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For this purpose it is, above all, necessary that determinations of specific rotation should be made with the most rigid accuracy. Special attention has therefore been paid in the present work to the needs of the scientific investigator, by affording a detailed account of the different polarimetric instruments, and the methods of observation of specific rotation, as well as of other data connected therewith. The methods described are those which ensure the highest accuracy, and care has been taken to indicate in each case the limits of accuracy attainable. Where only a rougher estimate is required, it will readily be seen that steps may be omitted so as to simplify the process.

The importance of the subject, from a practical point of view, has been long acknowledged in its application to the determination of sugar, and recently of other substances, more especially the cinchona bases. The methods of observation in these special cases have been fully treated, and the sugar-chemist in particular will find interest and novelty in the account of the different saccharimeters, and the corrections to be applied to the result.

The introductory chapter on the optical principles of the subject may, perhaps, be not unwelcome to many a chemist. It has been made as elementary and succinct as possible. The relation between rotatory power and crystalline form, as belonging rather to crystallographic physics, has only been briefly touched upon. For

any further account of the work the reader need only be referred to the table of contents, which has been made as complete as possible.

HANS LANDOLT.

AACHEN, January, 1879.

TRANSLATOR'S PREFACE.

A Few words will suffice to introduce the present edition to the English reader. Some months ago, Mr. Frank Faulkner, the energetic and intelligent brewer of St. Helens and Beeston, to whom the English public are already indebted for the appearance of Pasteur's “Studies on Fermentation,” placed in my hands, for revision and editing, a manuscript translation? of Dr. Landolt's work; and for what now appears as a corrected version, although I cannot claim all the credit, yet I alone am responsible. What has been kept in view throughout was to make the English edition, as far as possible, an exact reproduction, in all respects, of the original work. A few notes have been ventured where it was thought they would be useful. The longer note at the end of the introductory chapter is placed there for the sake of practical people who, wishing to understand more fully the physical explanation of the fundamental phenomena, do not have the time or opportunity to read up the subject in special treatises on physics. The advanced student will, it is hoped, indulgently consider it in that light.

A feature of the English edition, which will doubtless render it specially valuable to the technical chemist, is the appendix contributed by Mr. Faulkner's assistant, Mr. Ignatius Steiner, of Vienna University

Lastly, I would take this opportunity to claim for Mr. Faulkner publicly the merit due to a busy, practical man, who is, notwithstanding, intelligent and far-sighted enough to see that in the end knowledge wins the day over empiricism in all departments of human activity, and who has already shown, and now once more by the appearance of the present translation shows, that he is also disinterested and spirited enough to seek to disseminate among his brethren in trade a similar persuasion as to the value of knowledge, whilst at the same time he affords them the best help that he knows of for attaining it.

1 The translation here alluded to was executed at Mr. Faulkner's request by Mr. H. M. Chichester.

a

D. C. ROBB.

BLAIRGOWRIE, N.B., March, 1881.

POSTSCRIPT:—The lamented deccase of Mr. Robb delayed the publication of this work, and the final revision was entrusted to the writer, who cannot but allude to the appreciation of Mr. Robb's cotemporaries at Oxford, for one whose scientific work was so exact and unobtrusive, and whose character was so honest and sincere.

V. H. VELEY.

UNIVERSITY COLLEGE, OXFORD, December, 1881.

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