Experiments and Observations on Different Kinds of Air

book by Joseph Priestley

Experiments and Observations on Different Kinds of Air (1774–86) was a six-volume work published by 18th-century British polymath Joseph Priestley. Later editions were "in three volumes: being the former six volumes abridged and methodized, with many additions." The work reports a series of Priestleys experiments on "airs" or gases, most notably his contributions to the discovery of oxygen gas (which he named "dephlogisticated air") and its properties. The book is an original source for study in the history of science and the history of chemistry. Quotes below are from the three volume, 1790 edition.

Vol.1 (1790)



1775 Title page
  • Every publication I have frankly acknowledged to be very imperfect, and the present, I am as ready to acknowledge, is so. But, paradoxical as it may seem, this will ever be the case in the progress of natural science, so long as the works of God are, like himself, infinite and inexhaustible. In completing one discovery, we never fail to get an imperfect knowledge of others, of which we could have had no idea before; so that we cannot solve one doubt without creating several new ones.
  • The greater is the circle of light, the greater is the boundary of the darkness by which it is confined. But notwithstanding this, the more light we get, the more thankful we ought to be. For by this means we have the greater range for satisfactory contemplation. In time the bounds of light will be still farther extended; and from the infinity of the divine nature, and the divine works, we may promise ourselves an endless progress in our investigation of them: a prospect truly sublime and glorious. The works of the greatest and most successful philosophers are, on this account, open to our complaints of their being imperfect.
  • Newton, as he had very little knowledge of air, so he had few doubts concerning it.
  • If a man be not mistaken in the principal object of his pursuits, he has no occasion to distress himself about lesser things.
  • In the progress of his inquiries he will generally be able to rectify his own mistakes; or if little and envious minds should take a malignant pleasure in detecting them for him, and endeavouring to expose him, he is not worthy of the name of a philosopher, if he has not strength of mind sufficient to enable him not to be disturbed at it. He who does not foolishly affect to be above the failings of humanity, will not be mortified when it is proved that he is but a man.
  • The man who believes that there is a governor as well as a maker of the world (and there is certainly equal reason to believe both) will acknowledge his providence and favour at least as much in a successful pursuit of knowledge, as of wealth; which is a sentiment that entirely cuts off all boasting with respect to ourselves, and all envy and jealousy with respect to others; and disposes us mutually to rejoice in every new light that we receive, through whose hands soever it be conveyed to us.
  • This rapid process of knowledge, which, like the progress of a wave of the sea, of sound, or of light from the sun, extends itself not this way or that way only, but in all directions, will, I doubt not, be the means, under God, of extirpating all error and prejudice, and of putting an end to all undue and usurped authority in the business of religion, as well as of science; and all the efforts of the interested friends of corrupt establishments of all kinds, will be ineffectual for their support in this enlightened age; though, by retarding their downfall, they may make the final ruin of them more complete and glorious.
  • Men of leisure, spirit, and ingenuity, in the middle ranks of life... is a circumstance that promises better for the continuance of this progress in useful knowledge than any noble or royal patronage.
  • The system of nature is superior to any political system upon earth. If extensive usefulness be the object, science has the same advantage over politics. The greatest success in the latter seldom extends farther than one particular country, and one particular age; whereas a successful pursuit of science makes a man the benefactor of all mankind, and of every age. How trifling is the fame of any statesman that this country has ever produced to that of Lord Bacon, of Newton, or of Boyle; and how much greater are our obligations to such men as these, than to any other in the whole Biographia Britannica; and every country, in which science has flourished, can furnish instances for similar observations.
  • I have... repeatedly cautioned my readers... that they are to consider new facts only as discoveries and mere deductions from those facts, as of no kind of authority; but to draw all conclusions, and form all hypotheses, for themselves.
  • It is enough for us to see that nature is inexhaustible, that it is a rich mine, in which we shall never dig in vain, and that it is open to infinitely more labourers than are now employed in exploring its contents, or in digging for them.
  • Persons who have only one object of pursuit, never fail to over-rate it, and of course to undervalue other things. ...the attention I have given to theology ...does not engross so much of my time as some persons may imagine ...these different studies so relieve one another, that I believe I do more in each of them, by applying to them alternately, than I should do, if I gave my whole attention to one of them only. But my principal defence rests on the superior dignity and importance of theological studies to any other whatever, and with some observations of this kind I shall chuse to conclude this long Preface.
  • I... address my brother philosophers on a subject equally interesting to us as philosophers, and as men. Do not disregard a question of infinite moment. Give it that degree of attention to which it is naturally intitled; and especially do not so far abandon the serious character of philosophers, as to laugh where you ought to reason. At least, do this great subject [theology], and yourselves, the justice to consider the facts, and endeavour to frame some hypothesis by which to account for them; and do not decide in half an hour, on an inquiry which well deserves the study of a great part of your lives.
  • Could I imagine that the knowledge of nature would ever be exhausted, and that we were approaching to a termination of our enquiries, I could more contentedly shut my eyes on a scene in which nothing more was to be seen, or done. But to quit the stage at present (and I believe the aspect of things will be exactly similar in any future period of our existence) without the hope of re-visiting it, would fill me with the deepest regret. The general who, like Epaminondas, or Wolfe, dies in the arms of victory, dies with satisfaction; but not so he that is cut off in the beginning of a doubtful, though promising, engagement. Thus I feel on the idea of ceasing to breathe, when I have but just begun to know what it is that I breathe.
  • Till I hear better reasons than have yet been offered to me for changing my conduct, I shall continue to give my attention to my different pursuits, according to my own ideas of their respective importance; and my friends have no reason to fear that I shall neglect philosophy. It has, perhaps, but too strong charms for me. I shall endeavour, however, to keep it in its proper place, and not so much attach myself to the study of the laws, which govern this world, as to lose sight of the subserviency of this world, and of all things in it, to another and a better; in which I hope to resume these pleasing philosophical pursuits, and to see, in a comprehensive view, those detached discoveries which we are now making here.
  • When a sufficient number of new facts shall be discovered (towards which even imperfect hypotheses will contribute) a more general theory will soon present itself; and perhaps to the most incurious and least sagacious eye. Thus, when able navigators have, with great labour and judgment, steered towards an undiscovered country, a common sailor, placed at the mast head, may happen to get the first sight of the land.
  • Let us not... contend about merit, but let us all be intent on forwarding the common enterprize, and equally enjoy any progress we may make towards succeeding in it; and above all, let us acknowledge the guidance of that Great Being, who has put a spirit in man, and whose inspiration giveth him understanding.

