Bergman, Torbern Olof
Bergman, Torbern Olof
(b. Katrineberg, Sweden, 9 March 1735; d. Medevi, Sweden, 8 July 1784)
chemistry, mineralogy, entomology, astronomy, physics, geography.
The son of Barthold Bergman, sheriff on the royal estate at Katrineberg, and Sara Hägg, Bergman received a conventional early education in classical subjects at Skara, and was also given private instruction in natural history by Sven Hof, a teacher in the Gymnasium there. He entered Uppsala University in 1752 and graduated in 1756, after studying mathematics, philosophy, physics, and astronomy. In 1758 he gained his doctorate with a thesis entitled De interpolatione astronomica, published De attractione universali, and became a lecturer in physics at the university. Bergman was appointed associate professor of mathematics in 1761, and in 1767 succeeded J. G. Wallerius as professor of chemistry, a subject that was new to him but in which he became famous. He corresponded with scientists all over Europe and Frederick II offered him an appointment in the Berlin Academy, but he preferred to stay in Sweden. Often in poor health, he regularly visited the medicinal springs at Medevi, where he died. In 1771 he had married Catherine Trast, who survived him.
While a student, Bergman made important contributions to natural history, the most interesting being his discovery, praised by Linnaeus, that the “insect” coccus aquaticus was in fact a leech’s egg from which ten to twelve young hatched. He studied and classified insect larvae, and in 1762 the Stockholm Academy of Science awarded him a prize for his research on the winter moths that damaged fruit trees. He observed that the female was wingless, and found that metamorphosis occurred in the ground and that after mating, the female climbed the tree and laid eggs around the buds. Damage could therefore be prevented by tying a wax-covered band around the trunk, and this became standard practice in orchards.
Bergman’s early contributions to physical science included studies of the rainbow, twilight, and the aurora borealis, of which he estimated the height to be about 460 miles. More important was his discovery of an atmosphere on Venus during the transit of 6 June 1761. Others who took part in this early example of international scientific cooperation included Lomonosov, Dunn, and Chappe d’Auteroche. Like Bergman, they saw a luminous aureole around the planet when it entered and left the sun’s disk, and interpreted it as being due to refraction in an atmosphere, but Bergman gave the clearest description of the phenomenon, which was overlooked by some other observers.
Bergman’s, inaugural address to the Stockholm Academy in 1764 was “The Possibility of Preventing the Harmful Effects of Lightning,” and he was one of the first to support Franklin’s belief in lightning conductors. However, he disagreed with Franklin’s one-fluid theory of electricity, and developed a two-fluid theory similar to that of Wilcke in order to explain why a luminous discharge apparently flowed from both negative and positive conductors.
Following Aepinus, Bergman investigated the pyroelectricity of tourmaline. In 1766 he showed that when the temperature was raised, one end of the crystal became positive and the other negative, and that reducing the temperature reversed the polarity. This was discovered independently by B. Wilson and J. Canton, but none of the three offered an explanation. In 1785 R.J.Haüy was the first to relate crystal structure to electrical properties.
A comprehensive work on cosmography was published in Uppsala in three volumes. F. Mallet gave an account of astronomy; S. Insulin described the customs of the various races inhabiting the world; and in 1766 Bergman contributed Physical Description of the Earth. This was an important treatise on physical geography, but its influence was probably diminished by the lack of English and French translations at a time when British and French navigators were rapidly adding to knowledge of the globe. Bergman included a long account of minerals, and he soon became actively interested in mineralogy and chemistry.
Wallerius had lectured on chemistry without demonstrations, and Bergman reformed the teaching arrangements as soon as he succeeded to the chair. Since he believed in applying chemistry to mining and industry, he provided two displays of minerals, one arranged according to chemical composition and one according to geographical distribution, and an exhibition of models of industrial equipment. He taught his students, who came from many countries, not only theoretical chemistry but also new experimental methods, especially in mineral analysis.
The blowpipe had been used by Swedish analysts at least as early as the 1740’s. A. Swab and S. Rinman were the pioneers, and A. F. Cronstedt introduced soda, borax, and microcosmic salt (sodium ammonium phosphate) as fluxes. In De tubo feruminatoria (1779) Bergman gave a full account of the instrument. He recorded the reactions of minerals with the three fluxes, fused in hollow charcoal supports or silver or gold spoons, and he distinguished between the oxidizing and reducing flames, as they are now called. The blowpipe was an excellent instrument for qualitative analysis, but he recognized that it was unsuitable for quantitative analysis, a branch of the art that he greatly improved by wet methods.
