Page:EB1911 - Volume 07.djvu/895

 Appointed minister of war, he reorganized the French army as far as the limited time available permitted, and he was so far indispensable to the war department that Napoleon kept him at Paris during the Waterloo campaign. To what degree his skill and bravery would have altered the fortunes of the campaign of 1815 can only be surmised, but it has been made a ground of criticism against Napoleon that he did not avail himself in the field of the services of the best general he then possessed. Davout directed the gallant, but hopeless, defence of Paris after Waterloo, and was deprived of his marshalate and his titles at the second restoration. When some of his subordinate generals were proscribed, he demanded to be held responsible for their acts, as executed under his orders, and he endeavoured to prevent the condemnation of Ney. After a time the hostility of the Bourbons towards Davout died away, and he was reconciled to the monarchy. In 1817 his rank and titles were restored, and in 1819 he became a member of the chamber of peers. He died at Paris on the 1st of June 1823.

 DAVY, SIR HUMPHRY, Bart. (1778–1829), English chemist, was born on the 17th of December 1778 at or near Penzance in Cornwall. During his school days at the grammar schools of Penzance and Truro he showed few signs of a taste for scientific pursuits or indeed of any special zeal for knowledge or of ability beyond a certain skill in making verse translations from the classics and in story-telling. But when in 1794 his father, Robert Davy, died, leaving a widow and five children in embarrassed circumstances, he awoke to his responsibilities as the eldest son, and becoming apprentice to a surgeon-apothecary at Penzance set to work on a systematic and remarkably wide course of self-instruction which he mapped out for himself in preparation for a career in medicine. Beginning with metaphysics and ethics and passing on to mathematics, he turned to chemistry at the end of 1797, and within a few months of reading Nicholson’s and Lavoisier’s treatises on that science had produced a new theory of light and heat. About the same time he made the acquaintance of two men of scientific attainments—Gregory Watt (1777–1804), a son of James Watt, and Davies Giddy, afterwards Gilbert (1767–1839), who was president of the Royal Society from 1827 to 1831. By the latter he was recommended to Dr Thomas Beddoes, who was in 1798 establishing his Medical Pneumatic Institution at Bristol for investigating the medicinal properties of various gases. Here Davy, released from his indentures, was installed as superintendent towards the end of 1798. Early next year two papers from his pen were published in Beddoes’ West Country Contributions—one “On Heat, Light and the Combinations of Light, with a new Theory of Respiration and Observations on the Chemistry of Life,” and the other “On the Generation of Phosoxygen (Oxygen gas) and the Causes of the Colours of Organic Beings.” These contain an account of the well-known experiment in which he sought to establish the immateriality of heat by showing its generation through the friction of two pieces of ice in an exhausted vessel, and further attempt to prove that light is “matter of a peculiar kind,” and that oxygen gas, being a compound of this matter with a simple substance, would more properly be termed phosoxygen. Founded on faulty experiments and reasoning, the views he expressed were either ignored or ridiculed; and it was long before he bitterly regretted the temerity with which he had published his hasty generalizations.

One of his first discoveries at the Pneumatic Institution on the 9th of April 1799 was that pure nitrous oxide (laughing gas) is perfectly respirable, and he narrates that on the next day he became “absolutely intoxicated” through breathing sixteen quarts of it for “near seven minutes.” This discovery brought both him and the Pneumatic Institution into prominence. The gas itself was inhaled by Southey and Coleridge among other distinguished people, and promised to become fashionable, while further research yielded Davy material for his Researches, Chemical and Philosophical, chiefly concerning Nitrous Oxide, published in 1800, which secured his reputation as a chemist. Soon afterwards, Count Rumford, requiring a lecturer on chemistry for the recently established Royal Institution in London, opened negotiations with him, and on the 16th of February 1801 he was engaged as assistant lecturer in chemistry and director of the laboratory. Ten weeks later, having “given satisfactory proofs of his talents” in a course of lectures on galvanism, he was appointed lecturer, and his promotion to be professor followed on the 31st of May 1802. One of the first tasks imposed on him by the managers was the delivery of a course of lectures on the chemical principles of tanning, and he was given leave of absence for July, August and September 1801 in order to acquaint himself practically with the subject. The main facts he discovered from his experiments in this connexion were described before the Royal Society in 1803. In 1802 the board of agriculture requested him to direct his attention to agricultural subjects; and in 1803, with the acquiescence of the Royal Institution, he gave his first course of lectures on agricultural chemistry and continued them for ten successive years, ultimately publishing their substance as Elements of Agricultural Chemistry in 1813. But his chief interest at the Royal Institution was with electro-chemistry. Galvanic phenomena had already engaged his attention before he left Bristol, but in London he had at his disposal a large battery which gave him much greater opportunities. His first communication to the Royal Society, read in June 1801, related to galvanic combinations formed with single metallic plates and fluids, and showed that an electric cell might be constructed with a single metal and two fluids, provided one of the fluids was capable of oxidizing one surface of the metal; previous piles had consisted of two different metals, or of one plate of metal and the other of charcoal, with an interposed fluid. Five years later he delivered before the Royal Society his first Bakerian lecture, “On some Chemical Agencies of Electricity,” which J. J. Berzelius described as one of the most remarkable memoirs in the history of chemical theory. He summed up his results in the general statement that “hydrogen, the alkaline substances, the metals and certain metallic oxides are attracted by negatively electrified metallic surfaces, and repelled by positively electrified metallic surfaces; and contrariwise, that oxygen and acid substances are attracted by positively electrified metallic surfaces and repelled by negatively electrified metallic surfaces; and these attractive and repulsive forces are sufficiently energetic to destroy or suspend the usual operation of elective affinity.” He also sketched a theory of chemical affinity on the facts he had discovered, and concluded by suggesting that the electric decomposition of neutral salts might in some cases admit of economical applications and lead to the isolation of the true elements of bodies. A year after this paper, which gained him from the French Institute the medal offered by Napoleon for the best experiment made each year on galvanism, he described in his second Bakerian lecture the electrolytic preparation of potassium and sodium, effected in October 1807 by the aid of his battery. According to his cousin, Edmund Davy, then his laboratory assistant, he was so delighted with this achievement that he danced about the room in ecstasy. Four days after reading his lecture his health broke down, and severe illness kept him from his professional duties until March 1808. As soon as he was able to work again he attempted to obtain the metals of the alkaline earths by the same methods as he had used for those of the fixed alkalis, but they eluded his efforts and he only succeeded in preparing them as amalgams with mercury, by a process due to Berzelius. His attempts to decompose “alumine, silica, zircone and glucine” were still less fortunate. At the end of 1808 he read his third Bakerian lecture, one of the longest of his papers but not one of the best. In it he disproved the idea advanced by Gay Lussac that potassium was a compound of hydrogen, not an element; but on the other hand he cast doubts on the elementary 