Chemistry in the Nineteenth Century
The beginning, and still more, the middle of the nineteenth century witnessed a whole series of discoveries and achievements in mathematics, astronomy, physics, chemistry and biology. New facts and natural laws were established, new theories and hypotheses conceived and new branches of science brought into being.
In the beginning of that century, Dalton published his atomic theory.
The concept of a chemical element was first formulated by Robert Boyle in 1661 in his book The Sceptical Chymist. It was fully established by Lavoisier in 1789. Lavoisier gave a list of 33 elementary substances, of which more than 20 can still be regarded as elements even today. In 1819, J. J. Berzelius increased the number to 50.
John Dalton (1766 - 1844) first wrote on atomic theory in October 1803. The Irish chemists Bryan Higgins (1737 - 1844) and his nephew William Higgins (1769 - 1825) also wrote on the subject of combination of atoms some years before that, but the credit is usually given to Dalton because he formulated a quantitative theory and computed relative atomic weights. His definitive paper New System of Chemical Philosophy was published in 1808.
In 1811, the Italian physicist Amadeo Avogadro came to the concept of the molecule and proposed that under the same conditions of temperature amd pressure, equal volumes of different gases contain the same number of molecules.
A rather spectacular breakthrough was made in 1819 by Alexis-Therese Petit (1719) and Pierre-Louis Dulong (1785 - 1839)who observed that the product of the atomic weight and specific was constant for a list of 13 elements, all of them metals except for sulphur and tellurium. Their paper can be found at http://web.lemoyne.edu/~giunta/PETIT.html. The authors observe, regarding previous studies of heat:
"Of all the chemical actions considered as sources of heat, none has been recognised till very lately, except combustion. It would be useless to look for a plausible theory for the mode of production of heat before the epoch marked by the remarkable discoveries of Lavoisier. The illustrious chemist having more particularly studied the action of oxygen in the state of gas, formed an opinion respecting the cause of the phenomenon in question naturally suggested by the observations of Black on latent heat. hence the idea that the heat disengaged during combustion comes from the change of state of the oxygen. The determination which he made, together with M. Laplace, of the quantities of heat disengaged by the combustion of several substances appeared to furnish a powerful argument in favour of his conjectures.
This gives us some idea about the early development of calorimetry and thermochemistry
In 1838 Wöhler prepared the first inorganic body, urea, from inorganic materials. He started with silver isocyanate and used the reaction
AgCNO + NH4Cl -> (NH2)2CO + AgCl
and thereby inadvertently discredited vitalism, the theory that the chemicals of living organisms are fundamentally different from inanimate matter. By the middle of the century it was possible to prepare every organic substance, the composition of which was accurately known.
a more startling demonstration of the effectiveness came from the investigations in electrolysis made by Michael Faraday in the period 1831 - 1834. As a result of this work, Faraday discovered that a given quantity of electricity always sets free at the electrodes chemically equivalent weights of different substances.
| The combining weight ot equivalent weight of an element is the weight which combines with or replaces one part by weight of hydrogen. It is generally the equivalent weight of an element which is determined experimentally and the atomic weight calculated from it. |
The final development of atomic theory by 19th century chemists was Mendeleyev's enunciation of the periodic law in 1869. Frederick Engels, writing as a philosopher of science commented about this in the chapter on Dialectics in his book Dialectics of Nature.
"(The general nature of dialectics is to be developed as the science of inter-connections, in contrast to metaphysics.)
..............
It is therefore, from the history of nature and human society that the laws of dialectics are to be abstracted. For they are nothing but the most general laws of these two aspects of historical development as well as of thought itself. and indeed they can be reduced in the main to three.
The law of the transformation of quantity into quality and vice versa;
The law of the interpenetration of opposites;
The law of the negation of the negation.
all these are developed by Hegel in his idealist fashion as mere laws of thought, the first, in the first part of his Logic, in the Doctrine of Being, the second fills the whole of the second and by far the most important part of his Logic, the Doctrine of Essence; finally the third figures as the fundamental law for the construction of the whole system."
