SURFACE-FILMS 347 



boiling point of chloroform, under a layer of water, the droplets 

 burst and coalesce, forming a homogeneous layer of chloroform. 

 If treated with alcohol they immediately dissolve, leaving a fine 

 membraneous precipitate of protein floating in water. Thus, if we 

 shake up chloroform with about twice its volume of a 1 per cent 

 solution of protamin sulphate, and, after standing, separate the 

 chloroform droplets by pouring off the supernatant liquid, and 

 then, after repeatedly washing the droplets in water by decanta- 

 tion, add to the small amount of supernatant water about an equal 

 volume of alcohol and gently agitate, the droplets which are thus 

 stirred up into the alcohol-water layer can be seen to swell up 

 rapidly and burst, and the fine membranes which surround them 

 can be seen falling down through the alcohol-water. If we now 

 add several volumes of alcohol and shake up the liquid, the chloro- 

 form droplets all disappear, and what we now have is a clear, 

 homogeneous solution in which innumerable minute membranes 

 can be clearly seen floating.* 



That these surface films possess quite different properties from 

 the protein in the body of the fluid is evident; this is shown by 

 their great insolubility and by the fact that they are not readily 

 acted upon by acids and alkalies. Now many investigators have 

 pointed out that at the surface separating two phases of a system 

 marked changes in chemical equilibrium frequently occur (74) 

 (62) (48), owing to the alteration in chemical potential which 

 occurs at such surfaces (124). It appears probable that at surfaces 

 within protein solutions similar changes in equilibrium occur, 

 leading to the formation of polymers or anhydrides of the protein.f 

 These alterations in equilibrium are very slowly reversed upon 

 removal of the protein from the surface which caused the change 

 in equilibrium; this is shown by the insolubility of the coagula 

 which are produced in this way. Evidently some phenomenon 

 analogous to hysteresis prevents or greatly delays complete return 



* The formation of these films also explains the power which proteins 

 possess to render many emulsions stable, which are not stable in pure water 

 (Cf., for example, Jamison and Hertz (50)). It also explains the tendency of 

 protein solutions to form foams. For the analogous part which is played by 

 soap films Cf. Quincke (84) and T. Brailsford Robertson (104). 



t In this connection it should be noted that the increase in the concentra- 

 tion of proteins at such surfaces, due to the diminution in the surface energy 

 which the protein causes, must be accompanied by a corresponding diminution 

 of the active mass of water at these surfaces. 



