SIR HUMPHRY DAVY
Davy was born on December 17, 1778 in Penzance, Cornwall, England. He received his education in Penzance and in Truro. His father died in 1794, and Davy, in an effort to help support his family, became an apprentice to a surgeon-apothecary, J. Binghan Borlase. After reading Antoine Lavoisier's Traite Elementaire , Davy in 1797 became interested in chemistry.(2)
The Oxides of Nitrogen
When Davy was released from his indenture as a apprentice, he became superintendent of the Medical Pneumatic Institution of Bristol. This organization was devoted to the study of the medical value of various gases, and it was here that Davy first made his reputation. He studied the oxides of nitrogen and discovered the physiological effects of nitrous oxide, which became known as laughing gas. He "breathed 16 quarts of the gas in seven minutes" and became "completely intoxicated" with it. (7) It would be forty-five years later before nitrous oxide would be used as a anesthetic by dentists. (2)
From a notebook that he kept at this time are analytical results that document the discovery of nitrous oxide and that illustrate the law of multiple proportions:
"When two elements combine and form more than one compound, the masses of one element that react with a fixed mass of the other are in the ratio of small whole numbers."
|Compound||Percent N||Percent O||Grams of N
1.00 g of O
The ratios in the last column are proportional to 1:1.88:4.13. (The compounds analyzed are NO2, NO, and N2O.) Today we see in data such as these a confirmation of one tenet of Dalton's atomic theory: Compounds consist of atoms of their constituent elements combined in small whole number ratios. But at this time Davy dismissed Dalton's theory as "rather more ingenious than important." To Dalton's claim that "chemical analysis and synthesis go no farther than to the separation of particles one from another, and their reunion. No new destruction or creation of matter is within the reach of chemical agency", Davy replied: "There is no reason to suppose that any real indestructible principle has yet been discovered." (7)
Electrolysis and the Alkali Metals
Davy's next and most important investigations were devoted to electrochemistry. Following Galvani's experiments and the discovery of the voltaic pile, interest in galvanic electricity had become widespread. The first chemical decomposition by means of the pile was carried out in 1800 by Nicholson and Carlisle, who obtained hydrogen and oxygen from water, and who decomposed the aqueous solutions of a variety of common salts. Davy, too, began to example the chemical effects of electricity in 1800. He soon found that when he passed electrical current through some substances, these substances decomposed, (a process later called electrolysis). Thus it was certain that electrical forces could act (generate current) only when the electrolyte was capable of oxidizing one of the metals, and that the intensity of its effect (the voltage generated) was directly related to the reactivity of the electrolyte with the metal. Evidently, Davy understood that the actions of electrolysis and of the voltaic pile were the same. His work led him to propose that the elements of a chemical compound are held together by electrical forces:
"In the present state of our knowledge, it would be useless to attempt to speculate on the remote cause of the electrical energy . . . ; its relation to chemical affinity is, however, sufficiently evident. May it not be identical with it, and an essential property of matter?"
Davy must have known of Lavoisier's suggestion that the alkali earths were oxides of unknown metals. At first, he tried to separate the metals by electrolyzing aqueous solutions of the alkalis, but this yielded only hydrogen gas. He then tried passing current through molten compounds, and his persistence was rewarded when he was able to separate globules of pure metal by this means. His first successes came in 1807 with the separation of potassium from molten potash and of sodium from common salt.(6) He described potassium as particles which, when thrown into water, "skimmed about excitedly with a hissing sound, and soon burned with a lovely lavender light." Dr. John Davy, Humphry's brother, said that Humphry "danced around and was delirious with joy" at his discovery. These results were presented in the Bakerian lecture of November, 1807.(8)
Through electrolysis, Davy eventually discovered magnesium (Magnesia, a district in Thessaly), calcium (calx, L for lime), strontium, and barium in 1808.(10) For all these discoveries, much groundwork had of course been done by others. Thus, Scheele had distinguished baryta from lime in 1774, and Berzelius and Pontin had prepared calcium amalgam by electrolyzing lime in mercury. But Davy was able to isolate the pure metals.(6)
Davy utilized the reducing power of potassium to prepare boron, and he developed the method of separating potassium from sodium based upon the insolubility of potassium perchlorate and the solubility of sodium perchlorate in 97% alcohol.(1)
Davy's research on chlorine is of an importance comparable with those on the alkali metals. Chlorine was first isolated by the Swedish chemist Carl Wilhelm Scheele (1742-1786) in 1774. Scheele did not regard this pungent green gas as an element. He referred to it as "dephlogisticated marine acid". To Scheele, phlogiston was practically synonymous with hydrogen, so in a curious sense, his view of chlorine was essentially correct. Lavoisier, however, chiefly occupied with phenomena of combustion, assumed that chlorine was an oxide of an unknown "radical". Davy performed many experiments to confirm the presence of oxygen. He reacted "oxymuriatic acid", as the English called it, with ammonia, and found only muriatic acid and nitrogen in the products:
3 Cl2 + 2 NH3 ------> 6 HCl + N2
He exposed the gas to white-hot carbon in an attempt to remove the oxygen as carbon dioxide. He was never able to produce oxygen or any compound known to contain oxygen, and he finally concluded that it was an element. (12) He called it "chlorine" after the Greek "chloros" meaning yellow-green, the same association with color as found in "chlorophyll".
