Messrs Hauy and Tremery likewise observed the height to which water ascended between two parallel plates of glass placed vertically, at the distance of 1 millimetre, and obtained the following result : The constant quantity is here 14.51, or 0.02251, when reduced to English inches, for a distance of of an inch.
It is obvious from these experiments, that water as cends to twice the distance in capillary tubes that it does between two plates, whose distance is equal to the diameter of the tube.
We have already seen, under CAPILLARY ATTRACTION, that if the two plates of glass are inclined to each other at a small angle, the water will rise between them in such a manner that its surface is a hyperbola. Thus, in Plate CCCXVI. Fig. 4. let ABEF, CDEF be the two plates of glass, and DE the surface of the water, then E n p D, E in o B will be the surface of the fluid, which Mr Hawks bee found to be hyperbolic, by measuring the ordinates of abscissx of the curves.• The hyperbolic form of the surface may be deduced from the observed fact, that the altitudes of the fluids in capillary tubes, or between parallel glass plates, are in versely as the diameters of the tubes, or the distance of the plates. The distance of the plates at m is obviously m n, or s t, and their distance at o is o p or g r. But in s and o q, being the altitudes of the fluid at m and o, we have 7ns:oq=op:mn,butF t:Fr=storinn:qr, orop. Hence F t :Fr= inn : But in the Apollonian hy perbola, the ordinates are inversely proportioned to their respective abscissa:, and therefore E m o B is the Apollo nian hyperbola. Mr Hawksbee's experiments have already been given in p. 809.
If a capillary tube of glass is immersed in mercury, or any of the metals in a fluid state, the metallic fluid, in stead of being elevated like water, stands considerably lower in the tube than in its natural surface. The most correct experiments on the depression of mercury were made by Lord Charles Cavendish. The following are the results which he obtained : The ultimate product or constant quantity inferred by Dr T. Young from Lord C. Cavendish's experiments is 0.015, whereas Hauy's experiments make it 0.01137.
The results of the experiments of Gellert have already been given in p. 811.
Water suffers also a depreSsion like mercury in tubes of glass that have been coated with grease. This was first observed by Carve, and was afterwards verified by the ex periments of Cigna and Dutour.
M. Dutour took two tubes, each of which was about two lines in diameter, and having lined one of them with a thin film of wax, and the other with grease, he plunged them about four lines deep in water. The water was depressed in both the tubes, but less in the first than in the second.
In our article ADHESION, we have already given an ac count of the experiments of Taylor, Morveau, Achard, and Dutour.
The following results were obtained by M. Gay Lussac for a circular plate of white glass, with water, alcohol, and oil of turpentine.
M. Gay Lussac made many experiments, on the adhe sion of a disc of glass to mercury, but the results which he obtained differed widely from one another. In making his experiments on the adhesion of discs of glass, the disc was suspended at one scale of a balance, and raised ver tically by placing, successively and slowly, small weights in the other scale. The sum of these weights at the mo ment when the disc detached itself, indicated the force of adhesion. In making these experiments on mercury, how ever, he observed, that the sum of the weights was more or less great according to the slowness with which they were successively added ; and in adding them at very great intervals, the sum varied from 158 grammes to 296 gram mes for a disc 118.366 millimetres in diameter.
Besile found, that the adhesion of 25 square lines of mercury was 82 French grains, while that of the same surface of water was 81 grains. In some cases, he found that the apparent adhesion was diminished under the ex hausted receiver of an air pump.
The effect of the cohesion of fluids is very finely ex emplified in the formation of drops. It is obvious, that drops of fluids that have the least force of cohesion, will have the least magnitude, provided their specific gravities are the saute ; for the effect of the force of cohesion must be diminished by the weight of the drop which will be sooner detached, and therefore of a less magnitude, than if the fluid had less weight. Dr Young infers, from the law of the superficial cohesion of fluids, 44 that the linear dimen sions of similar drops depending from a horizontal surface, must vary precisely in the same ratio as the heights of ascent of the respective fluids against a vertical surface, or as the square roots of the heights of ascent in a given tube. Hence the magnitudes of similar drops of different fluids must vary as the cubes of the square loots of the heights of ascent in a tube." In water, for example, Dr Young found the weight of a drop to be 1.8 grains, and the weight of a drop of diluted alcohol 0.85 of a grain ; whereas the height of the same alcohol was to the height of water in the same tube as 100 to 64. The weight of the drop should have been .82, as inferred from the consideration of the heights of ascent combined with that of the specific gravities. This result is widely different from that which was obtained by Dr Brewster (See p. 742.) with his capil lary hydrometer. The magnitude of a drop of water was to the magnitude of a drop of spirit nearly proof as 2.93 to 1 ; and, therefore, taking the specific gravity of spirit at 0.920, the weights of the drops were to one another as 3.255 to 1, or as 100 to 31 nearly.