THE COLLOID-CHEMISTRY OF SOAPS 137 



It is of importance next to distinguish between the production 

 of a foam and its maintenance after production. Authors who 

 have written on this subject have rarely done so. Mere contact 

 between a gas and a foaming agent does not produce a foam the 

 gas must be stirred, blown or mixed into it. When we speak 

 off-hand of a foam-producing material we really mean something 

 which will stabilize the foam once it is produced. 



1 



In order to discover if any relationship existed between the 

 colloid properties (or more particularly the hydration capacities) 

 of different soaps and their foaming qualities we chose for first 

 study the sodium soaps of the acetic acid series. To obtain com- 

 parable results, 10 cc. of equimolar " solutions " of the different 

 soaps were placed in tall test-tubes (30 cm.X2 cm.) and shaken. 

 In order that all might be treated equally from the point of view 

 of foam production, all the tubes were clamped in a frame, the 

 shaking being continued for thirty seconds. For reasons which 

 will become clear later, the temperature is an important factor 

 and must be watched carefully. Moreover, since the systems 

 resulting at any fixed temperature when soap/water mixtures 

 are brought to the desired temperature from a higher point differ l 

 from those which result when they are brought to such temper- 

 ature from a lower one, all the soap " solutions " about to be 

 deseril>ed were started at a low temperature and then brought 

 to the higher ones. Tubes, water and soaps were therefore all 

 first reduced to the lowest temperature used in these experiments, 

 namely, 8 C. After they had remained at this temperature for 

 twenty-four hours the proper molar solutions were made by mix- 

 ing the soaps with the water. After another period (twenty- 

 four hours) of standing and careful mixture until (apparent) 

 homogeneity had been attained, the tubes were shaken violently 

 for thirty seconds to permit of the, formation of foam. They 

 were photographed after four ininnte>. then left to themselves 

 for two hours, still in the thermostat, and photographed a second 

 tune \fter i hi < first series of observations, the tubes with their 

 reaction mixtures were then wanned to the next higher temper- 

 ature, namely, 26 C. and kept at this for twenty-four hours. 



8eep*fe74. 



