1. It is something extraordinary that, though ether, as I found, cannot be made to assume the form of air (the vapour arising from it by heat, being soon condensed by cold, even in quicksilver) yet that a very small quantity of ether put to any kind of air, except the acid, and alkaline, which it imbibes, almost instantly doubles the apparent quantity of it; but upon passing this air through water, it is presently reduced to its original quantity again, with little or no change of quality.
I put about the quantity of half a nut-shell full of ether, inclosed in a glass tube, through a body of quicksilver, into an ounce measure of common air, confined by quicksilver; upon which it presently began to expand, till it occupied the space of two ounce measures. It then gradually contracted about one sixth of an ounce measure. Putting more ether to it, it again expanded to two ounce measures; but no more addition of ether would make it expand any farther. Withdrawing the quicksilver, and admitting water to this air, without any agitation,it began to be absorbed; but only about half an ounce measure had disappeared after it had stood an hour in the water. But by once passing it through water the air was reduced to its original dimensions. Being tried by a mixture of nitrous air, it appeared not to be so good as fresh air, though the injury it had received was not considerable.
All the phenomena of dilatation and contraction were nearly the same, when, instead of common air, I used nitrous air, fixed air, inflammable air, or any species of phlogisticated common air. The quantity of each of these kinds of air was nearly doubled while they were kept in quicksilver, but fixed air was not so much increased as the rest, and phlogisticated air less; but after passing through the water, they appeared not to have been sensibly changed by the process.
2. Spirit of wine yields no air by means of heat, the vapours being soon condensed by cold, like the vapour of water; yet when, in endeavouring to procure air from it, I made it boil, and catched the air which had rested on the surface of the spirit, and which had been expelled by the heat together with the vapour, in a vessel of quicksilver, and afterwards admitted acid air to it, the vessel was filled with white fumes,as if there had been a mixture of alkaline air along with it. To what this appearance was owing I cannot tell, and indeed I did not examine into it.
3. Having been informed by Dr. Small and Mr. Bolton of Birmingham, that paper dipped in a solution of copper in spirit of nitre would take fire with a moderate heat (a fact which I afterwards found mentioned in the Philosophical Transactions) it occurred to me that this would be very convenient for experiments relating toignitionin different kinds of air; and indeed I found that it was easily fired, either by a burning lens, or the approach of red-hot iron on the outside of the phial in which it was contained, and that any part of it being once fired, the whole was presently reduced to ashes; provided it was previously made thoroughly dry, which, however, it is not very easy to do.
With this preparation, I found that this paper burned freely in all kinds of air, but not invacuo, which is also the case with gunpowder; and, as I have in effect observed before, all the kinds of air in which this paper was burned received an addition to their bulk, which consisted partly of nitrous air, from the nitrous precipitate, and partly of inflammable air, from the paper. As some of the circumstancesattending the ignition of this paper in some of the kinds of air were a little remarkable, I shall just recite them.
Firing this paper ininflammableair, which it did without any ignition of the inflammable air itself, the quantity increased regularly, till the phial in which the process was made was nearly full; but then it began to decrease, till one third of the whole quantity disappeared.
A piece of this paper being put to three ounce measures ofacidair, a great part of it presently turned yellow, and the air was reduced to one third of the original quantity, at the same time becoming reddish, exactly like common air in a phial containing smoking spirit of nitre. After this, by the approach of hot iron, I set fire to the paper; immediately upon which there was a production of air which more than filled the phial. This air appeared, upon examination, to be very little different from pure nitrous air. I repeated this experiment with the same event.
Paper dipped in a solution of mercury, zinc, or iron, in nitrous acid, has, in a small degree, the same property with paper dipped in a solution of copper in the same acid.
4. Gunpowder is also fired in all kinds of air, and, in the quantity in which I tried it, did not make any sensible change in them, except that the common air in which it was fired would not afterwards admit a candle to burn in it. In order to try this experiment I half exhausted a receiver, and then with a burning-glass fired the gunpowder which had been previously put into it. By this means I could fire a greater quantity of gunpowder in a small quantity of air, and avoid the hazard of blowing up, and breaking my receiver.
