
133
Principes de la philosophie . The latter, as we have seen, had confessed, in a letter
to Huygens, that he had given up experimenting to gain access to the “individual
knowledge of each thing,” thus acknowledging the fact that the singular knowledge
of the properties of the diverse objects of chemistry had been of no use to him to
operate the mechanical reduction of chemistry. On the contrary, Rohault insisted,
“every useful Science ought to descend immediately to Particulars.”
33
According to
him, the properties of chemical bodies had to be established through laboratory
experiment, and not, as with Descartes, by means of a deduction of their process of
formation in the earth. No doubt he wrote that “all that which is produced by art in
the Laboratories of Chymists, is done naturally in the Bowels of the Earth,”
34
but
this parallelism, frequent in the works of alchemists, resulted in nothing but a greater
importance given to laboratory work, thus considered as a natural process. Thus, it
became possible to transmute Salts into acid liquids, “which the Chymists call Oyl ,
or Spirit of Salt , or Aqua-Fortis which is used to dissolve Metals with.”
35
Rohault then
gave the recipe for this operation, which consisted in distilling salt mixed up with
piled up clay. A little further on, he saw “the Experiments of Chymists, who by the
Resolution of Metals, can draw Salt and Sulphur out of them,”
36
as a confi rmation of
his theses on the constitution of metals, which accounted for his former assertion that
the transmutation of metals was a “moral impossibility,” but not an “absolute one.”
37
In the fi rst part of his work, Rohault had fully recognized the importance of the
works of chemists, granting them praises such as could not be found in Descartes:
Without doubt the whole World, and the Philosophers particularly, are very much obliged
to them for the Pains they have taken, and which they continue to take, to make a great
Number of Experiments, whereby they come to the Knowledge of diverse Properties of
many different Things. This gives them opportunity to fi nd out and discover the Nature
of Things…
38
33
Rohault 1671 , unpaginated preface: “une science d’usage doit bientôt descendre dans le particulier.”
An English translation was made available in the early eighteenth century and reprinted as
Rohault
1987 . For Rohault and his Cartesian experimental physics, see Chap. 9 by Dobre.
34
Rohault 1671 , II, 177: “tout ce que l’artifi ce produit dans les laboratoires des Chymistes se fait
naturellement dans les entrailles de la Terre.” Rohault
1987 , II, 148.
35
Rohault 1987 , II, 148.
36
Rohault 1987 , II, 155. Clarke’s English translation misses the reference to mercury in the French
text. For the original French text, see Rohault
1671 , II, 188: “l’expérience des Chymistes, qui par
la résolution des métaux en peuvent tirer leur sel et leur soufre, et même, si l’on en croit quelques-
uns, leur Mercure.” The experiments usually put forward as evidence for validating their theses,
were aimed at distilling vegetals and particularly wood. It is noteworthy that Rohault took up, for
his own account, the distillation of a metal, which could hardly be effected, and which is one
example of the extrapolations of which alchemists were often guilty.
37
Rohault 1671 , II, 186. Quite strangely the expression “moralement impossible” is not present in
the English translation, Rohault
1987 , II, 154.
38
Rohault 1987 , I, 109. Rohault 1671 , I, 137: “Tout le monde sans doute, et les Philosophes en
particulier, leur sont fort obligés de la peine qu’ils se sont donnée, et qu’il se donnent encore tous
les jours, à faire un très grand nombre d’expériences, par le moyen desquelles ils leur font connaître
les diverses propriétés de plusieurs Êtres différents. Ce qui leur donne la commodité de rechercher
et découvrir la Nature des choses.”
6 Could a Practicing Chemical Philosopher Be a Cartesian?