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is certain, and it is to this repulsion that we may attribute the movement which takes to the surface of the water all the floating bodies, which are there dissolved ; this is what is observed not only in the alkalies, the acids, and the salts, but also in certain gum-resinous substances, such as opium, succotrine aloes, &c. We now come to the movement which takes place of oily or resinous bodies on water.
12. A drop of the essential oil of turpentine or of lavender, thrown on the surface of the water, spreads itself rapidly there, in a lamina so thin, that it reflects the colours of the iris; a second drop does not produce the same effect. The fixed oils present a similar phenomenon when they are not too viscous. Thus, for example, the oil of wild cabbage, which is very viscous, does not spread on the surface of water; but when it is rendered more fluid by purification, which renders it fit for being used for lighting, it spreads itself very well on the surface of the water. This phenomenon does not always take place with the first drop; the second drop preserves its globular form at the surface of the water. Having one of these gross drops of fixed oil floating in the water, I have deposited gently in its centre a drop of the essential oil of turpentine; this gradually pierced through the thickness of the drop of fixed oil, as if it was attracted by the subjacent water, and at the moment of its contact with the water it made a sort of explosion, by projecting circularly its substance on the surface of the water ; chasing before it in a circular movement the fixed oil which imprisoned it, and which after this explosion, returned on itself, so as to form itself anew into a drop. The cause of this centrifugal movement is exactly the same as that which has been determined above with relation to soluble bodies. The solution, considered in its latter limits, is, in fact, only the reunion of molecule with molecule of the liquid dissolving and of the body dissolved. We then have the penetration of the dissolving liquid until this end is obtained. But if the dissolving liquid and the body to be dissolved are not miscible, then there will be no penetration of liquid, and the solution only operates at its surface. This is what takes place with oils brought into contact with water. The drop of oil, which by a centrifugal movement, extends itself on the water in a thin and irisated lamina, here presents, in fact, the phenomenon of the solution considered in its latter limits, that is to say, the reunion, side by side, of each molecule of water at the surface, with the molecule of oil. In the action of this superficial and non-penetrating solution, we observe, as in all the solutions which have the property of penetration, a movement of repulsive projection, parting centrally from the body which is being dissolved, by projecting around it its own substance. Here it is each molecule of oil which repels the neighbouring ones, in such a manner that a circular projection is the result of this assemblage of repulsions. If a second drop of fixed oil projected on the water does not produce the same phenomenon as the first, it is because it has saturated the surface of the water ; but this saturation of fixed oil does not hinder the subsequent solution of a drop of essential oil. The oil, by thus
rapidly invading the surface of the water, mechanically chases before it the light bodies which float on the surface of this liquid, as we have just seen that the drop of essential oil chases around it the drop of gross fixed oil which imprisoned it. This propulsion of floating bodies is quite mechanical; it is not repulsion in the sense generally attached to that word; the true repulsion exist here only between the molecules of the oil. These observations directly conduct us to the study of the movements of camphor on water.
13. Camphor is an essential oil concreted; it ought then to offer the same phenomena as the essential oils upon its contact with water, with this difference, always: that it is not in the state of an oily liquid that it unites at the surface of the water, but much in the state of oily vapour, which is in reality the same thing. This inanner of viewing this phenomenon conciliates the opinions of Benedict Prévost and of Carrodori, whose opinions represent, each in part, a part of the truth. The oily vapour of camphor becoming united to the surface of the water and undergoing an active molecular repulsion in the action of this superficial solution, extends itself rapidly on the surface of these liquids, by chasing before it all the light and Aoating bodies which it there encounters. This apparent repulsion, which is in fact only a propulsion, is often extended to a distance of more than thirty millimetres around the piece of camphor. If we project on the water a drop of essential or fixed oil, this oil invades the surface of the water in preference to the vapour of camphor, and the latter instantly ceases its movement. We here have a phenomenon of elective affinity. The surface of the water becomes saturated with the fixed or essential oil, and from that time is no longer susceptible of dissolving the vapour of camphor; it is sufficient even that the air be charged with the odour of an essential oil, or of any odour whatever, to present an obstacle to the movement of camphor or water; and that because of the odorous vapour being dissolved on the surface of water in preference to the vapour of camphor. When the air is highly charged with the vapour of camphor, the movement of the latter on water is equally arrested, and that because the surface of the water saturates itself completely with this vapour. We now see why the movement of camphor is arrested when the vase which contains the water in which it moves is covered. It is necessary that the vapour of camphor dissolved by the surface of the water be able to evaporate freely and promptly, in order to give up its place to a new dissolution.
