232 SOAPS AND PROTEINS 



in the soaps. On dilution and application of heat the light metal 

 soaps, especially of the higher fatty acids, suffer great hydrolysis, 

 and this hydrolysis is not reversible on simple lowering of tem- 

 perature. But let the freed fatty acid be treated with more con- 

 centrated alkali, and reversion to a " swelling and soluble fatty 

 acid " to speak for the moment in the terms of protein chemis- 

 try gradually comes about. 



In a careful study of this problem KRAFFT l boiled a unit 

 weight (1 gram) of soap (sodium palmitate) with increasing vol- 

 umes (200 to 900 cc.) of water. Just as when certain protein 

 " solutions " are thus boiled, these soap mixtures become milky. 

 On cooling, a shining precipitate settles out which on analysis 

 shows a progressively lower percentage of sodium and higher per- 

 centage of fatty acid when compared with the composition of the 

 pure soap, as the volume of water in which the soap was boiled is 

 increased. The original soap contained 8.27 percent sodium. 

 In contrast to this the cooled fraction when boiled with 200 cc. 

 water showed but 7.01 percent; with 450 cc. water, 6.32 percent; 

 with 900 QC. water, 4.20 percent. KRAFFT interpreted this finding 

 as indicating that there was a splitting of the soap into sodium 

 hydroxid and " acid-soap " (sodium bipalmitate). This idea has 

 since been frequently adopted by other workers. It is, to our 

 minds, only partly correct. There is, undoubtedly, with increas- 

 ing dilution and increasing temperature, an increasing fraction of 

 free alkali formed. This is the consequence of the better condi- 

 tions offered for hydrolysis of the soap into free alkali and free 

 fatty acid. But the mass which separates on cooling is certainly no 

 true bipalmitate, for chemical reasons alone make it hard to see 

 how a monovalent fatty acid can give rise to " acid " salts. The 

 separated mass is not a chemical compound, but simply free fatty 

 acid with which has been admixed mechanically a smaller and 

 smaller amount of neutral soap. 



What has been said of sodium palmitate holds also for sodium 

 si rural c and for all the higher members of the acetic series. It is 

 true also for sodium oleate. The amount of such hydrolysis, 

 however, decreases as the acetic series is descended so that for 

 sodium caprate and for .soaps lying below this it is very small 

 indeed. Were we to convert this finding into the terms of " pro- 

 tein " " coagulation," we would have to say that the " protein " 

 1 KRAFFT: Ber. d. deut. chem. Gesellsch., 27, 1747 (1894). 



