J 74 



TABLES 173-176. 



TENSION OF LIQUIDS. 



TABLE 173. -Surface Tension of 



TABLE 174. - Surface Tension of Liquids at Solidifying Point, t 



TABLE 175. Tension of Soap Films. 



Elaborate measurements of the thickness of soap films have been made by Reinold and 

 Rucker.y They find that a film of oleate of soda solution containing i of soap to 70 of 

 water, and having 3 per cent of KNO 3 added to increase electrical conductivity, breaks at 

 a thickness varying between 7.2 and 14.5 micro-millimeters, the average being 12.1 micro- 

 millimeters. The film becomes black and apparently of nearly uniform thickness round 

 the point where fracture begins. Outside the black patch there is the usual display of 

 colors, and the thickness at these parts may be estimated from the colors of thin plates 

 and the refractive index of the solution. 



When the percentage of KNO 3 is diminished, the thickness of the black patch increases. 

 For example, KN() :J =3 i 0.5 o.o 



Thickness = 12.4 13.5 14.5 22.1 micro-mm. 



A similar variation was found in the other soaps. 



It was also found that diminishing the proportion of soap in the solution, there being 

 no KNQs dissolved, increased the thickness of the film. 



i part soap to 30 of water gave thickness 21.6 micro-mm. 



I part soap to 40 of water gave thickness 22.1 micro-mm. 



i part soap to 60 of water gave thickness 27.7 micro-mm. 



i part soap to 80 of water gave thickness 29.3 micro-mm. 



Qa,.,^c ,u.i-. ,1 ..... m K vui. zo, inn 5 ; wnn me exception ot those in brackets, which were not corrected by 

 bout Jo^C ' 3re somewhat too high, for the reason stated by Worthington. The temperature was 



t Quincke, " Pogg. Ann." vol. 13?, p. 661. 



It will be observed that the value here given on the authority of Quincke is much higher than his subsequent 

 measurements, as quoted above, give. 



" Proc. Roy. Soc." 1877, and " Phil. Trans. Roy. Soc." 1881, 1883, and 1893. 



NOTE. Quincke points out that substances may be divided into groups in each of which the ratio of the surface 

 tension to the dens.ty ,. nearly constant. Thus, ,f this ratio for mercury be taken as unit, the ratio for the bromides 

 and iodides is about a half : that of the nitrates, chlorides, sugars, and fats, as well as the metals, lead, bismuth, and 

 antimony, about i : that of water, the carbonates, sulphates, and probably phosphates, and the metals platinum, gold, 

 silver, cadmium, tin, and copper, 2 ; that of zinc, iron, and palladium, 3; and that of sodium, 6. 

 SMITHSONIAN TABLES. 



