THE COLLOID-CHEMISTRY OF SOAPS 



of its importance for the general theory 

 of the colloid state, 1 is illustrated for 

 a number of the sodium and potas- 

 sium soaps of the fatty acids of the 

 acetic series in Fig. 13. Each pair of 

 tubes contains 10 cc. of a half molar 

 " solution " of the sodium or potassium 

 salt of propionic, butyric, valeric, cap- 

 roic, caprylic,* capric, lauric, myristic, 

 palmitic, margaric or stearic acid. It 

 will be observed that the first six pairs 

 of tubes from the left all contain mobile, 

 clear liquids in other words, liquids 

 that look like true solutions. In the 

 seventh pair (laurates) the sodium salt 

 lies as a colloid mass in a solution of 

 sodium laurate while the potassium 

 salt yields only a solution. In the 

 eighth pair (myristates) the sodium 

 salt yields a solid white gel while the 

 potassium salt still yields in part a 

 " true " solution with a colloid mass 

 lying in the bottom. Beginning with 

 the palmitate pair and through the 

 margarate and stearate, only solid white 

 gels are obtained. This experiment 

 suffices to show that a colloid soap 

 system may be obtained with water only 

 when the concentration of the water is 

 kept sufficiently low and that when 

 equivalent concentrations are compared 

 a sodium soap becomes colloid sooner 

 than a corresponding potassium soap. 

 As we shall see later, this is because 

 potassium soaps are more sol n Mr in 

 water and tm<l in consequence t<> \i.-M 

 molecular (true) solution^ over higher 

 soap concentration than the 

 soaps. 



1 SIT p:inc O'J. 



