Humphry Davy, Poet and Philosopher

by T. E. Thorpe

Davy once said that “analogy was the fruitful parent of error”; and the whole history of science probably furnishes no more extraordinary instance of perverted analogy, or one more unexpected in its consequences. In another of his lectures he said of the alchemists that “even their failures developed some unsought-for object partaking of the marvellous”—and the statement in this case is even more true of himself. Each phase in the story of this discovery indeed partakes of the marvellous. Sometime during the first fortnight in October, 1807, he obtained his first decisive result; and on the 19th of November he delivered what is generally regarded as the most memorable of all his Bakerian lectures, “On some new Phenomena of chemical Changes produced by Electricity, particularly the Decomposition of the fixed Alkalies, and the Exhibition of the new substances which constitute their bases; and on the general Nature of alkaline Bodies.” Few discoveries of like magnitude have been made and perfected in so short a time, and few memoirs have been more momentous in result than that which Davy put together in a few hours, and in which he announced his results to the world. The whole work was done under conditions of great mental excitement. His cousin Edmund Davy, who at the time acted as his assistant, relates that when he saw the minute globules of the quicksilver-like metal burst through the crust of potash and take fire, his joy knew no bounds; he actually danced about the room in ecstasy, and it was some time before he was sufficiently composed to continue his experiments. The rapidity with which he accumulated results after this first feeling of delirious delight had passed was extraordinary. Before the middle of November he had obtained most of the leading facts. In a letter dated November 13th he tells W. H. Pepys—

“I have decomposed and recomposed the fixed alkalies, and discovered their bases to be two new inflammable substances very like metals; but one of them lighter than ether, and infinitely combustible. So that there are two bodies decomposed, and two new elementary bodies found.”

The stories told by Paris of his habits at this period, and of his various expedients to gain time—of his rushing off to dinner with persons of the highest rank with no fewer than five shirts on, and as many pairs of stockings, because in his haste he could not put on fresh linen without removing that which was underneath; of his continuing his chemical labours on his return to the laboratory until three or four in the morning; and of his then being up before the servants, are certainly much exaggerated, if not wholly apocryphal. He was, it is true, not very systematic in the disposal of his time, but he seldom entered the laboratory before ten or eleven in the morning, and rarely left it later than four, and he was scarcely ever known to visit it after he had dressed for dinner. Except when preparing a lecture, he seldom dined in his rooms at the Institution: his brother tells us that his invitations to dinner were so numerous that he was, or might have been, constantly engaged; and after dinner he was much in the habit of attending evening parties, and devoting the evening to amusement, “so that to the mere frequenters of such parties he must have appeared a votary of fashion rather than of science.”

It was characteristic of him, that on the very eve of the announcement of the discovery which raised him to the summit of his scientific fame, he could unbend the strung bow and thus write to his youngest sister:—

“My dear Sister, ... I looked last week at the pattern of the gown that my sister put into my hands, and found it so worn and tattered that nothing can be made of it; I cannot therefore get your gowns made till you send me another. The best way will be to give me measure of the waist, shoulders, length &c., in this way, and there can then be no difficulties: thus waist, 15 inches, or whatever it may be; between shoulders: length from waist to skirt or train.

“I do not wish to send gowns you cannot wear, and in this way they can be well made. By a piece of tape you can easily measure and then try the length by a carpenter’s rule, and give me the results for yourself, and for Kitty, and Grace, and I shall then be able to send your gowns a few days after I receive your letter....

“I shall write to my mother soon, about John. And now, my dear sister, having written you as stupid a letter as ever was written about gowns, I shall end with love to my mother, Kitty, Grace, and my aunts.

“Your affectionate brother
“H. Davy.”

The Bakerian lecture in which Davy announces the discovery of the compound nature of the fixed alkalis opens with a reference to the concluding remarks of his lecture of the previous year, “that the new methods of investigation promised to lead to a more intimate knowledge than had hitherto been obtained concerning the true elements of bodies. This conjecture, then sanctioned only by strong analogies, I am now happy to be able to support by some conclusive facts.”

In the first attempts he made to decompose the fixed alkalis he acted upon concentrated aqueous solutions of potash and soda with the highest electrical power he could then command at the Royal Institution—viz. from voltaic batteries containing 24 plates of copper and zinc of 12 inches square, 100 plates of 6 inches, and 150 of 4 inches, charged with solutions of alum and nitric acid; but although there was high intensity of action nothing but hydrogen and oxygen was disengaged. He next tried potash in igneous fusion, and here the results were more encouraging: there were obvious and striking signs of decomposition: combustible matter was produced accompanied with flame and a most intense light. He had observed that although potash when dry is a non-conductor, it readily conducts when it becomes damp by exposure to air, and in this state “fuses and decomposes by strong electrical powers.”

“A small piece of pure potash, which had been exposed for a few seconds to the atmosphere, so as to give conducting power to the surface was placed upon an insulated disc of platina, connected with the negative side of the battery of the power of 250 of 6 and 4, in a state of intense activity;[G] and a platina wire communicating with the positive side was brought in contact with the upper surface of the alkali....

“Under these circumstances a vivid action was soon observed to take place. The potash began to fuse at both its points of electrization. There was a violent effervescence at the upper surface; at the lower, or negative surface, there was no liberation of elastic fluid; but small globules having a high metallic lustre, and being precisely similar in visible characters to quicksilver appeared, some of which burnt with explosion and bright flame, as soon as they were formed, and others remained, and were merely tarnished, and finally covered by a white film which formed on their surfaces.”

[G] It is frequently stated that Davy was enabled to isolate the metals of the alkalis because of the large and powerful voltaic battery which he had at his disposal in the Royal Institution. This is not correct. The battery he employed was of very moderate dimensions, and not by any means extraordinary in power. It was the success he thus achieved that caused the large battery, which is probably referred to, to be constructed, by special subscription, in 1809.

The platina, as such, was, he found, in no way connected with the result: a substance of the same kind was produced when copper, silver, gold, plumbago, or even charcoal was employed for completing the circuit.