138 SOAPS AND PROTEINS 



After shaking, photographing, allowing to rest and rephoto- 

 graphing, we repeated the whole process at 50 C. and finally 

 at 100 C. 



The results obtained in the case of the sodium soaps of the 

 acetic acid series at the concentration 2 m. are shown in the photo- 

 graphs of Figs. 77 and 78. This was really an attempt to dis- 

 cover where in the series and at what concentration foaming 

 will begin. At 8 C. (the lowermost row of tubes in Fig. 77) 

 it is apparent that no foam is formed by the formate, acetate, 

 propionate, butyrate or valerate of sodium. There is just a sug- 

 gestion of a foam in the case of the caproate, but clear formation 

 of such does not begin until the caprylate is reached. At this 

 temperature soaps higher 1 in the series fail to yield homogeneous 

 mixtures (" solutions ") with the water. The mixtures also do 

 not foam. The absence of the tubes from the series in this 

 and the subsequent photographs expresses this fact. 



When the temperature is raised to 26 C. the findings are much 

 the same except that the caproate shows no signs of foaming and 

 the caprylate less than at the lower temperature. At 50 and 

 100 C. the picture is largely repeated the caprylate alone foams, 

 though less than at the lower temperatures. Fig. 78, which 



1 These higher soaps take up the water offered them but yield such viscid 

 systems that they are practically solid. In consequence, air cannot be easily 

 shaken or beaten into them. Just as in the case of the emulsions (see MARTIN 

 H. FISCHER and MARIAN O. HOOKER: Fats and Fatty Degeneration, 36, 

 New York (1917)) the production of a foam is best accomplished when the soap 

 is present in a medium concentration and when the resulting system is essen- 

 tially a liquid hydra ted colloid. At ordinary temperatures the soaps of the 

 acetic series, especially the higher ones, are all more solid even in the 

 presence of considerable water, than the soaps of the less saturated fatty 

 acids. For this reason none of them is as good a foaming or emulsifying 

 agent as an oleate, linolate or other liquid soap. 



In general, the melting points of the soaps of the acetic series lie par- 

 allel to but above that of their fatty acids. All the fatty acids below 

 caproic are liquid near C. or below. Caprylic acid is liquid at 16.5; 

 capric at 31.3; lauric at 43.6; myristic at 53.8; palmitic at 62; margaric 

 at 60; stearic at 69.3; arachidic at 77 C. 



The lowermost soaps of the acetic series are "soluble" in water and yield 

 liquid systems even at a low temperature. In the middle of the series and at 

 ordinary temperatures the acetic series soaps yield liquid hydrated colloid 

 systems with water, and are the best foam producers. Above this they yield 

 highly viscid to solid hydrated systems and less favorable ones for foam pro- 

 duction. Rise in temperature shifts the whole arrangement to the right, the 

 lower soaps going into the region of the true solutions of soap in water and 

 thus losing their foaming qualities while the higher ones move from the region 

 of the hydrated solid colloids into that of the hydrated liquid ones. 



