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"STÖCKHARDT'S Principles of Chemistry," in its English dress, has for many years filled a definite and useful place among elementary text books. It has appealed to the numerous class of students, both men and boys, who in spite of limited means and opportunities are anxious to acquire some experimental knowledge of the science-who intend to work at chemistry instead of merely reading about it. To such students it is useless to describe experiments which can only be performed with the aid of costly and elaborate apparatus, or with the skill derived from long practice.

The great merit of Dr. Stöckhardt's book is that, while the experiments are clearly described and very numerous, they do not require for their successful performance any but the simplest and cheapest forms of apparatus. It is astonishing what an amount of good work may be done in chemistry with Florence flasks, tumblers, medicine bottles, basins, saucepans, tin plate, iron wire, corks and other articles, which are always at hand. If to these are added some glass and caoutchouc tubing, a few funnels, test tubes and beakers, a mortar and pestle, spirit lamp (if gas cannot be used), a small set of scales and weights, and a measuring glass, the student will be able to perform the great majority of the elementary experiments of chemistry.

Of course other apparatus may be added with great advantage, and apparatus is so cheap in the present day that almost every student will find it possible to make such additions to his stock as he goes on. But it is better not to begin with too much, as the beginner is almost sure to order many things which he will not really require.

When the publishers put Dr. Stöckhardt's work in my hands, I hoped that it might be possible to bring it into accordance with modern chemical ideas, without entirely altering its plan. This soon proved to be impracticable, and I found myself compelled to re-cast, and to a great extent to re-write the book. In doing so I have tried to preserve as far as I could the spirit of the original; but so much has been added, so much subtracted and so much altered, that I have not thought it right to retain the original title of the work. Nearly the whole of the original work which remains consists of experimental details and technical descriptions, which, though they have required much pruning and revision, are as useful now as when first written. A great many new experiments have been added in every part of the work.

The systematic classification adopted in Parts II. and III. has not been attempted in Part IV. (Organic Chemistry), because the more old-fashioned arrangement seemed better adapted for the purposes of a simple experimental study. But I have endeavoured, in two introductory chapters, to give the student some idea of the modern system of classification, and have, in the subsequent pages, referred constantly to these chapters.

In Part I., a somewhat lengthy chapter (Chapter III.) has been devoted to the laws of chemical force. This chapter is longer than it might otherwise have been, because I have thought it right to establish the laws of constitution and chemical action, and the primary meaning of symbols and formulæ, before taking advantage of the great assistance of

the atomic hypothesis. I trust I have succeeded in proving to the careful student that the symbols and formulæ of chemistry might be used with propriety and advantage, even if the atomic hypothesis were swept away.

In Parts II. and III. I was much assisted by Mr. E. Francis, F.C.S., Demonstrator of Chemistry in the Medical School of this Hospital. It is a pleasure to me to take this opportunity of thanking him for his valuable help in this and in many other things.


Christmas, 1871.

C. W. H.

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