] Double-Layer of Solid and Liquid Bodies. 317 



•confirmed by experiment*. Further, the ionization of metals 

 in the solid or liquid state must be much larger than that 

 of the dielectrics under the same conditions, which accounts 

 for the presence of free electrons in the former and their 

 absence in tbe latter. 



Lastly, the surface-tension of metals must be much larger 

 than that of dielectrics, since, other things equal, it is pro- 

 portional to the cube of the atomic radius. This conclusion 

 is in a striking agreement with the facts f. The surface- 

 tension of dielectrics does not, indeed, exceed a few tens, 

 while that of the metals, as shown above, is measured by 

 hundreds and even thousands of dynes per cm. The salts 

 (fused) occupy in this respect an intermediate position. 



A few examples, taken from Freundlich's KapillarcJiemie, 

 are collected in the following Table (V.), illustrating the 

 .above law. 



Table V. — Surface-tension of dielectrics. 



Substance 



temperature L e . 

 (centigr.). 



H 2 



N 2 



-259° 

 - 195-9 

 -182-7 

 - 1861 

 - 72 

 + 160 

 4- 15-2 

 + 20 

 + 54 

 + 20 

 4- 20 

 + 20 

 820 

 790 

 850 

 880 



2 

 8-3 



o. 



A 



13 

 11 



Cl 2 



33-6 



Sulphur 



CO 



60 

 1-8 



so; 



30 

 30 



Benzene 



Acetone 



Chloroform 



28-8 



23 



26 



NaCl 



KC1 



Na CO., 



120 

 100 

 213 



K,CO, 



170 







Argon is mono-atomic, as Fe and Pt, and has the same 

 number of electrons in the external ring (8), while its 

 surface-tension is about 100 times smaller than that of the 

 other two elements. On our theory this is simply explained 



* The ionizing- potential of Zn, Cd, Mg, IIg , is 3-96, 3-74, 4-28, 4-9 

 volts respectively ; that of helium is 20*5 volts, of neon 16"0, of argon 12, 

 hydrogen 10 volts. 



t Strictly speaking, it refers only to mono-atomic substances ; but, as 

 .vill be shown later, the combination of atoms in molecules usually tends 

 co diminish the surface-tension. 



