TENSION OF LIQUIDS. 



TABLE 143. Surface Tension of Liquids. 41 



TABLES 143-145. 



TABLE 144. Surface Tension of Liquids at Solidifying Point, t 



TABLE 145. Tension of Soap Films. 



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

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

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

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

 millimetres. 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 (vide Newton's rings, Table 146). 



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

 For example, KNOs =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 KNO 3 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. 



* This table of tensions at the surface separating the liquid named in the first column and air, water or mercury 

 as stated at the head of the last three columns, is from Quincke's experiments (Pogg. Ann. vol. 130, and Phil. Mag. 

 1871). The numbers given are the equivalent in degrees per centimetre of those obtained by Worthington from 

 Quincke's results (Phil. Mag. vol. 20, 1885) with the exception of those in brackets, which were not corrected by 

 Worthington ; they are probably somewhat too high, for the reason stated by Worthington. The temperature was 

 about 20 C. 



t Quincke, " Pogg. Ann." vol. 135, p. 661. 



i 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. 



II " Proc. Ry. Soc.'^iS??, 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 density is nearly constant. Thus, if 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. 



I2Q 



