138 Capillary Surface inside a Tube of Small Radius. 



§ 9. Whilst discussing the results of capillary- tube ex- 

 periments, attention may be drawn to a recent paper on the 

 surface-tension of liquid sulphur*, in which, by a curious 

 series of elementary mistakes, a number of otherwise careful 

 measurements have lost much of their value. After measuring 

 by direct methods the contact-angle between sulphur and 

 glass, and obtaining values of about 60° at 125° C, 43° at 

 190° C, and 27° at 257° C, the author proceeds to measure 

 the height to which the liquid sulphur rises in a tube of 

 which the diameter is expressly stated to be '103 cm. The 

 mean of a considerable number of readings — at a temperature 

 not stated — for the capillary rise was *246 cm. From which, 

 using " the approximate formula 



1 " 2 



we get 



T 



103 x 1-861 x 980 x -246 x *5 



11-56 nearly." 



A truly extraordinary value, due to a confusion of diameter 

 with radius, and a misplacement of the term cos 6 X . If we 

 transfer the peccant cos 1 to its usual place in the denomi- 

 nator and substitute for r ± the value "052 cm., we obtain 



T = 23*12 dynes per cm. 



If, on the other hand, we assume that "diameter" is a 

 misprint for " radius," and that the radius of the tube is 

 really '103 cm., we have 



T = 46*24 dynes per cm. 



This latter value is probably correct, as it is in fair agree- 

 ment with the number (59 dynes per cm. at 160° C.) obtained 

 by Zickendraht using Jaeger's method. 



University College of North Wales, Bangor, 

 April 1914. 



* Proc. Camb. Phil. Soc. xvi. p. 55 (1910). 



