108 SOAPS AND PROTEINS 



are generally regarded as completely insoluble. Looked at the 

 other way about, the first named are the best solvents for water, 

 while the alkaline earth soaps take a middle ground, and those 

 of the heavy metals stand last. With these general truths in 

 mind, it is obvious that we may classify the effects of adding 

 an alkali hydroxid or of adding any salt to potassium oleate as 

 follows : 



(1) a soap is formed more soluble in water and a better 



solvent for water; 



(2) a soap is formed less soluble in water and a poorer 



solvent for water; 



(3) no change occurs in the solubility characteristics of 



the soap. 



The last covers, perhaps, the item of greatest practical impor- 

 tance, namely, that of the ordinary salting-out of soaps, and that 

 about which most debate has centered; but since in practice it 

 is rarely seen in the pure form outlined in our experiments, but 

 is more or less blurred through the simultaneous action of pos- 

 sibilities (1) or (2), it is best taken up last. 



(1) A soap is formed more soluble in water and a better solvent 

 for water. This happens when ammonium hydroxid is added 

 in any amount whatsoever to a potassium (or sodium) soap. 

 In this case the viscosity of the soap mixture regularly falls. 

 This behavior of ammonium hydroxid is strikingly different from 

 that of either potassium or sodium hydroxid, either of which first 

 brings about a gelation of the soap solution followed by a second- 

 ary liquefaction and then a separation of the dehydrated soap 

 from the dispersion medium (a solution of the alkali hydroxid 

 in water). The effect of such fixed hydroxids is regularly attrib- 

 uted to " increases in alkalinity," " increases in hydroxyl ions " 

 and the vaguer concepts 'of " adsorption " and " permeability." 

 It is obvious that all such explanations are inadequate, for with 

 enough ammonium hydroxid at hand any degree of " alkalinity " 

 or any number of " hydroxyl ions " ought also to become avail- 

 able to bring about the effects observed with the fixed alkalies, 

 yet, when ammonium hydroxid is used, these effects never do 

 come about. The reason is that through interaction of the potas- 

 sium (or other) soap with the ammonium hydroxid, ammonium 

 soap is formed, and this is more soluble in water than the original 

 potassium (sodium or other) soap. The system as a whole 



