THE COLLOID-CHEMISTRY OF SOAPS 159 



character of the soap and (c) the temperature at which it is 

 employed. 



It is the common practice to rub solid or semi-solid soap directly 

 upon the soiled materials or to soak them in a strong soap stock. 

 Even after such soaking, more solid or semi-solid soap is com- 

 monly rubbed directly upon the more soiled areas. This is all 

 expressive of the need for a hydrated colloid of high concentration, 

 for only such will lead to easy and permanent stabilization of the 

 " dirt . " (fatty materials and mixed solids) in emulsified form in 

 the " soap water." 



The ordinary washing soaps (either laundry or toilet) are 

 the sodium soaps of several fatty acids. It is of interest to note 

 that manufacturers have long used mixtures of different fats for 

 their soap stocks. Beginning as they usually do with a liquid 

 fat (like cocoanut oil, olive oil, cottonseed oil) they add to this 

 varying amounts of the higher fats (like tallow, hydrogenated 

 cottonseed oil, etc.). The ultimate soap produced contains a 

 long and varied list of fatty acids. Such mixtures must obviously 

 satisfy most general needs. Because of the presence of soaps 

 of the lowermost fatty acids, quick foaming and quick emulsi- 

 fication are obtained even at low temperatures. These lower- 

 most soaps, however, dissolve so quickly that the f rugal house- 

 wife considers them wasteful. Especially is this the case when 

 the soaps are used with hot water in which they pass quickly 

 into the "true solution" stage. For this reason the presence 

 of fatty acid soaps frpiA the middle of the series will prove useful, 

 for these work well in flrdinary " lukewarm " waters. They too, 

 however, lose much of their virtue if the temperature is raised. 

 As effectively working soaps in waters near the boiling point, 

 the soaps of the higher fatty acids are required. The palmitates 

 and stearates, for example, still maintain their colloid character- 

 istics when soaps lower in the series have lost theirs through 

 " solution." 



The facts recited indicate why the temperature at which 

 any soap is used has so much to do with its effectiveness. Where 

 soaps are to be used in cold water, it is clear that none of the. 

 lu'uh -r fatty acid soaps are of any particular use. Only those 

 soaps which at low teni|xraiur. l 'finitely colloid character- 



and which as ordinarily employed yield liquid colloid 

 systems, are effective for washing under such circumstances. 



