Apart from his experiments with the compression of gases, Robert Boyle deserves to be remembered for his proposals about 'unmingled bodies' (atoms), his promotion of the experimental method, his debunking of promoters of bad science, and his major contributions to our understanding of the atmosphere.
Robert Boyle lived in an age when men of learning were coming to reject what we now call pseudoscience. Alchemy was reformed into a protoscience by applying the experimental method, giving rise to what we now know as chemistry.
In every age, it seems, there are those who will say anything for financial gain or fame. These are the professional perjurors, the merchants of doubt and the YouTubers of doom. Robert Boyle had something to say about such people:
"For I am troubled, I must complain, that even Eminent Writers, both Physitians and Philosophers, whom I can easily name, if it be requir’d, have of late suffer’d themselves to be so far impos’d upon, as to Publish and Build upon Chymical Experiments, which questionless they never try’d; for if they had, they would, as well as I, have found them not to be true. And indeed it were to be wish’d, that now that those begin to quote Chymical Experiments that are not themselves Acquainted with Chymical Operations, men would Leave off that Indefinite Way of Vouching the Chymists say this, or the Chymists affirme that, and would rather for each Experiment they alledge name the Author or Authors, upon whose credit they relate it; For, by this means they would secure themselves from the suspition of falshood (to which the other Practice Exposes them) and they would Leave the Reader to Judge of what is fit for him to Believe of what is Deliver’d, whilst they employ not their own great names to Countenance doubtfull Relations; and they will also do Justice to the Inventors or Publishers of true Experiments, as well as upon the Obtruders of false ones. Whereas by that general Way of quoting the Chymists, the candid Writer is Defrauded of the particular Praise, and the Impostor escapes the Personal Disgrace that is due to him." (sic)
The Sceptical Chymist, by Robert Boyle
Sir William Ramsay wrote expansively about Robert Boyle as a pioneer of the study of our atmosphere. Below is the part of his book concerning Robert Boyle. The text is error-checked for typos and a few footnotes have been added.
The Gases of the Atmosphere - the History of Their Discovery
By Sir William Ramsay, K.C.B., RR.S.
Officier de la Legion d'Honneur
Emeritus Professor of Chemistry in University College. London
Fourth edition 1915
THE EXPERIMENTS AND SPECULATIONS OF BOYLE, MAYOW, AND HALES
To tell the story of the development of men's ideas regarding the nature of atmospheric air is in great part to write a history of chemistry and physics. This history is an attractive and varied one : in its early stages it was expressed in the quaint terms of ancient mythology, while in its later developments it illustrates the advantage of careful experimental inquiry. The human mind is apt to reason from insufficient premises ; and we meet with many instances of incorrect conclusions, based upon experiment, it is true, but upon experiment inadequate to support their burden. Further research has often proved the reasoning of the Schoolmen to be futile ; not indeed from want of logical method, but because important premisses had been overlooked.
Among the errors which misled the older speculators, three stand out conspicuously. These are
First, The confusion of one gas with another. Since gases are for the most part colourless, and always transparent, they make less impression on the senses than liquids or solids do. It was difficult to believe in the substantiality of bodies which could not be seen, but the existence of which had to be inferred from the testimony of other senses ; indeed, in certain instances only by the sense of touch, for many gases possess neither smell nor taste. This peculiarity led, in past ages, to the notion that air possessed a semi-spiritual nature ; that its substantiality was less than that of other objects more accessible to our senses. We meet with a relic of this view in words still in common use. Thus the Greek words TH/OW, I blow, and Tr^eO/m, a spirit or ghost, are closely connected ; in Latin we have spiro, I breathe, and spiritus, the human spirit; in English, the words ghost and gust are cognate. And the same connection can be traced in similar words in many other languages.
