CAPILLARY ATTII ACT ION, from (Villas, "a hair," is properly that force by which water, or any other fluid, is raised above its level in glass tubes, whose diameter does not exceed that of a hair. It is now employed in a more gelieral sense, to denote that force with which so lids act upon fluids, either in raising them above, or de pressing them below, their natural level, when the Win is simply immersed in the fluid, or when the fluid is in cluded in a tube, or between two plates formed from the solid. In attempting to give as complete a view of this interesting portion of physics as the limits of our work will permit, we shall direct our readers attention to the different phenomena of capillary attraction, as they have been ascertained by direct experiment, and to the dif ferent theories by which these phenomena have been ex plained.
Phenomena of CapWary ?Ittraction.
Exii. I. If water, or any other fluid, excepting mer cury and the metals in a fluid state, be poured into a clean vessel, the fluid in contact with the sides of the vessel will be raised above the level of the fluid in the middle of the vessel, and the fluid surface will be terminated by an elevated ring of fluid. See Plate CX. Fig. I, where A B arc the sides of the vessel, and c, d, the elevated fluid.
Exp. 2. if a solid body is immersed in a fluid, the fluid will he raised round the sides of the solid, as in Fig. 2, where S is the solid, and c d the elevated fluids.
These phenomena may be seen most distinctly, by viewing the image of fi rectilineal object, seen by reflec tion from the fluid surface. The rectilineal image will indicate, by its change of form, the magnitude and ex tent of the elevated ring.
Exp. 3. If the fluid, used in experiments 1 and 2, is mercury, or any metal in a state of fusion, the fluid in contact with the sides of the vessel in Exp. 1, or with the sides of the solid body in Exp. 2, will be depressed be low the general level, as is exhibited in Figures 3d and 4th.
Exp. 4. If a glass tube A, whose internal diameter or bore is less than the loth of an inch, be immersed at one end into a fluid in the vessel MN, the fluid will rise to A to a considerable height above the fluid surface. if ano
ther capillary tube B of a greater bore is immersed in the same fluid, the fluid will also rise in the tube above its level, but not to such a height as in the tube A. By comparing the heights of the fluid in the two tubes, with the diameters of their bores, it is found that the heights are inversely as the diameters. That is, if I) be the diamm ter of the larger tube DB, d the diameter of the smaller tube CA, A the altitude of the fluid in the for mer, and a its altitude in the latter, we shall have A:a= d: D, and consequeialv AD=ad. I knee it follows, that the product formed by multiplying the diameter of any capillary tube, by the altitude to which any fluid rises in the tube, is a constant quantity.
The following are the heights to Ivhieli w ate r has been Observed to rise in capillary tubes, reduced to a tube whose diameter is thtli of an inch : The great discrepancy between these results, which amounts to more than a half of the whole altitude, is a most satisfactory proof of the total insufficiency of the method of measurement which was employed.
Es/:. 5. If the preceding experiment is tried with fluids of different kinds, it will be found that they rise to different altitudes. Messrs natty and 'l'remery found, that oil of oranges rose 6.74 thousandths of a metre, in a tube whose diameter was one thousandth of a metre, which reduced to a tube of an inch in diameter, gives only 1.0447 inch, or 0.010447 for the constant quantity. Mr Benjamin Martin made a variety of experiments on different fluids, with a tube of an inch in diameter, and obtained the following results.
Exp. 6. If tubes of different lengths are employed, the fluid will never ascend to the top of the tube, how ever short. Thus in Plate CX. Fig. 5. if the tube AC is broken off at P, the fluid will stand atp below the top P, though it formerly rose as high as A. We have tried this experiment repeatedly with a tube 0.36 of an inch long, and 0.043 in diameter, and have found that the fluid always rises to the very top of the tube.