Introduction, Sect.3

Plate I, facing Vol.1 title page
  • It will be seen that my apparatus for experiments on air is in fact nothing more than that of Dr. Hales, Dr. Brownrigg, and Mr. Cavendish, diversified and made a little more simple.
    • Vol. 1 (1790) Introduction, Sect.3 "An account of the Apparatus with which the following experiments were made."

Book I, Part I, Sect.1 Of the impregnation of water with fixed Air

  • It was in consequence of living for some time in the neighbourhood of a public brewery, a little after Midsummer in 1767, that I was induced to make experiments on fixed air, of which there is always a large body, ready formed, on the surface of the fermenting liquor, generally about nine inches, or a foot, in depth, within which any kind of substance may be very conveniently placed; and though, in these circumstances, the fixed air must be continually mixing with the common air and is therefore far from being perfectly pure, yet there is a constant fresh supply from the fermenting liquor, and it is pure enough for many purposes.
  • When this fixed air is very strong, the smoke of a small quantity of gunpowder fired in it will be wholly retained by it, no part escaping into the common air. ...if ...any of the fixed air be thrown over the side of the vessel the smoke, which is mixed with it will fall to the ground, as if it was so much water, the fixed air being heavier than common air.
  • Considering the near affinity between water and fixed air, I concluded that if a quantity of water was placed near the yeast of the fermenting liquor, it could not fail to imbibe that air, and thereby acquire the principal properties of Pyrmont, and some other medicinal mineral waters. Accordingly, I found, that when the surface of the water was considerable, it always acquired the pleasant acidulous taste that Pyrmont water has. The readiest way of impregnating water with this virtue, in these circumstances, is to take two vessels, and to keep pouring the water from one into the other, when they are both of them held as near the yeast as possible; for by this means a great quantity of surface is exposed to the air, and the surface is also continually changing. In this manner, I have sometimes, in the space of two or three minutes, made a glass of exceedingly pleasant sparkling water, which could hardly be distinguished from very good Pyrmont, or rather Seltzer water.
  • I had acquainted all my friends with what I had done, and frequently expressed my wishes that persons who had the care of large distilleries (where I was told that fermentation was much stronger than in common breweries) would contrive to have vessels of water suspended within the fixed air which they produced, with a fardier contrivance for agitating the surface of the water; as I did not doubt but that, by this means, they might, with little or no expence, make great quantities of Pyrmont water; by which they might at the same time both serve the public, and benefit themselves. For I never had the most distant thought of making any advantage of the scheme myself.
  • All calcareous substances contain fixed air, and any acids may be used in order to set it loose from them; but pounded lime stone, or the sawings of marble, and oil of vitriol are, both of them the cheapest, and upon the whole, the best for die purpose.

