The Alexandrian chemists were very near to a recognition of gases. - J. R. Partington

From the time when Guldberg and Waage gave quantitative form to the speculations of the physicist Berthollet, a clear conception of chemical equilibrium, in sharp contrast to an anthropomorphic theory of affinity dating back to Hippocrates and Barchausen, has yielded rich and abundant fruit.

As an instance of the remarkably far-reaching effect which a single mathematico-physical concept has had upon the development of chemical theory, one has but to recall the state of chemistry just before the revival of Avogadro's law by Cannizzaro, to be impressed by its confusion. Relying solely upon their "chemical instinct," the leaders of the various schools of chemical thought had developed each his own theoretical system. ...a host of ...conceptions strove for supremacy. The strife was stilled, order and unity were restored, as soon as Avogadro's great idea was seen in its true light, and the concept of the molecule was introduced into chemistry. A formula which had required pages of reasoning from a purely chemical standpoint to establish, and that insecurely, was fixed by a single numerical result.

If the present volume will help towards the comprehension of the fundamental principles on which the science of thermodynamics rests, and also serve to bring home the importance of a knowledge of these principles in the suggestion and interpretation of experimental work, the purpose which has been kept in view during its preparation will have been amply fulfilled. In any case, it is hoped that neither the extreme view that thermodynamic principles alone suffice in the construction of a systematic physical or chemical science, nor the equally mistaken opinion that they are of little practical utility to the experimental worker, can fairly result from its study.