Contents - BIBLIOGRAPHIC RECORD - INDEX TO CHAPTERS - INDEX TO BIBLIOGRAPHIES - INDEX TO AUTHORS

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

§ 23. Sir Humphry Davy; Electricity and Chemical Affinity

The words element and principle were used by the alchemist as nearly synonymous; both words were used vaguely. The meaning given to the term element, by Lavoisier, towards the end of the eighteenth century—a definite kind of matter which has not been decomposed, that is, separated into unlike parts— was elucidated, and confirmed as the only fruitful connotation of the term by the work of Sir Humphry Davy on potash and soda in 1808.

Humphry Davy was the most brilliant of English chemists. He was the friend of Wordsworth and Sir Walter Scott. Lockhart says that the conversation of Davy and Scott was fascinating and invigorating. Each drew out the powers of the other.

I remember William Laidlaw whispering to me, one night when their “rapt talk” had kept the circle round the fire until long after the usual bedtime of Abbotsford—“Gude preserve us! this is a very superior occasion!”

Davy sent an electric current through pieces of potash and soda; the solids melted, and “small globules, having a high metallic lustre, and being precisely similar in visible characters to quicksilver, appeared.” By burning the metal-like globules, Davy obtained potash and soda. Making his experiments quantitative, weighing the potash and the soda before passing the current, and the potash and soda obtained by burning the metal-like products of the first change, he proved that potash and soda, which, at that time, were classed with the elements, are composed each of a metal combined with oxygen. The new metals—potassium and sodium—are soft and very light, and instantly combine with oxygen when they are exposed to the air.

Everyone had been accustomed to think of a metal as a heavy, hard solid, unchanged, or very slowly changed, by exposure to air. Had chemists strictly defined the term metal, they could not have allowed the bases of potash and soda (as Davy called the new substances) to be included among metals. Happily, the definitions of natural science are not as the definitions of the logician; they are descriptive summaries of what is known, and suggestive guides to further enquiry.

As every attempt to separate potassium and sodium into unlike parts failed, Davy put them into the class elements; he said—“Till a body is decomposed, it should be considered as simple.”

In 1810, Davy investigated a substance concerning the composition of which a fierce controversy raged. Oxymuriatic acid was said by almost all chemists at that time to be a compound of oxygen with an unknown base. No one had been able to get oxygen from it, or to isolate the base supposed to be a constituent of it. By putting away, for the time, all hypotheses and speculations, and by conducting his experiments quantitatively, Davy showed that oxymuriatic acid is not an acid, but is a simple substance, that is, a substance which is not decomposed in any of the changes it undergoes. He proposed to name this simple substance chlorine; a name, Davy said, “founded upon one of its obvious and characteristic properties —its colour.” Davy remarked—“Names should express things not opinions.”

Davy thought much about the connections between chemical affinity and electrical energy, and investigated these connections by well-planned experiments. In 1807, he said —“May not the electrical energy be identical with chemical affinity?” He used the expressions—“different electrical states,” and “degrees of exaltation of the electrical states,” of the particles of bodies. Recent researches into the subject of chemical affinity have established the great importance of the conceptions adumbrated by Davy in these expressions.

Chemistry, the study of the changes of composition and properties which happen when homogeneous substances interact, has always been closely connected with physics, the study of the behaviour of substances apart from those interactions of them in which composition is changed. Among the earlier physical chemists, Graham occupies and important place.