The 100 Most Influential Scientists of All Time (19 page)

Beginning in 1816, Gay-Lussac served in a wide array of appointments, attesting to the value his contemporaries
placed upon applying chemistry toward solving social and economic concerns. Among his more lucrative positions was his 1829 appointment as director of the assay department at the Paris Mint, for which he developed a precise and accurate method for the assaying of silver.

Gay-Lussac was a key figure in the development of the new science of volumetric analysis. Previously a few crude trials had been carried out to estimate the strength of chlorine solutions in bleaching, but Gay-Lussac introduced a scientific rigour to chemical quantification and devised important modifications to apparatuses. In a paper on commercial soda (sodium carbonate, 1820), he identified the weight of a sample required to neutralize a given amount of sulfuric acid, using litmus as an indicator. He went on to estimate the strength of bleaching powder (1824), using a solution of indigo to signify when the reaction was complete. In his publications are found the first use of the chemical terms
burette, pipette
, and
titrate
. The principles of volumetric analysis could be established only through Gay-Lussac's theoretical and practical genius but, once established, the analysis itself could be carried out by a junior assistant with brief training. Gay-Lussac published an entire series of
Instructions
on subjects ranging from the estimation of potash (1818) to the construction of lightning conductors. Among the most influential
Instructions
was his estimation of silver in solution (1832), which he titrated with a solution of sodium chloride of known strength. This method was later employed at the Royal Mint.

(b. Dec. 17, 1778, Penzance, Cornwall, Eng.—d. May 29, 1829, Geneva, Switz.)

E
nglish chemist Sir Humphry Davy discovered several chemical elements (including sodium and
potassium) and compounds, invented the miner's safety lamp, and became one of the greatest exponents of the scientific method.

Early in his career Davy formed strongly independent views on topics of the moment, such as the nature of heat, light, and electricity and the chemical and physical doctrines of Antoine-Laurent Lavoisier. In his small private laboratory, he prepared and inhaled nitrous oxide (laughing gas), in order to test a claim that it was the “principle of contagion,” that is, caused diseases. Davy subsequently investigated the composition of the oxides and acids of nitrogen, as well as ammonia, and persuaded his scientific and literary friends to report the effects of inhaling nitrous oxide. He nearly lost his own life inhaling water gas, a mixture of hydrogen and carbon monoxide sometimes used as fuel. The account of his work, published as
Researches, Chemical and Philosophical
(1800), immediately established his reputation.

In 1801 Davy moved to London, where he delivered lectures and furthered his researches on voltaic cells, early forms of electric batteries. His carefully prepared and rehearsed lectures rapidly became important social functions and added greatly to the prestige of science. In 1802 he conducted special studies of tanning: he found catechu, the extract of a tropical plant, as effective as and cheaper than the usual oak extracts, and his published account was long used as a tanner's guide.

In 1803 Davy was admitted a fellow of the Royal Society and an honorary member of the Dublin Society and delivered the first of an annual series of lectures before the board of agriculture. This led to his
Elements of Agricultural Chemistry
(1813), the only systematic work available for
many years. For his researches on voltaic cells, tanning, and mineral analysis, he received the Copley Medal in 1805. He was elected secretary of the Royal Society in 1807.

Davy early concluded that the production of electricity in simple electrolytic cells resulted from chemical action and that chemical combination occurred between substances of opposite charge. He therefore reasoned that electrolysis, the interactions of electric currents with chemical compounds, offered the most likely means of decomposing all substances to their elements. These views were explained in 1806 in his lecture “On Some Chemical Agencies of Electricity,” for which, despite the fact that England and France were at war, he received the Napoleon Prize from the Institut de France (1807). This work led directly to the isolation of sodium and potassium from their compounds (1807) and of the alkaline-earth metals from theirs (1808). He also discovered boron (by heating borax with potassium), hydrogen telluride, and hydrogen phosphide
(phosphine). He showed the correct relation of chlorine to hydrochloric acid and the untenability of the earlier name (oxymuriatic acid) for chlorine; this negated Lavoisier's theory that all acids contained oxygen. He explained the bleaching action of chlorine (through its liberation of oxygen from water) and discovered two of its oxides (1811 and 1815), but his views on the nature of chlorine were disputed. He was not aware that chlorine is a chemical element, and experiments designed to reveal oxygen in chlorine failed.

Davy later published the first part of the
Elements of Chemical Philosophy
, which contained much of his own work; his plan was too ambitious, however, and nothing further appeared. Its completion, according to a Swedish chemist, J.J. Berzelius, would have “advanced the science of chemistry a full century.”

Davy conducted a number of other studies as well. He investigated the substance “X” (later called iodine), whose properties and similarity to chlorine he quickly discovered, and he analyzed many specimens of classical pigments and proved that diamond is a form of carbon. Davy also investigated the conditions under which mixtures of firedamp and air explode. This led to the invention of the miner's safety lamp and to subsequent researches on flame.

After being created a baronet in 1818, he again went to Italy, where he had been years earlier, inquiring into volcanic action and trying unsuccessfully to find a way of unrolling the papyri found at Herculaneum. During the 1820s, he examined magnetic phenomena caused by electricity and electrochemical methods for preventing saltwater corrosion of copper sheathing on ships by means of iron and zinc plates. Though the protective principles were made clear, considerable fouling occurred, and the method's failure greatly vexed him. His Bakerian
lecture for 1826, “On the Relation of Electrical and Chemical Changes,” contained his last known thoughts on electrochemistry and earned him the Royal Society's Royal Medal.

