of G ibis's Theory of Surface Concentration. 491 



Another possibility however presents itself — namely, the 

 existence of some electrical effect, such as an electrostatic 

 attraction, causing the discrepancy, since sodium glycocholate 

 and the dyes are electrolytes. If this were so, one would 

 also expect somewhat of the same order of discrepancy 

 manifesting itself in the case of the ordinary inorganic salts. 

 Such does not take place. Caustic soda alone has marked 

 effects, and shows an adsorption 20 times greater than the 

 calculated. The other substances generally show a discre- 

 pancy of about 5 to 8 times. To whatever cause this smaller 

 discrepancy is due, it is unlikely that the same reason is to be 

 assigned to the very much larger discrepancies observed for 

 sodium glycocholate. 



The only other possible means, apparently, of explaining 

 the want of agreement is on the assumption that we are 

 dealing with some irreversible phenomenon of the nature of 

 gelatinization upon the oil surface. The fact of the surface- 

 concentration being much greater than the ordinarily accepted 

 value for the solubility, is in agreement with this view. It 

 should be pointed out. however, that the overstepping of the 

 solubility limit does not seem to be essential to gelatinization, 

 as w r ill be seen by referring to the determinations carried out 

 with saponin. The solubility of this substance is great ; 

 according to JBeilstein it is completely miscible with water, 

 and although this cannot actually be the case, the constancy 

 of the tension at comparatively dilute solutions cannot be 

 explained by the solubilit} r having been reached. This is a 

 very striking case showing the sensitiveness of the tension 

 "to gelatinizing effects. The hypothesis of gelatinization has 

 been put forward by Milner* to explain the behaviour of 

 sodium oleate, although in this case the tension curve 1 was 

 continuous and quite similar to the sodium-glycocholate curve. 

 From some unpublished experiments by Mr. H. E. Potts in 

 this Laboratory, it was found that sodium oleate showed an 

 adsorption at the oil surface, the magnitude of which was of 

 the order 10 -c; grm./em. 2 , while the calculated was of the 

 order 10 -s grm./cm. 2 , that is to say a discrepancy very 

 similar to sodium glycocholate. 



Mention may also be made that Freundlich and Losevf 

 have found that certain dyestuffs produced amorphous pre- 

 cipitates on the charcoal surface during adsorption deter- 

 minations. This was an irreversible process (the precipitates 

 being insoluble in water), and as such might be considered 

 as analogous to gelatinization, 



* Loc. cit. 



f Freundlich and Loser, Zeit. Phys. Chem. vol. lix. p. i?84 (1907). 