Bergman published analyses of many individual minerals and mineral waters, and dissertations on most of the metals. These frequently contained new qualitative and quantitative results, but three general treatises were more important. In De analysi aquarum (1778), he gave the first comprehensive account of the analysis of mineral waters. Dissolved gases, usually carbon dioxide or hydrogen sulfide, were driven out by heating and were collected over mercury. The water was then evaporated to dryness and the residue extracted by four solvents in succession: alcohol, water, acetic acid, and hydrochloric acid. The resulting solutions were each treated with about twenty-five reagents, but not in any particular order. Many were well known, but Bergman introduced important new reagents, notably oxalic acid as a test for lime, and barium chloride for sulfate. His method represented an advance in the analysis of mineral waters, but it was soon improved, notably by A. F. de Fourcroy, who in 1781 pointed out the desirability of using the reagents in a systematic order and found that several were redundant. However, Bergman determined the compositions of some important mineral waters, and from 1773 he successfully prepared artificial seltzer and Pyrmont waters by dissolving the necessary compounds in water saturated with carbondioxide, which he called “aerial acid” after discovering its acidity.
In De minerarum docimasia humida (1780) Bergman described his procedures for qualitative and quantitative analysis of minerals by wet methods. The mineral was finely ground and dissolved in purified acids. Reagents were used for qualitative analysis, as in the case of mineral waters, but for quantitative analysis he introduced an entirely new procedure that soon was generally adopted. Previously it had been customary to attempt to isolate the substance being estimated (metal, earth, and so forth) in the pure state, but Bergman precipitated it as an insoluble compound of known composition, which was filtered through a previously weighed paper and then weighed after drying at the temperature of boiling water. It was necessary to ensure that the precipitate was not contaminated. Thus, iron was precipitated by potassium ferrocyanide; this reagent also formed an insoluble salt with manganese that could be removed by nitric acid.
The method depended on the purity and insolubility of precipitates of known composition. Bergman discussed these factors in a third treatise. De praecipitatis metallicis (1780), which contained a table listing the weights of precipitates obtained from 100 parts by weight of different metals by various reagents. Other chemists, notably R. Kirwan and C. F. Wenzel, obtained different results, but Bergman’s prestige caused his figures to be generally accepted for many years. In 1789 L. B. Guyton de Morveau proved that Bergman’s results were inconsistent, and most of them were abandoned (as were Kirwan’s and Wenzel’s), but his new analytical methods were of permanent value.
In De praecipitatis metallicis Bergman also considered the phenomena observed when metals dissolved in acids, and, as in other writings by him, he accepted the view that phlogiston was lost by the metal. He adopted the phlogistic explanation of combustion and calcination Proposed by C. W. Scheele: phlogiston from the combustible or metal combined with “fire air” (oxygen) to form heat, a subtle material that escaped through the vessel. Bergman did, however, make an important original contribution to the phlogiston theory in 1782, when he attempted to measure the relative quantities of phlogiston in different metals by determining the weight of one metal that would precipitate another from solution. Thus, from solution in nitric acid, 100 parts of silver were precipitated by 135 of mercury, 234 of lead, 31 of copper, and so on; and these weights were considered to contain the same amount of phlogiston, for the reaction involved only its transfer. There were inconsistencies due to such effects as incomplete precipitation and the occasional evolution of hydrogen, and it would be reading too much into these results to say that Bergman had grasped the idea of equivalents. This work is, however, important as one of the few attempts ever made to put the phlogiston theory on a quantitative basis.
With his early mathematical training, Bergman was well equipped to seek a geometrical as well as a chemical explanation of the composition of matter, and he made a notable contribution to the early development of crystallography. He may have been influenced by C. F. Westfeld, who in 1767 expressed the opinion that all calcite crystals were composed of rhombohedra and that other shapes were built up from these. A similar suggestion was made by Gahn, but Bergman was the first to demonstrate this in the case of a definite form in which calcite occurred, the scalenohedron. In 1773 he showed how from a rhombohedral nucleus with angles of 101.5° and 78.5° the scalenohedron could be constructed by superimposing rhombic lamellae in sizes that decreased according to some law as the layers developed. This was not merely a geometrical construction on paper, but agreed with the results of cleavage experiments. Dodecahedral garnet crystals were similarly explained, but Bergman could not derive the hexagonal calcite prism with plane ends. This line of research was later developed by Haüy, whose earliest investigations were on garnet and the forms of calcite discussed by Bergman, Haüy’s denial that he knew of Bergman’s theories has been questioned, but of course there is no doubt about the originality of his subsequent work.
