156 SOAPS AND PROTEINS 



to represent the breaking length of oil threads, the breaking length 

 of a soap, like hydrated sodium oleate, is represented by the lower 

 line of the diagram. For this reason, other things being equal, 

 the oil tends to break into droplets sooner than the hydrated 

 sodium oleate which in consequence remains the non-dispersed 

 or enveloping phase. There are, however, other soaps which, 

 while capable of hydration, yield liquids whose fibers tend to 

 break sooner when drawn into threads than does hydrated sodium 

 oleate, or which at the ordinary temperatures employed are so 

 nearly solid that they break into short fragments. Magnesium 

 oleate, sodium stearate, etc., may be cited as hydrated soaps of 

 this type. Their breaking length may be represented diagram- 

 matically, as compared with the breaking length of an oil, by 

 the upper line of Fig. 92. Other things being equal, these materi- 

 als, therefore, tend to become enmeshed within the oil, yielding, 

 in other words, emulsions of the type water-in-oil. 



The experiments detailed above, in which were compared 

 the emulsifying properties of different soaps (like sodium palmi- 

 tate and potassium palmitate, sodium stearate and potassium 

 stearate) or the behavior of these soap/water systems, when 

 subjected to heat manipulation, prove the truth of this general 

 contention. We have also tried to measure the breaking length 

 of the different systems which may be used successfully for the 

 production of foams, fogs or the two types of emulsions. We 

 hope to be able to detail numerical values covering these points 

 at another time. The so-called " finger tests " of the glue tech- 

 nologists permit one to predict what kind of system is most likely 

 to result from dispersion in each other of a gas with a liquid or a 

 liquid with a liquid. 



We are not unconscious of the fact that there may be arranged 

 under this conception many of the so-called theories of foaming 

 and emulsification adduced to explain the behavior of these 

 systems. As previously emphasized 1 there is nothing mutually 

 exclusive in the ideas of solvation and the relative breaking lengths 

 of any two materials, and the changes in surface tension and 

 viscosity, the quantitative relationship between the amounts of 

 the two phases, the formation of a continuous third phase between 

 the two general substances making up a foam or an emulsion, the 



1 MARTIN H. FISCHER and MARIAN O. HOOKER: Fats and Fatty Degen- 

 eration, 29, New York (1917). 



