The rational examination of a volatile oil in a chemical manner is possible only if its composition or at least its main constituents are known. The chemical investigation must be directed as much as possible toward the isolation and quantitative estimation of the constituents recognized as being the most valuable. The methods of testing must, therefore, conform to the analysis of the oil. If this really self-evident supposition had been generally recognized earlier, those methods of investigation, which are designated as quantitative reactions, as for instance the iodine absorption, or Maumene's sulphuric acid test, which had given good results with the fatty oils, would not have been applied offhand to the volatile oils.
1) Chemist and Druggist 53 (1898), 749.
2) Chemist and Druggist 57 (1900), 169. Report of Schimmel & Co. April 1901, 31.
The fatty oils are a group of chemically closely related bodies; they are glycerides of the fatty and oleic acid series. The constituents of the volatile oils, however, recruit themselves from the greatest variety of classes of bodies. Among them may be found terpenes, sesquiterpenes, paraffins, alcohols, aldehydes, ketones, phenols, ethers, oxides and esters. It should be no matter for surprise, therefore, that the methods of testing which are useful with the fatty oils, fail utterly with the volatile oils. Nor is there any sense in subjecting the fatty and the volatile oils to the same reactions, just because they both bear the same designation "oils".
The application of Hubl's iodine addition method to volatile oils has been recommended by Barenthin,1) Kremel,2) Williams,3) Davies4) and Snow.5) By a direct comparison of the results of these separate observers it could not have been difficult for Cripps6) to show the utter uselessness of this method. This result is not altered by the fact that individual analysts again and again recommend this method.7)
The use of bromine in place of iodine was first suggested by Levallois8) and later by Klimont.9) More recently it has again been recommended by Vaubel10) and Mosler.11) In as much, however, as the variety in the composition of volatile oils renders it impossible to pass judgement as to which of the constituents it is with which the bromine combines, the value of the results obtained will remain problematical. The method will, therefore, find application in emergency cases only.
1) Arch, der Pharm. 224 (1886), 848.
2) Pharm. Post 21 (1888), 789, 821.
3) Chem. News 60 (1889), 175.
*) Pharmaceutical Journ. III. 19 (1889), 821. 5) Pharmaceutical Journ. III. 20 (1889), 4. 6) Chem. News 60 (1889), 236.
7) Sangle-Ferriere and Cuniasse, Journ. de Pharm. etChim. II. 17(1903), 169; Report of Schimmel & Co. April 1903, 82; F. Hudson-Cox and W. H. Simmons, Analyst 29 (1904), 175; Pharmaceutical Journ. 72 (1904), 861; Report of Schimmel & Co. October 1904, 80; Worstall, Journ. Soc. chem. Industry 23 (1904), 302; Report of Schimmel & Co. October 1904, 85; Harvey, Journ. Soc. chem. Industry 23 (1904), 413; Report of Schimmel & Co. October 1904, 86.
8) Compt. rend. 99 (1884), 977. 9) Chem. Ztg. 18 (1894), 641.
10) Zeitschr. f. off. Chem. 11 (1905), 429; Chem. Zentralbl. 1906, I. 199; Report of Schimmel & Co. April 1906, 66.
11) Zeitschr. d. allg. osterr. Apoth. Ver. 45 (1907), 223, 235, 251, 267, 283, 299; Report of Schimmel & Co. October 1907, 116.
According to Maumene's test the fatty oil to be investigated is mixed in a certain proportion with concentrated sulphuric acid and the rise in temperature which takes place is observed. Its application to volatile oils was recommended by Williams') as well as by Duyk2) but it has found just as little favor in practice as the other methods named above.
With these methods are also to be classed the much recommended color reactions. They mostly consist in bringing together a volatile oil and e. g. sulphuric acid or nitric acid, whereby some coloration is produced, which only in rare cases can be ascribed to a definite chemical change. As the shades of color produced are difficult to describe, and often change from one to the other, these tests may therefore easily give rise to mistakes. Hence the color reactions in general are to be designated as useless. This does not exclude, however, the occasional use of a color reaction in the detection of adulterants. This is especially true if these color tests are used for the characterization of chemical individuals isolated from the volatile oils (e. g. cadinene, sylvestrene). It is, however, never to be considered as conclusive in itself.
Besides the methods of testing already enumerated, many others have been suggested in the course of time, which however have acquired as little practical importance as these. Only such methods are to be discussed here as have really proven satisfactory in the investigation of volatile oils.