THE COLLOID-CHEMISTRY OF SOAP MANUFACTURE 189 



properties of the sodium and potassium soaps of different fatty 

 acids. STIEPEL found that 100 parts of the following dry soaps 

 would take up from the air the following number of parts by weight 



of water: 



Potassium oleate 162 



Potassium palmitate 55 



Potassium stearate 30 



Sodium oleate 



Sodium palmitate . 

 Sodium stearate . . 



12 

 8 

 7.5 



As we consider the water-holding power of different soaps 

 against the forces of evaporation of much biological importance 

 (since the metallic fatty acid compounds are analogous, in our 

 minds, to the metallic amino (fatty) acid compounds which 

 make up protoplasm l ) we wish to insert here some experiments 

 on the rate of water loss by various soaps when exposed to ordi- 

 nary atmospheric conditions. The relationship between the 

 chemical constitution of a soap and that of the rate at which 

 any amount of water it holds in colloid-chemical union is lost 

 to the air is shown by the following: 



When 10 grams of half molar " solutions " of different soaps 

 of the acetic series are placed in low evaporating dishes, 10 cm. 

 in diameter, and allowed to lose water at 18 C., the relative 

 percentages of weight lost at the end of seventy-two hours are 

 as indicated in Table LVI. There is obviously an inhibition to 

 water loss by evaporation as the acetic series is ascended and a greater 

 water loss in the case of the sodium soaps than in that of the potassium 

 soaps. 



TABLE LVI 



,.:i K .. -jo:,. 