Book II, Part I, Sect.1 Of inflammable Air from Metals, by means of Acids, &c.

  • It is something remarkable, that all the acids that produce any air by the solution of metals give inflammable air, except spirit of nitre only, which forms a different kind of union with the inflammable principle; making nitrous air, more or less modified. Besides oil of vitriol and spirit of salt, I have observed that the vegetable acid also produces inflammable air, by the solution of metals, though in a much less quantity. Perhaps the proportion of the strength of the acids may be ascertained by this means. The concentrated vinegar which I made use of in my experiments on the vegetable acid air, dissolved zinc almost as rapidly as spirit of salt, and produced inflammable air; and radical vinegar, which is unquestionably a pure vegetable acid, had the same effect when applied both to zinc and iron.

Vol.2 (1790)

Plate I, facing Vol.2 title page

Book IV, Part 1, Sect. 1 An Account of the Discovery of dephlogisticated Air and its general Properties

  • More is owing to what we call chance, that is, philosophically speaking, to the observation of events arising from unknown causes, than to any proper design, or preconceived theory in this business [of science]. This does not appear in the works of those who write synthetically upon these subjects; but would, I doubt not, appear very strikingly in those who are the most celebrated for their philosophical acumen, did they write analytically and ingenuously.
  • I will frankly acknowledge, that, at the commencement of the experiments recited in this section, I was so far from having formed any hypothesis that led to the discoveries I made in pursuing them, that they would have appeared very improbable to me had I been told of them; and when the decisive facts did at length obtrude themselves upon my notice, it was very slowly, and with great hesitation, that I yielded to the evidence of my senses. And yet, when I re-consider the matter, and compare my last discoveries relating to the constitution of the atmosphere with the first, I see the closest and the easiest connexion between them, so as to wonder that I should not have been led immediately from the one to the other. That this was not the case, I attribute to the force of prejudice, which, unknown to ourselves, biasses not only our judgments, properly so called, but even the perceptions of our senses; for we may take a maxim so strongly for granted, that the plainest evidence of sense will not entirely change, and often hardly modify, our persuasions; and the more ingenious a man is, the more effectually he is entangled in his errors; his ingenuity only helping him to deceive himself, by evading the force of truth.
  • There are, I believe, very few maxims in philosophy that have laid firmer hold upon the mind, than that air, meaning atmospherical air, (free from various foreign matters, which were always supposed to be dissolved, and intermixed with it) is a simple elementary substance, indestructible, and unalterable, at least as much so as water is supposed to be.
  • In the course of my inquiries I was... soon satisfied that atmospherical air is not an unalterable thing; for that, according to my first hypothesis, the phlogiston with which it becomes loaded from bodies burning in it, and animals breathing it, and various other chemical processes, so far alters and depraves it, as to render it altogether unfit for inflammation, respiration, and other purposes to which it is subservient; and I had discovered that agitation in water, the process of vegetation, and probably other natural processes, restore it to its original purity.
  • At the time of my first publication, I was not possessed of a burning lens of any considerable force; and for want of one, I could not possibly make many of the experiments that I had projected, and which, in theory, appeared very promising. I had, indeed, a mirror of force sufficient for my purpose. But the nature of this instrument is such, that it cannot be applied, with effect, except upon substances that are capable of being suspended, or resting on a very slender support. It cannot be directed at all upon any substance in the form of powder, nor hardly upon any thing that requires to be put into a vessel of quicksilver; which appears to me to be the most accurate method of extracting air from a great variety of substances...
  • But having afterwards procured a lens of twelve inches diameter, and twenty inches focal distance, I proceeded with great alacrity to examine, by the help of it, what kind of air a great variety of substances, natural and factitious, would yield, putting them into the vessels represented fig. a, Plate IV. which I filled with quicksilver, and kept inverted in a bason of the same.
  • On the 1st of August, 1774, I endeavoured to extract air from mercurius calcinatus per se; and I presently found that, by means of this lens, air was expelled from it very readily. Having got about three or four times as much as the bulk of my materials, I admitted water to it, and found that it was not imbibed by it. But what surprized me more than I can well express, was, that a candle burned in this air with a remarkably vigorous flame, very much like that enlarged flame with which a candle burns in nitrous air, exposed to iron or liver of sulphur; but as I had got nothing like this remarkable appearance from any kind of air besides this particular modification of nitrous air, and I knew no nitrous acid was used in the preparation of mercurius calcinatus, I was utterly at a loss how to account for it.
    • A description of the production of oxygen gas from mecury(II) oxide
  • This experiment might have satisfied any moderate sceptic, but, however, being at Paris in the October following, and knowing that there were several very eminent chymists in that place, I did not omit the opportunity... to get an ounce of mercurius calcinatus prepared by Mr. Cadet, of the genuineness of which there could not possibly be any suspicion; and at the same time, I frequently mentioned my surprise at the kind of air which I had got from this preparation to Mr. Lavoisier Mr. le Roy, and several other philosophers who honoured me with their notice in that city; and who I dare say cannot fail to recollect the circumstance.
  • On the 8th of this month [March, 1775] I procured a mouse, and put it into a glass vessel, containing two ounce measures of the air from mercurius calcinatus. Had it been common air, a full grown mouse, as this was, would have lived in it about a quarter of an hour. In this air, however, my mouse lived a full half hour; and though it was taken out seemingly dead, it appeared to have been only exceedingly chilled; for, upon being held to the fire, it presently revived, and appeared not to have received any harm from the experiment.