I own that I was rather afraid of firing gunpowder in inflammable air, but there was no reason for my fear; for it exploded quite freely in this air, leaving it, in all respects, just as it was before.
In order to make this experiment, and indeed almost all the experiments of firing gunpowder in different kinds of air, I placed the powder upon a convenient stand within my receiver, and having carefully exhausted it by a pump of Mr. Smeaton's construction, I filled the receiver with any kind of air by the apparatus described, p. 19, fig. 14, taking the greatest care that the tubes, &c. which conveyed the air should contain little or no common air. In the experiment with inflammable air aconsiderable mixture of common air would have been exceedingly hazardous: for, by that assistance, the inflammable air might have exploded in such a manner, as to have been dangerous to the operator. Indeed, I believe I should not have ventured to have made the experiment at all with any other pump besides Mr. Smeaton's.
Sometimes, I filled a glass vessel with quicksilver, and introduced the air to it, when it was inverted in a bason of quicksilver. By this means I intirely avoided any mixture of common air; but then it was not easy to convey the gunpowder into it, in the exact quantity that was requisite for my purpose. This, however, was the only method by which I could contrive to fire gunpowder in acid or alkaline air, in which it exploded just as it did in nitrous or fixed air.
I burned a considerable quantity of gunpowder in an exhausted receiver (for it is well known that it will not explode in it) but the air I got from it was very inconsiderable, and in these circumstances was necessarily mixed with common air. A candle would not burn in it.
I begin to be apprehensive lest, after being considered as adry experimenter, I should pass, with many of my readers, into the opposite character of avisionary theorist. A good deal of theory has been interspersed in the course of this work, but, not content with this, I am now entering upon a long section, which contains nothing else.
The conjectures that I have ventured to advance in the body of the work will, I hope, be found to be pretty well supported by facts; but the present section will, I acknowledge, contain manyrandom thoughts. I have, however, thrown them together by themselves, that readers of less imagination, and who care not to advance beyond the regions of plain fact, may, if they please, proceed no farther, that their delicacy be not offended.
In extenuation of my offence, let it, however, be considered, thattheoryandexperimentnecessarily go hand in hand, every process being intended to ascertain some particularhypothesis, which, in fact, is only a conjecture concerning the circumstances or the cause of some natural operation; consequently that the boldest and most original experimenters are those, who, giving free scope to their imaginations, admit the combination of the most distant ideas; and that though many of these associations of ideas, will be wild and chimerical, yet that others will have the chance of giving rise to the greatest and most capital discoveries; such as very cautious, timid, sober, and slow-thinking people would never have come at.
Sir Isaac Newton himself, notwithstanding the great advantage which he derived from a habit ofpatient thinking, indulged bold and excentric thoughts, of which his Queries at the end of his book of Optics are a sufficient evidence. And a quick conception of distant analogies, which is the great key to unlock the secret of nature, is by no means incompatible with the spirit ofperseverance, in investigations calculated to ascertain and pursue those analogies.
§ 1.Speculations concerning theconstituentprinciplesof the different kinds ofair, and theconstitutionandoriginof theatmosphere, &c.
All the kinds of air that appear to me to be essentially distinct from each other arefixed air,acidandalkaline; for these, and another principle, calledphlogiston, which I have not been able to exhibit in the form ofair, and which has never yet been exhibited by itself inany form, seem to constitute all the kinds of air that I am acquainted with.
Acid air and phlogiston constitute an air which either extinguishes flame, or is itself inflammable, according, probably, to the quantity of phlogiston combined in it, or the mode of combination. When it extinguishes flame, it is probably so much charged with the phlogistic matter, as to take no more from a burning candle, which must, therefore, necessarily go out in it. When it is inflammable, it is probably so much charged with phlogiston, that the heat communicated by a burning candle makes it immediately separate itself from the other principle with which it was united, in which separationheatis produced, as in other cases of ignition; the action and reaction, which necessarily attends the separation of the constituent principles,exciting probably a vibratory motion in them.
