"Chemical research conducts to the knowledge of philosophi cal truth, and forms the mind to philosophical enlargement and accuracy of thought, more happily than almost any other species of investigation in which the human intellect can be employed." TILLOCH.

"Tout homme qui reçoit une éducation libérale, compte aujourd'hui la chimie parmi les objets les plus indispensables de ses études."

FOURCHOY.

PREFACE

TO

THE FOURTH EDITION.

THE

HE very flattering reception which "THE CHEMICAL CATECHISM" has met with from the public, three large impressions having been sold within a very short period, and the respectable character it has received in the reviews and other periodical publications, have encouraged the author to devote a large portion of his time to the correction and enlargement of the work;-a fourth edition of which he now offers, in a form that he trusts will be approved, and with a confidence that he did not at first allow himself to entertain.

The late highly interesting and truly important discoveries of Davy having thrown new light upon

many branches of chemical science, it became necessary to review every part of the following sheets with great care, that no opportunity might be overlooked of recording the new facts and opinions, in order that the whole of the Text and the Notes might be accommodated to the present state of chemical knowledge.

The author, however, is very far from claiming any merit on this account; for he conceives that he could never deserve the continuance of that patronage which the public has so liberally bestowed, were he to neglect giving that public a faithful detail of all such discoveries of importance as have transpired since the former editions were prepared for the press.

In the hope of rendering the present impression still more acceptable, a variety of new matter has been added, particularly in the notes; a large portion of the text has been entirely re-written; the collection of Experiments has been enlarged; and he has obtained permission to make drawings of the Laboratory at the Surry Institution, which he has had engraved by an eminent artist, on purpose

for the work and as this elaboratory contains a set of the latest and most approved chemical furnaces of any in the metropolis, the measures have all been accurately taken, and the drawings made to a correct scale, so that any gentleman at a distance from town, might, by inspecting the engraving, be able to direct a workman to erect a similar establishment, either wholly, or in part.

J

Though the author might now, perhaps, be justified in omitting to state the motives that first induced him to engage in writing a Treatise on Chemistry, it may nevertheless be observed, that, in considering the great importance of chemistry to the arts and manufactures, it occurred to him, that an initiatory book, in which simplicity was united with perspicuity, would be an acceptable present to a variety of persons, who have not had leisure or opportunity to study more elaborate works; and especially to those parents who are not qualified by previous acquirements, to instruct their children in the elements of this science, than which there can be nothing more essential, in whatever line of life they may be destined to move. As an attempt, therefore, to supply this desideratum. "The