By a similar series of experiments, Davy showed in 1810 that muriatic acid or marine acid was a compound only of hydrogen and chlorine, and contained no oxygen. For example, he found that two volumes of muriatic acid react with mercury to give calomel and one volume of hydrogen:
2 HCl + 2 Hg ------> Hg2Cl2 + H2
This put an end to Lavoisier's theory that oxygen was an essential constituent of acids.
Iodine was first prepared in 1811 by Bernard Courtois (1777-1838) who observed purple vapors rising from kelp ashes that he had acidified with sulfuric acid and heated. The purple vapors condensed on a cold surface, forming nearly black crystals. Others, notably Joseph Gay-Lussac and Humphry Davy, proved that the crystals were an element, and it was named after the Greek iodes, meaning violet.(9)
Davy first made iodine pentoxide, a colorless, odorless, crystalline substance of high density in 1815. It is a strong oxidizing agent, and with oxidizible substances sometimes detonates.(3,4)
I2O5 + 10 H+ + 10 e- ------> I2 + 5 HOH
Davy developed the method for the decomposition of silicates into silica by treatment with hot HCl.(1)
SiO44- + 4 H+ ------> SiO2 + 2 HOH
Davy was evidently the first to observe that platinum induced the oxidation of alcohol vapor in air.(11)
Association with Michael Faraday
In 1801, the Royal Institution in London engaged Davy as a public lecturer. Michael Faraday (1791-1867) began attending Davy's lectures in 1810. In December, 1811, Faraday impressed Davy by sending him copious bound notes of these lectures, including exact drawing of Davy's apparatus. The previous October, Davy had been temporarily blinded by an explosion in his laboratory, and he needed help. He hired Faraday at once, beginning a close personal and professional association that lasted for years.
Davy twice opposed the election of Faraday to fellowship in the Royal Society. At one point he objected to honoring Faraday for achieving the first liquefication of chlorine, claiming that he himself deserved credit for the feat. Another time, Davy said his opposition was due to his belief that William Wollaston (1766-1828) had preceded Faraday in discovering electromagnetic rotation. Perhaps Davy had simply become envious of his (successful) former assistant. Faraday did finally become a Fellow of the Royal Society in 1824.(7)
In 1799, Davy did an experiment which showed that when two pieces of ice (or other substance with a low melting point) were rubbed together they could be melted without any other addition of heat. This experiment provided evidence that helped to disprove the caloric theory of heat.(13)
In 1802, Thomas Wedgwood in cooperation with Sir Humphry Davy published a paper entitled "An Account of a Method of Copying Paintings on Glass, and Making Profiles, by the Agency of Light upon Nitrates of Silver". The pictures made by this process were very temporary. As soon as the negatives were removed the pictures turned black.(5)
Davy was knighted in 1812. Three days after being knighted, he married a rich widow, Jan Apreece. Davy along with his wife and his assistant, Michael Faraday, toured Europe from 1813 to 1815. Upon their return to England, Davy invented his miner's safety helmet. The lamp of this safety helmet would burn safely and emit light even when there was an explosive mixture of methane and air present. Davy did not patent the lamp. This error lead to later false claims by locomotive engineer George Stephenson that it was he that invented the miner's safety helmet, not Davy.(2)
In 1825, Hans Christian Oersted first successfully isolated aluminum in a pure form. Sir Humphry Davy had previously been unsuccessful at such attempts. It was Davy who named the element "aluminum", the name used in the United States. The rest of the world uses the term "aluminium".
Among Davy's other accomplishments are the introduction of a chemical approach to agriculture and the tanning and mineralogy industries. He designed an Arc Lamp and invented a process that could be used to desalinate sea water. He also designed a method whereby copper-clad ships could be protected by having zinc plates connected to them.
In 1827, Davy became seriously ill. The illness was later attributed to his inhalation of many gases over the years. In 1829 he made his home in Rome. While in Rome, he had a heart attack and he later died on May 29, 1829 in Geneva, Switzerland.
Davy's qualitative work was excellent but this could not always be said for his quantitative work. He was quick to make decisions and easily distracted. In his life time he went after many honors and won many of them. He had great perception, was good in the laboratory, but was very erratic at times
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