Buffon's Natural History. Volume X (of 10)

Fire is the lightest of all bodies, notwithstanding which it has weight, and it may be demonstrated, that even in a small volume it is really heavy, as it obeys, like all other matters, the general law of gravity, and consequently must have connections or affinities with other bodies. All matters it renders more weighty will be those with which it has the greatest affinity. One of the effects of this affinity in the matters is to retain the substance even of fire, with which it is incorporated, and this incorporation supposes that fire not only loses its heat and elasticity, but even all its motion, since it fixes itself in these bodies, and becomes a constituent part. From which it may be imagined that there is fire under a fixed and concrete form in almost every body.

It is evident, that all matters, whose weight increases by the action of fire, are endowed with an attractive force superior to the expansive, the fiery particles of which are animated; this being extinguished the motion ceases, and the elastic and fugitive particles become fixed, and take a concrete form. Thus matters, whose weight is increased by fire, as tin, lead, &c. are substances which, by their affinity with fire, attract and incorporate. All matters, on the contrary, which, like iron, copper, &c. become lighter in proportion as they are calcined, are substances whose attractive forces, relative to the igneous particles, is less than the expansive force of fire; and hence the fire, instead of fixing in these matters, carries off and drives away the least adherent parts which cannot resist its impulsion. Those which, like gold, platina, silver, &c. neither lose nor acquire by the application of fire, are substances which, having no affinity with fire, and not being able to unite, cannot, consequently, either retain or accompany it when it is carried off. It is evident that the matters of the two first classes have a certain degree of affinity with fire, since those of the second class are loaded with fire, which they retain; and the fire loads itself with those of the first class, which it carries off; whereas the matters of the third class, to which it neither lends nor borrows, have not any affinity or attraction with it, but are indifferent to its action, which can neither unnaturalize nor even change them.

This division of every matter into three classes, relative to the action of fire, does not exclude the more particular and less absolute division of all matters into two other classes, hitherto regarded as relative to their own nature, which is said to be always vitrifiable, or calcareous. Our new division is only a more elevated point of view, under which we must consider them, to endeavour to deduce therefrom even the agent that is used by the relations fire can have with every substance to which it is applied.

We might say, with naturalists, that all is vitrifiable in Nature, excepting that which is calcareous: that quartz, chrystals, precious stones, flints, granites, porphyries, agates, gypsums, clays, lava, pumice stone, with all metals and other minerals, are vitrifiable either by the fire of our furnaces, or that of mirrors; whereas marble, alabaster, stones, chalk, marl, and other substances which proceed from the residue of shells and madrepores, cannot be reduced into fusion by these means. Nevertheless I am persuaded, that if the power of our furnaces and mirrors were further increased, we should be enabled to put these calcareous matters in fusion; since there are a multiplicity of reasons to conclude, that at the bottom their substance is the same, and that glass is the common basis of all terrestrial matter.

By my own experiments I have found, that the most powerful glass furnaces is only a weak fire, compared with that of bellows furnaces; and that fire produced in the focus of a good mirror, is stronger than that of the most glowing fire of a furnace. I have kept iron ore for thirty-six hours in the hottest part of the glass furnace of Rouelle, in Burgundy, without its being melted, agglutinated, or even in any manner changed; whereas, in less than twelve hours this ore runs in a forge furnace. I have also melted, or volatilized, by a mirror many matters which neither the fire, nor reverberatory furnace, nor the most powerful bellows furnace could cause to run.

It is commonly supposed, that flame is the hottest part of fire, yet nothing is more erroneous than this opinion; the contrary may be demonstrated by the most simple and familiar experiments. Offer to a straw fire, or even to the flame of a lighted faggot, a cloth to dry or heat, and treble the time will be required to what would be necessary if presented to a brasier without flame. Newton very accurately defines flame to be a burning smoke, and this smoke, or vapour, has never the same quantity or intensity of heat as the combustible body from which it escapes. By being carried upwards and extending, it has the property of communicating fire, and carrying it further than the heat of the brasier, which alone might not be sufficient to communicate it when even very near.

The communication of fire merits a particular attention. I found, after repeated reflections that besides the assistance of facts which appear to have a relation to it, that experiments were necessary to understand the manner in which this operation of Nature is made. Let us receive two or three thousand weight of iron in a mould at its issuing from the furnace; this metal in a short time loses its incandescence, and ceases from its redness, according to the thickness of the ingot. If at the moment its redness leaves it, it is drawn from the mold, the under parts will be still red, but this colour will fly off. Now so long as the redness subsists, we can light combustible matters by applying them to the ingot; but as soon as it has lost its incandescent state, there are numbers of matters which it will not set fire to, although the heat which it diffuses is, perhaps a hundred times stronger than that of a straw fire, which would inflame them. This made me think that flame being necessary to the communication of fire, there is therefore a flame in all incandescence. The red colour seems, in fact, to indicate it; and indeed I am convinced, that combustible, and even the most fixed matters, such as gold and silver, when in an incandescent state, are surrounded with a dense flame which extends only to a very short distance, and which is attached to their surface; and I can easily conceive, that when flame becomes dense to a certain degree, it ceases from obeying the fluctuation of the air. This white or red body, which issues from all bodies in incandescence, and which strikes our eyes, is the evaporation of this dense flame which surrounds the body by renewing itself incessantly on its surface; and even the light of the sun, which emits such an amazing brightness, I presume to be only an evaporation of the dense state that constantly plays on its surface; and which we must regard as a true flame, more pure and dense than any proceeding from our combustible matters.

