It is only within the last few decades that the former empiric manufacture of volatile oils has been placed on a scientific basis, which has enabled it to develop into an independent branch of chemical industry. During the period of transition in which this branch still finds itself, those factories which have done pioneer work, both scientifically and technically, as well as those which use the oils in various manufactures, are often compelled to suffer from the competition of inferior and adulterated products. As a matter of fact, the proper understanding of the estimation and appreciation of quality and purity of the much used volatile oils is not as common as is desirable for industry, commerce and the trades. The principal cause for this condition is the fact that the recent chemical investigations and their application to the arts have not yet been generally offered in suitable form.

The want of a work which from a modern standpoint treats in an exhaustive and critical manner the entire subject of volatile oils, has induced the firm of Schimmel & Co. of Leipzig to commission the authors with the preparation of a treatise that would meet the present demands. The successful completion of this task has been greatly facilitated by having placed at their disposal the observation records of many years of manufacturing on a large scale.

Special stress has been laid on the description of properties and on tried methods of testing the commercially more important oils. Thus the consumer is placed in a position to distinguish pure from adulterated oils, good oils from those of inferior quality. Inasmuch as rational methods of examination are dependent on a knowledge of the physical properties and chemical composition of the oils, it became necessary to discuss thoroughly the results of the scientific investigations of the subject. Those investigations, however, that cannot claim permanent value, as well as antiquated methods, such as color reactions, etc., have not been included.

Fully realizing the importance of a historical basis for such a work, this has received special attention. Detailed references to the original sources enable the reader to make further investigations in this direction.

Although the aim and object of this book is primarily of a practical nature, the authors venture to hope that it also offers to the scientific investigator a complete summary, with numerous references to original literature, of everything that has been accomplished in this line.

The authors acknowledge with thanks the co-operation of Dr. C. von Rechenberg who wrote the chapter "Theoretical foundation for the preparation of volatile oils by steam distillation;" also of Dr. J. Helle who contributed "The more common constituents of volatile oils;" finally that of Dr. J. Bertram who kindly assisted in reading proof and who repeatedly made valuable suggestions.

With regard to the share in the work by the two authors whose names appear on the title page: the "Historical introduction," also everything that pertains to the history of the volatile oils and the raw materials, as well as the description of the methods of production of the American products, and in part the statements regarding origin and production of the drugs, are from the pen of Dr. Friedrich Hoffmann; the entire chemical text and those parts not specially enumerated have been written by Dr. Eduard Gildemeister.

Leipzig and Berlin, June 1899.