THE COLLOID-CHEMISTRY OF SOAPS 141 



perature 8 C. sodium caprate is still solid and remains essentially 

 only mechanically subdivided in the water. When the temper- 

 ature is raised to 26 C. the "liquef action" point of the soap in 

 water is exceeded. In this region most of the soap is in the 

 state of a (liquid) hydrophilic colloid, least in true solution, and 

 the greatest foam production is in consequence manifest. At 

 the two higher temperatures a shift in the soap/water system 

 occurs in the direction of true solution of the soap in the water 

 at the expense of the water in the soap fraction and hence the 

 diminished tendency to foam. 



Fig. 79 shows well how this general law is repeated as we 

 ascend in the soap series. Sodium laurate fails to foam at the 

 temperatures 8 and 26 C. At 50 a decided foam appears 

 as evidenced in the tubes marked 9, the foaming being increased 

 at 100 C. Sodium myristate fails to foam at the three lower 

 temperatures. At 100 C., as shown in the tube marked 10 of 

 the top row of Fig. 79, it foams beautifully. Not until the temper- 

 ature lies above 50 does the myristate yield a (liquid) hydro- 

 phi IK; colloid (and a foam). Even at this highest temperature 

 sodium palmitate, as indicated in tube 11 of Fig. 79, foams only 

 badly. The soap absorbs all the water offered, to yield a thick, 

 gelatinous mass into which the air does not enter easily. The 

 resulting foam is therefore practically a solid one. 



Fig. 80 shows how the tubes just described look two hours 

 later. It is easily observed that the foams die down most rapidly 

 (a) in the lower soaps and (6) at the higher temperatures. 



3 



>. 81 and 82 respectively show tin* foaming characteristics 

 of the sodium soaps of the acetic series at the concentration m/2 

 iim Mediately after the production of the foams and two hours 

 later. It will be observed that at this concentration the caprate 

 is the lowest member to yield a foam; the amount of foam 

 produced in all the caprate tubes of this scries (the vertical row 

 marked 8) is distinctly less than in tin- OOfrapOodiliq set of tubes 

 I. 79. Tin- lam-ate foams at thi> I>\\,T ronernt ration almost 

 as well as at the higher concent ration previously described. It 

 is noteuorfhv. however, that in Fiir. 7!> ft In- eoneent ration m) 

 the better foam i- <.l>tained at the temperature of 100 (' 



