He next took three pieces of camphor, each of which weighed twenty-four grains, and he placed one of them in dry air, another in water, and the third on the surface of water. After four days the piece on the surface of the water was entirely dissipated, while each of the other two had lost only four or five grains.
M. Venturi next placed some of his camphor cylinders on the surface of water, in vessels of different sizes, and he always found that the cylinder was cut through soonest in those vessels that presented the greatest surface. This singular fact arises from the camphor being dissolved by the water, and extending itself over all the fluid surface, when it is the more readily evaporated by its coming into contact with a greater quantity of air. The dissolution of the camphor may be seen detaching itself from the cylin der in the form of a very transparent liquid oil, and spread ing itself over the whole surface of the water. When in the contour of the cylinder, there is some place which fur nishes this oil more abundantly, if small light substances are thrown upon the surface, they are repelled from this place with great briskness, and then turning round, they come back to the same place, and again enter the current, where they continue to circulate in this manner. If a small piece of camphor previously wetted at its extremity ap proaches the margin of the vessel, and then touches the vessel itself, it deposits a visible to the eye. This fluid is oily ; and on attaching itself to the vessel, it de stroys its capillary attraction for the water, and the water retires from it and becomes convex at this place. When the piece of camphor is taken away, the water does not re turn to its place till the oily liquor is evaporated. When the cylinders of camphor are half immersed in water, the oily liquor which issues from it destroys the cohesion be tween the water and the cylinder, and a small depression takes place round the cylinder. The dissolution stops for a moment till the oily liquor expanded over the water has evaporated. The water then returns to its elevated state round the cylinder ; the camphor is dissolved and diffused; and the same operations are repeated.
The motions of small pieces of camphor observed by M. Romieu are produced by the mechanical re-action of the jet of dissolution against the camphor ; and if the centre of percussion of all the jets do not coincide with the centre of gravity, a rotatory and progressive motion will be produc ed. As the jets are generated only on the circumference
of the section of the piece of camphor, it ought to revolve round an axis perpendicular to the horizon; and the smallest pieces will obviously turn round with more velocity than larger ones.
i'slM. Lichtenburg and Volta ascribed this rotation to an emanation from the camphor, and also from the benzoic and succinic acids, which have the same property. Brug natelli discovered, that the bark of aromatic plants, when thrown upon water, moved round like camphor ; and Ven turi remarked a similar motion in the saw-dust of different woods, that had imbibed either a fixed or a volatile oil. Romieu ascribed these motions to electricity. He found that the camphor sometimes refused to turn, and at other times its movements were suddenly stopped, by touching the water with particular bodies. The cause of these irregularities, which long perplexed philosopliet s, was dis covered by Venturi. He found, that whenever the water was touched by any body which was fat or oily, or which diffused a small portion of fixed oil, or a great portion of volatile oil over the surface, the dissolution and the motion of the camphor were immediately stopped. In order to prove that this effect was not produced by electricity, as Romieu and several Italian philosophers believed, Venturi touched the surface of the water both with conductors and non-conductors of electricity, which were well cleared of all oily or greasy matter, and the motions of the camphor were never in the slightest degree affected. When the same substance was afterwards greased with a small drop of oil of olives, and again brought into contact with the water, an oily film immediately advanced over the whole surface of the water, repelled the small bits of camphor, and, as if by a magic stroke, deprived them of their appa rent vitality. Venturi repeated this experiment in a basin of water 20 feet in diameter.• The camphor turned round in one end of the basin ; and when an ounce of oil was pour ed in at the other extremity, the motions of the camphor were speedily stopped.