Almost immediately after the publication of Volta’s discovery attempts were made—notably by Berzelius in Sweden and by Davy in England—to prove that electrical and chemical phenomena are correlated and mutually dependent. This assumption was more fully worked out by Berzelius in 1812, and it served as the basis of a chemical system which exercised considerable influence on chemical doctrine during the first half of the nineteenth century.
Berzelius assumed that electric polarity was an attribute of all atoms—that these were bipolar, in fact, but that in them either positive or negative electricity predominated. Hence the elements were capable of being divided into two classes—that is, positive or negative, depending upon the excess of either charge. Which of the electricities predominated might be ascertained by determining the particular pole at which the element was separated on electrolysis. Combinations of dissimilar elements—or, in other words, chemical compounds—were also endowed with polarity. The chemical affinities of elements and compounds were related to the excess of either kind of electricity resident in them; and chemical combination resulted from, and was a consequence of, the more or less perfect neutralisation of the two kinds. From a study of the electrical deportment of the elements Berzelius sought to arrange them in series, starting with oxygen as the most electro-negative member.
These conceptions were employed by him as the basis of a method of classification. The attempt is historically interesting as being the first systematic endeavour to gain an insight into the constitution of chemical compounds—that is, to determine the manner in which the constituent atoms are grouped or arranged with respect to one another, or, in other words, to distinguish between the empirical and the rational composition of substances, which is the ultimate aim of modern chemistry.
A necessary consequence of these views was that every compound was to be considered as made up of two parts in electrically different states. Thus baryta, consisted of a combination of the electro-positive barium, combined with the electro-negative oxygen; it combined with sulphuric oxide because the preponderating positive electricity it contained met with the negative electricity which prevailed in the sulphuric oxide. Generalising, it may be said that the basic oxides are invariably the positive constituents of salts, whereas the acid oxides are the negative constituents, as proved by the mode in which the two kinds of oxides separated at the poles on electrolysis. Barium sulphate, then, was to be regarded as made up of two entities—BaO and SO3—and hence was to be called sulphate of baryta. Berzelius extended this conception in order to explain the formation of double salts—such, for example, as potash alum, which he regarded as a binary compound of positive potassium sulphate and negative aluminium sulphate, each of which, in its turn, could be resolved into an acidic and a basic oxide of opposite electricities.
The dualistic notions of Berzelius led him to the construction of a system of chemical nomenclature and notation which, in its main features, has persisted to this day, and is universally current, with certain modifications, in modern chemical literature. We owe to him the grouping of the elements into metals and metalloids, and also our present system of symbolic notation, whereby even complicated chemical reactions may be expressed in a concise and intelligible manner. Chemical symbols were used by the alchemists; but Berzelius first suggested that a chemical symbol should not only represent the element to which it refers, but also its relative atomic weight. Chemical equations became quantitative as well as qualitative expressions of the facts they denote. Such equations implicitly assumed that, to use Davy’s words, chemistry had passed under the dominion of the mathematical sciences. Professed mathematicians were, however, slow to recognise that the phenomena of chemical action were capable of formal mathematical treatment. Davy relates that on speaking to Laplace of the atomic theory in chemistry, and expressing his belief that the science would ultimately be referred to mathematical laws similar to those he had so profoundly and successfully established with respect to the mechanical properties of matter, the idea was treated in a tone bordering on contempt.
Berzelius’s electro-chemical system, and the dualistic ideas associated with it, were of considerable service when applied to the inorganic branch of the science; but attempts to fit them to the facts of organic chemistry, which began to accumulate rapidly after the first quarter of the century, failed. Its inadequacy as a comprehensive generalisation became more and more manifest, and it eventually fell. In fact, it may be said to have received its death-blow by Davy’s discovery of the elementary nature of chlorine, and by the recognition of the fact that the acids do not necessarily contain oxygen. Davy and, later, Dulong made it obvious that, if any one element was to be regarded as the acidifying principle, it was hydrogen, and not oxygen; and, in a sense, this view ultimately prevailed in the recognition of the acids as salts of hydrogen.
In France the study of electro-chemistry was undertaken by Gay Lussac and Thénard, largely owing to the action of the Emperor Napoleon, who furnished the funds for the construction of a powerful galvanic battery. The results were published, in 1811, under the title, Recherches Physico-Chimiques, faites sur la Pile, etc. Gay Lussac, whose name has already been mentioned as one of the discoverers of the Law of Combination of Gases, played a considerable part in the history of chemistry at this period. He was one of the earliest to appreciate the importance of Dalton’s generalisation, and to point out the significance of his own discovery in strengthening it. He was probably led, in the first instance, to the recognition of the law of gaseous combination by Berthollet’s work on the volumetric composition of ammonia gas, and by his own discovery—made in 1805, in conjunction with Humboldt, in the course of their analysis of atmospheric air—that one volume of oxygen combined with exactly two volumes of hydrogen to form water. The regularities thus indicated he found to be general: all gases which are capable of chemical union combine in simple proportions by volume, and the volume of the product, if a gas, always stands in some simple relation to the volumes of the constituents.
Joseph Louis Gay Lussac was born in 1778, at Saint Leonard, studied chemistry in Paris, and was associated in chemical inquiry with Berthollet. As Eleve-Ingenieur in the École Nationale des Ponts et des Chaussées he began the experimental work in physics and chemistry upon which his fame rests. In 1804 he undertook, with Biot, a series of balloon ascents for the purpose of investigating the physics and chemistry of the upper regions of the atmosphere. In 1806 he became Professor of Chemistry at the École Polytechnique, and in 1832 Professor at the Jardin des Plantes. He was one of the chief assayers of the French Mint, and, as member of many commissions, exerted considerable influence in official circles. He died in 1850.
Gay Lussac and Thénard were the first to devise a method of obtaining potassium and sodium by a purely chemical process, whereby these metals could be procured in far larger quantities than was at that time possible by electrolytic means. They were thus enabled to make use of the strong deoxidising power of these metals to effect a number of reductions, notably that of boric oxide to boron. Gay Lussac and Thénard were also the first to make known the existence of boron fluoride. We further owe to Gay Lussac the discovery of cyanogen, the first of the so-called compound radicals. He first prepared ethyl iodide, investigated sulphovinic acid and grape sugar, studied etherification and fermentation, etc. We are also indebted to him for a method of determining vapour densities which proved of great service in ascertaining the molecular weights of substances. He worked on iodine and its compounds, discovered, with Welter, thiosulphuric acid, and investigated fulminic acid in collaboration with Liebig.
Among his services to analytical chemistry were his method for the analysis of gunpowder, his volumetric estimation of silver (wet silver assay), chlorometric analysis, alkalimetry, etc. He devised the system still in use in France for the estimation of alcohol in spirits of wine.