52 



LIBERATION OF ENERGY 



(Fig. 13). Fatty acids (Experiment 11) lower the surface tension of 

 water because the unsatisfied valencies at the surface are satisfied 

 by the soluble COOH group, while the insoluble paraffin portion 

 remains out of the water. That is, the fatty acid or other capillary 

 active substance goes to the surface because that portion of the 

 molecule which does not wet tends to leave the water, but is 

 anchored to the water by the polar group. If there is sufficient 

 of the substance present to cover the surface with a layer at least 

 one molecule thick, then the surface tension will be decreased. 

 Compare this surface orientation with Experiment 18, where small 

 bits of paper coated on one side with lamp-black or printer's ink 

 orient themselves on the interface between paraffin oil and water 

 so that the blackened sides are turned towards the oil. 



Adam has found that the gathering together of fats or fatty acids 



COOH 



Fig. 13. — To show how an oil like Olein containing Oleic Acid has its molecules oriented 

 on the surface of water, COOH radicle attracted to OH radicle. 



in an orderly fashion like this on a surface produces changes in the 

 physical state of the substances so oriented. For instance, 

 palmitic acid at room temperature is solid, but if placed on the 

 surface of water at the same temperature is clearly liquid. Further, 

 the surface layer is able to withstand a considerable lateral force 

 without buckling. When the packing force is applied the molecules 

 on the surface fit into one another like spoons in a box and so allow 

 of more molecules per unit surface. If the polar portion is bulky 

 the molecules pack into a curved film having the hydrophobic 

 portion concave and the hydrophilic polar part convex. Not until 

 something like 100 atmos. pressure has been applied laterally 

 will buckling of the film occur. Some substances go completely 

 out of solution when so adsorbed on a surface. The molecules of 

 albumin, for instance, when oriented on a surface adhere together 

 and form an irreversible gel, i.e., they coagulate. This adherence 