Since inflammable, air, by agitation in water, first comes to lose its inflammability, so as to be fit for respiration, and even to admit a candle to burn in it, and then comes to extinguish a candle; it seems probable that water imbibes a great part of this extraordinary charge of phlogiston. And that watercanbe impregnated with phlogiston, is evident from many of my experiments, especially those in which metals were calcined over it.
Water having this affinity with phlogiston, it is probable that it always contains a considerable portion of it; which phlogiston having a stronger affinity with the acid air, which is perhaps the basis of common air, may by long agitation be communicated to it, so as to leave it over saturated, in consequence of which it will extinguish a candle.
It is possible, however, that inflammable air and air which extinguishes a candle may differ from one another in themodeof the combination of these two constituent principles, as well as in the proportional quantity of each; and by agitation in water, or long standing, that mode of combination may change. This weknow to be the case with other substances, as withmilk, from which, by standing only,creamis separated; which by agitation becomesbutter. Also many substances, being at rest, putrefy, and thereby become quite different from what they were before. If this be the case with inflammable air, the water may imbibe either of the constituent parts, whenever any proportion of it is spontaneously separated from the rest; and should this ever be that phlogiston, with which air is but slightly overcharged, as by the burning of a candle, it will be recovered to a state in which a candle may burn in it again.
It will be observed, however, that it was only in one instance that I found that strong inflammable air, in its transition to a state in which it extinguishes a candle, would admit a candle to burn in it, and that was very faintly; that then the air was far from being pure, as appeared by the test of nitrous air; and that it was only from a particular quantity of inflammable air which I got from oak, and which had stood a long time in water, that I ever got air which was as pure as common air. Indeed, it is much more easy to account for the passing of inflammable air into a state in which it extinguishes candles, without any intermediate state, in which it will admit a candle to burn in it, than otherwise. This subject requires and deserves farther investigation.It will also be well worth while to examine what difference the agitation of air in natural or artificialsea-waterwill occasion.
Since acid air and phlogiston make inflammable air, and since inflammable air is convertible into air fit for respiration, it seems not to be improbable, that these two ingredients are the only essential principles of common air. For this change is produced by agitation in water only, without the addition of any fixed air, though this kind of air, like various other things of a foreign nature, may be combined with it.
Considering also what prodigious quantities of inflammable air are produced by the burning of small pieces of wood or pit-coal, it may not be improbable but that thevolcanos, with which there are evident traces of almost the whole surface of the earth having been overspread, may have been the origin of our atmosphere, as well as (according to the opinion of some) of all the solid land.
The superfluous phlogiston of the air, in the state in which it issues from volcanos, may have been imbibed by the waters of the sea, which it is probable originally covered the surface of the earth, though part of it might have united with the acid vapour exhaled from the sea, andby this union have made a considerable and valuable addition to the common mass of air; and the remainder of this over-charge of phlogiston may have been imbibed by plants as soon as the earth was furnished with them.
That an acid vapour is really exhaled from the sea, by the heat of the sun, seems to be evident from the remarkably different states of the atmosphere, in this respect, in hot and cold climates. In Hudson's bay, and also in Russia, it is said, that metals hardly ever rust, whereas they are remarkably liable to rust in Barbadoes, and other islands between the tropics. See Ellis's Voyage, p. 288. This is also the case in places abounding with salt-springs, as Nantwich in Cheshire.
That mild air should consist of parts of so very different a nature as an acid vapour and phlogiston, one of which is so exceedingly corrosive, will not appear surprising to a chemist, who considers the very strong affinity which these two principles are known to have with each other, and the exceedingly different properties which substances composed by them possess. This is exemplified in commonsulphur, which is as mild as air, and may be taken into the stomach with the utmost safety, though nothing can be more destructive than one of itsconstituent parts, separately taken, viz. oil of vitriol. Common air, therefore, notwithstanding its mildness, may be composed of similar principles, and be a realsulphur.
That the fixed air which makes part of the atmosphere is not presently imbibed by the waters of the sea, on which it rests, may be owing to the union which this kind of air also appears to be capable of forming with phlogiston. For fixed air is evidently of the nature of an acid; and it appears, in fact, to be capable of being combined with phlogiston, and thereby of constituting a species of air not liable to be imbibed by water. Phlogiston, however, having a stronger affinity with acid air, which I suppose to be the basis of common air, it is not surprising that, uniting with this, in preference to the fixed air, the latter should be precipitated, whenever a quantity of common air is made noxious by an over-charge of phlogiston.
