1Messieurs,

2As announced in the previous session, we will now examine the works in chemistry of the English school in the first half of the eighteenth century. This school never adopted Stahl’s ideas on combustion and only had a vague knowledge of the phenomenon. A Frenchman, Jean Rey,1 a physician from our old Province of Périgord, was the one who explained the combustion of bodies by their combination with one of the elements of air. As we saw earlier, his theory was explained in a work published in 1630, Recherches sur les causes pour lesquelles le plomb et l’étain augmentent de poids quand on les calcine.2 Libavius3 and other chemists did observe that metallic limes were heavier than uncalcined metals but they did not provide an explanation. Rey’s vague overview is restricted to an individual case and is far from Lavoisier’s theory.4 However, those jealous of the famous chemist accused him of plagiarism, reprinting Jean Rey’s pamphlet. It is probable that Lavoisier was not aware of it before his discovery. The remarkable school of R. Boyle5 inspired the part that was not his work. We mentioned this chemist during last year’s lecture.6 We will recall his works before presenting his pupils’ to assess the global results of his school.

3Boyle studied several sciences but mainly chemistry, focusing on combustion. Like Rey, he noticed that calcination of metals increased their weight but he thought it was by fixing fire, a substance he assumed to have a mass. Recounting his experiments, he noticed that when he opened the closed cup he used for metal calcination, air penetrated energetically, proving that the air initially contained in the cup was absorbed. He did not discover this consequence. Other experiments were more relevant: he learned that air in which a substance was calcined was unsuitable to maintain an animal alive, and therefore that air was necessary for both combustion and respiration. In addition, Boyle observed the gas formed during fermentation and shared some of its proprieties. He was aware of the inflammable air exploding in coalmines, called firedamp7 by miners. As I mentioned earlier, Van Helmont8 referred to it as spiritus sylvester.

4A compatriot of Boyle I mentioned before, Quesnel Digby9 also studied chemistry but for therapeutic applications. His work is recalled here only because he had the same ideas on calcination as J. Rey.

5A chemist from Boyle’s school you already know, Mayow,10 did some experiments clearing any doubt on Rey and Digby’s assumptions of air absorption during combustion. He became convinced that the element of air producing combustion was also the principle of acidity. He verified that this principle was absorbed during animal respiration, as it was during combustion. This observation caused a revolution in animal physiology.

6Plant physiology was later revolutionized by discoveries in pneumatic chemistry. Hales11 presented in his Vegetable Staticks12 the circumstances of plant respiration. He demonstrated that plants absorbed a great quantity of atmospheric air and exhaled a gas he was the first to name fixed air. He also observed the air emitted by some metallic limes when submitted to fire, an emission due to the beginning of disorganization. However, he seemed to not have been aware of the decisive reduction of mercury lime under heat.

7Towards the middle of the eighteenth century, Joseph Black13 also did some research on gas breathed by plants. Black was born in Bordeaux in 1728 from Scottish parents. He worked as a professor in Glasgow and died in 1799. He discovered, for example, that magnesia under heat could emit carbonic acid and noticed that afterwards, magnesia lost its causticity. He did not draw any conclusion but deducted from another fact that the causticity of alkali in general was due to the presence of carbonic acid.14 Black left one of the most important discoveries in chemistry: the theory of latent heat that we will examine in the second part of the eighteenth century because it was not published until 1757.

8These were, Messieurs, the chemistry theories in the first half of the eighteenth century in the English, German, and French schools. However, chemistry does not only focus on facts in relation to general theories, but for themselves. We will now present the works of men who did some experiments during the same period, either to draw a specific conclusion, or to obtain useful results for arts or medicine. The first one is Friedrich Hoffmann,15 born in Halle in 1660. He first taught at the University of Jena but was called to his native city by the Elector of Brandenburg16 who just funded a university and mandated Hoffmann to select lecturers for the faculty of medicine. Hoffmann called on Stahl17 whose knowledge he recognized even if their opinions differed, mainly in physiology. Their personalities were also entirely opposed. Hoffmann was more sociable and cheerful and never gave to mysticism. His lectures and writings were also clearer and simpler, his discussions moderate. Even if he had the favors of powerful men who offered him the best positions available, he remained in his country where he died in 1742.