Our sense of smell is affected by extremely minute traces of gases and vapours, traces so small as to be unrecognisable by any other method of perception, direct or indirect. A piece of musk retains its fragrant odour for years, and the most delicate balance fails to detect any appreciable loss of weight in it. We are capable of smelling gases only : liquids and solids, if introduced into the nostrils, irritate the olfactory nerves, but do not stimulate them so as to incite the sense of smell ; yet the admixture of a minute trace of some odorous vapour with air appears entirely to change its properties. The effect of inhaling such air, although sometimes pleasant, is very different from the sensation produced by pure inodorous air, and such admixtures were in olden times naturally taken to be air modified in its properties. But such modifications are obviously almost infinite in number, for varieties of scent are excessively numerous ; and it was therefore perhaps deemed useless to attempt to investigate such a substance as air, whose properties could change in so inexplicable and mysterious a manner. Owing, therefore, to its elusive and, as it were, semi-spiritual properties, and to its unexpected changes of character, it was long before its true nature was discovered. It had not escaped observation that " air " obtained by distilling animal and vegetable matter, or by the action of acids on iron and zinc, differed from ordinary air by being inflammable ; but such " airs " were regarded as atmospheric air, modified in some manner, as it is modified when perfumed. And " airs " escaping from fermenting liquids, or produced by the action of acids on carbonates, were neglected. For long no attempt was made to catch them ; and the frothing and bubbling were regarded as a species of boiling, as is still seen in the use of our word " fermentation " (fervere, to boil).
Second, Erroneous ideas regarding the phenomena of combustion. While it was recognised that a burning candle was extinguished if placed in a confined space, its extinction was attributed not to the absence of air, but to the impossibility of the escape of flame. Indeed, flame was regarded as possessing the same semi-spiritual, semi-material nature as air. Together with earth and water, air and flame or fire formed the four elementary principles of the Ancients ; and all substances stones, metals, animals, and vegetables were regarded as partaking of the properties of these elements, and often as being constituted of the latter in varying proportions, according as they were cold and dry (earth), cold and moist (water), hot and moist (air), or hot and dry (fire). It is not within the scope of this book to enter into details regarding such ancient views. Those who are interested in the matter will find them expounded in Kopp's History of Chemistry, Kodwell's Birth of Chemistry, E. von Meyer's History of Chemistry, and in other similar works. But we shall be obliged to consider the later developments of such ideas in the phlogistic theory, by means of which all chemical changes connected with combustion were interpreted from the latter part of the seventeenth to the end of the eighteenth century. With erroneous views regarding the nature of combustion, and ignorance as to the part played by the atmosphere in the phenomena of burning, the true nature of air was undiscoverable.
Third, The lack of attention to gain or loss of weight. It was in past times not recognised that nothing could be created and nothing destroyed. In popular language, a candle is destroyed when it is burned, nothing visible being produced from it. The products, we now know, are gaseous and invisible, and possessed of greater weight than the unburnt candle ; but for want of careful experiment, it was formerly concluded that the candle, when burnt, was annihilated. The formation of a cloud in a cloudless sky ; the growth of vegetables in earth, from which, apparently, they did not derive their substance ; and the reputed growth of metalliferous lodes in mines these were all adduced as proofs of the creative power of Nature. With such ideas, therefore, the necessity of controlling the gain or loss of material during experiment, by determining gain or loss of weight, did not appear imperative ; and hence but few quantitative experiments were made, and little importance was attached to these few. It had, for example, long been noticed that certain metals gained weight when burned and converted into a " calx," or, as we should now say, a metallic oxide, but such gain in weight was not regarded as of any consequence. When considered in relation to the supposed loss of " phlogiston" suffered by a metal on being converted into a calx, it was explained by the hypothesis that phlogiston possessed " levity," the antithesis of gravity, and that the calx weighed more than the metal, owing to its having lost a principle which was repelled instead of being attracted by the earth.
Among the most remarkable early attempts to elucidate the true nature of air, we meet with one by the Hon. Robert Boyle, who published about the middle of the seventeenth century his Memoirs for a General History of the Air. Boyle was one of the most distinguished scientific men of his own, or indeed of any, age, and in his spirit of calm philosophical inquiry he was far in advance of his contemporaries. He was born in the early part of the year 1626, in Ireland, whither his father, Richard Boyle, had emigrated at the age of twenty-two. Boyle's mother, daughter of Sir Geoffrey Fenton, principal Secretary of State for Ireland, died while he was still a child. Yet she must have lived in the recollection of her son Eobert, for he wrote : "To be such parents' son, and not their eldest, was a happiness that our Philarethes (himself) would mention with great expressions of gratitude ; his birth so suiting his inclinations and designs, that had he been permitted an election, his choice would scarce have altered God's discernment."
