306 Dr. G. Quincke on the Formation of Emulsions, 



Simultaneously with this dispersion of the soap-solution, a 

 current is set up from the interior of the fluid towards the 

 centre of dispersion, and continued onwards from its surface. 

 This current is much stronger in the tenacious oil than in the 

 water. The bubble becomes for a short time concave at its 

 vertex ; isolated particles of oil are torn away by the cur- 

 rent from the main body, and form spherical globules in 

 the surrounding aqueous fluid ; and vortices are produced in 

 the oil similar to those caused by blowing a stream of air 

 through a vertical and narrow glass tube on to a free and 

 plane surface of oil. If a layer of oil of from 5 to 10 milli- 

 metres thickness be poured on water, and alcohol allowed to 

 spread itself over either the upper or under surface of the 

 oil, those parts of the oil which are opposite to the centre of 

 dispersion will move towards that centre ; the layer of oil may 

 even be pierced by this means, so that air and water come into 

 contact. Excessive rapidity of dispersion in the applied fluid, 

 or too much tenacity in the oil, will impede the expulsion of 

 the oil particles or the piercing of the oil layer just as much 

 as sluggishness in the dispersion or too great ductility in the 

 oil. 



4. Explanation of the Spontaneous Formation of Emulsions 

 by means of Dispersion. 



By the phenomena described in the above paragraphs we 

 are now able to explain the formation of an emulsion. 



When a solution of soda and an oil come into contact, a solid 

 soap is formed by the action of the free fatty acid of the oil. 

 Gradually a portion of this soap dissolves in the adjoining 

 aqueous fluid. So soon as the fluid solution of soap comes 

 into contact with the oil, it spreads itself over the bounding 

 surface of the oil and aqueous fluid, and carries with it the 

 undissolved particles of soap with any adhering oil-globules. 

 In this way there are detached from the oil and borne into the 

 adjoining fluid a number of filaments, which, possessing the 

 tendency to assume the shape of bodies of least surface, are 

 converted into larger or smaller globules of a spherical form, 

 just as a jet of water in the air breaks up into larger and smaller 

 drops. To a certain extent this conversion of the oil into glo- 

 bules will be retarded by the solid and fluid soap already pre- 

 sent or newly formed; and then the length of the filaments 

 will be increased, or the size of the nascent globules diminished. 

 By the original dispersion, however, fresh oil particles will be 

 brought into contact with the soda solution, and after a time 

 the newly formed solid soap is again dissolved and a second 

 dispersion occurs. Similar periodic dispersions of oil on the 



