Davy's "Elements of Chemical Philosophy" examined.--His Memoir on some combinations of Phosphorus and Sulphur, &c.--He discovers Hydro-phosphoric gas.--Important Illustrations of the Theory of Definite Proportionals--Bodies precipitated from water are Hydrats.--His letter to Sir Joseph Banks on a new detonating compound.--He is injured in the eye by its explosion.--His second letter on the subject.--His paper on the Substances produced in different chemical processes on Fluor Spar.--His work on Agricultural Chemistry. The "Elements of Chemical Philosophy," a work to which he has alluded in several of the preceding letters, was published in June 1812. It is dedicated to Lady Davy, to whom he offers it "as a pledge that he shall continue to pursue Science with unabated ardour." This work, although only a small part of the great labour he proposed to accomplish, must be considered as one of high importance to the cause of science. It has not perhaps announced any discoveries which had not been previously communicated to the Royal Society, but it has brought together his original results, and arranged them in one simple and digested plan--it has given coherence to disjointed facts, and has exhibited their mutual bearings upon each other, and their general relations to previously established truths. Very shortly after the publication of this first part, it was asserted by a scientific critic that the work could never be completed upon the plan on which it had commenced, which was little less than a system of chemistry, in which all the facts were to be verified by the author: an undertaking far too gigantic for the most intrepid and laborious experimentalist to accomplish. There was too much truth in the remark:--the life of the Author has closed--the work remains unfinished. Although it bears the title of "Elements," its plan and execution are rather adapted for the adept than the Tyro in science; it has, however, enabled the discoverer to expand several of his opinions with a freedom which is not consistent with the studied compression and elaborate brevity that necessarily characterise the style of a Philosophical Memoir,--and thus far it may have served the more humble labourer. The first impression which this volume must produce, is that of admiration at the rapid and triumphant progress of Chemistry, during the period of a very few years; while a comparison of this work with others, even of very recent date, will show how much we are indebted for this progress to the unrivalled labours of Davy. The first part of his projected system, which constitutes the volume under review, extends only to the general laws of chemical changes, and to the primary combinations of undecompounded bodies. It is resolved into seven divisions, upon each of which I propose to offer some remarks.