14. When it happens that a small fragment of camphor, which is moving on the surface of the water, becomes divided into two parcels, these two pieces repel each other with extreme vivacity at the moment of their separation. This effect is due to the expansion, or to the molecular repulsion of the vapour of camphor interposed between these two pieces. We can perfectly conceive, that in the expansion of the vapour of camphor at the surface of the water, it meets with a resistance on the part of this liquid which ought to
induce a reaction against the piece of camphor, and the latter ought consequently to move by the effect of recoil. Now, it is not on this cause alone that the movement of camphor placed on the surface of water depends; the most powerful cause, and the most important in consideration in the production of this phenomenon has hitherto escaped observation. We now proceed to observe the developement of physical phenomena whose existence has been far beyond our suspicion. I shall now resort to experiment.
15. I put a small quantity of water in a watch glass; it amounted to two or three millimetres in height, and I placed on this water a piece of camphor less than half a millemeter in diameter. This piece of camphor, confined in a small space, was not long in gaining the side of the water, and it there remained fixed, agitated solely by a trembling movement. I submitted it to the microscope, employing the feeble magnifying power of ten times its diameter, which enabled me to perceive a field of seven or eight millimetres of diametrical extent. I then added to the water a drop of muddy water, holding particles of white clay in suspension. 'Instantly a curious phenomenon was presented to my observation. The particles of the clay were observed to be precipitated towards the piece of camphor; the current which they formed, having arrived in the neighbourhood of the camphor, then divided into two currents, one of which was directed towards the right and the other towards the left; that is to say, towards the two opposite extremities of the piece of camphor; there they undergo a sudden repulsion, and retreat from each other with a quickness which gradually diminishes. On arriving at three or four millimetres distance from each other, they describe a curve which brings them back into the flowing current, and they are, now, again precipitated towards the camphor which attracts them, and impresses on them an accellerated movement. There is thus established two vortices, directed in inverse directions, and in each of which the terreous particles in suspension undergo a real circulation which operates in an ovoïde curve, the smaller end of which is near the camphor, and the larger end at that part opposed to this curve. Thus the two actions of attraction and of repulsion which the terreous particles undergo are not exercised in right lines, but following the two parts opposed to an ovoïde curve more or less elongated. We observe that the repulsion takes place at a small distance from the camphor, in such a manner that the particles of clay are repulsed by it without having touched it. This repulsion takes place at a distance from the camphor which I value as to of a millimetre, and sometimes at 3 or of a millimetre at most.
16. I have rendered these phenomena still more easy to be observed by replacing the terreous particles in suspension by the yellow and flocky precipitate which is formed in the solution of sulphate of iron in water. In that case, in place of adding, as in the preceding case, a drop of muddy water to that contained in the watch glass, I here add a drop of the solution of sulphate of iron, highly
charged with the flocky precipitate of which I have just spoken. The fleeces of this precipitate, by reason of their size, are more easily observed than the particles of clay. It happens sometimes that these flocks suspended in water, in place of describing in their movement the ovoïde curves of which I have above spoken, rest near the piece of camphor, and there, at I of a millimetre distant from this piece, they present a rapid rotatory movement on themselves, and on a horizontal axis, sometimes in one direction and sometimes in an opposite one. There is here, however, no change in the direction of the rotation; when that is established in one direction it persists in it. There exists then at one or two tenths of a millimetre around the particle of camphor a rotatory moving force, the direction of which is not the same at all points of its periphery; the corpuscles floating in the water, and which are attracted by the camphor, all receiving on arriving near it, this rotating movement on themselves, whilst at the same time they receive the movement of repulsion. They promptly lose this rotating movement on retreating from it, and that by the effect of the resistance which the water subjects them to by reason of their irregularity of form; they would probably retain this rotatory movement during their revolution, if their form was perfectly spherical. As for the rest, it is evident that the rotation of the corpuscles themselves and their revolution in a limited curve, are two modifications of the same phenomenon. In fact, the two moities of the revolution, the first of which is due to attraction and the second to repulsion, are, in relation to each other, just the same as the two moities of the rotation are to each other: of which the first, which is analogous to that moiety of the revolution due to attraction, commences at that part of the turning body actually opposed to the camphor, and finished in regard to the latter; and the second, analogous to that moiety of the revolution due to repulsion, commences with regard to the camphor, and finishes at the opposite place.
