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 fur? naces 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.

1.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

Chemical Catechism" was first prepared for the. eye of the public,-the author having, at the same time, had it in his contemplation to exhibit, in a popular form, a body of incontrovertible evidence of the wisdom and beneficence of the Deity, in the establishment and modification of those laws of matter which are so infinitely and beautifully varied, and whose operation is too minute to be the object of general notice. For, if it could be proved to the satisfaction of youth, that matter is subject to a vast variety of laws which escape common observance, and that, in the adjustment of those laws, the utmost attention, if it may be so expressed, has been paid to our convenience and comfort,

such a detail, it was imagined, would tend to make a more indelible impression on the young mind, than the display of the same goodness in the ope ration of causes which come under our daily notice and observation.

- With these views it naturally occurred to the author, that the work would be very incomplete, should he neglect to offer to the student some of those moral reflections which spontaneously arise in every contemplative mind, when considering the

magnificent system of nature; and though such re marks may perhaps be regarded by some as irrelevant to chemical science, yet, to repeat the former apology, it may be observed that, in compiling any initiatory book, no writer, as a parent, could lose sight of the necessity of embracing every favourable opportunity of infusing such principles into the youthful mind, as might defend it against immorality, irreligion, and scepticism.

For the accommodation of schools, and to ren der the generality of parents and preceptors more competent to explain and expatiate upon the var riety of facts which the science of chemistry presents, and to qualify them in some measure to afford such answers to a number of questions, which the young pupil, in proportion as he advances and becomes more interested in the experiments, will not fail to demand, the author has added a variety of explanatory notes. Many of these will be found to contain new matter, or, at least, what is not generally known or published; others, and perhaps the majority, were drawn from various sources; but as many were quoted from memory, and still more from the commonplace-book of the compiler,

he was obliged, in some instances, either to omit the authorities, or entirely forgo the advantages he had derived from the works, experiments, and opinions of some of the most enlightened chemical philosophers of the age. Here, however, he has constantly been guided by one rule-to produce rather what is useful than original*.

It may also be remarked, that the catechetical form, which was first chosen for this work, has been found to possess at least all the advantages that any other mode of instructing youth in che mistry can claim, the work having already been introduced with advantage into several of the most eminent seminaries in the kingdom; and, that, if the author's original intention be followed, the progressive improvement of the student will be pleasant, rapid, and correct.

* With this view, not only a succinct account of the different branches of chemical knowledge has been given, but he has uniformly endeavoured throughout the work to direct the reader to the best treatises in each department of the science, with a view to facilitate higher attainments; and to render The Chemical Catechism" a kind of text-book for the student.