Capillary tubes, ascent

Page 27. Capillary attraction or repulsion is the cause which determines the ascent or descent of a fluid in a capillary tube. If a piece of thermometer tubing, open at each end, be plunged into water, the latter will instantly rise in the tube considerably above its external level. If, on the other hand, the tube be plunged into mercury, a repulsion instead of attraction will be exhibited, and the level of the mercury will be lower in the tube than it is outside. 

Lucas found for the rate of ascent of a liquid in. a capillary tube to height h in time t, h ==(alrj)(rI2)t cos a, if a is the contact angle and rj the viscosity. RideaF found that the rate of penetration of a liquid into a capillary tube depends on the surface tension a and viscosity 97, the time t for a distance X in a horizontal tube of radius r with a liquid of density q being given by ... 

Valsonio applied a law of moduli, based on his results for densities ( 4. VIIIB), to the effect that the ascent of equivalent solutions of salts in the same capillary tube is the sum of two constants, one depending on the metal and the other on the, acid radical. VolkmannH found, however, that the product of capillary rise and density of the solutions used was practically constant, and Valson s results imply equal surface tensions, so that his law really concerns only the densities of equivalent solutions. Further measurements of the surface tensions of salt solutionsgave similar general results the value of a for the... 

L=l,o-(PolQg) (PolP) l —gft,. (9) where gg=density of vapour and /i=height of ascent of liquid in the capillary tube. 

Arrhenius s viscosity formulae, 98, 122 ascent of liquid in capillary tube, 175 ... 

Jurin s law describes the spontaneous ascent of a liquid up a fine capillary tube (radius R < n ) (see Fig. 1.10). Dip the end of an extremely clean glass capillary tube (cleaned with sulfochromic acid) into water. The water will rise up to a height h and, as the water totally wets the glass, the meniscus will be hemispherical. The pressure at point A, just inside the liquid, can be calculated using Laplace s formula. If Pq is the outside pressure, then... 

Fig. 1.10. Ascent of a liquid in a capillary tube, (a) Total wetting (b) partial wetting with < 7t/2, the liquid is said to be wetting (c) partial wetting with Oe > tt/2, the liquid is said to be non-wetting ...

First of all the capillary is filled as normal with closed ventilation tube as shown in Fig. 3.14a. Afterwards the filling tube is to be closed (Fig. 3.14b), then the ventilation tube is to be opened and slight pressure has to be applied on the capillary tube manually (with a pipette filler for example). The bubbles have to be driven into the ventilation tube carefully so that the capillary is free of bubbles. It is important to assure that the meniscus in the capillary tube reaches the opening of the ventilation tube, but does not fall below the opening so that the bubbles can ascent into the ventilation tube completely. Afterwards the ventilation tube has to be closed and the capillary has to be refilled with bubble free solution from the reservoir... 

Capillary action The action by which the surface of a liquid,where if contacfs a solid, is elevated or depressed because of the relative attractions of fhe molecules of the liquid for each other and for the solid. It is particularly observable in capillary tubes, where it determines the ascent (descent) of fhe liquid above (below) fhe level of the liquid in which the capillary tube is immersed. 

J. Jurin, An account of some experiments shown before the Royal Society with an enquiiy into the cause of the ascent and suspension of water in capillary tubes, Philos. Trans., 30,739 (1717). 

The black spots on soap films, which are not more than 10 to 20 molecules thick, can remain for weeks in equilibrium with the thicker, coloured parts of the film,4 and hence it is assumed that they have the same vapour pressure as the normal liquid, and that Thomson s formula can be applied for a radius of curvature of 200 x 10 cm. or less. Bakker<5 gave reasons for supposing that the surface tension is independent of the radius of curvature of the capillary layer, although he recognised that in very thin films it has abnormal values, and he calculated that the maximum ascent of a liquid occurs in a tube of 2 5 m[jL radius. Woodland and Mack found no change of surface tension in a tube of 6 7 [I radius. 

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