68 SOAPS AND PROTEINS 



tions of water in phenol. The seventh bottle shows two layers 

 below, one of phenol saturated with water; above, a solution of 

 phenol in water. With further additions of water the latter type 

 of solution grows at the expense of the former, until finally, in 

 the bottle second from the extreme right of the series nothing 

 but a solution of phenol in water remains. 1 



Of importance for our further discussion is, first, the existence 

 of the two types of solution, that of water-in-phenol and that of 

 phenol-in-water. The physical constants of these two solutions 

 are totally different and they behave differently, too, toward 

 changes in external conditions like temperature or the effects 

 of added substances (acids, bases, salts, indicators, etc.). A 

 second point of importance is the behavior of such a system as 

 is represented in the fourth or fifth bottle from the right when 

 subjected to increases or decreases in temperature. When the 

 temperature is raised the watered -phenol phase goes over and into 

 solution in the phenolated-water phase. It is characteristic of 

 liquids, when their temperature is being lowered, to show a pro- 

 gressive increase in viscosity. The warmed solution of phenol- 

 in-water also shows such a progressive increase in viscosity as 

 its temperature is lowered, but, as first noted by FRIEDLANDER 

 and ROTHMPND, this progressive increase shows a sharp break 

 upon reaching the critical temperature, at which the phenol 

 begins to separate out. 



This break expresses itself as a sharp rise in viscosity, which 

 increases for a time and then falls off again, so that with further 

 lowering of temperature a viscosity curve more like the original 

 " normal " is again obtained. 



We are indebted to WOLFGANG OSTWALD for pointing out 

 that, in this critical zone during which the phenol/water system 

 is opalescent, we are in reality dealing with a colloid system (con- 

 sisting of watered-phenol dispersed in phenolated-water). 



1 In analogy to what happens in the "salting-out" of soaps, which is the 

 subject of Section X (page 93), it is well to explain the nature of the con- 

 tents of this right-hand bottle in the series. This was originally nothing but 

 a solution of phenol in water, but through the addition of ordinary table salt 

 the phenol was "salted out" so that now a phenol phase with some water 

 dissolved in it (analogous to the salted-out soap of the manufacturer) is seen 

 floating at the surface of the liquid in the bottle. 



