The distillation of pure volatile oils and the skill to mix them so as to produce agreeably fragrant mixtures, not only stimulated the improvement of methods of preparation, but also their extended use. With the distillation of the oils of lavender and rosemary, a volatile oil industry, as has already been indicated,1) seems to have developed from small beginnings in southern France during the fifteenth and sixteenth centuries. In like manner, the perfume industry seems to have had its origin. The preparation of "Hungarian water" in the sixteenth century by making an alcoholic distillate from fresh rosemary has already been referred to.1) During the seventeenth century, a Karmeliter Geist, an alcoholic distillate from balm and lavender,2) was introduced. In 1725 Johann Maria Farina of Cologne introduced his famous Eau de Cologne. The successful mixture of several odors and the prime quality of the oils used proved an important stimulus to the manufacture of these oils.3) From these small beginnings the perfume industry gradually developed into the important position it has held since the middle of the past century.

1) See p. 48.

With the increased importance of the volatile oils, more attention was bestowed upon their nature and composition. Boerhaave (born 1668, died 1738), who at the beginning of the eighteenth century was professor of medicine, botany and chemistry at the University of Leyden, in his treatise on chemistry4) states that volatile oils consist of two elements: the one cruder and resinous, insoluble in water (mater); the other more subtle, ethereal, which can scarcely be weighed and which by itself is possibly gaseous (spiritus rector). The first part he considered to be common to all oils and a unit by itself. The characteristic odor and taste, however, of the various oils were due to the spiritus rector which was peculiar to each oil. It was water soluble and therefore gave to the distilled waters their odor, taste and medicinal virtue. The changes produced in volatile oils upon exposure to air and light were attributed, in harmony with this theory, to the escape of the spiritus rector.5)

This conception was perfectly in harmony with the belief, current during the middle ages and up to the 17. century, in the subtle properties and medicinal virtues of aromatic plant substances and their aqueous distillates. With the assumption of the water solubility of the spiritus rector the distilled waters were naturally regarded as being charged in the highest degree with the medicinal properties of the crude drugs. Boerhaave's dualistic theory concerning the composition of the volatile oils was therefore received as the most rational explanation of the firmly established belief in the efficacy of distilled waters, and was also accepted as a further argument for their retention in medicine. Even after the antiphlogistic nomenclature came into vogue after 1787, the spiritus rector was not discarded, being rebaptized as arome.

1) See p. 30.

2) See the history of the oils of lavender and spike.

3) See the history of oil of balm.

4) Elementa chemiae, quae anniversario labore docuit in publicis priva-tisque scholis, Hermannus Boerhaave. Tomus primus, qui continet historiam et artis theoriam. Tomus secundus, qui continet operationes chemicas. Lugduni Batavorum 1732 - Londini 1732, 1735 - Parisii 1732, 1733, 1753 - Lipsiae 1732 - Basiliae 1745 - Veneti 1745, 1759.

5) In hoc autem oleo essentiali rursus subtilissimus, volatilis, paucus, acerrimus, vix ponderandus, spiritus iterum complecticur illud omne, quod huic toti oleo dabat banc vim; eoque ablato nihil in oleo. . . . Inquisivi in pondus spirituum, invenire non potui est. (Boerhaave's Elementa chemiae, Tom. 2, p. 124-131.)

The first chemists who discarded the dualistic theory of the volatile oils in their writings, and claimed that odor and taste are due to the oil as such, are F. A. C. Gren,1) Professor of Medicine in Halle, and the French chemist Ant. Francois de Fourcroy2) of Paris. The former exposed the untenability of Boerhaave's theory in 1796, the latter in 1798. Indeed Fr. Hoffmann (born 1660, died 1743), a contemporary of Boerhaave and professor at Halle, had not accepted the latter's theory without reserve. A many-sided investigator and writer, he had prepared and studied the volatile oils with great care.3) Yet he had no clearer conception concerning the nature and composition of the oils than his contemporaries. He distinguished between oils obtained by expression, by destillatio per ascensum and per descensum.4) He regarded sulphur as a fundamental principle of all oils, the bituminous and empyreumatic oils containing a

1) Grens GrundriB der Chemie nach den neuesten Entdeckungen ent-worfen und zum Gebrauch akademiscner Vorlesungen eingerichtet.. Halle 1796. Vol. 2, p. 217.

2) Annal. de Chim. 25 (1798), 232 and Fourcroy, Systeme des con-naissances chimiques. Paris 1801.

3) Frederici Hoffmannii Opera omnia physico-medica. Denuo revisa correcta et aucta. In sex tomos distributa. Genevae 1740 - 1761 - Veneti 1745, 17 Volumina - Neapel 1753, 25 Volumina.

4) The destillatio per ascensum corresponds to the method now generally used, allowing the vapors to pass upwards in the still and removing them from above. In the destillatio per descensum the vapors were forced downward through the material and collected in a receptacle underneath the still. An incomplete extraction was thus effected. (Comp. chapter IV.) relatively large amount of sulphur.1) He also believed that the color and odor of oils was influenced by their larger or lesser sulphur content.

It should be of interest to note that camphor which had been regarded as a volatile organic salt, was pronounced by Hoffmann to be a congealed volatile oil.2) He also made the observation that most of the commercial oils of his time were adulterated with turpentine oil, oleum vini, alcohol and fatty oils.3) Further he determined the yield4) and specific gravity5) of many oils. At the beginning of the 18. century, distillation was regarded as a well known and universally practiced method of laboratory technique. Hence the special interest of that period was directed mainly toward the determination of the yield of oils and the study of their properties. This interest was, no doubt, stimulated by Glauber's suggestion to rectify by distillation with dilute muriatic acid oils that had become colored by age.