6 



terms of hydrolysis. The writer regards the extent of hydrolysis 

 as being identical Avith observed alkalinity, in this particular case, 

 as in most cases. Bancroft, however, in the Second Report (1919, 

 p. 15) has expressed his opinion that soaps are reaUy greatly hydro- 

 lysed, but that the hydroxyl ion is almost completely adsorbed by 

 undissociated sodium palmitate. Not to mention the difficulty in 

 accounting for the disposal of the equivalent quantities of palmitic 

 acid set free, this interpretation is diametrically opposed to experi- 

 mental data, which show that any excess of hydxoxyl ion added 

 to a soap solution, remains free in the solution as such and is not 

 adsorbed. 



(c) Products of H't^drolysis. 



Since all soap solutions are sUghtly alliaUne, they must contain 

 at least small amounts of products of hydrolysis. This has been 

 observed from the time of Chevreul, who found that most soap 

 solutions exhibit fine suspensions of acid soap of varying composition, 

 varying between nearly neutral soap and a soap in which the alkali 

 is deficient by any value up to one -third of the theoretical value for 

 a neutral soap. The more dilute the solution, as Krafft and Stern" 

 have found, the more nearly the composition of the suspensions 

 approaches that of a sodium hyckogen soap (NaHPj. McBain, 

 Laing and Taylor find that acid soap formed in palmitate solutions 

 at 9U^ has the coiuposition HP.2NaP. • 



Whereas in aqueous solution even the presence of one complete 

 equivalent excess of palmitic acid still leaves free OH' present, a 

 concentration 40 times as great as that required for coloration 

 of phenol phthalein, the alkah is so rapidly diminished by the 

 addition of alcohol that titration can be carried out in 40 per cent, 

 ethyl alcohol, although 60 or 80 per cent, solution is distinctly 

 preferable. 



(fZ) Effect of Carbon Dioxide. 



Although the dissociation constants of the fatty acids are perhaps 

 40 times greater than that of carbonic acid, yet the comparative 

 insolubihty of the fatty acids and of the acid soaps often results in 

 extensive decomposition of the soap by excess of carbon dioxide. 

 Even alcohohc solutions are decomposed. As a rule, the result of 

 the interaction is the visible separation of acid soaps, as Krafft," Stern," 

 and Wiglow", and Fendler-^ and Kuhn^^ showed. In the case of soaps 

 from such oils as ohve oil, however, the solution remains clear. Repeated 

 treatment Avith carbon dioxide removed progressively less of the 

 fatty acid, although ultimately nearly aU may be removed. The 

 equihbria mvolved have not as yet received quantitative study. 



The solubihty of the fatty acids is sHght, nevertheless they are 

 suflficiently strong to make it impossible for them to exist even in 

 such concentrations in the presence of more than the merest traces 

 of alkaU hydioxide. The theoretical necessity for the existence of 

 minute traces of free acid in all soap solutions is substantiated by the 

 observation of Krafft and Wiglow, that soap solutions yield appreciable 

 concentrations of fatty acid when shaken out with toluene or petroleum 