The fixed air with which our atmosphere abounds may also be supplied by volcanos, from the vast masses of calcareous matter lodged in the earth, together with inflammable air. Also a part of it may be supplied from the fermentation of vegetables upon the surface of it. Atpresent, as fast as it is precipitated and imbibed by one process, it may be set loose by others.
Whether there be, upon, the whole, an increase or a decrease of the general mass of the atmosphere is not easy to conjecture, but I should imagine that it rather increases. It is true that many processes contribute to a great visible diminution of common air, and that when by other processes it is restored to its former wholesomeness, it is not increased in its dimensions; but volcanos and fires still supply vast quantities of air, though in a state not yet fit for respiration; and it will have been seen in my experiments, that vegetable and animal substances, dissolved by putrefaction, not only emit phlogiston, but likewise yield a considerable quantity of permanent elastic air, overloaded indeed with phlogiston, as might be expected, but capable of being purified by those processes in nature by which other noxious air is purified.
That particles are continually detaching themselves from the surfaces of all solid bodies, even the metallic ones, and that these particles constitute the most permanent part of the atmosphere, as Sir Isaac Newton supposed, does not appear to me to be at all probable.
My readers will have observed, that not only is common air liable to be diminished by a mixture of nitrous air, but likewise air originally produced from inflammable air, and even from nitrous air itself, which never contained any fixed air. From this it may be inferred, that the whole of the diminution of common air by phlogiston is not owing to the precipitation of fixed air, but from a real contraction of its dimensions, in consequence of its union with phlogiston. Perhaps an accurate attention to the specific gravity of air procured from these different materials, and in these different states, may determine this matter, and assist us in investigating the nature of phlogiston.
In whatmannerair is diminished by phlogiston, independent of the precipitation of any of its constituent parts, is not easy to conceive; unless air thus diminished be heavier than air not diminished, which I did not find to be the case. It deserves, however, to be tried with more attention. That phlogiston should communicate absolutelevityto the bodies with which it is combined, is a supposition that I am not willing to have recourse to, though it would afford an easy solution of this difficulty.
I have likewise observed, that a mouse will live almost as long in inflammable air, when ithas been agitated in water, and even before it has been deprived of all its inflammability, as in common air; and yet that in this state it is not, perhaps, so much diminished by nitrous air as common air is. In this case, therefore, the diminution seems to have been occasioned by a contraction of dimensions, and not by a loss of any constituent part; so that the air is really better, that is, more fit for respiration, than, by the test of nitrous air, it would seem to be.
If this be the case (for it is not easy to judge with accuracy by experiments with small animals) nitrous air will be an accurate test of the goodness ofcommon aironly, that is, air containing a considerable proportion of fixed air. But this is the most valuable purpose for which a test of the goodness of air can be wanted. It will still, indeed, serve for a measure of the goodness of air that does not contain fixed air; but, a smaller degree of diminution in this case, must be admitted to be equivalent to a greater diminution in the other.
As I could never, by means of growing vegetables, bring air which had been thoroughly noxious to so pure a state as that a candle would burn in it, it may be suspected that something else besidesvegetationis necessary to produce this effect. But it should be considered, thatno part of the common atmosphere can ever be in this highly noxious state, or indeed in a state in which a candle will not burn in it; but that even air reduced to this state, either by candles actually burning out in it, or by breathing it, has never failed to be perfectly restored by vegetation, at least so far that candles would burn in it again, and, to all appearance, as well, and as long as ever; so that the growing vegetables, with which the surface of the earth is overspread, may, for any thing that appears to the contrary, be a cause of the purification of the atmosphere sufficiently adequate to the effect.
It may likewise be suspected, that sinceagitation in waterinjures pure common air, the agitation of the sea may do more harm than good in this respect. But it requires a much more violent and longer continued agitation of air in water than is ever occasioned by the waves of the sea to do the least sensible injury to it. Indeed a light agitation of air inputrid waterinjures it very materially; but if the water be sweet, this effect is not produced, except by a long and tedious operation, whereas it requires but a very short time, in comparison, to restore a quantity of any of the most noxious kinds of air to a very great degree of wholesomeness by the same process.