In those days of early development, Boyle had finished his school-days at Eton by his twelfth year. He informs us that he devoured books omnivorously, and could hardly be induced to join in games. The next six years of his life he spent on the Continent with his elder brother; and on his father's death, which happened when he was abroad, he returned to England, and settled at Stalbridge, in Dorsetshire, where he had inherited a manor. Here he passed most of his life in great retirement, with only an occasional visit to London ; for though he lived through troublous times, he avoided politics. Indeed, he is known only to have appeared once on a public platform, and that was in defence of the Royal Society, then in its infancy, from attacks made upon it by some too scrupulously loyal Churchmen.
Boyle did not confine his attention exclusively to scientific pursuits : he interested himself deeply in theology, and published numerous tracts on religious subjects. He wrote with equal ease in English, French, and Latin, and his books appeared simultaneously in the first and last of these languages. His researches are remarkable for their wide range and for the boldness of his conceptions. But Boyle, ingenious though he was, was unable to fathom the mystery of atmospheric air. His views regarding it are succinctly stated by him in his Memoirs for a General History of the Air, and in the same work he sums up the views of the Ancients. His words are :
" The Schools teach the air to be a warm and moist element, and consequently a simple and homogeneous body. Many modern philosophers have, indeed, justly given up this elementary purity in the air, yet few seem to think it a body so greatly compounded as it really appears to be. The atmosphere, they allow, is not absolutely pure, but with them it differs from true and simple air only as turbid water from clear. Our atmosphere, in my opinion, consists not wholly of purer aether, or subtile matter which is diffused thro' the universe, but in great number of numberless exhalations of the terraqueous globe ; and the various materials that go to compose it, with perhaps some substantial emanations from the celestial bodies, make up together, not a bare indetermined feculency3, but a confused aggregate of different effluvia4. One principal sort of these effluvia4 in the atmosphere I take to be saline, which float variously among the rest in that vast ocean ; for they seem not to be equally mixed therein, but are to be found of different kinds, in different quantities and places, in different seasons. . . . Many men talk much of a volatile nitre in the air, as the only salt wherewith that fluid is impregnated. I must own the air, in many places, seems to abound in corpuscles of a nitrous nature ; but I don't find it proved by experiments to possess a volatile nitre. In all my experiments upon salt-peter, I found it difficult to raise that salt by a gentle heat; and spirits of nitre, which is drawn by means of a vehement one, has quite different properties from crude nitre, or the supposed volatile kind in the air, for 'tis exceeding corrosive."1
Boyle then proceeds to collect and comment on the effluvia4 from volcanoes and from decaying vegetables and animals, and proposes tests for the presence of such ingredients. He even attributes the darkening of silver chloride to its being a reagent for certain salts present in air at one time and not at another, and draws attention to the sulphurous smell produced by " thunder." Farther on (p. 61) he writes :
" The generality of men are so accustomed to judge of things by their senses, that because the air is invisible they ascribe but little to it, and think it but one remove from nothing. And this fluid is even by the Schoolmen considered only as a receptacle of visible bodies, without exerting any action on them unless by its manifest qualities, heat and moisture; tho', for my part, I allow it other faculties, and among them, such as are generative, maturative, and corruptive; and that, too, in respect not only of animals and bodies of a light texture, but even of salts and minerals."
In another place (p. 17) he states :
" I conjecture that the atmospherical air consists of three different kinds of corpuscles : the first, those numberless particles which, in the form of vapours or dry exhalations, ascend from the earth, water, minerals, vegetables, animals, etc. ; in a word, whatever substances are elevated by the celestial or subterraneal heat, and thence diffused into the atmosphere. The second may be yet more subtile, and consist of those exceedingly minute atoms the magnetical effluvia4 of the earth, with other innumerable particles sent out from the bodies of the celestial luminaries, and causing, by their impulse, the idea of light in us. The third sort is its characteristic and essential property I mean permanently elastic parts."