It is, therefore, by light that fire communicates, and heat alone cannot produce the same effect as when it becomes very strong to be luminous. Even water, that destructive element to fire, by which alone we can prevent its progress, nevertheless communicates when in a well-closed vessel, such as Papin’s digester, where it is penetrated with a sufficient quantity of fire to render it luminous, and capable of melting lead and tin, whereas when it is only boiling, far from communicating fire, it extinguishes it immediately. It is true, that heat alone is sufficient to prepare and dispose combustible bodies for inflammation, by driving off the humid parts from bodies; and what is very remarkable, this heat, which dilates all bodies, does not desist from hardening them by drying. I have an hundred times discovered, by examining the stones of my great furnaces, especially the calcareous, they increased in hardness in proportion to the time they had undergone the heat, and they also at the same time became specifically heavier. From this circumstance, I think an induction may be drawn, which would prove, and fully confirm, that heat, although in appearance always fugitive and never stable in the bodies which it penetrates, nevertheless deposits in a positive manner many parts which fixes there even in greater quantities than the aqueous and other parts which it has driven off. But what appears very difficult to be reconciled, this same calcareous stone, which becomes specifically heavier by the action of a moderate heat a long time continued, becomes near a half lighter, when submitted to a fire sufficient for its calcination, and, at the same time, not only loses all the hardness it had acquired by the action of heat, but even the natural adherence of its constituting parts.

Calcination generally received, is, with respect to fixed and incombustible bodies, what combustion is to volatile and inflammable. Calcination, like combustion, needs the assistance of air; it operates so much the quicker, as it is furnished with a greater quantity of that element, without which the fiercest fire cannot calcine nor inflame any thing, except such matters as contain in themselves all the air necessary for those purposes. This necessity for the concurrence of air in calcination, as in combustion, indicates, that there are more things common between them than has been suspected. The application of fire is the principle of both; that of air is the second cause, and almost as necessary as the first; but these two causes are equally combined, according as they act in more or less time, and with more or less power on different substances.

Combustion operates almost instantaneously; calcination is sometimes so long, as to be thought impossible; for in proportion as matters are more incombustible, the calcination is there more slowly made; and when the constituent parts of a substance, such as gold, are not only incombustible, but appear so fixed as not to be volatilized, calcination produces no effect. They must both, therefore, be considered as effects of the same cause, whose two extremes are delineated to us by phosphorus, which is the most inflammable of all bodies, and by gold, which is the most fixed and least combustible. All substances comprized between these two extremes, will be more or less subjected to the effects of combustion and calcination, according as they approach either of them; insomuch, that in the middle points there will be found substances that endure an almost equal degree of both; from which we may conclude, that all calcination is always accopmanied with a little combustion, and all combustion with a little calcination. Cinders and other residue of the most combustible matters, demonstrate that fire has calcined all the parts it has not burned, and consequently, a little calcination is found here with combustion. The small flame which rises from most matters, that are calcined, demonstrates also that a slight combustion is made. Thus, we must not separate these two effects, if we would find out the results of the action of fire on the different substances to which it is applied.