Dr. Hales found that he could breathe the same air much longer when, in the course of his respiration, it was made to pass through several folds of cloth dipped in vinegar, in a solution of sea-salt, or in salt of tartar, especially the last. Statical Essays, vol. 1. p. 266. The experiment is valuable, and well deserves to be repeated with a greater variety of circumstances. I imagine that the effect was produced by those substances, or by thewaterwhich they attracted from the air, imbibing the phlogistic matter discharged from the lungs. Perhaps the phlogiston may unite with the watery part of the atmosphere, in preference to any other part of it, and may by that means be more easily transferred to such salts as imbibe moisture.
Sir Isaac Newton definesflameto befumus candens, considering allsmokeas being of the same nature, and capable of ignition. But the smoke of common fuel consists of two very different things. That which rises first is merewater, loaded with some of the grosser parts of the fuel, and is hardly more capable of becoming red hot than water itself; but the other kind of smoke, which alone is capable of ignition, is properlyinflammable air, which is also loaded with other heterogeneous matter, so as to appear like a very dense smoke. A lighted candle soon shews them to be essentially differentfrom each other. For one of them instantly takes fire, whereas the other extinguishes a candle.
It is remarkable that gunpowder will take fire, and explode in all kinds of air, without distinction, and that other substances which containnitrewill burn freely in those circumstances. Now since nothing can burn, unless there be something at hand to receive the phlogiston, which is set loose in the act of ignition, I do not see how this fact can be accounted for, but by supposing that the acid of nitre, being peculiarly formed to unite with phlogiston, immediately receives it. And if the sulphur, which is thereby formed, be instantly decomposed again, as the chemists in general say, thence comes the explosion of gunpowder, which, however, requires the reaction of some incumbent atmosphere, and without which the materials will onlymelt, and bedispersedwithout explosion.
Nitrous air seems to consist of the nitrous acid vapour united to phlogiston, together, perhaps, with some small portion of the metallic calx; just as inflammable air consists of the vitriolic or marine acid, and the same phlogistic principle. It should seem, however, that phlogiston has a stronger affinity with the marineacid, if that be the basis of common air; for nitrous air being admitted to common air, it is immediately decomposed; probably by the phlogiston joining with the acid principle of the common air, while the fixed air which it contained is precipitated, and the acid of the nitrous air is absorbed by the water in which the mixture is made, or unites with any volatile alkali that happens to be at hand.
This, indeed, is hardly agreeable to the hypothesis of most chemists, who suppose that the nitrous acid is stronger than the marine, so as to be capable of dislodging it from any base with which it may be combined; but it agrees with my own experiments on marine acid air, which shew that, in many cases, thisweaker acid, as it is called, is capable of separating both the vitriolic and the nitrous acids from the phlogiston with which they are combined.
On the other hand, the solution of metals in the different acids seems to shew, that the nitrous acid forms a closer union with phlogiston than the other two; because the air which is formed by the nitrous acid is not inflammable, like that which is produced by the oil of vitriol, or the spirit of salt. Also, the same weight of iron does not yield half the quantity of nitrous air that it does of inflammable.
The great diminution of nitrous air by phlogiston is not easily accounted for, unless we suppose that its superabundant acid, uniting more intimately with the phlogiston, constitutes a species ofsulphurthat is not easily perceived or catched; though, in the process with iron, and also in that with liver of sulphur, part of the redundant phlogiston forms such an union with the acid as gives it a kind of inflammability.
It appears to me to be very probable, that the spirit of nitre might be exhibited in the form ofair, if it were possible to find any fluid by which it could be confined; but it unites with quicksilver as well as with water, so that when, by boiling the spirit of nitre, the fumes are driven through the glass tube, fig. 8, they instantly seize upon the quicksilver through which they are to be conveyed, and uniting with it, form a substance that stops up the tube: a circumstance which has more than once exposed me to very disagreeable accidents, in consequence of the bursting of the phials.
