In general terms, it may be said that all chemistry, at least all theoretical chemistry, properly belongs to the province of physical chemistry, and the title, while in many ways convenient, is misleading.