Boyle also relates experiments designed to " produce what appears to be air"; and he describes
the production, by the action of oil-of-vitriol5 on steel filings, of "air" (now known as hydrogen) which possessed the property of elasticity ; although he failed to notice its inflammability. He further obtained carbon dioxide by the fermentation of raisins, and probably also hydrogen chloride in the gaseous form by breaking a bulb containing " some good spirit-of-salt " in a vacuous receiver.
The result of shrewd reasoning power, applied, however, to imperfect observations, is well illustrated by the following passages :
" For tho', by reason of its great thinness and of its being, in its usual state, devoid both of taste and smell, air seems wholly unfit to be a menstruum [or solvent] ; yet it may have a dissolving, or at least a consuming, power on many bodies, especially such as are peculiarly disposed to admit its operations. For the air has a great advantage by the vast quantity of it that may come to work, in proportion to the bodies exposed thereto. . . . Thus we find a rust [corrosion] on copper that has been long exposed to the air." 2
Boyle, shortly after, describes the production of " an efflorescence of a vitriolic5 nature " on marcasite (or sulphide of iron) which has been exposed to the air ; and he relates that the " ore of alum, robb'd of its salt, will in tract6 of time recover it by being exposed to the air, as we are assured by the experienced Agricola."
To account for such actions, and for combustion, he proceeds (p. 81) :
" The difficulty we find in keeping flame and fire alive, tho' but for a little time, without air, renders it suspicious that there may be dispersed thro' the rest of the atmosphere some odd substance, either of a solar, astral, or other foreign nature ; on account whereof the air is so necessary to the subsistance of flame. ... It also seems by the sudden wasting or spoiling of this fine substance, whatever it be, that the bulk of it is but very small in proportion to the air it impregnates with its vertue ; for after the extinction of the flame the air in the receiver was not visibly alter'd ; and for ought I could perceive by several ways of judging, the air retained either all, or at least the far greatest part of its elasticity ; which I take to be its most genuine and distinguishing property. And this undestroyed springyness of the air, with the necessity of fresh air to the life of hot animals, suggest a great suspicion of some vital substance, if I may so call it, diffused thro' the air; whether it be a volatile nitre, or rather some anonymous substance, sidereal or subterraneal ; tho' not improbably of kin to that which seems so necessary to the maintenance of the other flames."
The experimental part of Boyle's work in this connection relates to the oxidation of cuprous to cupric compounds, with the change of colour from brown to blue or green, either in ammoniacal or in hydrochloric acid solution ; and he goes so far as to prove that two ounces of marcasites broken into small lumps, and kept in a room " freely accessible to the air, which was esteemed to be very pure," for somewhat less than seven weeks, gained above twelve grains by oxidation.
In his Memoirs for a General History of the Air, Boyle draws up a programme of research, of the carrying out of which, however, there is no record. He proposes (p. 23) :
"1. To produce air by fermentation in well clos'd receivers.
" To produce air by fermentation in sealed glasses.
" To separate air from liquors by boiling.
" To separate air from liquors by the air-pump.
" To produce air by corrosion, especially with spirit of vinegar.
" To separate air by animal and sulphureous dissolvants.
" To obtain air in an exhausted receiver by burning-glasses and red-hot irons.
" To produce air out of gunpowder and other nitrous bodies.
"2. To examine the produced aerial substances by their preserving or reviving animals, flame, fire, the light of rotten wood, and of fish.
"To examine it by its elasticity, and the duration thereof.
"To do the same by its weight, and its elevating the fumes of liquors."
We shall all agree that if Boyle had successfully carried out such experiments, our knowledge of the true nature of air would have come quite a century before it did. Some of these experiments were indeed made by John Mayow, his contemporary, whose work and speculations we shall now proceed to consider.
To be continued.
1 Memoirs for a General History of the Air ; Shaw's Abridgment of
Boyle's works, edition 1725, vol. iii. p. 26.
2 "Suspicions about some hidden qualities of the Air," ibid. p. 77.
3 feculency / feculancy variant spelling of feculence (archaic)
1. the state or quality of being feculent
2. dregs; sediment; filth ; (scientific term ) precipitate ; encrustation etc.
4 effluvia - emissions / emanations / fumes
5 oil of vitriol - sulphuric acid
vitriolic - highly corrosive
6 tract - archaic an extended period
in tract of time - in the course of time