On the third law (quantity vs. quality) in connection with Mendeleyev's theory, Engels comments as follows:
"Finally, the Hegelian law is valid not only for compound substances but also for the chemical elements themselves. We now know that
"the chemical properties of the elements are a periodic function of their atomic weights" (Roscoe-Schorlemmer, Ausfuhrlisches Lehrbuch der chemie, II, S 823, 1879).
and that, therefore, their quality is determined by the quantity of their atomic weight. as the best of this has been brilliantly carried out, Mendeleyev proved that various gaps occur in the series of related elements arranged according to atomic weights indicating that here new elements remain to be discovered. He discovered in advance the general chemical properties of these unknowh elements, which he termed eka-aluminium, because it follows after aluminium in the series beginning with the latter, and he predicted its approximate specific heat and atomic weight as well as its atomic volume. A few years later, Lecoq de Boisbaudran actually discovered this element and Mendeleyev's predictions fitted with only slight discrepencies. Eka-aluminium was realised in gallium (ibid., p. 828). By means of the -- unconscious -- application of Hegel's law of the transformation of quantity into quality, Mendeleyev achieved a scientific feat which it is not too bold to put on par with Leverrier in calculating the orbit of the then unknown planet Neptune."
Further development of atomic theory was in fact the work of physicists rather than chemists. The planet Neptune was discovered in 1846 as a result of the predictions of Urbain Jean Joseph Leverrier and John Couch Adams. Uranus, the closest planet visible through only a telescope, was discovered in 1781 by William Herschel. In 1879, M. H. Klaproth isolated a "half-metallic substance" from the mineral pitchblende, which was named uranium in honour of Herschel's discovery. E. M. Peligot proved that Klaproth's element was really an oxide of uranium, and he isolated the metal itself in 1842. The radioactivity of uranium was discovered by Becquerel in 1896.
A reproduction of Mendeleyev's original periodic table is given below:
This image, copied from the wikipedia, is a page of Mendeleyev's Principles of Chemistry, Ist English ed., 1891. It will be noticed that the inert gases are missing from his list of elements. The first inert gas argon was isolated in 1894 by Ramsay by removing carbon dioxide, water vapour, oxygen and nitrogen from air. The presence of a new gas was suspected because of accurate determinations of gas densities made by Lord Rayleigh in 1892.
Rayleigh and Ramsey undertook further investigations, which soon led to the recognition of a whole family of inert gases, viz., helium, neon, argon, krypton and xenon, which are found to fit into the Periodic Table between the strongly electronegative halogens and the strongly electropositive alkali metals.
In his Inaugural Address to the British Association (Nature, 1911, vol 86, pp. 282 - 9), Ramsey stated:
"It might have been supposed that our knowledge of the elements was practically complete; that perhaps a few more might be discovered to fill the outstanding gaps in the periodic table. True, a puzzle existed, and still exists, on the classification of "rare earths," oxides of metals occurring in certain minerals, these metals have atomic weights between 139 and 180, and their properties preclude their arrangement in the columns of the periodic table. besides these, the discovery of the inert gases of the atmosphere, of the existence of which Jonathan Stoney's spiral curve, published in 1888, pointed a forecast, joined the elements like sodium and potassium, strongly electronegative, to those of fluorine and chlorine, highly electropositive, by a series of bodies electrically as well as chemically inert, and neon, argon, krypton, and xenon formed links between fluorine and sodium, chlorine and potassium, bromine and rubidium, and iodine and caesium.
