PREFACE.

THE Class-Book of Chemistry published some ten years ago has been rewritten, reillustrated, and much enlarged, and now appears as essentially a new work. Its aim is to present the most important facts and principles of the science, in their latest aspects, and in such a manner as shall be suitable for purposes of general education.

So rapid is the progress of Chemical Science, that a book upon the subject, however faithfully it may represent the state of knowledge at the time of its publication, requires frequent and thorough revision. The past ten years have been remarkably fruitful in new facts and principles bearing upon Chemistry, the most important of which will be found embodied in the present volume.

New views of the nature and connections of the forces have been accepted in the scientific world, which compel a new treatment of this branch of the subject. The old notion, that the forces are separate and peculiar forms of imponderable matter, has given way to the idea that they are closely allied and mutually convertible forms of activity or motion in ordinary matter. The older views are held to be self-contradictory, and as they do not explain and cannot represent the present facts of science, they are abandoned by the body of advanced scientific thinkers of the present time. The newer doctrines may be still incomplete, and are not without their difficulties, but they are more simple and rational; they harmonize with the later facts of discovery, and open many new paths of investigation of the highest interest and promise.

An earnest desire to make this book a faithful reflex of the present state of Chemistry, and its connected questions, has led to the adoption of the more recent views,

and to a much fuller treatment of Chemical Physics than was contained in the earlier editions of the work. It may be proper here to remark that the author has taught these views for several years in his lectures on the Chemistry of the Sunbeam;' the section placed under that title in this volume touching only a single branch of the discussion.

The work will be found to embrace also other subjects of recent investigation: as Spectrum Analysis and the elements discovered by it; Prof. GRAHAM's interesting views of Dialysis and the colloidal condition of matter; and BERTHELOT's remarkable researches in organic synthesis, or the artificial production of organic substances, together with various other particulars of scientific progress which are not to be found in contemporary text-books.

The present work is not designed as a Manual for Chemists. To such vast proportions has the science grown that voluminous and constantly enlarging treatises are published upon each of its numerous branches. A school textbook can therefore be but a brief compend of general principles and their most important applications, and is not to be judged by the completeness of its details, or its fulness as a work of reference. In this volume descriptions of those chemical substances which are not frequently met with, as the rare metals, are omitted, and directions for making experiments have been much condensed. By this means space is gained to treat with unusual fulness the more familiar objects of nature, as oxygen, air, water, food, &c., and to introduce much new and interesting information.

Chemistry is not now what it was a few years ago—a mere matter of acids and alkalies, colored fires, and gas explosions, beginning and ending in the lecture room. It is an unfolding of the great laws of Nature, around and within us, and has an interest, not for experimenters alone, but for all who care to understand anything of the scheme of being which the Creator has established, and in the midst of which they are placed. The Class-Book is therefore designed for the wants of that large class, both in and out of school, who would like to know something of this interesting science, but cannot pursue it in a detailed and experimental way. Its copious illustrations will partially supply the lack of experiments, but lectures and demon

strations are always invaluable whenever they can be obtained.

While the application of Chemistry to the most important arts has been duly noticed, more than usual attention has been given to the Chemistry of Nature. The order of subjects has been so presented as to unfold the order of forces in nature-what may be reverently termed the divine logic of her activities. In the First Part are considered the great natural forces by which matter is moved and transformed; in the Second Part, the application of these forces to the lower or mineral world, and the change of properties which they produce in inorganic bodies. Part Third treats of the organic kingdom, which rises out of the preceding, with the composition and changes of organic substances. In Part Fourth we see the completion of Nature's scheme in the world of life. The facts and principles of the three former divisions are here applied to the illustration of Physiological Chemistry.

In preparing the volume the author has kept constantly in view that Chemistry is not only a branch of education to be acquired, but that it is a means of education-a valuable · instrument of intellectual culture. His aim has been, not only to present important information but to arouse the mind and awaken a spirit of inquiry. He has striven te carry the thoughts upward to those larger and nobler views of scientific truth which are more and more clearly revealed by the advance of inquiry, and which are fitted not only to expand the thoughts, but to awaken the best emotions of our nature.

A brief statement of the relations of science to the mind is made in the Introduction. The subject pertains to Mental Philosophy; but many will study Chemistry who have not taken up that subject, and it is thought, that to such, the suggestions offered may prove serviceable. Should teachers think it too abstract and difficult for beginners in Chemistry, it may be passed by.

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In preparing this volume the author has resorted to various authentic sources of information; but the second edition of Prof. W. A. MILLER'S excellent Elements of Chemistry' has been taken as the chief guide in revising chemical data. Several passages have been transferred, with slight changes, from the Household Science' to Part IV.

The author would acknowledge especial indebtedness to the new 'Lectures on Heat' by Prof. TYNDALL, which contains an able and attractive exposition of the new views of heat and its connections with the other forces. He is happy in being able to state that this valuable work has been republished in this country, and he would earnestly recommend it to all teachers and students who take an interest in natural science.

He would also renew his expressions of obligation to the writings of Dr. J. W. DRAPER, of New York, a gentleman who stands alike distinguished in the field of original scientific research and of high philosophic thought.

Grateful for the kindness with which former efforts have been received, he would indulge the hope that the present may be found still more worthy the confidence of the friends of education.

NEW YORK, June, 1863.