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PREFACE.

The use of numerical problems on the properties and reactions of substances, as a means of emphasizing statements made in lectures, was suggested many years ago by Mr Galloway, and has become to some extent common among teachers of chemistry in this country, but has been far more systematically and thoroughly adopted by Professor Cooke and other chemists in America.

The present book is an endeavour to put into a concise and simple form suitable for beginners in chemistry and for tyros in mathematics a considerable quantity of matter which is usually given by teachers in the form of manuscript notes, and to furnish a collection of easy numerical examples, a few of which may

be set at the conclusion of each lecture.

The problems are arranged in the order of the chemical reactions on which they depend, and not according to the mathematical methods used in their solution, in the hope that they may tend to fix in the mind of the learner the chief points which he has just heard dwelt upon. They are not arranged according to their difficulty, since this depends to a considerable extent on the mind of the individual pupil and on the bent and scope of the master's teaching, but each chapter is divided into an elementary and an advanced portion. For the sake of simplicity atomic instead of molecular equations and approximate instead of exact values have been very frequently given.

After some doubt and deliberation the answers are placed at the end of the book. In the elementary portion of each chapter they have been obtained by the use of 22-4 litres as "two-volumes” according to the proposal of Professor Williamson and of zt, as the coefficient of expansion of a gas, in the advanced portion tbe more exact values 22:32 litres and ·00367 have been used and the calculations have been usually made by four-figure logarithms.

A considerable number of the usual tables will also be found, some of which have been recalculated from recent results. The approximate atomic weights used throughout have in some cases of conflicting evidence been chosen to preserve well-known numbers or to avoid labour in calculation, and not from the assurance of their accuracy. The values calculated by Professor Clarke as the most probable results of all the best experiments are also given for the use of those who may wish to work with the greatest attainable precision.

With some diffidence an introduction has been prefixed to the examples, which is not intended in any way to supersede oral instruction, but if possible to supply two different wants.

Boys and masters too often find when separated

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