A History of Science — Volume 4

by Henry Smith Williams; Edward Huntington Williams

In this epoch of chemical discoveries England had produced such mental giants and pioneers in science as Black, Priestley, and Cavendish; Sweden had given the world Scheele and Bergman, whose work, added to that of their English confreres, had laid the broad base of chemistry as a science; but it was for France to produce a man who gave the final touches to the broad but rough workmanship of its foundation, and establish it as the science of modern chemistry. It was for Antoine Laurent Lavoisier (1743-1794) to gather together, interpret correctly, rename, and classify the wealth of facts that his immediate predecessors and contemporaries had given to the world.

The attitude of the mother-countries towards these illustrious sons is an interesting piece of history. Sweden honored and rewarded Scheele and Bergman for their efforts; England received the intellectuality of Cavendish with less appreciation than the Continent, and a fanatical mob drove Priestley out of the country; while France, by sending Lavoisier to the guillotine, demonstrated how dangerous it was, at that time at least, for an intelligent Frenchman to serve his fellowman and his country well.

"The revolution brought about by Lavoisier in science," says Hoefer, "coincides by a singular act of destiny with another revolution, much greater indeed, going on then in the political and social world. Both happened on the same soil, at the same epoch, among the same people; and both marked the commencement of a new era in their respective spheres."(8)

Lavoisier was born in Paris, and being the son of an opulent family, was educated under the instruction of the best teachers of the day. With Lacaille he studied mathematics and astronomy; with Jussieu, botany; and, finally, chemistry under Rouelle. His first work of importance was a paper on the practical illumination of the streets of Paris, for which a prize had been offered by M. de Sartine, the chief of police. This prize was not awarded to Lavoisier, but his suggestions were of such importance that the king directed that a gold medal be bestowed upon the young author at the public sitting of the Academy in April, 1776. Two years later, at the age of thirty-five, Lavoisier was admitted a member of the Academy.

In this same year he began to devote himself almost exclusively to chemical inquiries, and established a laboratory in his home, fitted with all manner of costly apparatus and chemicals. Here he was in constant communication with the great men of science of Paris, to all of whom his doors were thrown open. One of his first undertakings in this laboratory was to demonstrate that water could not be converted into earth by repeated distillations, as was generally advocated; and to show also that there was no foundation to the existing belief that it was possible to convert water into a gas so "elastic" as to pass through the pores of a vessel. He demonstrated the fallaciousness of both these theories in 1768-1769 by elaborate experiments, a single investigation of this series occupying one hundred and one days.

In 1771 he gave the first blow to the phlogiston theory by his experiments on the calcination of metals. It will be recalled that one basis for the belief in phlogiston was the fact that when a metal was calcined it was converted into an ash, giving up its "phlogiston" in the process. To restore the metal, it was necessary to add some substance such as wheat or charcoal to the ash. Lavoisier, in examining this process of restoration, found that there was always evolved a great quantity of "air," which he supposed to be "fixed air" or carbonic acid—the same that escapes in effervescence of alkalies and calcareous earths, and in the fermentation of liquors. He then examined the process of calcination, whereby the phlogiston of the metal was supposed to have been drawn off. But far from finding that phlogiston or any other substance had been driven off, he found that something had been taken on: that the metal "absorbed air," and that the increased weight of the metal corresponded to the amount of air "absorbed." Meanwhile he was within grasp of two great discoveries, that of oxygen and of the composition of the air, which Priestley made some two years later.

The next important inquiry of this great Frenchman was as to the composition of diamonds. With the great lens of Tschirnhausen belonging to the Academy he succeeded in burning up several diamonds, regardless of expense, which, thanks to his inheritance, he could ignore. In this process he found that a gas was given off which precipitated lime from water, and proved to be carbonic acid. Observing this, and experimenting with other substances known to give off carbonic acid in the same manner, he was evidently impressed with the now well-known fact that diamond and charcoal are chemically the same. But if he did really believe it, he was cautious in expressing his belief fully. "We should never have expected," he says, "to find any relation between charcoal and diamond, and it would be unreasonable to push this analogy too far; it only exists because both substances seem to be properly ranged in the class of combustible bodies, and because they are of all these bodies the most fixed when kept from contact with air."

As we have seen, Priestley, in 1774, had discovered oxygen, or "dephlogisticated air." Four years later Lavoisier first advanced his theory that this element discovered by Priestley was the universal acidifying or oxygenating principle, which, when combined with charcoal or carbon, formed carbonic acid; when combined with sulphur, formed sulphuric (or vitriolic) acid; with nitrogen, formed nitric acid, etc., and when combined with the metals formed oxides, or calcides. Furthermore, he postulated the theory that combustion was not due to any such illusive thing as "phlogiston," since this did not exist, and it seemed to him that the phenomena of combustion heretofore attributed to phlogiston could be explained by the action of the new element oxygen and heat. This was the final blow to the phlogiston theory, which, although it had been tottering for some time, had not been completely overthrown.

In 1787 Lavoisier, in conjunction with Guyon de Morveau, Berthollet, and Fourcroy, introduced the reform in chemical nomenclature which until then had remained practically unchanged since alchemical days. Such expressions as "dephlogisticated" and "phlogisticated" would obviously have little meaning to a generation who were no longer to believe in the existence of phlogiston. It was appropriate that a revolution in chemical thought should be accompanied by a corresponding revolution in chemical names, and to Lavoisier belongs chiefly the credit of bringing about this revolution. In his Elements of Chemistry he made use of this new nomenclature, and it seemed so clearly an improvement over the old that the scientific world hastened to adopt it. In this connection Lavoisier says: "We have, therefore, laid aside the expression metallic calx altogether, and have substituted in its place the word oxide. By this it may be seen that the language we have adopted is both copious and expressive. The first or lowest degree of oxygenation in bodies converts them into oxides; a second degree of additional oxygenation constitutes the class of acids of which the specific names drawn from their particular bases terminate in ous, as in the nitrous and the sulphurous acids. The third degree of oxygenation changes these into the species of acids distinguished by the termination in ic, as the nitric and sulphuric acids; and, lastly, we can express a fourth or higher degree of oxygenation by adding the word oxygenated to the name of the acid, as has already been done with oxygenated muriatic acid."(9)

This new work when given to the world was not merely an epoch-making book; it was revolutionary. It not only discarded phlogiston altogether, but set forth that metals are simple elements, not compounds of "earth" and "phlogiston." It upheld Cavendish's demonstration that water itself, like air, is a compound of oxygen with another element. In short, it was scientific chemistry, in the modern acceptance of the term.