This method was first applied to flowers in 1835 by Robiquet.31 Somewhat later Buchner,32 and Favrot33 experimenting independently, processed flowers with diethyl ether. Around 1856, Millon34 in Algeria extracted flowers with various solvents; Hirzel35 in 1874 suggested petroleum ether as the most suitable solvent and obtained patents for his apparatus in several countries of Europe. Gradually the new method attracted the attention of the manufacturers in Southern France (Grasse and Cannes) and large-scale experiments were conducted independently by several industrial workers such as Piver, Vincent, Roure, Naudin, Massignon, Chiris, Charabot, and Garnier.36 The latter obtained a patent for a novel type of rotatory extractor and extended his activities from Southern France to Bulgaria, Syria, Egypt and Reunion Island. Finally all the flower oil manufacturers in Grasse were forced to adopt the volatile solvent process, and constructed special extraction plants in addition to their existing enfleurage buildings.
The principle of extraction with volatile solvents is simple: fresh flowers are charged into specially constructed extractors and extracted systematically at room temperature, with a carefully purified solvent, usually petroleum ether. The solvent penetrates the flowers and dissolves the natural flower perfume together with some waxes and albuminous and coloring matter. The solution is subsequently pumped into an evaporator and concentrated at a low temperature. After the solvent is completely driven off in vacua, the concentrated flower oil is obtained. Thus the temperature applied during the entire process is kept at a minimum; live steam, as in the case of distillation, does not exert its action upon the delicate constituents of the flower oils. Compared with distilled oils the extracted flower oils, therefore, more truly represent the natural perfume as originally present in the flowers.
31 J. Pharm. 21 (1835), 335. Buchner's Repert. f. d. Pharm. 54 (1835), 249. Pharm. ZentraM. (1835), 553.
82 Buchner's Repert. f. d. Pharm. 56 (1836), 382.
83 J. Chem. med. (1838), 221. Pharm. Zentralbl. (1838), 442.
84 J. Pharm. chim. [3] 30 (1856), 407. Compt. rend. 43 (1856), 197.
35 "Toiletten-Chemie," 3d Ed., Leipzig (1874), 77.
86 For details see Perfumery Essential Oil Record 12 (1921), 197-222.

Despite this obvious advantage the volatile solvent process cannot entirely replace steam distillation, which remains the principal method of isolating essential oils. Steam distillation, in most cases, is a simpler process: by employing portable direct fire stills, distillation can be carried out even in remote and primitive parts of the world, whereas solvent extraction necessitates complicated and expensive apparatus, and a crew of welltrained workers. Running expenses arc comparatively high; a mistake in operation can be costly; the unavoidable loss of solvent, of which large quantities are employed during the process, is an important factor in the price calculation of natural flower oils. Extraction with solvents can, therefore, be applied advantageously only to the higher priced materials, particularly the flowers. A loss of 10 liters of solvent per 100 kg. of flower charge remains rather insignificant in the calculation of absolute of jasmine which is normally valued at several hundred dollars per pound;37 but with low-priced oils such as rosemary or eucalyptus, ranging normally below $1.00 per pound, the loss of a few liters of solvent would make extraction prohibitive.
All extracted flower oils are of more or less dark color because they contain much of the natural plant pigments which are not volatile. Steam distilled oils, on the other hand, are in most cases of light color. Furthermore, they usually are soluble even in dilute alcohol, while extracted oils require 95 per cent alcohol for complete solution.
Despite these drawbacks, the products of extraction possess one supreme advantage, i.e., their true-to-nature odor. In addition, certain types of flowers e.g., jasmine, tuberose, jonquil, hyacinth, acacia, mimosa and violet do not yield their volatile oil on steam distillation, and must, therefore, be extracted with solvents.
c. The Evaluation of Natural Flower Oils and Resinoids
37 Up to $2,000.00 per Ib. in 1946.

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