Crystallization was commonly believed to be caused by a “saline principle,” but Bergman’s analyses showed that many gems and crystalline minerals contained no saline materia1, and he rejected the concept. Like Guyton de Morveau, with whom he regularly corresponded, he accepted the Newtonian theory that crystals were formed by the mutual attraction of the molecules of matter, but he did not go so far as Guyton, who suggested that these molecules themselves had definite geometrical shapes that could be inferred from the shapes of the crystals.
His belief in attraction between molecules and the vast knowledge of chemical reactions acquired in the course of his analytical work put Bergman in a good position to study chemical affinity. Much had been written about this since E. F. Geoffory published his table of affinities in 1718, after Newton expressed the view that chemical change was caused by a force acting between particles at very small distances.
Geoffroy’s table contained sixteen columns, each with the symbol for one substance at the head and below it the symbols for the substances with which it combined, arranged so that each displaced only those below it. As chemica1 knowledge increased, affinity tables grew larger; Spielmann’s table (1763) had twenty-eight columns, and Fourcy’s (1773) had thirty-six. These tables were convenient for summarizing chemical knowledge, but their compilers generally did not speculate about the cause of reactions. Newton’s followers were convinced that a modified gravitational attraction was the sole cause of affinity. While using the words “affinity” and “attraction” indiscriminately, Bergman made it clear that he was a Newtonian, although, unlike Guyton and some others, he made no attempt to calculate the strength of intermolecular forces.
Eighteenth-century chemists sometimes thought that the affinity between two substances was a variable quantity, for the course of many reactions could be altered, particularly by the action of heat. A. Baumé pointed this out in 1763, and suggested that two affinity tables should be drawn up, one for reactions “in the wet way” (in aqueous solution) and the other for reactions “in the dry way” (at high temperature, in the absence of water). Bergman was the first to do this, but he did not accept the view that affinities were variable. He stated emphatically that reactions in aqueous solution showed the true affinities of substances, and that changes in the order of affinities in the dry way were due to the action of heat. The first version of his Disquisitio de attractionibus electivis (1775) included a table with fifty columns representing reactions in the wet way and thirty-six in the dry way; in 1783 he enlarged these to fifty-nine and forty-three columns, respectively. These tables were widely praised and were reprinted as late as 1808 in William Nicholson’s Dictionary of Chemistry, but it must be doubted whether they were of great utility, for, like all previous tables, they summarized experimental information without explaining it. Further, Lavoisier pointed out that while separate tables for wet and dry reactions were useful, the effect of heat was so great that there should really be an individual table for each degree of temperature.
In his theoretical discussion Bergman advanced a simplified version of P. J. Macquer’s classification of the types of attraction. The union of two or more particles of the same substance was an example of “attraction of “aggregation” when two different substances united, it was “attraction of composition.” “Single elective attraction” occurred when a simple substance combined with one of the constituents of a binary compound and set the other free; and “double elective attraction,” when two binary compounds reacted and their constituents were exchanged to form two new binary compounds. Affinity tables showed single elective attractions, and Bergman considered that from these it should be possible to find the results of reactions involving several substances, for double elective attractions were to be calculated from the algebraic sums of single attractions. Bergman did not himself attempt to do this, for he did not give numerical values for elective attractions, although soon after the publication of his work this was done by Kirwan, Guyton, and others.
Although Bergman believed that single elective attractions were constant, he admitted that this was not immediately obvious. The apparent exceptions could, however, be explained. For example, it was sometimes difficult to ascertain the exact number of reactants, phlogiston in particular being often over tooked, so that what was apparently an example of single elective attraction might in fact be double. Bergman also noted that the proportions as well as the nature of reactants Sometimes seemed to affect the course of a reaction—a line of investigation developed fruitfully by C. L. Berthollet between 1798 and 1803.
Descriptions of reactions in conventional prose were cumbersome, and Bergman introduced diagrams to represent reactions involving single and double elective attractions. These served the same purpose as the earlier diagrams of J. Black and W. Cullen, but were differently constructed. The reaction in the wet way between muriate (chloride) of soda and nitrate of silver is an example.
The vertical and horizontal brackets show the constituents of the reactants and the products, respectively.