Vol.3 (1790)


Book IX, Sect.1 Of the Restoration of Air in which a Candle has burned out by Vegetation

  • I have been so happy, as by accident to have hit upon a method of restoring air, which has been injured by the burning of candles, and to have discovered at least one of the restoratives which nature employs for this purpose. It is vegetation. This restoration of vitiated air, I conjecture, is effected by plants imbibing the phlogistic matter with which it is overloaded.
  • One might have imagined that, since common air is necessary to vegetable, as well as to animal life, both plants and animals had affected it in the same manner; and I own I had that expectation, when I first put a sprig of mint into a glass jar, standing inverted in a vessel of water; but when it had continued growing there for some months, I found that the air would neither extinguish a candle, nor was it at all inconvenient to a mouse, which I put into it.
  • On the 17th of August 1771, I put a sprig of mint into a quantity of air, in which a wax candle had burned out, and found that, on the 27th of the same month, another candle burned perfectly well in it.

Book XII, Sect.1 Of the constituent Principles of the different Kinds of Air

  • Fluctuating... as the present state of this branch of knowledge is, I shall not decline to give my present views of it; nor shall I find any more difficulty in retracting any opinion I shall now advance, than I have hitherto done in retracting what I have advanced before. The sketch that I shall now give may at least serve, like former theories, to amuse us when we look back upon it, after having gained a more perfect knowledge of the subject.

Quotes about Experiments

  • That the vegetable creation should restore the air which is spoiled by the animal part of it, looks like a rational system, and seems to be of a piece with the rest. Thus fire purifies water all the world over. It purifies it by distillation, when it raises it in vapours, and lets it fall in rain; and farther still by filtration, when keeping it fluid, it suffers that rain to percolate the earth. We knew before that putrid animal substances were converted into sweet vegetables when mixed with the earth and applied as manure; and now, it seems, that the same putrid substances, mixed with the air, have a similar effect. The strong, thriving state of your mint, in putrid air, seems to show that the air is mended by taking something from it, and not by adding to it. I hope this will give some check to the rage of destroying trees that grow near houses, which has accompanied our late improvements in gardening, from an opinion of their being unwholesome. I am certain, from long observation, that there is nothing unhealthy in the air of woods; for we Americans have everywhere our country habitations in the midst of woods, and no people on earth enjoy better health or are more prolific.
  • The Royal Society... voted to award him the Copley Medal, the most prestigious scientific prize of its day, "on account of the many curious and useful Experiments contained in his observations on different kinds of Air." In receiving the prize, Priestley was joining the ranks of his friends Canton and Franklin, who had three medals between them. Only five years after they had encouraged him to turn his experimental hobbies into a serious vocation, Priestly had reached the highest pinnacle of scientific achievement.
  • In 1774 he thought he had obtained nitrous oxide... in 1775 he saw the gas as dephlogisticated air... If we refuse the palm to Priestley, we cannot award it to Lavoisier for the work of 1775... Lavoisier insisted that oxygen was an atomic "principle of acidity"... formed only when that "principle" united with "caloric"... Ignoring Scheele, we can safely say that oxygen had not been discovered before 1774, and we would probably say that it had been discovered by 1777 or shortly thereafter. But... any attempt to date the discovery must inevitably be arbitrary because discovering a new sort of phenomenon is necessarily a complex event, one which involves recognizing both that something is and what it is.
  • Priestley had discovered in 1772 that metals on calcination absorbed at most one-fifth of the volume of air in which they were enclosed.
    • Stephen F. Mason, A History of the Sciences (1956)

See also

  • Archive.org
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