444 SMITH'S INTERMEDIATE CHEMISTRY 



much of the powder, and little of the soap in solution, the powder 

 takes the soap out of the solution. When, however, there is 

 much of the colloid in the form of soap solution, and little of the 

 solid, and that very finely divided, the same tendency to adsorp- 

 tion exists, only, in this case, the colloidal particles carry off the 

 powder. In short, the dirt is removed by adsorption into the 

 solution. 



Possible Objections to the Foregoing Explanation. For- 

 merly soap solution was supposed to remove grease (and soot?) 

 because of its slight alkaline reaction, due to hydrolysis. This 

 explanation must be given up because: (1) an alkali so dilute that 

 it exists in equilibrium with the free fatty acid, can not possibly 

 saponify the ester contained in a grease spot. (2) Pure alkali of 

 the same concentration (or stronger) has no more emulsifying 

 power than water. Such an alkaline solution will indeed emulsify 

 an animal or vegetable oil (cod-liver oil, cotton oil, castor oil), but 

 it does so by interacting with the free fatty acid always present 

 in such oil (p. 432) and forming therefrom a soap. Such an alkaline 

 solution does not emulsify kerosene, although soap solution does. 

 The emulsifying agency is always a soap. (3) Very dilute alkali 

 has no more effect upon soot than has water but soap solution 

 takes clean (greaseless) soot instantly into permanent suspension. 



The power of forming an emulsion depends, theoretically, upon 

 the abnormally low surface tension of dilute soap solution. Very 

 dilute alkali has the same high surface tension as has pure water. 



Exercises. 1. Make equations for the formation: (a) of malt- 

 ose from starch; (b) of glucose from maltose. 



2. Make a connected statement showing the stages in the 

 digestion of milk. 



3. Why does fat appropriately form a larger proportion of the 

 diet in the Arctic regions than elsewhere? 



4. Give the weights of carbohydrate, protein, and fat which 



