JACQUES LOEB 579 



have its origin in an adsorption of ions. He assumes that the double 

 layer at the boundary of water and membrane is also entirely inside 

 the watery phase. This , seems, however, to be disproved by an 

 experiment of Coehn and Franken.^ A sphere of paraffin dipped into 

 water possesses a high negative charge which can be demonstrated 

 electrometrically when the paraffin is lifted out of the water. If, 

 however, a film of water is caused to adhere temporarily to the 

 surface of the paraffin when it is lifted out of the water, the 

 electrometer indicates no charge as long as this film exists, but indi- 

 cates a charge the moment the film has disappeared. This leaves no 

 doubt that when a solid is bounded by water the one charge is in the 

 membrane and the opposite charge in the watery phase. The fact 

 that paraffin and solid substances in general are negatively charged 

 when in contact with water is ascribed by Coehn to the difference in 

 the dielectric constant of the two phases. Coehn has found that sub- 

 stances of a higher dielectric constant assume a positive charge when 

 in contact with a substance of a lower dielectric constant. This 

 would explain why membranes in general assume a negative charge 

 when in contact with- water since the dielectric constant of the latter 

 is relatively high. 



The formation of a double layer at the boundary of two phases is 

 thus, according to Coehn, a phenomenon of contact (or frictional) 

 electricity. Lenard and more recently FrenkeP have offered sug- 

 gestions concerning the origin of the double layer which make it de- 

 pendent on the Rutherford model of the atom. Lenard points out 

 that the atoms at the surface of a body are generally oriented in such 

 a way that the electrons are at the surface and the more massive part 

 (the positive nucleus) is towards the interior. This idea has been elab- 

 orated by FrenkeP into a theory of surface electric double layers of 

 solid and liquid bodies. According to this theory "double layers 

 must exist on the surface of all liquid and amorphous solid bodies, 

 whatever their chemical constitution. The latter will determine but 

 the magnitude and distribution of electric charges on both sides of the 

 surface." 



^ Coehn, A., and Franken, J., Ann. Physik, 1915-16, xlviii, 1005. 

 6 Frenkel, J., Phil. Mag., 1917, xxxiii, 297. 



