312 On Emulsions, and the Action of the Bile in Digestion. 



solution is 5'58 mgr., of albumen 2*40 mgr., and of a ten- 

 per-cent. solution of tannic acid 2'88 mgr. 



With organic fluid substances like albumen and solution of 

 tannic acid, a thin membrane of the fixed substance seems to 

 form on the surface of the air-bubbles ; for they show angular 

 protuberances, and the surface becomes less mobile ; this im- 

 mobile membrane promotes the durability of the emulsion. A 

 permanent froth of this kind made with white of egg is well 

 known in the kitchen. 



With very volatile liquids, or such as are easily soluble in 

 the original aqueous fluid, such as alcohol and ether, the froth 

 soon subsides; for the film of extraneous liquid on the surface 

 of the water rapidly disappears, owing either to evaporation 

 or solution. The froth of beer is broken up by a small quan- 

 tity of ether ; for the tension of the common surface of 

 that substance and air is very slight, and the surface itself 

 tears under the dispersion of the fluid laminae forming the 

 foam, in a similar way as in the experiments on the dispersion 

 of soap- solution over the common surface of oil and water, 

 described above (under 3), where particles are split off from 

 the main mass of oil. 



8. Conclusions. 



(1) A solution of soap disperses itself over the common sur- 

 face of oil and water. 



(2) This dispersion causes, in the interior both of the oil 

 and the surrounding fluid, eddies or vortex-movements, by 

 which particles of the oil are isolated or detached, and are 

 drawn into the surrounding fluid, where they form small glo- 

 bules. 



(3) Very minute quantities of soap, so small that they 

 cannot even be recognized by the microscope, are enough to 

 produce this dispersion-phenomenon and the movements in the 

 whole body of oil caused by it. 



(4) Fixed oils containing free fatty acid form in a weak 

 solution of soda a solid soap, which dissolves in the surround- 

 ing fluid and is dispersed over the surface of the oil. 



(5) With a certain concentration of the solution of soda, 

 and a certain solubility of the soap that is formed, the disper- 

 sion occurs at certain intervals, and detaches a large number 

 of the small oil-globules. This explains the spontaneous for- 

 mation of an emulsion observed by Joh. Grad, and the Amoeba- 

 like movements of the oil-globules in dilute solution of soda. 



(6) The globules of oil are coated with a thin film of soap, 

 either solid or dissolved in water; and this film, by molecular 

 action, causes the oil-surface to be less mobile, prevents the 



