﻿250 M. G. Quincke on the Capillary Phenomena 



An air-bubble in water under a moistened horizontal plane 

 glass has the same form as a drop of water on a horizontal base 

 which it does not wet at all— for example, on a woollen cloth or 

 a glass plate sprinkled with lycopodium-powder. 



If the vertical distance — (K— h) of the lowest point of an 

 air-bubble from the vertical meridional element of its surface be 

 measured, « 2 is obtained ; if the distance — K of the extremity 

 of the air-bubble from the horizontal glass plate perfectly wetted 

 with liquid 2, then a qS /2 is obtained. 



This gives a method by which the capillary-constants of transpa- 

 rent liquids may be determined which has this great advantage — 

 that the liquid in question only comes into contact with air, and 

 the free liquid-surface is protected as much as possible from im- 

 purities, which even in small quantities, as I shall afterwards 

 show, may cause the tension of the surface or capillary-constant 

 to appear considerably too small. 



4. In order to compare the capillary-constants of liquids 

 examined according to other methods with those derived from 

 the observation of capillary heights h, the following method was 

 adopted. 



By means of a glass-blower's lamp threads of suitable thick- 

 ness were drawn out of a thicker glass tube purified as much as 

 possible; the upper ends were melted together, aud passed 

 through two caoutchouc rings, by which the capillary tube which 

 was formed by the threads was held fast to a strip of plate glass 

 10 millims. broad and from 100 to (500 millims. in length. A 

 scale of millimetres was etched on the strip of plate glass, which 

 simultaneously with the lower end of the capillary tube was 

 immersed in the liquid under examination. The height h to which 

 the latter rose above the horizontal level of the liquid after the 

 closed top of the capillary tube was cut off, was read on the 

 scale by means of a horizontal telescope ; the capillary tube was 

 cut with a glass knife at the place of the meniscus fluid surface, 

 and the greatest and least diameters of the sectional surface were 

 determined by means of a microscope with an eye-glass micro- 

 meter. The latter had a scale of 100 divisions, of which tenths 

 could be estimated. One division of the scale corresponded to a 

 magnitude of from 0*007 to 0*001 millim., according to the 

 magnifying-power used. The means of the estimated values 

 of the diameters of the tubes are given in the following Tables 

 under 2r. The last column contains the product 



Ar = tf 9 cos&> « . (11) 



I have neglected to apply a correction to the observed heights 

 on account of the meniscus, as other unavoidable sources of error 

 have a much greater influence than this correction. 