I do not know any inquiry more promising than the investigation of the properties ofnitre, thenitrous acid, andnitrous air. Some of the most wonderful phenomena in nature are connectedwith them, and the subject seems to be fully within our reach.
§ 2.Speculations arising from the consideration of the similarity of theelectric matterandphlogiston.
There is nothing in the history of philosophy more striking than the rapid progress ofelectricity. Nothing ever appeared more trifling than the first effects which were observed of this agent in nature, as the attraction and repulsion of straws, and other light substances. It excited more attention by the flashes oflightwhich it exhibited. We were more seriously alarmed at the electricalshock, and the effects of the electricalbattery; and we were astonished to the highest degree by the discovery of the similarity of electricity withlightning, and theaurora borealis, with the connexion it seems to have withwater-spouts,hurricanes, andearthquakes, and also with the part that is probably assigned to it in the system ofvegetation, and other the most important processes in nature.
Yet, notwithstanding all this, we have been, within a few years, more puzzled than ever with the electricity of thetorpedo, and of theanguille temblanteof Surinam, especially since that most curious discovery of Mr. Walsh's,that the former of these wonderful fishes has the power of giving a proper electrical shock; the electrical matter which proceeds from it performing a real circuit from one part of the animal to the other; while both the fish which performs this experiment and all its apparatus are plunged in water, which is known to be a conducting substance.
Perhaps, however, by considering this fact in connexion with a few others, and especially with what I have lately observed concerning the identity of electricity and phlogiston, a little light may be thrown upon this subject, in consequence of which we may be led to consider electricity in a still more important light. Many of my readers, I am aware, will smile at what I am going to advance; but the apprehension of this shall not interrupt my speculations, how chimerical soever they may be thought to be.
The facts, the consideration of which I would combine with that of the electricity of the torpedo, are the following.
First, The remarkable electricity of the feathers of a paroquet, observed by Mr. Hartmann, an account of which may be seen in Mr. Rozier's Journal for Sept. 1771. p. 69. Thisbird never drinks, but often washes itself; but the person who attended it having neglected to supply it with water for this purpose, its feathers appeared to be endued with a proper electrical virtue, repelling one another, and retaining their electricity a long time after they were plucked from the body of the bird, just as they would have done if they had received electricity from an excited glass tube.
Secondly, The electric matter directed through the body of any muscle forces it to contract. This is known to all persons who attend to what is called the electrical shock; which certainly occasions a properconvulsion, but has been more fully illustrated by Father Beccaria. See myHistory of Electricity, p. 402.
Lastly, Let it be considered that the proper nourishment of an animal body, from which the source and materials of all muscular motion must be derived, is probably some modification of phlogiston. Nothing will nourish that does not contain phlogiston, and probably in such a state as to be easily separated from it by the animal functions.
That the source of muscular motion is phlogiston is still more probable, from the consideration of the well known effects of vinous andspirituous liquors, which consist very much of phlogiston, and which instantly brace and strengthen the whole nervous and muscular system; the phlogiston in this case being, perhaps, more easily extricated, and by a less tedious animal process, than in the usual method of extracting it from mild aliments. Since, however, the mildest aliments do the same thing more slowly and permanently, that spirituous liquors do suddenly and transiently, it seems probable that their operation is ultimately the same.
This conjecture is likewise favoured by my observation, that respiration and putrefaction affect common air in the same manner, and in the same manner in which all other processes diminish air and make it noxious, and which agree in nothing but the emission of phlogiston. If this be the case, it should seem that the phlogiston which we take in with our aliment, after having discharged its proper function in the animal system (by which it probably undergoes some unknown alteration) is discharged aseffeteby the lungs into the great commonmenstruum, the atmosphere.
My conjecture suggested (whether supported or not) by these facts, is, that animals have a power of converting phlogiston, from the statein which they receive it in their nutriment, into that state in which it is called the electrical fluid; that the brain, besides its other proper uses, is the great laboratory and repository for this purpose; that by means of the nerves this great principle, thus exalted, is directed into the muscles, and forces them to act, in the same manner as they are forced into action when the electric fluid is thrown into themab extra.
