Glauber's views6) and those of his contemporaries were opposed by Hoffmann. He declared the employment of spiritus salis,"') dilute sulphuric acid,8) potash, tartar and alum9) in the distillation of volatile oils as useless, but consented to the use of common salt. He argued that the addition of salt facilitated the separation of the oil particles and prevented decay; that it made the water "heavier" and thus prevented the settling and burning of the plant material; that it also purified the distillate.1)

1) Frederici Hoffmannii Opera omnia physico-medica. Denuo revisa correcta et aucta. In sex tomos distributa. Genevae 1740 - 1761 - Veneti 1745. Tom. 4, Liber 1, p. 449-451.

2) Ibidem. Liber 72. Observatio 13, p. 44-50.

3) Ibidem. Liber 67. Observatio 2, p. 9 - 11.

4) Ibidem. Liber 65. Observatio 1, p. 1 - 9. "De oleis destillatis inque eorum destillatione observanda."

5) Ibidem. Liber 72. Observatio 8, p. 27 - 30. "Gravitas specific oleorum."

6) Johanni Rudolphi Glauberii Furni novi philosophici. Lugduni Bata-vorum 1648 - Amstelodami 1648 - Prag 1700. Pars 1, p. 35, 36 et 41, et pars 3, p. 30.

7) Ibidem. Pars 1, p. 36. This was crude hydrochloric acid prepared by the distillation of common salt and alum or sulphuric acid.

8) Crell's Chem. Journ. 3 (1780), 30. - Pfaff's System der Materia medica. 1815. Vol. 4, p. 50.

9) Glauberii Furni novi philosophici. Lugduni Batavorum 1648 - Prag 1700. Pars 1, p. 38 et pars 3, p. 31.

In some instances recourse was again taken to the process of fermentation before distillation which was in vogue during the fifteenth and sixteenth centuries. This was done e. g. with juniper berries, wormwood, sage and other herbs, honey and yeast-) occasionally being added. The old practice of previously moistening the plant material with alcohol3) was also resorted to. In this manner a larger yield of oil was obtained but it would seem that the dilution of the oil with alcohol was not recognized.

Downward distillation (destillatio per descensum) was applied by Hoffmann4) in the preparation of oils with high specific gravity such as the oils of cinnamon and cloves. This method was evidently regarded as being better because the dark colored oils thus obtained were supposed to contain more sulphur.

With the increased use of volatile oils during the first half of the eighteenth century it became more and more desirable not only to prepare oils of good quality but to obtain the largest possible yield as well. As guides there appeared new treatises on distillation5) which had little more than the title in common with the older Destillirbucher. They treated not only of distilled waters, but also of volatile oils and spirit of wine. Coupled with the scientific problem of the distillation of the volatile oils was the commercial problem of the largest possible yield.

1) Fr. Hoffmannii Opera omniaphysico-medica. Supplementum secundum. Geneva 1760. Pars 1, p. 730.

2) Berlinisches Jahrbuch fur Pharmacie 1804, 380.

3) Demachy, Laborant im GrotBen, oder die Kunst die chemischen Pro-dukte fabrikmaBig zu verfertigen. Aus dem FranzOsischen ubersetzt, mit Zusatzen versehen von Samuel Hahnemann, der Arzneikunde Doctor und Physikus des Amtes Gommern. Leipzig 1784, p. 238.

4) Fr. Hoffmannii Opera omnia physico-medica. Tom. 4. Observationum selectiorum libri. 1717. Liber 1, p. 449 - 451. - Supplementum secundum. 1760. Pars 1, p. 730.

5) Of these the following are the more important:

Die zum allgemeinen Gebrauch wohl eingerichtete Destillirkunst. Auch die Bereitung verschiedener destillierter Wasser und Ole. Von C. H. Burghart. Breslau 1736. Neue Auflage mit vie/en Zusatzen von J. Christian Wiegleb. 1754.

Das Brennen der Wasser, Ole und Geister. Wohleingerichtete Destillier-kunst und neue Zusatze. Von G. H. Burghart. Breslau 1748.

Following the lead of Winther,1) Boerhaave and Hoffmann, a number of investigators of the eighteenth century ascertained the yield of oil obtainable from the more common aromatic plant products. Of these the following deserve special mention: joh. Fr. Cartheuser2) (born 1704, died 1769), Professor of Medicine, Botany and Chemistry at the University of Frankfurt-on-the-Oder; Caspar Neumann3) (born 1683, died 1737), a Berlin apothecary; Claude Joseph Geoffroy (born 1685, died 1752), a Parisian apothecary; and Guillaume Francois Rouelle4) (born 1703, died 1770).

Their experiments were conducted on a small scale and with simple apparatus. Their results, however, published in their works and in journals,1) were regarded as standard and were quite generally introduced into the literature on the subject. Through the dispensatory of the English physician and chemist, William Lewis,-) the results of the above mentioned and of other continental investigators found their way into English literature.

Trait6 raisonne de la distillation, ou la distillation reduite en principes avec un trait6 des odeurs. Par Dejean. Paris 1753. - Deutsche Ausgabe, Altenburg 1754.

Traite des odeurs, Suite du trait6 de la distillation. Par Dejean. Paris 1764.

1) See p. 60.

2) Cartheuser's researches on the volatile oils are contained in the following of his treatises:

Fundamenta materiae medicae. Francofurt. ad Viadr. 1738 and edition of Paris 1752.

Elementa Chymiae dogmatico-experimentalis, una cum synopsi Materiae medicae selection's. Hallae 1736. Editio secunda priore longe emendatior.

Dissertatio chymico-physica de genericis quibusdam plantarum principiis hactenus neglectis. Francof. ad Viadr. 1754. Editio secunda 1764.

Dissertatio physico-chemica medica de quibusdam Materiae medicae subjectis exarat. ac publice habet nunc iter, resus. Francof. ad Viadr. 1774.

Dissertationes nonnul/ae selectiores physico-chemicae ac medicae, varii argumenti post novam lustrationem ad prelum revocat. Francof. ad Viadr. 1778.

Pharmacologia theoretico-practica praelectionibus academicis accommo-data. Berolini 1745.