372 



observed wavS H,,, = 1.230 wliicli gives: 



Ö = 427 (I + 0,028 — 0,003) — 438 

 When (he tube was filled to a smaller height and then left to 

 itself, the drop could be seen to bulge out more and more and 

 finally give way in consequence of the diminution of o. 



§ 9. When in a capillary tube, in which a liquid ascends, pressure 

 is exerted by means of a compressed gas, so that the meniscus is 

 forced down, until a gas bubble is formed at the bottom of the 

 capillary, the bubble is found to escape at a definite maximum value 

 of the difference between tiie gas-pressure and the hydrostatic pressure 

 at the bottom of the capillary. From this maximum of the pressure- 

 difference the surface-tension of (he liquid (in contact with the gas) 

 may be derived ^). 



The phenomenon is of entirely the same nature as the one described 



in § 5 and the theory may be developed in the same manner"). If 



2 

 H represents the said difference of pressure, whereas A = — - again 



repiesents the capillary pressure at (lie lowest point of the meniscus 

 and y (he height of (he bubble, then, as in § 5, H = h -\- i/ and, 

 as k and R are also positive, the same equations are obtained in 

 this case as in section 5 '). 



In this case h also obtains a maximum-value, which might also 

 be used as the basis for a determination of the surface-tension; in 

 that case eq. (4) would again apply. But the measurement of H is 

 simpler than that of h and therefore preferable from a practical 

 point of view. 



§ 10. Several observers have derived surface tensions from measure- 



^) The first to use this method was Simon (Ann. d. ch. et d. phys. (3), 32, 5, 

 1851), who assumed without sufficient proof, that tlie maximum pressure-difference 

 is determhied by the capillary rise, which is only correct for very narrow tubes. 

 Simon's method was used by several other, experimenters later on (see Winkelmann, 

 I.e., p. 1162). 



3) See also: M. Cantor. Ann. d. Phys. (3), 47 (1892) p. 418; R. Feustel. Ann. 

 d. Phys. (4), 16 (1905; p. 61; A. F^erguson, Pliil. Mag., 28, 1914 p. 13% and 

 E. ScHRÖDiNGER, AuH. d. Phys., (4), 46 (1915) p. 413. 



h In accordance with what was found by SghrOdinger, (1 c)- It is not astonishing 

 that Cantor, Feustel and Ferguson find an incorrect expression for the second 

 correction-term in these equations, seeing that — apart from errors of calculation 

 by Cantor and Ferguson — the authors in their reductions assume a spherical 

 shape for the drop, although tlie second correction-term is actually determined by 

 the deviation from the spherical shape. 