In the last months of his life, Davy wrote a series of dialogues, which were published posthumously as
Consolations in Travel, or the Last Days of a Philosopher
(1830).

(b. Aug. 20, 1779, near Linköping, Sweden—d. Aug. 7, 1848, Stockholm)

J
öns Jacob Berzelius was one of the founders of modern chemistry. He is especially noted for his determination of atomic weights, the development of modern chemical symbols, his electrochemical theory, the discovery and isolation of several elements, the development of classical analytical techniques, and his investigation of isomerism and catalysis, phenomena that owe their names to him. He was a strict empiricist and insisted that any new theory be consistent with the sum of chemical knowledge.

Berzelius is best known for his system of electrochemical dualism. The electrical battery, invented in 1800 by Alessandro Volta and known as the voltaic pile, provided the first experimental source of current electricity. In 1803 Berzelius demonstrated, as did the English chemist Humphry Davy at a slightly later date, the power of the voltaic pile to decompose chemicals into pairs of electrically opposite constituents. For example, water decomposed into electropositive hydrogen and electronegative oxygen, whereas salts degraded into electronegative
acids and electropositive bases. Based upon this evidence, Berzelius revised and generalized the acid/base chemistry chiefly promoted by Lavoisier. For Berzelius, all chemical compounds contained two electrically opposing constituents, the acidic, or electronegative, and the basic, or electropositive. Furthermore, according to Berzelius, all chemicals, whether natural or artificial, mineral or organic, could be distinguished and specified qualitatively by identifying their electrically opposing constituents.

In addition to his qualitative specification of chemicals, Berzelius investigated their quantitative relationships as well. As early as 1806, he began to prepare an up-to-date Swedish chemistry textbook and read widely on the subject of chemical combination. Finding little information on the subject, he decided to undertake further investigations. His teaching interests focused his attention upon inorganic chemistry. Around 1808 he launched what became a vast and enduring program in the laboratory analysis of inorganic matter. To this end, he created most of his apparatuses, prepared his own reagents, and established the atomic weights of the elements, the formulas of their oxides, sulfides, and salts, and the formulas of virtually all known inorganic compounds.

Berzelius's experiments led to a more complete depiction of the principles of chemical combining proportions, an area of investigation that the German chemist Jeremias Benjamin Richter named “stoichiometry” in 1792. Berzelius was able to establish the quantitative specificity by which substances combined. He reported his analytical results in a series of famous publications, most prominently his
Essai sur la théorie des proportions chimiques et sur l'influence chimique de l'électricité
(1819; “Essay on the Theory
of Chemical Proportions and on the Chemical Influence of Electricity”), and the atomic weight tables that appeared in the 1826 German translation of his
Lärbok i kemien (Textbook of Chemistry
).

The project of specifying substances had several important consequences. In order to establish and display the laws of stoichiometry, Berzelius invented and perfected more exacting standards and techniques of analysis. His generalization of the older acid/base chemistry led him to extend chemical nomenclature that Lavoisier had introduced to cover the bases (mostly metallic oxides), a change that allowed Berzelius to name any compound consistently with Lavoisier's chemistry. For this purpose, Berzelius created a Latin template for translation into diverse vernacular languages.

The project of specifying substances also led Berzelius to develop a new system of notation that could portray the composition of any compound both qualitatively (by showing its electrochemically opposing ingredients) and quantitatively (by showing the proportions in which the ingredients were united). His system abbreviated the Latin names of the elements with one or two letters and applied superscripts to designate the number of atoms of each element present in both the acidic and basic ingredient. In his own work, however, Berzelius preferred to indicate the proportions of oxygen with dots placed over the letters of the oxidized elements, but most chemists rejected that practice. Instead, they followed Berzelius's younger German colleagues, who replaced his superscripts with subscripts and thus created the system still used today. Berzelius's new nomenclature and notation were prominently displayed in his 1819
Essai
.

Berzelius applied his analytical method to two primary areas, mineralogy and organic chemistry. Mineralogy had long stimulated Berzelius's analytical interest. Berzelius himself discovered several new elements, including cerium (1803) and thorium (1828), in samples of naturally occurring minerals, and his students discovered lithium, vanadium, lanthanum, didymium (later resolved into praseodymium and neodymium), erbium (later resolved into erbium, ytterbium, scandium, holmium, and thulium), and terbium. Berzelius also discovered selenium (1818), though this element was isolated in the mud resulting from the manufacture of sulfuric acid rather than from a mineral sample.

In 1813 Berzelius received a mineral collection from a visiting British physician, William MacMichael, that prompted him to take up the analysis and classification of minerals. His major contribution, reported in 1814, was recognizing that silica, formerly seen as a base, frequently served as the electronegative or acidic constituent of minerals and that the traditional mineralogical class of “earths” could be reduced primarily to silicate salts. Distinguishing mineral species therefore demanded a knowledge of the stoichiometry of complex silicates, a conviction that led Berzelius in 1815 to develop his dualistic doctrine, which now anticipated a dualistic structure for substances formerly seen as “triple salts” and for other complex minerals.