17. It results from these observations that the movement of rotation is here a modification of the movement of revolution. The cause of these two movements is the same. Another result, also, is that the attraction and repulsion are here the two opposite directions of the same force, which are exercised according to a limited or closed curve,-a curve whose greater axis corresponds by one of its extremities with the neighbourhood of the body in which is found the origin of this force.
18. Hitherto I have not studied the movements which the camphor impinges on the particles suspended in the water, and that thus it only acts on this liquid upon one of its sides. It was important to observe what happened when the camphor is situated on the surface of the water which environs it circularly. It is not easy to make this observation with the microscope, because the piece of camphor placed on water is generally animated by a progressive movement. But it often happens that this progressive movement, after having lasted for some time, ceases; the piece of camphor may
then rest in its place in the middle of the water, being agitated solely by a slight trembling movement. We may then easily observe by the microscope the effects which it produces. We do not see in this case the two vortices, with opposite directions, which are constantly observed in the movements of light bodies suspended in the water, when the camphor is fixed at the edge of the liquid; we then see these light bodies precipitated equally on all sides on the piece of trembling camphor, and they there receive also the movement of repulsion which always takes place in a different direction to that in which is produced their movement of attraction, in such a manner that in returning incessantly towards the camphor, from which they afterwards retreat, they describe limited and ovoïde curves which are extremely multiplied, and which appear to cross each other in all directions. I have also observed, in this case, the movement of rotation of large focks situated at a very small distance from the camphor. I put water charged with argillous particles in suspension in a saucer, and at the height of some millimetres, I suffered the argillous particles to be precipitated to the bottom of the water; I then put a piece of camphor on the surface of this liquid, now become limpid. On observing it through a magnifier, I saw the pulverated argillous sediment raised from the bottom of the vessel, especially in those parts where the piece of camphor was transported to, and when the latter remained in one place by turning on itself, the argillous sediment being raised by its attraction turned with it, thus forming a sort of small truncated waterspout whose base is at the bottom of the vessel.
19. On the inspection of these phenomena, no one will doubt that they are due to electricity; but we may be permitted to ask, if these same phenomena are explicable by means of any facts known to science. The attraction and repulsion of light bodies only belongs to static electricity, again they produce this effect in the air only, and not at all in water. Some phenomena of rotation are produced under several circumstances by electro-magnetism; but in the experiments here under consideration, the phenomena of rotation takes place without the intervention of magnetism. I ought, however, to abstain from pronouncing on this question, and I will now pursue my observations.
20. The actions of attraction and repulsion which camphor exercises on light bodies floating in water, are here the indices that these same actions are exercised on the water itself; they are, then, the principal causes of movement whiclı are presented by camphor; it attracts and repulses alternately the water which surrounds it; it ought to be moved then, at the same time as the water, and even more than it, since it is more moveable. It is from the rapid and continual succession of these two opposite actions that the trembling movement presented by camphor results; its turning ought to be attributed according to my observations, to the fact that the piece of camphor, when turning, possesses a lateral point, on which the electric repulsive effluvia especially operates; and which, by reaction