Measuring the Surface- Tension of Liquids. 387 



contact-angle in some cases in which the wall is wet by the 

 liquid. In support of this assertion he gives the result of a 

 large number of measurements of bubbles and drops, from 

 which the surface-tension is found to be considerably greater 

 than the values found from the measurement of elevations in 

 capillary tubes. For water at 25° C. the mean of a small 

 number of measurements, which differ from each other by 

 ten per cent, in some cases, gives'* T = 81 dynes (84*5 at zero). 

 Worthingtonj points out that Quincke's formula is only 

 roughly approximate under the conditions of his measure- 

 ments, and recalculates some of his results. The number 81 

 is thus reduced to 72*1 (75*6 at zero). MagieJ prefers the 

 value 77*6 (81'1 at zero), calculating from the same data. 

 From his own measurements of drops and air-bubbles Magie§ 

 found for water T=71*9 dynes at 22°*5 C. (75\1 at zero). 

 TimbergH from similar measurements found T = 80'5 — *182£ 

 for water. BravaisH and others have used the same method 

 for other liquids. The discussion regarding these results has 

 put a premium on methods which are independent of a contact- 

 angle and whose mathematical relations are undisputed. 



Buys-Ballot**, who made a large number of determinations 

 of the surface-tension of water between 10° and 97 0, 8 0. by 

 adhesion-disks, calls attention to the rapid decrease in the 

 adhesion of the disk as the boiling-point is approached. This 

 is no doubt due to disengagement of vapour near the surface 

 of the disk, and may perhaps be an indication that the water 

 was not completely deprived of air. Buys-Ballot gives 

 T=75'l — '236 £ dynes. Merianff objects both to the calcu- 

 lation and to the. formula used, and calculates from the same 

 data T = 78*5 — *253£. HagenJt finds by this method a result 

 much too low for the tension of pure water. .Weinberg §§ 

 finds T=80'l — "177 1 dynes. Miss Poekels || || obtained some 

 interesting qualitative results with very simple apparatus. 



The surface-tension has been calculated from the weight of 

 drops falling from a small disk or tube of known perimeter by 

 HagenlHT, Timberg***, and others. Quincke ft t found in a 



* Quincke, Pogg. Ann. cxxxix. p. 1 (1870) ; Phil. Mag. April 1871, 

 p. 253. t Phil. Mag. July 1885, p. 51. 



\ Wied. Ann. xxv. p. 437 (1885). § Phil. Mag. Aug. 1888, p. 171. 

 || Wied. Ann. xxx. p. 545 (1887). % Ann. Chim. Phtjs. v. p. 492. 

 *» Pogg. Ann. Ixxi. p. 191 (1847). +t Ibid, lxxiii. p. 485 (1848). 

 X] Ibid, lxxvii. p. 464(1849). 



§§ Beibl. xvi. p. 496 (1892) ; Journ. de Physique, Sept. 1892, p. 378. 

 || || 'Nature,' xliii. p. 437 (March 1891). 

 1JH Pogg. Ann. lxxvii. pp. 449, 456 (1849). 

 *** Wied. Ann. xxx. p. 545 (1887). 

 ttt Pogg. Ann. cxxxv. p. 621 (1868). 



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