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THE

EDINBURGH NEW

PHILOSOPHICAL JOURNAL.

An Estimate of the Philosophical Character of Dr Priestley.

By WILLIAM HENRY, M. D., F. R. S. &c. &c. *

The principal source of the materials of the following sketch, is the work in which the discoveries of Dr Priestley were originally announced to the public. It consists of six volumes in octavo, which were published by him at intervals between the years 1774 and 1786; the first three under the title of “Experiments and Observations on different kinds of Air;" and the last three under that of “ Experiments and Observations relating to various Branches of Natural Philosophy, with a continuation of the Observations on Air.” These volumes were afterwards methodized by himself, and compressed into three octavos, which were printed in 1790. As a record of facts, and as a book of reference, the systematized work is to be preferred ; but as affording materials for the history of that department of science which Dr Priestley cultivated with such extraordinary success, and, still more, for estimating the value of his discoveries, and adjusting his station as an experimental philosopher, the simple narrative, which he originally gave in the order of time, supplies the amplest and the firmest ground-work.

In every thing that respects the history of this branch of experimental philosophy, the writings and researches of Dr Priestley, to which I have alluded, are peculiarly instructive. They

* Read to the first meeting of the British Association for the Promotion of Science, at York, September 28. 1831. A beautiful Biographical Memoir of Dr Priestley, by Baron Cuvier, is printed in the Number for July 1827 of this Journal.

VOL. XIII. NO. XXV.--JULY 1832.

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are distinguished by great merits, and by great defects; the lat-
ter of which are wholly undisguised by their author. He un-
veils, with perfect frankness, the whole process of reasoning,
which led to his discoveries ; he pretends to no more sagacity
than belonged to him, and sometimes disclaims even that to
which he was fairly entitled ; he freely acknowledges his mis-
takes, and candidly confesses when his success was the result of
accident, rather than of judicious anticipation; and by writing
historically and analytically, he exhibits the progressive improve-
ment of his views, from their first dawnings to their final and dis-
tinct development. Now, with whatever delight we may con-
template a systematic arrangement, the materials of which have
been judiciously selected, and from which every thing has been
excluded that is not essential to the harmony of the general de-
sign, yet there can be no question that, as elucidating the
tions of the human mind, and enabling us to trace and appreci-
ate its powers of invention and discovery, the analytic method
of writing has decided advantages.

To estimate, justly, the extent of Dr Priestley's claim to philosophical reputation, it is necessary to take into account the state of our knowledge of gaseous chemistry at the time he began his inquiries. Without underrating what had been already done by Van Helmont, Ray,Hooke, Mayow, Boyle, Hales, Macbride, Black, Cavendish, and some others, Priestley may be safely affirmed to have entered upon a field, which, though not altogether untilled, had yet been very imperfectly prepared to yield the rich harvest, which he afterwards gathered from it. The very implements with which he was to work were for the most part to be invented ; and of the merits of those which he did invent, it is a sufficient proof that they continue in use to this day, with no very important modifications. All his contrivances for collecting, transferring, and preserving different kinds of air, and for submitting those airs to the action of solid and liquid substances, were exceedingly simple, beautiful, and effectual. They were chiefly, too, the work of his own hands, or were constructed under his directions by unskilled persons; for the class of ingenious artists, from whom the chemical philosopher now derives such valuable aid, had not then been called into existence by the demands of the science. With a very limited knowledge of

1

the general principles of chemistry, and almost without practice in its most common manipulations ;-restricted by a narrow income, and at first with little pecuniary assistance from others ;compelled, too, to devote a large portion of his time to other pressing occupations, he nevertheless surmounted all obstacles ; and in the career of discovery outstripped many who had long been exclusively devoted to science, and were richly provided with all appliances and means for its advancement.

It is well known that the accident of living near a public brewery at Leeds, first directed the attention of Dr Priestley to pneumatic chemistry, by casually presenting to his observation the appearances attending the extinction of lighted chips of wood in the gas which floats over fermenting liquors. He remarked, that the smoke formed distinct clouds floating on the surface of the atmosphere of the vessel, and that this mixture of air and smoke, when thrown over the sides of the vat, fell to the ground; from whence he deduced the greater weight of this sort of air than of atmospheric air. He next found that water imbibes the new air, and again abandons it when boiled or frozen. These more obvious properties of fixed air having been ascertained, he extended his inquiries to its other qualities and relations; and was afterwards led by analogy to the discovery of various other gases, and to the investigation of their characteristic properties.

