160 SOAPS AND PROTEINS 



This is the reason why sodium and potassium oleate and the 

 soaps made from oils rich in the lower fatty acids (cocoanut oil 

 soap, palm kernel oil soap) are the soaps which, above all others, 

 are held useful. On the other hand, for warmer waters it is of 

 advantage to have present the soaps of the fatty acids higher in 

 the series. Hence the common practice of adding tallow, hydro- 

 genated cottonseed oil, etc., to the more liquid fats and oils 

 used for the manufacture of toilet and laundry soaps in " civilized " 

 countries. There is, however, a limit at this end of the series 

 also. The sodium soaps above the stearate in the acetic series 

 do not yield (liquid) hydrated colloid systems below the boiling 

 point of water. In this proportion they are valueless as wash- 

 ing agents. Even the stearate which, since the introduction 

 of hydrogenation methods, has been worked in increasing 

 amounts into the common toilet and laundry soaps already comes 

 close to the danger line. It will hardly foam or emulsify short 

 of the boiling point of water. A way. out of the difficulty, not 

 only for the stearate, but also for some of the other higher fatty 

 acids, may be found in the substitution of potassium for the 

 sodium of the common soaps. This trick is employed in " shaving 

 soaps " in which the waste of a more " soluble " soap is compen- 

 sated for by its readier foaming and emulsifying properties. But 

 the substitution of potassium for sodium has its defects at the 

 lower end of the series the potassium soaps, being more readily 

 " soluble " both in cold and hot waters, pass too quickly through 

 their working middle of liquid hydrated colloids and hence are 

 " wasteful." 