I farther suppose, that the generality of animals have no power of throwing this generated electricity any farther than the limits of their own system; but that thetorpedo, and animals of a similar construction, have likewise the power, by means of an additional apparatus, of throwing it farther, so as to affect other animals, and other substances at a distance from them.
In this case, it should seem that the electric matter discharged from the animal system (by which it is probably more exhausted and fatigued than by ordinary muscular motion) would never return to it, at least so as to be capable of being made use of a second time, and yet if the structure of these animals be such as that the electric matter shall dart from one part of them only, while another partis left suddenly deprived of it, it may make a circuit, as in the Leyden phial.
As to themannerin which the electric matter makes a muscle contract, I do not pretend to have any conjecture worth mentioning. I only imagine that whatever can make the muscular fibres recede from one another farther than the parts of which they consist, must have this effect.
Possibly, thelightwhich is said to proceed from some animals, as from cats and wild beasts, when they are in pursuit of their prey in the night, may not only arise, as it has hitherto been supposed to do, from the friction of their hairs or bristles, &c. but that violent muscular exertion may contribute to it. This may assist them occasionally to catch their prey; as glow-worms, and other insects, are provided with a constant light for that purpose, to the supply of which light their nutriment may also contribute.
I would not even say that the light which is said to have proceeded from some human bodies, of a particular temperament, and especially on some extraordinary occasions, may not have been of the electrical kind, that is, produced independently of friction, or with lessfriction than would have produced it in other persons; as in those cases related by Bartholin in his treaticeDe luce animalium. See particularly what he says concerning Theodore king of the Goths, p. 54, concerning Gonzaga duke of Mantua, p. 57, and Gothofred Antonius, p. 123: But I would not have my readers suppose that I lay much stress upon stories no better authenticated than these.
The electric matter in passing through non-conducting substances always emitslight. This light I have been sometimes inclined to suspect might have been supplied from the substance through which it passes. But I find that after the electric spark has diminished a quantity of air as much as it possibly can, so that it has no more visible effect upon it, the electric light in that air is not at all lessened. It is probable, therefore, that electric light comes from the electric matter itself; and this being a modification of phlogiston, it is probable thatall lightis a modification of phlogiston also. Indeed, since no other substances besides such as contain phlogiston are capable of ignition, and consequently of becoming luminous, it was on this account pretty evident, prior to these deductions from electrical phenomena, that light and phlogiston are the same thing, in different forms or states.
It appears to me thatheathas no more proper connexion with phlogiston than it has with water, or any other constituent part of bodies; but that it is a state into which the parts of bodies are thrown by their action and reaction with respect to one another; and probably (as the English philosophers in general have supposed) the heated state of bodies may consist of a subtle vibratory motion of their parts. Since the particles which constitute light are thrown from luminous bodies with such amazing velocity, it is evident that, whatever be the cause of such a projection, the reaction consequent upon it must be considerable. This may be sufficient not only to keep up, but also to increase the vibration of the parts of those bodies in which the phlogiston is not very firmly combined; and the difference between the substances which are calledinflammableand others which also contain phlogiston may be this, that in the former the heat, or the vibration occasioned by the emission of their own phlogiston, may be sufficient to occasion the emission of more, till the whole be exhausted; that is, till the body be reduced to ashes. Whereas in bodies which are not inflammable, the heat occasioned by the emission of their own phlogiston may not be sufficient for this purpose, but an additional heatab extramay be necessary.
Some philosophers dislike the termphlogiston; but, for my part, I can see no objection to giving that, or any other name, to areal something, the presence or absence of which makes so remarkable difference in bodies, as that ofmetallic calcesandmetals,oil of vitriolandbrimstone, &c. and which may be transferred from one substance to another, according to certain known laws, that is, in certain definite circumstances. It is certainly hard to conceive how any thing that answers this description can be only a merequality, or mode of bodies, and notsubstanceitself, though incapable of being exhibited alone. At least, there can be no harm in giving this name to anything, or anycircumstancethat is capable of producing these effects. If it should hereafter appear not to be a substance, we may change our phraseology, if we think proper.
