376 SCIENCE PROGRESS 



water and perhaps associated with the true colloid. He 

 suggests the following formula for the colloidal ion : 



(NaP).P„»<-'(H.O)„ 



and points out that this would be the same as 



(NaPUHPUOH)„"<->- (H.0)._„. 



The mobility of this colloidal ion is dependent upon the 

 quantity of adsorbed water, and since the vapour pressure of the 

 solution diminishes with increase in concentration, the particle 

 becomes dehydrated and the mobility is increased. These 

 heavily hydrated micelles are extremely sensitive to lowering 

 of the vapour pressure ; the addition of small quantities of 

 electrolytes to sodium palmitate solutions decreases the 

 hydration of the micelle, and thus diminishes the viscosity. The 

 enormous viscosities of soap solutions are due largely to the 

 hydration of the micelle. The addition of larger quantities of 

 electrolytes, however, produces more undissociated colloid and 

 finally salts out the soap. 



In dilute solutions the ions are simple, but with increase in 

 concentration the simple fatty ion is replaced by the colloidal 

 micelle, and at moderate concentrations the only crystalloid 

 constituent is the potassium or sodium ion. In concentrated 

 solution nearly half of the current is carried by the colloidal 

 micelle, so that its mobility must be comparable with that of 

 the cation. On diluting the solution the colloid breaks up into 

 simple ions and the simple undissociated soap, and this points 

 to the existence of an equilibrium between the colloid and its 

 ions. The composition of the micelle appears to vary with the 

 concentration, and the conductivity results are best explained 

 on the assumption that there is a gradual transition of ionic 

 micelles to ordinary ions on the one hand, and through slightly 

 charged to typically neutral colloids on the other. 



The sodium and potassium salts of the fatty acids have been 

 examined from the acetates to the behenates, and it is found 

 that there is a gradual change in properties as the series is 

 ascended. The solution is the more collodial the greater the 

 number of carbon atoms in the molecule ; the greatest change 

 in this respect takes place between the caprate (Cio) and the 

 laurate (C12). Generally the potassium soaps are more colloidal 

 than the sodium soaps. In N solutions the total colloid 

 present is at least 15 per cent, in the case of the hexoates, 

 increasing to nearly 100 per cent, in the higher soaps, but the 

 proportion of the colloid rapidly falls off with the dilution. 



The theory may be extended to many other colloidal solu- 

 tions, such as acid and alkali proteins, indicators, sodium 



J 



