The Cambridge History of English and American Literature in 18 Volumes (1907–21).
Volume XIV. The Victorian Age, Part Two.

VIII. The Literature of Science

§ 22. Frankland

The conception of equivalency, that is, equal value in exchange, of determinate weights of different homogeneous substances, has been helpful in chemistry. In 1852, Edward Frankland applied the notion of equivalency to the atoms of elements, that is, homogeneous substances which have not been separated into unlike parts. He arranged the elements in groups, the atoms of those in any one group being of equal value in exchange, inasmuch as each of these atoms combines with the same number of other atoms to form molecules.

When Frankland’s conception had been developed, and the method of determining the equivalency of atoms made more definite and more workable, a vast new field of enquiry was opened, a field which has proved remarkably fruitful both in purely scientific work, and in applied chemistry. It is not an exaggeration to say that the great industry of making aniline colours is an outcome of the notion of atomic equivalency introduced by Frankland into chemical science.