June 27, 1919] 



SCIENCE 



617 



ammonium hydroxide is added in any amount 

 ■whatsoever to a potassium or sodium soap. 



2. Soaps are formed less soluble in the dis- 

 persion medium. This is observed when mag- 

 nesium, calcium, iron or copper salts are added 

 to a solution of sodium or potassium oleate. 

 The systems as a whole again become more 

 liquid though not in this instance because the 

 soaps are better " dissolved " in the solvent 

 but because they fall out and allow the vis- 

 cosity of the pure solvent (essentially salt 

 water) to come to the front. 



3. The change in kind of soap is negligible 

 or absent. This happens, for example, when a 

 neutral potassium salt or potassium hydroxide 

 is added to a potassiiun soap. Under these 

 circumstances the most interesting of all 

 series of changes are to be noted with in- 

 creasing concentration of the added material. 

 There is, first, an increase in viscosity which, 

 if the amount of solvent is not too great, 

 results in gelation, followed by a secondary 

 liquefaction and then a progressively in- 

 creasing separation of soap from the disper- 

 sion medium imtil it finally floats as a dry 

 mass upon the \mderlying solution of salt or 

 alkali. 



If, in explanation, we do not wish to make 

 too many violent assumptions the following 

 seems a reasonable way out. The fixed alka- 

 lies and the various neutral salts are hydrated 

 in water. As more and more salt is added the 

 number of such h.vdrated particles (or their 

 size) increases. The effect is two-fold. 

 Through deprivation of solvent the concentra- 

 tion of the soap is increased while the par- 

 ticles of hydrated salt remain emulsified in 

 the hydrated soap.' This emulsification (with 

 the increase in the concentration of the soap 

 itself) accounts for the initial increase in vis- 

 cosity. As more salt is added the hydrated 

 salt phase attains a value which makes the 

 particles begin to touch. The hydrated soap 

 now becomes the internal phase and the hy- 

 drated salt the external one. This change in 

 type of emulsion explains the secondary lique- 



3 Regarding the making and breaking of emul- 

 sions, see Martin H. Fischer and Marian O. 

 Hooker, Scikxce, 43, 468, 1916; "Fats and Fatty 

 Degeneration," 29, New York, 1917. 



faction of the gel, a characteristic of these 

 systems not previously noted so far as we are 

 aware. More salt increases further the hy- 

 drated salt phase which now begins to separate 

 off at the bottom while the still hydrated soap 

 floats to the top. By adding enough salt all 

 the water is taken from the soap which then 

 floats as a dry layer upon the concentrated salt 

 solution. 



rv 



Various incidental observations upon the 

 reaction of soap-water systems toward indi- 

 cators of various kinds have proved of im- 

 portance not only for the theory of these 

 systems but for the understanding of various 

 biological problems, for living matter, too, as 

 so often emphasized, is essentially nothing but 

 a hydrophilic colloid system. The findings 

 show how dangerous it is to assume that 

 physico-chemical methods and opinions (such 

 as hydrogen ion determinations) as derived 

 from the study of the dilute solutions may, 

 without reserve, be applied to living proto- 

 plasm. 



To be sure of strictly reproducible ground 

 materials we have always prepared our soaps 

 by adding to each other the necessary gram 

 equivalents of fatty acid and alkali. Any soap 

 as thus formed is either acid, neutral or alka- 

 line to such an indicator as phenolphthalein 

 depending upon the concentration of the water 

 in the system. Phenolphthalein added to a 

 concentrated sodium oleate solution remains 

 colorless, but this oleate with its contained in- 

 dicator turns pink or strongly red as more and 

 more water is added to the system. It does 

 not suffice to say that a hydrolysis of the soap 

 is suppressed in the concentrated solution to 

 come to the fore in the dilute solution. It is 

 more reasonable to say that when the water 

 is dissolved in the soap the system is some- 

 thing different from that resulting when the 

 soap is dissolved in the water. If a gel of 

 sodium stearate is used, direct application of 

 phenolphthalein to its fresh section shows the 

 framework of the gel (the water-in-soap por- 

 tion of the system) to remain imcolored while 

 the soap-in-water portion of the system tume 

 bright red. 



