THE COLLOID-CHEMISTRY OF SOAPS 81 



2 



We emphasize these points because in technological practice 

 it is often of much importance to know whether the system 

 worked upon is "acid," "alkaline" or "neutral" in reaction. 

 The above observations may serve to show with what extreme 

 care any deductions derived from the application of indicator 

 methods (or other methods of determining hydrogen or hydroxyl 

 ion concentration) must be applied to such systems if they are of 

 the lyophilic colloid type. The indicators may help us for those 

 portions of the system which are of the composition x-dissolved-in- 

 water bid they do not necessarily tell us anything of those portions 

 composed of water-dissolved-in-x. 



With regard to the specific problem of soap manufacture, we 

 may say that the proportions of fat (or fatty acid), alkali and 

 water as chosen in common practice are such as yield only water- 

 in-soap types of systems when the cold process is followed. The 

 same is true for the cooled systems when the soap is made by the 

 hot process and independently of whether the soap has been salted 

 out (by sodium chlorid) or not. While the so.-ip i- boiling it 

 represents a mixture of water-in-soap and soap-in-water. If indi- 

 cator methods are used on such a system and at higher tempera- 

 lures this much may be said for them. Any boiling soap which I'K 

 just alkaline to phenolphthalein (decidedly pink) will be less alkaline 

 (colorless) when cooled. It may, on cooling, still contain free fatty 

 acid, but it will not hold uncombined alkali. 



We have already emphasized the important applications of 

 these principles to various biochemical reactions and to problems 

 in biology and medicine. 1 We shall return to the problem later. 2 

 Suffice it at this time to emphasize the fact that the reactions in the 

 solid tissues of the body (including for the most part those in the 

 major portions of the blood and lymph) are reactions in a m< 

 analogous to a concentrated soap. The reactions, on the other 

 hand, occurring in the watery secretions fmm tin* |MM!V dike the 

 mm" and sweat) occur for the mo-t p.-u-t. in a system analogous 

 to diluted soap. Indicator methods may be applied ami with a 

 fair degree of accuracy only to the latter systems; then applira- 



1 See MAIM-IN II I , : , and NVplmt.s. 2nl 1-xl . .TJ4. M2, 629, 



New York (1915); 3rd Ed., 368, 642, 765, N< v 

 'Seepage 229. 