It would be inconsistent with the scope of this essay to give a full catalogue of Dr Priestley’s discoveries, or to enumerate more of them than are necessary to a just estimate of his philosophical habits and character. He was the unquestionable author of our first knowledge of oxygen gas, of nitrous oxide, of muriatic, sulphurous, and fluor acid gases, of ammoniacal gas, and of its condensation into a solid form by the acid gases. Hydrogen gas was known before his time; but he greatly extended our acquaintance with its properties. Nitrous gas, barely discovered by Dr Hales, was first investigated by Priestley, and applied by him to eudiometry. To the chemical history of the acids derived from nitre, he contributed a vast accession of original and most valuable facts. He seems to have been quite aware that those acids are essentially gaseous substances, and that they might be exhibited as such, provided a fluid could

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are distinguished by great merits, and by great defects; the latter of which are wholly undisguised by their author. He unveils, with perfect frankness, the whole process of reasoning, which led to his discoveries ; he pretends to no more sagacity than belonged to him, and sometimes disclaims even that to which he was fairly entitled; he freely acknowledges his mistakes, and candidly confesses when his success was the result of accident, rather than of judicious anticipation; and by writing historically and analytically, he exhibits the progressive improvement of his views, from their first dawnings to their final and distinct development. Now, with whatever delight we may contemplate a systematic arrangement, the materials of which have been judiciously selected, and from which every thing has been excluded that is not essential to the harmony of the general design, yet there can be no question that, as elucidating the operations of the human mind, and enabling us to trace and appreciate its powers of invention and discovery, the analytic method of writing has decided advantages.

To estimate, justly, the extent of Dr Priestley's claim to philosophical reputation, it is necessary to take into account the state of our knowledge of gaseous chemistry at the time he began his inquiries. Without underrating what had been already done by Van Helmont, Ray,Hooke, Mayow, Boyle, Hales, Macbride, Black, Cavendish, and some others, Priestley may be safely affirmed to have entered upon a field, which, though not altogether untilled, had yet been very imperfectly prepared to yield the rich harvest, which he afterwards gathered from it. The very implements with which he was to work were for the most part to be invented ; and of the merits of those which he did invent, it is a sufficient proof that they continue in use to this day, with no very important modifications. All his contrivances for collecting, transferring, and preserving different kinds of air, and for submitting those airs to the action of solid and liquid substances, were exceedingly simple, beautiful, and effectual. They were chiefly, too, the work of his own hands, or were constructed under his directions by unskilled persons; for the class of ingenious artists, from whom the chemical philosopher now derives such valuable aid, had not then been called into existence by the demands of the science. With

With a very limited knowledge of

the general principles of chemistry, and almost without practice in its most common manipulations ;-restricted by a narrow income, and at first with little pecuniary assistance from others ;compelled, too, to devote a large portion of his time to other pressing occupations, he nevertheless surmounted all obstacles ; and in the career of discovery outstripped many who had long been exclusively devoted to science, and were richly provided with all appliances and means for its advancement.

It is well known that the accident of living near a public brewery at Leeds, first directed the attention of Dr Priestley to pneumatic chemistry, by casually presenting to his observation the appearances attending the extinction of lighted chips of wood in the gas which floats over fermenting liquors. He remarked, that the smoke formed distinct clouds floating on the surface of the atmosphere of the vessel, and that this mixture of air and smoke, when thrown over the sides of the vat, fell to the ground; from whence he deduced the greater weight of this sort of air than of atmospheric air. He next found that water imbibes the new air, and again abandons it when boiled or frozen. These more obvious properties of fixed air having been ascertained, he extended his inquiries to its other qualities and relations; and was afterwards led by analogy to the discovery of various other gases, and to the investigation of their characteristic properties.

It would be inconsistent with the scope of this essay to give a full catalogue of Dr Priestley's discoveries, or to enumerate more of them than are necessary to a just estimate of his philosophical habits and character. He was the unquestionable author of our first knowledge of oxygen gas, of nitrous oxide, of muriatic, sulphurous, and fluor acid gases, of ammoniacal gas, and of its condensation into a solid form by the acid gases. Hydrogen gas was known before his time; but he greatly extended our acquaintance with its properties. Nitrous gas, barely discovered by Dr Hales, was first investigated by Priestley, and applied by him to eudiometry. To the chemical history of the acids derived from nitre, he contributed a vast accession of original and most valuable facts. He seems to have been quite aware that those acids are essentially gaseous substances, and that they might be exhibited as such, provided a fluid could

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