9Hoffmann left some works on medicine, physiology, and chemistry. The complete collection of his works, published after his death, is in eleven volumes in octavo.18 The part on medicine constitutes one of the most important collections for a physician, particularly on modern physiology of which Hoffman could be considered the founder. Six years after his death, his book on chemistry, Chemia rationalis et experimentalis,19 first published the year of his death, was reprinted separately. This work shows that Hoffman was the first to make the distinction between magnesia and lime. He also addressed fixed air and acidulous gaseous waters. He left descriptions of experiments on alcohol and essential oils. He was the one who induced the compound spirit of alcohol and sulfur ether, known in medicine as Hoffmann’s anodyne.

10One of his and Stahl’s pupils, who took after the latter in terms of personality, left some experiments in lithogeognosy published in Breslau in 1746 and the following years. His name was Johann Heinrich Pott,20 born in Halberstadt in 1692 and who died in Berlin in 1777. Pott submitted stones and earths to a violent glaring fire and deduced a classification method based on its effects on the various substances. He divided them into fusible, calcinable, and apyrous. He included under the latter category any stone and earth left unmodified by fire, such as quartz. This classification led to the establishment of the true mineralogical method.

11Andreas Sigismund Marggraf,21 a member of the Academy of Berlin and the director of the physics department, left experiments as numerous as Pott’s, some more important. Marggraf was born in Berlin in 1709 and was the son of a pharmacist. He died in 1782. In 1754, he discovered alumina, the principal base of clay and described the proprieties of this earth. In 1760, he communicated the characteristics of magnesia, which until then were poorly described including by Black.22 He also described the process to extract the Prussian blue,23 a process discovered by accident by Berlin artisans at the beginning of the century and the elements of which were only recognized by Mr. Gay-Lussac.24 Marggraf also analyzed vegetable substances using alcohol and discovered through this process the presence of sugar in beets. One of his students, Achard,25 who was the director of the physics department at the Berlin Academy after him, applied his master’s sugar extraction process on a large scale. This discovery is one of the most important in chemistry as it contributed to the abolition of Negro slavery.

12Among the authors of notable works in chemistry, we also have Johann Andreas Cramer,26 born in Quedlinburg in 1710, who died in 1777. His Elementa artis docimasticae, and his principles in metallurgy published in Berlin between 1771 and 1777, long remained classic works for German miners.27

13We will also mention Christlieb Gellert,28 the older brother of the famous German poet.29 He was born in 1713 and died in 1795. He was an academician in Petersburg for ten years and returned to his homeland in 1746. He taught in Freiberg and his writings on docimasy and metallurgy also remained classics for a long period. He was the first to apply the amalgamation process on a large scale. He also produced many observations on alloy densities and assumed that the increase in weight observed in metallic lime was due to the combination of an acid and metallic elements during calcination. The same theory was supported and developed by J. Friedrich Meyer, an apothecary in Osnabrück, in a work published in 1764.30 This author stated that to substances submitted to fire, air provided an acid he called acidum pingue. He pursued by saying that this acid was an elastic substance, analogous to fire, and a universal agent in nature. Lime causticity was due to the presence of this acid. Meyer made an error even more shocking that Gellert’s when he assimilated the formation of ordinary lime and metallic limes. Both phenomena are totally opposed. A fragment of marble submitted to fire loses its carbonic acid and part of its weight. On the contrary, a piece of lead under the same circumstance absorbs part of the ambient air oxygen and becomes heavier. This confusion between metallic limes and other limes is found throughout the Stahlian School that often neglected to weigh the substances and did not take gases into consideration in all of its practical works. In this school, it is even recommended to use imperfect lutes to let out any gases that could break the apparatus.

14In the next session, I will finish this history of chemistry in the first half of the eighteenth century and will start on mineralogy during the same period.