CHAPTER VIII
Lavoisier and La Révolution Chimique

We have seen how chemistry made a new departure during the political upheaval which occurred in this country about the middle of the seventeenth century. It acquired a new impetus and took a fresh course during the political cataclysm which overwhelmed France and alarmed Europe towards the close of the eighteenth century. The instigator and leader of this second revolution in chemistry was Lavoisier, one of the most distinguished men of his age, and himself a victim of the political fury of his own people.

Antoine-Laurent Lavoisier was born in Paris in 1743. At the Jardin du Roi he came under the influence of Rouelle, one of the best teachers of his time, who eventually shaped his career as a chemist. In 1765 he sent to the Academy his first paper on gypsum, which is noteworthy as giving for the first time the true explanation of the “setting” of plaster of Paris, and the reason why overburnt gypsum will not rehydrate. Three years later he became a member of the Ferme-général—a company of financiers to whom the State conceded, for a fixed annual sum, the right of collecting the indirect taxes of the country. It was this connection that brought Lavoisier to the scaffold during the revolution of 1794. Like Stahl, Lavoisier discovered no new substance; but, also like Stahl, he created a new epoch by destroying the philosophical system which Stahl had established.

It is commonly stated that the exception is a proof of the rule. The history of science can show many instances whereby the rule has been demolished by the exception. Little facts have killed big theories, even as a pebble has slain a giant. During the reign of phlogiston a few of such facts were not unknown—at least to some of the better informed of Stahl’s followers.

Some of the alchemists had discovered that a metal gained, not lost, weight by calcination. This was known as far back as the sixteenth century. It had been pointed out by Cardan and by Libavius. Sulzbach showed that such was the case with mercury. Boyle proved it in the case of tin, and Rey in that of lead. Moreover, as knowledge increased it became certain that Stahl’s original conception of the principle of combustion as a ponderable substance—he imagined, with Becher, that it was of the nature of an earth—was not tenable. The later phlogistians were disposed to regard it as probably identical with hydrogen. But even hydrogen has weight, and facts seemed to require that phlogiston, if it existed at all, should be devoid of weight.

Towards the latter half of the eighteenth century clearer views began to be held concerning the relations of atmospheric air to the phenomena of combustion and of calcination; many half-forgotten facts relating to these phenomena were recalled, and the inconsistencies and insufficiency of phlogiston as a dogma became gradually manifest. Three cardinal facts conspired to bring about its overthrow—the isolation of oxygen by Priestley; the recognition by him of the nature of atmospheric air, and of the fact that one of its constituents is oxygen; and, lastly, the discovery by Cavendish that water is a compound, and that its constituents are oxygen and hydrogen. The significance of these facts was first clearly grasped by Lavoisier, and to him is due the credit of their true interpretation. By reasoning and experiment he proved conclusively that all ordinary phenomena of burning are so many instances of the combination of the oxygen of the air with the combustible substance; that calcination is a process of combination of the oxygen in the air with the metal, which thereby increases in weight by the amount of oxygen combined. Water—no longer a simple substance—is formed by the union, weight for weight, of oxygen and hydrogen. Lavoisier’s reasoning was so sound and his experimental evidence so complete that his views gradually gained acceptance in France. The phlogiston myth was thus exploded. Inspired by Lavoisier, a small band of French chemists—Berthollet, Fourcroy, Guyton de Morveau—thereupon set to work to remodel the system of chemistry and to recast its nomenclature so as to eliminate all reference to phlogiston. The very names “oxygen,” “hydrogen,” “nitrogen,” corresponding respectively to the “dephlogisticated air,” “phlogiston,” and “phlogisticated air” of Priestley, were coined by the new French school. For a time le principe oxygine was regarded by this school in much the same relation as phlogiston was regarded by Stahl and his followers. The one fetich was exchanged for the other. The combustible principle—phlogiston—was renounced for the acidifying principle—oxygen. The new chemistry for a time centred itself round oxygen, just as the old chemistry had centred itself round phlogiston. The views of the French school met with no immediate acceptance in Germany, the home of phlogistonism, or in Sweden or England, possibly owing, to some extent, to national prejudices. The spirit of revolution, even although it might be an intellectual revolution, had not extended to these countries. Priestley, Cavendish, and Scheele could not be induced to accept the new doctrine. It was, however, accepted by Black, and its principles taught by him in Edinburgh; and before the end of the century it had practically supplanted phlogistonism in this country. Some of those who, like Kirwan, had energetically opposed the new theory ended by enthusiastically embracing it. Its introduction into Germany was mainly due to the influence of Klaproth.

We further owe to Lavoisier the recognition of the principle which lies at the basis of chemical science—the principle of the conservation of matter. Lavoisier was not the first to introduce the use of the balance into chemistry: quantitative chemistry did not actually originate with him. Boyle, Black, and Cavendish, as a matter of fact, preceded him in recognising the importance of studying the quantitative relations of substances. Nevertheless, no one before him so clearly foreshadowed the doctrine of the indestructibility of matter, and it was mainly through his teaching that the balance came to be recognised as indispensable to the pursuit of chemistry. Before his untimely death he had succeeded in impressing upon the science the main features which at present characterise it.

Lavoisier was one of the most distinguished men of his age, and his merits as a philosopher were recognised throughout Europe. Indeed, it is not too much to say that at the time of his death he was the dominant figure in the chemical world of the eighteenth century. In addition to his position as a member of the Ferme-général he was made by Turgot a commissioner of the Régie des Poudres; and in this capacity he effected improvements in the manufacture and refining of saltpetre, and greatly increased the ballistic properties of gunpowder. He became Secretary of the Committee of Agriculture, and drew up reports on the cultivation of flax, of the potato, and on the liming of wheat; he prepared a scheme for the establishment of experimental farms, and for the collection and distribution of agricultural implements. He introduced the cultivation of the beet root in the Blesois, and improved the breed of sheep by the importation of rams and ewes from Spain. He was successively member of the Assembly of the Orléanais, Député suppléant of the States-General, and of the Commune of Paris. In 1791 he was named Secretary and Treasurer of the famous Commission of Weights and Measures, out of which grew the international system, based theoretically on a natural unit, known as the metric system, and now adopted by most civilised countries in the world. He was not only the administrative officer of the Commission: he contributed to the nomenclature of the system, and directed the determination of the physical constants on which the measurements rested, and especially the determination of the weight of the unit volume of water on which the value of the standard of mass was based. Lastly he was Treasurer of the French Academy until its suppression in 1793 by the Convention, which shortly afterwards ordered the arrest of Lavoisier and others of the Fermiers-généraux—twenty-eight in all. They were sentenced to be executed within twenty-four hours, and their property confiscated. Coffinhal, who pronounced their doom, declared: “La republique n’a pas besoin de savants.” Thus in the fifty-first year of his age, perished the creator of modern chemistry—a victim to the senseless, sanguinary fury of the “Friends of the People.” His rectitude, his public services, the purity of his private life, the splendour of his scientific achievements—all were unheeded. As Lagrange said to Delambre: “It required but a moment to strike off this head; a hundred years may not suffice to reproduce such another.”

Lavoisier and Berthollet
in the Laboratory of the Sorbonne, Paris.