But it may be said, that combustion always diminishes the volume or mass, on account of the quantity of matter it consumes; and that, on the contrary, calcination increases the weight of many substances. Ought we then to consider these two effects whose results are so contrary, as effects of the same nature? Such an objection appears well-founded, and deserves an answer, especially as this is the most difficult point of the question. For that purpose let us consider a matter in which we shall suppose one half to be fixed parts, and the other volatile or combustible. By the application of fire to this, all the volatile or combustible parts will be raised up or burnt, and consequently separated from the whole mass; from hence this mass or quantity of matter will be found diminished one half, as we see it in calcareous stones, which lose near half their weight in the fire. But if we continue to apply the fire for a very long time to the other half, composed of fixed parts, all combustion and volatilization being ceased, that matter, instead of continuing to lose its mass, must increase at the expense of the air and fire with which it is penetrated; and those are matters already calcined, and prepared by Nature to the degree where combustion ceases, and consequently susceptible of increasing the weight from the first moment of the application. We have seen, that light extinguishes on the surface of all bodies which do not reflect; and that heat, by long residence, fixes partly in the matters which it penetrates; we know also that air is necessary for calcination, or combustion, and the more so for calcination as having more fixity in the external parts of bodies, and becomes a constituent part: hence, it is natural to imagine, that this augmentation of weight proceeds only from the addition of the particles of light, heat, and air, which are at length fixed and united to one matter, against which they have made so many efforts, without being able either to raise or burn them. This appears clearly to be the fact, for if we afterwards present a combustible substance to them they will quit the fixed matter, to which they were only attached through force, retake their natural motion, elasticity, and volatility, and all depart with it; from hence, metal, or calcinized matter, to which these volatile parts has been rendered, retakes its pristine form, and its weight is found diminished by the whole quantity of fiery and airy particles which were fixed in it, and which had been just raised by this new combustion. All this is performed by the sole law of affinities; and there seems to be no more difficulty to conceive how the lime of a metal is reduced, than to understand how it is precipitated in dissolution; the cause is the same, and the effects are similar. A metal dissolved by an acid, will precipitate when to this acid another substance is offered with which it has more affinity than metal, the acid then quits it and falls to the bottom. So, likewise, this metal calcines, that is, loaded with parts of air, heat, and fire, which being fixed, keeps it under the form of a lime, and will precipitate, or be reduced, when presented to this fire and fixed air, from the combustible matters with which they have more affinity than with the metal; the latter will retake its first form as soon as it is disembarrassed from this superfluous air and fire, at the expence of the combustible matters offered to it, and the volatile parts it had lost.

I think I have now demonstrated, that all the little laws of chemical affinities, which appeared so variable and different, are no other than the general laws of attraction, common to all matter; that this great law, always constant and the same, appeared only to vary in its expression, which cannot be the same when the figure of bodies enters, like an element, into their distance. With this new key we can unlock the most profound secrets of Nature; we can attain the knowledge of the figure of the primitive parts of different substances; assign the laws and degrees of their affinities; determine the forms which they take by re-uniting, &c. I think also I have made it appear that impulsion depends on attraction; and that, although it may be considered as a different force, it is, notwithstanding, a particular effect of this sole and general one. I have shewn the communication of motion to be impossible without a spring, whence I have concluded, that all bodies in Nature are more or less elastic, and that there is not one perfectly hard; that is, entirely deprived of a spring, since all are susceptible of receiving motion. I have endeavoured to shew how this sole force may change direction, and attraction become repulsion; and from these grand principles, which are all founded on rational mechanics, I have sought to deduce the principal operations of Nature, such as the production of light, heat, and fire, and their action on different substances; this last object which interests us the most is a vast field, but of which I can only cultivate a little spot, yet I presume I may render some assistance, by putting into more capable and laborious hands the instruments I made use of. These instruments were the three modes of making use of fire, that is, by its velocity, volume, and mass; by applying it concurrently to the three classes of substances, which either lose, gain, or are not affected by the application of fire. The experiments which I had made on the refrigeration of bodies, on the real weight of fire, on the nature of flame, on the progress of heat, or its communication, its diperdition, its concentration, or its violent action without flame, &c. are also so many instruments which will spare much labour to those who choose to avail themselves of them, and will produce an ample harvest of knowledge.

