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GUARDIAN OF EXPERIMENTAL SCIENCE.
Abstract of a Memoir read at the Sitting of the French National
Institute, on the 26th Pluviose, containing an account of some Experiments concerning the Section which Cylinders of Camphor undergo at the Surface of Water ; with Reflections on the Motions which accompany this Section.* By J. B. Venturi. "
Romieu formerly observed that small pieces of camphor have a progressive and rotatory motion upon water, and attributed this effect to electricity. Lichtenberg attributed it to the emanation of an etherial spirit from the camphor itself. Volta produced the same motion of turning by throwing upon water small bodies soaked in ether, or particles of the acids of benzoin and amber. Brugnatelli found that the bark of aromatic plants moves on the surface of water like camphor. There was always a certain mysterious caprice in these motions, according to which they sometimes could not be produced; and on other occasions the motions were instantly stopped when the water was touched with certain bodies, without its being easy to guess the reason. When particles of camphor were fixed to the extremity of a very delicate electrical fly, they produced no motion. All these circumstances tended to envelope the phenomenon with obscurity. Other philosophers in Italy constantly supported the opinion of Romieu in their publications. Citizen Venturi communicated his notions on these facts two years ago at one of the public sittings of the Literary Society of Modena, his country. He was present at the sitting of the National Institute on the 21st Pluviose, when a memoir of Citizen Prevost on the emanations of odorant bodies was read. I He announced the observations he had made;
• This paper has been pointed out to us, as a suitable accompanyment to that by M. Dutrochet, in our last number.-Edit.
† Annales de Chimie, XXI, 262. Philosophical Journal, 1, 153. Ann. of Elec. Vol. IIIV. No. 48, June, 1842.
and in consequence of an invitation to that purpose, he communicated a memoir of which the following is an abstract :
Pieces of camphor were cut into the form of small columns, one inch in length ; a base of lead was fixed to each column; they were then placed upright in very clean saucers, and pure water poured in, to half the height of the column. Two or three hours afterwards, a horizontal notch was manifest in the column of camphor at the surface of the water ; in the course of twenty-four hours, or thereabouts, by the notch becoming gradually deeper, the column of camphor was cut in two at the middle. The two pieces of the column, nevertheless, that is to say, the lower, which was immersed in the water, and the upper, in the air, suffered scarcely any perceptible diminution.
From this experiment, and others made with different pieces of camphor, kept separately in the air, in the water, and at the surface of the water, the author deduces that the most active virtue for dissolving camphor resides at that part where both the air and the water touch the camphor at the same time. Hence he explains, why, in like circumstances, camphor evaporates more quickly in a moist than in a dry air; and why the Hollanders use water in their process for subliming this substance.
It might be thought that the camphor was decomposed at the surface of the water; that the water might seize the acidifying part which renders the camphor concrete ; and that the volatile part is dissipated in the atmosphere. The author rejects this notion. He thinks that water with camphor floating on its surface becomes charged with no more than a very small portion : 1. Because in these circumstances the water acquires the same taste and smell of camphor as it obtains when a small quantity of this substance is kept plunged in the same fluid. This water, by exposure to the air, loses the qualities with which it had been charged, and becomes insipid and without smell. 2. Because when the water is saturated with all it can take up, the dissipation of the camphor continues at its surface as before. 3. Because the aerial emanations of camphor made at the surface of water, do themselves crystallise into camphor.
Camphor at the surface of the water does nothing, therefore, but dissolve; and when dissolved at the ordinary temperature of the atmosphere, it is not at first in a state of vapour, as has been thought. It is simply a liquid which extends itself over the surface of water itself; and by this means coming into contact with a great surface of air, it is afterwards absorbed and evaporated. This is proved by the following facts : 1. The solution of camphor at the surface of water is more rapid in proportion to the extent of the surface. In narrow vessels, the section of the column would not be completed in a decade (ten days), even though the water might be extremely pure. 2. When the column of camphor has projecting parts, the liquid may be seen issuing by preference from certain points of the column, covering the surface of the water, and driving small floating bodies
before it, in the same manner as floating bodies go and return in a basin into which the water of a canal enters with rapidity. 3. If a small piece of camphor, already wetted at one end, be brought near the edge of water contained in a broad saucer, and be made to touch the saucer itself, it deposits a visible liquor, which is oily, and by attaching itself to the saucer destroys the adhesion between the vessel and the border of the water; so that the water retires on account of the affinity of aggregation, which not being opposed by the attraction of the saucer, causes the water to terminate in a round edge. If you remove the piece of camphor the water will not return to its place until the oily Auid is evaporated. 4. In the same manner, when the column of camphor is half immersed in the water, the oily liquor which issues forth destroys the adhesion of the water to the column, and produces a small surrounding cavity. The solution stops, or is retarded for a moment, until the Auid, extending itself over the water, becomes evaporated : the water then returns to its place, and touches the same part of the camphor ; the solution begins again, and in this manner the process is effected by alternations of contact and apparent repulsion.
The rotation of small pieces of camphor at the surface of the water, is simply the mechanical effect of the re-action which the oily liquor, extending itself upon the water, exercises against the camphor itself. If the retro-active centre of percussion of all the jets do not coincide with the centre of gravity, a combined motion of rotation and progression must follow. Since the departure of the oily solư: tion takes place only at the surface of the water, the rotation cannot be effected but round an axis perpendicular to the horizon; and since in similar bodies of different magnitudes the algebraic ratio of the sides to the mass increases in the inverse duplicate ratio of the sides themselves,* the small particles must have proportionally more jets and must revolve more speedily than the larger.
The author reduces to one general rule all the apparent irregularities observable in the motions of the camphor. When these small parts are briskly moved at the surface of the water, if you touch this Auid with any other body, whether conductor or non-conductor of electricity, is of no consequence, provided it be well cleaned from every oily substance, in this case the motion of the camphor will not be affected. But if the same body be afterwards greased by a small drop of fixed oil, or a greater quantity of volatile oil, and then applied to the water at one extremity of the plate, you will discern a scarcely perceptible film advancing at that instant over the whole surface of the water, which will repel the small morsels of camphor, and, as if by a stroke of magic, deprive them of their motion and vivacity. One ounce of oil, poured on one extremity of a bason of
So in the original. In truth, the sides of like solids are in the inverse triplicate ratio of their solidities. This oversight of the ingenious author does not impair his deduction with regard to the velocities of rotation. N.