Louis Jacques Thénard was born in 1777 at Nogent-Sur-Seine, and was a pupil of Vauquelin and of Berthollet. In 1797 he became repétiteur at the Polytechnic School of Paris, and eventually its professor. He subsequently occupied the chair of chemistry at the Collège de France, and of the Faculty of Science of the University of Paris. He was ennobled by Charles X. in 1824, and died at Paris in the eightieth year of his age.
In addition to his work with Gay Lussac already mentioned, we owe to Thénard the discovery of hydrogen peroxide and hydrogen persulphide. Together with Dulong he studied the catalytic action of platinum on mixtures of oxygen and hydrogen. He investigated the fatty acids, and worked on fermentation and on ether-formation; and he was the first to isolate citric and malic acids. He also occupied himself with the chemistry of bile, perspiration, albumen, the acids of urine and milk, and with the theory of mordants.
In 1834 Faraday made known the important fact that on passing the same galvanic current through a number of electrolytes—water, hydrochloric acid, solutions of metallic chloride—these were decomposed in such manner that definite amounts of hydrogen or metal were separated at the negative pole, and corresponding amounts of oxygen or chlorine were evolved at the positive pole. These observations were comprehended by Faraday under his “law of definite electrolytic action.” The electro-chemical equivalents thus obtained were in some cases identical with the atomic weights deduced by Berzelius; in others they were not; but, nevertheless, when they differed, they stood in some simple relation to the assumed atomic weight. The significance of Faraday’s observation was not lost sight of, although his anticipation that the determination of electro-chemical equivalents would be of use in fixing atomic weights was not immediately appreciated. A clear distinction between the equivalent, the atom, and the molecule was not then apprehended. As will be subsequently shown, it was only during the latter half of the nineteenth century that the discrepancies and inconsistencies thus revealed were definitely reconciled and cleared up.
CHAPTER XI
The Foundations of Organic Chemistry
As the horizon of chemistry widened and its operations extended, it became necessary to treat its subject-matter methodically. Accordingly attempts were made in the various systematic treatises which began to appear in the seventeenth century to group its facts into an orderly and rational arrangement. One of the earliest of such systematic treatises was the Cours de Chimie of Nicolas Lemery, published in 1675. Although this work was styled by Boerhaave “a tumultuary mass of pharmaceutical processes, without any certain design or coherence,” it is noteworthy as being the first of its kind to divide the science into its present main branches of inorganic and organic chemistry.
It may be desirable to indicate, as briefly as possible, the general state of knowledge respecting the chemistry of organic substances down to the early years of the last century. As already mentioned, such substances as acetic acid, turpentine, starch, sugar, certain dye stuffs, and oils, had long been known; and such processes as saponification and fermentation had been practised from very early times. The alchemists had prepared a variety of essential oils, aliphatic ethers, and esters; and the iatro-chemists had obtained benzoic and succinic acids, and acetic acid from wood. Milk sugar was first prepared by Fabrizio Bartoletti in 1619. Grape sugar was first mentioned as occurring in honey by Glauber in 1660. Boyle first detected the presence of a spirit among the products of the destructive distillation of wood. Few of the followers of Stahl occupied themselves with organic products; and it was only towards the end of the phlogistic period that attention was once more directed to products of animal and vegetable origin. Scheele isolated glycerin in 1784, and obtained ethyl chloride by the distillation of a mixture of common salt, pyrolusite, oil of vitriol, and alcohol. Ethyl acetate was first prepared by Lauraquais in 1759. Arvidson obtained ethyl formate in 1777. Oxalic ether was first made by Savary in 1773. What was long known as oil of wine appears to have been first mentioned by Libavius, but its true nature was discovered by Hennel in 1826. The formation of aldehyde was first recognised by Scheele in 1774, and it was in turn investigated by Fourcroy and Vauquelin, Döbereiner, and Gay Lussac; but it was first definitely isolated in 1835 by Liebig, who gave it its name.
The first organic acid known was vinegar (acetic acid), and for a long time all naturally occurring organic acids having a sour taste were regarded as identical with or as forms of vinegar. It was only during the second half of the eighteenth century that it was clearly ascertained that a variety of organic acids exist, perfectly distinct from acetic acid. Glacial acetic acid was first obtained by Löwiz in 1789. Acetic acid, as a product of the destructive distillation of wood, was first obtained by Göttling in 1779. The acetic fermentation has been studied from very early times. Surmises as to the mode in which wine was converted into vinegar are to be met with in the works of Basil Valentine, Becher (1669), Lemery (1675), and Stahl (1667). Priestley, for a time, held the opinion that vinegar contained a vegetable acid air, but he subsequently discovered and corrected his error. The direct conversion of spirit of wine (ethyl alcohol) into acetic acid was studied by Lavoisier and Berthollet, who first clearly recognised that it was a process of oxidation. The quantitative composition of acetic acid was first established by Berzelius in 1814. Many of the acetates have been known from early times. Verdigris is mentioned by Theophrastus, Dioscorides, and Pliny. Zinc acetate was known to Geber, and potassium acetate to Pliny, who mentions its use in medicine. Ammonium acetate was also used in medicine as far back as the beginning of the seventeenth century, and was particularly recommended by the physician, Raymond Minderer. Sodium acetate was prepared by Duhamel in 1736. Lead acetate was known in the fifteenth century, and was styled by Libavius saccharum plumbi quintessentiale, in allusion to its sweet taste. What was called by the alchemists lac virginis was a turbid solution of basic lead acetate, and it was frequently used in medicine, more particularly by Goulard in 1760. What we now call acetone was first observed by Libavius, in 1595, and subsequently by Boyle, during the destructive distillation of lead acetate: its formation from other acetates was noticed by Trommsdorff, Derosne, and Chenevix, by whom it was termed pyroacetic spirit. Its true nature and composition were first ascertained by Liebig in 1831.
The formation of tartar in the manufacture of wine has been known from the earliest times. It was regarded as, and originally styled, the faex vini. The word “Tartarus” is first met with in alchemistic literature in the eleventh century, and is the Latinised form of an Arabic word. Marggraf, in 1764, recognised that the tartar of wine contained potash; but tartaric acid itself was first isolated by Scheele in 1769.
The double tartrate of potash and soda was first prepared in 1672 by Peter Seignette, an apothecary of Rochelle, and was used by him in medicine. Tartar emetic was discovered by Adrian von Mynsicht in 1631, and its true nature explained by Bergmann in 1773. Racemic acid was first mentioned by a wine manufacturer named Kestner, and was recognised as an acid in 1819. Its relation to tartaric acid, with which it is isomeric, was first explained by Berzelius, who gave it its name.