140 SOAPS AND PROTEINS 



shows the appearance of these tubes two hours later, indicates 

 that the foams do not last. They die down fastest at the higher 

 temperatures, the greatest permanency, in other words, being 

 shown by the foams produced at the lower temperatures. 



It is well to state at once what we hold to be the relationship 

 between these findings and our previous considerations of the 

 hydrophilic properties of these soaps. The lowermost soaps form 

 only solutions in water, they show no hydrophilic properties, 

 and they do not foam. Sodium caprylate, with its more distinct, 

 even though still low, hydration capacity, yields the first satis- 

 factory foam. It does this best, however, at a low temperature. 

 At this it has its highest hydrophilic value. To raise the temper- 

 ature of this soap/water system is to make the sodium caprylate 

 go into true solution in the water, and as this happens the hydro- 

 philic colloid properties of the system are diminished, and, simi- 

 larly, the foaming properties. The higher soaps do not foam 

 because not enough of them " goes into solution " to yield a 

 (liquid) hydrated colloid system the water, in other words, 

 is either taken up to form an essentially solid mixture into which 

 the air cannot be driven, or the soap is so " insoluble " that 

 the water remains " free " and hence there is no lasting foam. 



2 



It will be noticed that the first foaming qualities in these 

 soaps developed in the experiment just described at the concen- 

 tration 2 m. If the experiment with these soaps is repeated at 

 the concentration m, the previously foaming soaps no longer foam 

 while soaps higher in the series which did not foam now do so. The 

 former of these truths is readily apparent if the vertical set of 

 tubes marked 7 (the caprylate) in Fig. 77 is compared with the 

 similarly numbered set of Fig. 79. To explain this finding we 

 would say that in the lower concentration of sodium caprylate 

 illustrated in Fig. 79 the soap is more nearly in " true " solution 

 and that the hydrophilic properties of the system are diminished 

 in proportion. But the next higher soap, namely, sodium caprate 

 (the tubes 8 of Fig. 79) foam nicely. At 8 the sodium caprate 

 does not foam. Most foaming is obtained at 26, with less at 

 the two higher temperatures 50 and 100 C. 



To explain these findings it must be recalled that at the tern- 