Including the inactive gases, and the more recently discovered elements of the rare earths, and radium, of which I shall have more to say presently, there are eighty-four definite elements, all of which find places in the periodic table if merely numerical values be considered. Between lanthanum, with atomic weight 139, and tantalum, 181, there are in the periodic table seventeen spaces, and although it is impossible to admit, on account of their properties, that the elements of the rare earths can be distributed in successive columns (for they all resemble lanthanum in properties), yet there are now fourteen such elements, and it is not improbable that other three will be separated from the complex mixture of their oxides by further work. Assuming that the metals of the rare earths fill these seventeen spaces, how many still remain to be filled? We will take for granted that the atomic weight of uranium, 238.5, which is the highest known, forms an upper limit not likely to be surpassed. It is easy to count the gaps; there are eleven."
As already mentioned, Wohler's synthesis of urea in 1828 led to the overthrow of vitalism. The discovery of the structure of hydrocarbons in the next few decades is discussed in the chapter of Dialectics of Nature quoted above. A startling development in the theory of molecular structure was made by Kekule who, in 1865, proposed the ring model of the benzene molecule.
The explosive liquid nitroglycerine was first made by Ascanio Sobrero in 184 by treating glycerol with a mixture of nitric and sulphuric acid. being extremely sensitive to shock, it was difficult to handle. Alfred Nobel (1866) found that by mixing it with the diatomaceous earth keigelguhr, a paste could be made which was safe to handle. With the profits made by this discovery, the Nobel prizes were instituted in 1901.
Although Mendeleyev died in 1907, six years after the Nobel Prize was instituted, it was not awarded to him. But quite strangely, the 1909 Nobel Laureate in Chemistry, Wilhelm Ostwald, did not believe in atomic theory. His opinions seems even more strange when we read the following extracts from the Nobel Prize Presentation Speech:
"The Royal Academy of Sciences has resolved to award the former professor at Liepzig University and Geheimret, Wilhelm Ostwald, the Nobel Prize for Chemistry 1909 in recognition of his work on catalysis and associated fundamental studies on chemical equilibrium and rates of reaction. As early as the first half of last century it had in certain cases been observed that chemical reactions could be induced by substances which did not appear to participate in the reaction themselves and which were at all events not altered in any way. This led Berzelius in his famous annual reports on the progress of Chemistry for 1935 to make one of his not infrequent brilliant conclusions whereby scattered observations were collated in accordance with a common criterion and new concepts were introduced in science. he termed the phenomenon catalysis ... Some 50 years later Wilhelm Ostwald carried out a number of studies to determine the relative strength of acids and bases. After Arrhenius had formulated his well-known theory that acids and bases in aqueous solution are separated into ions and that their strength depends on their electrical conductivity, or more accurately their degree of dissociation, Ostwald tested the correctness of this view by measuring the conductivity and hence the concentration of the hydrogen and hydroxyl ions with the acids and bases which he had used in his previous experiments. He found Arrhenius' theory corroborated in all of the many cases which he himself investigated. His explanation why he consistently found the same values for the relative strength of the acids and bases whichever method he used was that in all cases the hydrogen ions of the acids and the hydroxyl ions of the bases acted catalytically and that the relative strength of the acids and bases was determined solely by their ion concentration."
[See also: Leon Trotsky: Dialectical Materialism and Science (1925).]
However, the existence of the atom was considered to be conclusively established in 1905 by Einstein's work on Brownian motion!
Fianlly, we have to mention the development of photography, without which the discoveries of radiation by Rontgen and Becquerel would not have been possible. Modern photography owes its beginning to two Frenchmen, Niecephon Niepce and Louis Daguerre, from whose researches the daguerreotype process was evolved in 1839. They used silver chloride as the light sensitive substance and covered a pewter plate with a kind of bitumen. After exposure to light for eight hours, the bitumen was dissolved with vegetable oil and the parts hardened by light remained. At the same time, an Englishman, William Fox Talbot, using paper coated with silver iodide, invented the negative-positive process. Despite limitations in the speed of early photography, Roger Fenton's photographs brought to life the Crimean War in 1854, and Matthew Brady recorded the full horror of the American Civil War.
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