On the other hand I dislike the use of the termfire, as a constituent principle of natural bodies, because, in consequence of the use that has generally been made of that term, it includes another thing or circumstance, viz.heat, and thereby becomes ambiguous, and is in danger of misleading us. When I use the term phlogiston, as a principle in the constitution of bodies, I cannot mislead myself or others, because I use one and the same term todenote only one and the sameunknown causeof certain well-known effects. But if I say thatfireis a principle in the constitution of bodies, I must, at least, embarrass myself with the distinction of firein a state of action, and fireinactive, or quiescent. Besides I think the term phlogiston preferable to that of fire, because it is not in common use, but confined to philosophy; so that the use of it may be more accurately ascertained.
Besides, if phlogiston and the electric matter be the same thing, though it cannot be exhibited alone, in aquiescent state, it may be exhibited alone under one of its modifications, when it is inmotion. And if light be also phlogiston, or some modification or subdivision of phlogiston, the same thing is capable of being exhibited alone in this other form also.
In my paper on theconducting power of charcoal, (See Philosophical Transactions, vol. 60. p. 221) I observed that there is a remarkable resemblance between metals and charcoal; as in both these substances there is an intimate union of phlogiston with an earthy base; and I said that, had there been any phlogiston inwater, I should have concluded, that there had been no conducting power in nature, but in consequence of an union of this principle withsome base; for while metals have phlogiston they conduct electricity, but when they are deprived of it they conduct no longer. Now the affinity which I have observed between phlogiston and water leads me to conclude that water, in its natural state, does contain some portion of phlogiston; and according to the hypothesis just now mentioned they must be intimately united, because water is not inflammable.
I think, therefore, that after this state of hesitation and suspence, I may venture to lay it down as a characteristic distinction between conducting and non-conducting substances, that the former contain phlogiston intimately united with some base, and that the latter, if they contain phlogiston at all, retain it more loosely. In what manner this circumstance facilitates the passing of the electric matter through one substance, and obstructs its passage through another, I do not pretend to say. But it is no inconsiderable thing to have advanced butone stepnearer to an explanation of so very capital a distinction of natural bodies, as that into conductors and non-conductors of electricity.
I beg leave to mention in this place, as favourable to this hypothesis, a most curious discovery made very lately by Mr. Walsh, whobeing assisted by Mr. De Luc to make a more perfect vacuum in the double or arched barometer, by boiling the quicksilver in the tube, found that the electric spark or shock would no more pass through it, than through a stick of solid glass. He has also noted several circumstances that affect this vacuum in a very extraordinary manner. But supposing that vacuum to be perfect, I do not see how we can avoid inferring from the fact, that somesubstanceis necessary to conduct electricity; and that it is not capable, by its own expansive power, of extending itself into spaces void of all matter, as has generally been supposed, on the idea of there being nothing to obstruct its passage.
Indeed if this was the case, I do not see how the electric matter could be retained within the body of the earth, or any of the planets, or solid orbs of any kind. In nature we see it make the most splendid appearance in the upper and thinner regions of the atmosphere, just as it does in a glass tube nearly exhausted; but if it could expand itself beyond that degree of rarity, it would necessarily be diffused into the surrounding vacuum, and continue and be condensed there, at least in a greater proportion than in or near any solid body, as Newton supposed concerning hisether.
If that mode of vibration which constitutes heat be the means of converting phlogiston from that state in which it makes a part of solid bodies, and eminently contributes to the firmness of their texture into that state in which it diminishes common air; may not that peculiar kind of vibration by which Dr. Hartley supposes the brain to be affected, and by which he endeavours to explain all the phenomena of sensation, ideas, and muscular motion, be the means by which the phlogiston, which is conveyed into the system by nutriment, is converted into that form or modification of it of which the electric fluid consists.
These two states of phlogiston may be conceived to resemble, in some measure, the two states of fixed air, viz. elastic, or non-elastic; a solid, or a fluid.
In this Appendix I shall present the reader with the communications of several of my friends on the subject of the preceding work. Among them I should with pleasure have inserted some curious experiments, made by Dr. Hulme of Halifax, on the air extracted from Buxton water, and on the impregnation of several fluids, with different kinds of air; but that he informs me he proposes to make a separate publication on the subject.