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place in that admirable treatise. I have also regarded the whole subject from a stand-point somewhat different from that occupied by the German Professor.

To name all the books and journals from which I have derived assistance would be tedious and absurd; they are sufficiently indicated in the notes and references'.

I have tried to rest every important statement on firsthand authority. When chemistry is regarded from the point of view of the great workers therein, it wears an aspect very different from that with which it confronts the mere text-book-taster.

The book is divided into two parts. The first part is occupied with the statement and discussion of the atomic and molecular theory, and the applications thereof to such subjects as allotropy, isomerism, and the classification of elements and compounds. Somewhat full accounts are also given, in this part, of thermal, optical, and other departments of physical chemistry, in so far as the results and methods of these branches of the science are applicable to the questions regarding the composition of chemical systems which are connoted by the term Chemical Statics.

The second part of the book is devoted to the subjects of dissociation, chemical change and equilibrium, chemical affinity, and the relations between chemical action and the distribution of the energy of the changing system. These, and cognate questions, I have ventured to summarise in the expression Chemical Kinetics.

I have been much aided in my task by my friends Mr C. Slater, B.A., of St John's College, and Mr R. Threlfall, B.A., Scholar of Gonville and Caius College. The former has read considerable portions of the proofs and has made many valuable suggestions; the latter has read all, except the first chapter of Book I, and by his criticisms and remarks has helped me to make many important points much clearer and more accurate than they would otherwise have been.

1 The full titles of the various journals referred to are given on pp. xxi, xxii.

b M. C.

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Further explanation of expression valency of an atom.
Deduction (from data) of values to be assigned to this constant for

different elements
Consideration of possible meanings of expression bonds' or 'units

of affinity' as applied to atoms

Lossen's use of terms monovalent, divalent, &c.

Saturated and unsaturated molecules

Lossen's definitions of these terms

General considerations regarding valencies of atoms, especially as

these are supposed to be deduced from study of non-gasifiable

compounds •

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