OF AIR, WATER, AND EARTH

BY our former observations it appears that air is the necessary and first food of fire, which can neither subsist nor propagate but by what it assimilates, consumes, or carries off, of that element, whereas of all material substances, air is that which seems to exist the most independently of the aid or presence of fire; for although it habitually has nearly the same heat as other matters on the surface of the earth, it can do without it and requires infinitely less than any of the rest to support its fluidity, since the most excessive cold cannot deprive it of that. The strongest condensations are not capable of breaking its spring; the active fire, in combustible matters, is the only agent which can alter its nature by rarefying and extending its spring to the point of rendering it ineffectual, and thus destroying its elasticity. In this state, and in all the links which precede, the air is capable of re-assuming its elasticity, in proportion as the vapours of combustible matters evaporate and separate from it. But if the spring have been totally weakened and extended that it cannot re-instate itself, from having lost all its elastic power, the air, volatile as it might before have been, becomes a fixed substance which incorporates with the other substances, and forms a constituent part of all those to which it unites by contact. Under this new form it can no longer forsake the fire, except to unite, like fixed matter, to other fixed matters; and if there remain some parts inseparable from fire, they then make a portion of that element serve it for a base, and are deposited with it in the substance they heat and penetrate together. This effect is manifested in all calcinations, and is the more sensible as the heat is longer; but combustion demands only a small time to completely effectuate the same. If we wish to hasten calcination the use of bellows may be necessary, not so much to augment the heat of the fire as to establish a current of air on the surface of the matters; yet it is not requisite for the fire to be very fierce to deprive air of its elasticity, for a very moderate heat, when constantly applied on a small quantity, is sufficient to destroy the spring; and for this air, without spring, to fix itself afterwards in bodies, there is only a little more or less time required, according to the affinity it may have under this new form, with the matters to which it unites. The heat of the body of animals, and even vegetables, is sufficiently powerful to produce this effect. The degrees of heat are different in different kinds of animals: birds are the hottest, from which we pass successively to quadrupeds, man, cetaceous animals, reptiles, fish, insects, and, lastly, to vegetables, whose heat is so trifling as to have made some naturalists declare they had not any, although it is very apparent, and in winter surpasses that of the atmosphere. I have frequently observed in trees that were cut in cold weather, that their internal part was sensibly warm, and that this heat remained for many minutes. This heat is only moderate while the tree is young and sound, but as soon as it grows old the heart heats by the fermentation of the pith, which no longer circulates there with the same freedom; and as soon as this heat begins the centre receives a red tint, which is the first index of the perishing state of the tree, and the disorganization of the wood. The reason naturalists have not found there was a difference between the temperature of the air, and the heat of vegetables is, because they have made their observations at a bad time of the year, and not paid attention, that in the summer the heat of the air exceeds that of the internal part of a tree; whereas in winter it is quite the contrary. They have not remembered that the roots have constantly the degree of heat which surrounds them, and that this heat of the internal part of the earth is, during all winter, considerably greater than that of the air, and the surface of the earth. They did not consider that the motion alone of the pith, already warm, is a necessary cause of heat, and that this motion, increasing by the action of the sun, or by an external heat, that of vegetables must be so much the greater as the motion of their pith is more accelerated, &c.

Here the air contributes to the animal and vital heat, as we have seen that it does to the action of fire in combustible and calcinable matters. Animals, which have lungs, and which consequently respire the air, have more heat than those deprived of them; and the more the internal surface of the lungs is extended, and ramified in a greater number of cells, the more it presents greater superficies to the air which the animal draws by inspiration; the more also its blood becomes hotter, the more it communicates heat to all parts of the body it nourishes, and this proportion takes place in all known animals. Birds, relatively to the volume of their body, have lungs considerably more extended than man or quadrupeds. Reptiles, even those with a voice, as frogs, instead of lungs have a simple bladder. Insects which have little or no blood breathe the air only by some pipes, &c. Thus taking the degree of the temperature of the earth for the term of comparison, I have observed that this heat being supposed ten degrees, that of birds was nearly thirty-three, that of some quadrupeds more than thirty-one and a half, that of man thirty and a half, or thirty-one, whereas that of frogs is only fifteen or sixteen, and that of fishes and insects only eleven or twelve, which is nearly the same as that of vegetables. Thus the degree of heat in man and animals depends on the force and extent of the lungs; these are the bellows of the animal machine: the only difficulty is to conceive how they carry the air on the fire which animates us, a fire whose focus seems to be indeterminate; a fire that has not even been qualified with this name, because it is without flame or any apparent smoke, and its heat is only moderate and uniform. However, if we consider that heat and fire are effects, and even elements of the same class; that heat rarefies air, and, by extending its spring, it may render it without effect; we may imagine, that the air drawn by our lungs being greatly rarefied, loses its spring in the bronchiæ and little vesicles, where it is soon destroyed by the arterial and venous blood, for these blood-vessels are separated from the pulmonary vesicles by such thin divisions that the air easily passes into the blood, where it produces the same effect as upon common fire, because the heat of this blood is more than sufficient to destroy the elasticity of the particles of air, and to drag them under this new form into all the roads of circulation. The fire of the animal body differs from common fire only in more or less; the degree of heat is less, hence there is no flame, because the vapours, which represent the smoke, have not heat enough to inflame; every other effect is the same: the respiration of a young animal absorbs as much air as the light of a candle, for if inclosed in vessels of equal capacities, the animal dies in the same time as the candle extinguishes: nothing can more evidently demonstrate that the fire of the animal and that of the candle are not of the same class but of the same nature, and to which the assistance of the air is equally necessary.

Vegetables, and most insects, instead of lungs, have only aspiratory tubes, by which they pump up the air that is necessary for them; it passes in very sensible balls into the pith of the vine. This air is not only pumped up by the roots but often even by the leaves, and forms a very essential part of the food of the vegetable which assimilates, fixes, and preserves it. Experience fully confirms all we have advanced on this subject, and that all combustible matters contain a considerable quantity of fixed air, as do also all animals and vegetables, and all their parts, and the waste which proceeds therefrom; and that the greatest number likewise include a certain quantity of elastic air. And, notwithstanding the chimerical ideas of some chemists, respecting phlogiston, there does not remain the smallest doubt but that fire or light produces, with the assistance of air, all the effects thereof.