The Method of Distillation
Bourdelin's first technique was to distill a plant and collect the distillant in a single container. He then subjected the product to further operations in order to separate it into spirit, oil, salt, phlegm, and earth. This was plant distillation as Le Febvre had taught it at the Jardin royal, and Duclos recommended the same procedures to the Academy in 1668. Duclos described how to change the temperature of the fire, explained that the ashy residue (the teste-morte or charbon ) in the receptacle containing the plant was to be calcinated and lixiviated to extract salts, and recommended that various distillants be tested with color reactors similar to those he used for mineral waters. The distinguishing feature of this method was that the distillant was collected in one container, to be separated and analyzed later. Forty-two plants were examined this way in 1670.
In 1670, shortly before Dodart joined the Academy, Duclos's method was abandoned for one that obtained more varied products. The new procedure changed the recipient (the glass receptacle that collected the distillant) every time the heat of the fire changed, Bourdelin varied this second method over the next three decades, while other academicians tried to improve it. By the time Dodart wrote the Mémoires des plantes, more than one hundred plants had been analyzed this way.
Dodart described this new technique, which he in fact revised, in some detail. He named the vessels used, told how to regulate the fire, discussed the substances obtained, and described how the ashes were treated. Everything was distilled in a glass or earthenware retort, to which was attached either a balon à tétine or a balon sans tétine, that is, a recipient with or without an udder-like protrusion. Organic matter was placed in the retort, the recipient was attached, and the retort was placed over a fire. Bourdelin regulated the fire and changed the recipient carefully.
We start the fire so slowly that it can scarcely heat the retort. We increase it slightly until some liquid passes into the receiver, and we keep the fire in this state. We increase the heat only when scarcely any more liquid comes out. We increase it slightly degree by degree during a period of fourteen or fifteen days, and we make it as hot as possible. We empty the receiver, not only whenever we
increase the fire, but more often, and we keep all parts of the distillant separated.
Distillation continued until the fire had reached its maximum temperature and no more liquid would come out. Then the ashes remaining in the retort were removed and treated. As many as fourteen different distillants might be extracted from the plant, in this order: sharp (acres ) spirits; essential oils, given by aromatic plants; sulphurous spirits; simple waters; waters with a hidden taste of acid or sulphur; acid spirits; mixed spirits; urinous spirits, either with or without acid; volatile salts; black oils; fixed or saline or lixivial salt; and earth. These products were tested with color reactors and by other means to classify them further. Each watery liquid was characterized as either "insipid, acid, sulphurous, urinous, or mixed." All the insipid liquids were combined and set aside, then all the acid liquids were combined and set aside, and so on. Once all the products had been identified and organized, each was examined for its weight and other observable properties (propriétés sensibles ).
This new method was not an invention of the Academy, but academicians applied it more rigorously than did their contemporaries. Glaser, for example, also changed recipients during distillation, but not so frequently, and as a result he did not obtain so many different distillants. But Glaser and Dodart had different purposes. Glaser simply wanted to extract certain substances that he could use as medicaments, whereas academicians wanted to identify all the constituents of plants.
By the 1690s, when Tournefort studied Bourdelin's research, the chemist had abbreviated his procedures. He removed the branches and juices from a plant and crushed it before distilling it. Then he put five livres of the plant in a tinned cucurbit, covered it with a glass head, and placed it in a water bath or a steam bath for two to three days, with the fire going day and night. Bourdelin next tested the liquid products with his repertory of indicators to determine whether they were acid or alkali. Next he distilled the dry residue in a retort with a large balloon or recipient, increasing the fire gradually. After twelve or fourteen hours he put the distillant in a glass alembic and attached a new recipient to the retort. He increased the heat of the fire and collected further distillants, separating them with a large glass funnel. By this time, the chemist was no longer regulating the fire and treating the teste-morte as he had in the 1670s, and distillations lasted only a few days instead of a fortnight. The changes perhaps reflect his declining stamina.
Bourdelin's procedures never satisfied academicians, who suggested either embellishing or replacing distillation. Dodart was frankly overwhelmed by the data and asked Bourdelin to focus his work. By distilling
more selectively, he would avert interminable research. Thus Dodart abandoned a Baconian search for every possible phenomenon. Instead he adopted a more carefully designed program that chose the objects of inquiry according to some preconceptions. Dodart's stamp was felt on the Academy's choice of plants for distillation thereafter.
Chemical analyses, like dissections of animals, required painstaking work and could be dangerous or unpleasant. Just as a slip of the knife might cause an infection (like the one that killed Perrault, who cut himself while dissecting a camel), so distillants were risky, for chemists identified many of them by taste. Rotting corpses and distilled plants stank. Anatomists treated decaying flesh with eau de vie, and Bourdelin treated plants by digesting (that is, heating without boiling), fermenting, or macerating before he distilled them. Unfortunately, this treatment altered them. Dodart wanted to assess any changes caused by prior treatment, but other academicians tried to overcome any effects. Perrault thought this could be accomplished by distilling macerated or digested plants over lower heat for a longer time. His idea was to compensate for the diminished force of the fire by increasing the duration of the distillation, a principle of substitution that he derived from mechanics.
The quest for a more satisfactory method of analysis continued well after the Mémoires des plantes appeared, but with few new ideas. By mid-November 1678, Bourdelin was on the defensive. He may well have been resisting pressure to disband his distillations. Borelly reflected on Bourdelin's recalcitrant research in the 1680s (as Homberg would do in the 1690s), probably as a result of a ministerial request. He stressed ways of rectifying distillants and designed a furnace for extracting substances from the testes-mortes . Above all he favored solvents for analysis. Some academicians had high hopes for his work. La Hire, for example, wrote to Huygens that Borelly "is searching as hard as he can for new ways of testing the liquids extracted in analyses." The chemist had discovered "something very curious," but La Hire's ignorance of chemistry prevented him from explaining Borelly's discovery.
For years after Dodart published the Mémoires des plantes, academicians debated distillation. They were so dissatisfied that they nearly abandoned it. Researchers could not be certain that their methods were adequate or that their results were meaningful. Instead of rejecting distillation, however, they refined the process.