In tables and diagrams Bergman represented substances by symbols, but his successors frequently preferred words. Their binary nomenclature for salts was partly due to Bergman, an early critic of the old unsystematic nomenclature in which the name of a substance was usually derived from its appearance, its discoverer, or some other chemically irrelevant factor. From 1775 he began to coin names related to chemical composition, and he attempted a general reform in Sciagraphia regni mineralis (1782). Guyton de Morveau’s proposals for a systematic nomenclature were also published in 1782, and their influence can be seen in Bergman’s final system, presented in Meditationes de systemate fossilium naturali (1784). Guyton wrote in French, but Bergman preferred Latin, which could be translated into all modern languages. Following Linnaeus, Bergman divided inorganic substances into classes, general and species; and, as Linnaeus had done for plants and animals, he defined each class and genus by one word and each species by two. There were four classes: salts (including acids and alkalies as well as neutral salts), earths, metals, and phlogistic materials. In the important and numerous class of salts, each acid or alkali constituted a genus, and a neutral salt was a species belonging to the genus of its acid. The acids were named vitriolicum, nitrosum, and so on; and the alkalies became potassinum, natrum, and ammoniacum. Neutral salts received such names as vitriolicum potassinatum and nitrosum argentatum. Provision was made for unusual salts containing excess acid or base, for example, or having more than two constituents. This was more comprehensive than Guyton’s nomenclature of 1782; had he lived, Bergman would have collaborated with Guyton in perfecting the system.
Bergman’s nomenclature was closely related to his classification of minerals by composition. Some mineralogists based their classification on external form, but he insisted that the best method demonstrated the inner composition of each mineral, for only thus would we know its utility. However, different external appearances were sometimes associated with the same composition; so while classes, genera, and species had to be defined by composition, varieties could be distinguished by appearance. This was the basis of Meditationes de systemate fossilium naturali (1784), his last major work. In the preface he announced his latest discoveries. He had found two sulfides of tin, one containing twice as much sulfur as the other; and resemblances between baryta (barium oxide) and calx (oxide) of lead made him suspect that baryta contained a metal. These final examples of experimental skill and chemical insight show that Bergman deserved the high esteem in which he was held by his contemporaries.
BIBLIOGRAPHY
1. Original Works. More than 300 items are described in Birgitta Moström. Torbern Bergman, A Bibliography of His Works (Stockholm, 1957), which includes reprints and translations published up to 1956.
Bergman’s manuscripts are preserved in the University Library, Uppsala. The letters that he received from foreigners are published in G. Carlid and J. Nordström, eds., Torbern Bergman’s Foreign Correspondence, I (with an introductory biography by H. Olsson). Letters From Foreigners to Torbern Bergman (Stockholm, 1965). Vol. II will contain letters from Swedes living abroad, and Bergman’s letters to his foreign correspondents.
II. Secondary Literature. Several short biographies were written soon after Bergman’s death, and later biographical accounts are based on these: P. F. Aurivillius, Åminnelse-tal öfver … Bergman (Uppsala, 1785); P. J. Hjelm. Åminnelse-tal öfver … Bergman (Stockholm, 1786); F. Vicq d’Azyr, in Histoire de la Société royale de médecine de Paris (1782/1783, pub. 1787), 141–187, repr. in his Éloges historiques, I (Paris, 1805), 209–248; A. N. de Condorcet, in Historie de l’Acadé Societé royale des sciences (1784, pub. 1787), 31–47, repr. in his Oeuvres (Paris, 1847), III, 139–161.
Recent studies of several aspects of Bergman’s scientific work can be listed in the order in which the topics are discussed above: D. Müller-Hillebrand. “Torbem Bergman as a Lightning Scientist,” in Daedalus, Tekniska museets arsbok, Stockholm (1963), 35–76; A. J. Meadows. “The Discovery of an Atmosphere on Venus,” in Annals of Science, 22 (1966), 117–127; F. Szabadvary, History of Analytical Chemistry (Oxford, 1966), pp. 71–81, 86–89; U. Boklund, “Torbern Bergman as a Pioneer in the Domain of Mineral Waters,” in T. Bergman, On Acid of Air … (Stockholm, 1956), pp. 105–128; R. Hooykas,” Les Débuts de la théorie cristallographique de R. J. Haüy, d’apres les documents originaux,” in Revue d’histoire des sciences, 8 (1955), 319–337; J. G. Burke, Origins of the Science of Crystals’ (Berkeley–Los Angeles, 1966), pp. 26–27, 79–84; A. M. Duncan, “Some Theoretical Aspects of Eighteenth-Century Tables of Affinity,” in Annals of Science, 18 (1962), 177–194, 217–232; and “Introduction” to a facsimile repr. of Thomas Beddoes’ trans. (London, 1785) of Bergman’s A Dissertation on Elective Attractions (London, 1969); W. A. Smeaton, “The Contributions of P. J. Macquer, T. O. Bergman and L. B. Guyton de Morveau to the Reform of Chemical Nomenclature,” in Annals of Science, 10 (1954), 87–106; and M. P. Crosland, Historical Studies in the Language of Chemistry (London, 1962), pp. 144–167.
W. A. Smeaton