ON THE FOKMATION OF SOAP-BUliULES. 475 



On the Formation of Soap-bubbles by the Contact of Alkaline Oleates 

 with Water. By Professor G. Quincke, F.B.S. 



[Ordered by the General Committee to be printed in extenso.l 



80ME years ago I showed that soap-solution could be spread out on 

 the common surface of oil and water or of oleic acid and water. The 

 surface tension is diminished by this spreading more than 80 per cent. 

 The spreading forms vortices in both liquids, and attracts all matter to the 

 centre of spreading. If the soap-solution is formed by tiie oleic acid in 

 contact with water containing potassium, sodium, or ammonia on the sur- 

 face of a drop of oil, suspended in water of the same density, near the 

 wall of the glass vessel or near viscous substances, the drop of oil is 

 attracted by the wall or the viscous matter. The formation and the spread- 

 ing out of soap-solution may be periodical and the movement periodical. If 

 the period is very short the movement is apparently continuous. Oil- 

 bubbles filled with water or small bodies covered with very thin films of 

 oil are displaced in the same manner as oil spheres by the spreading of 

 soap-solution. 



I think that this new principle of movement will also explain a great 

 many phenomena in organic nature, and I have tried also to explain by 

 this new principle the spontaneous formation of emulsion or foam by the 

 contact of oil (with oleic acid) and alkaline water, the foam -structure and 

 the motion of the protoplasm in the cells of the plants. 



Very thin films of oil are sufficient to show this motion by periodical 

 spreading of the solution of very small quantities of soap, so thin and so 

 small that they cannot be seen with the microscope or recognised in any 

 other way. 



Recently I have studied the phenomena by the contact of the oleates 

 of potassium, sodium, and ammonia with water. The neutral oleates are 

 dissolved by water, and form a viscous liquid. With more water an acid 

 salt is formed and the alkali is dissolved in the water. These acid salts or 

 acid soaps are not soluble in water, or only slightly soluble in water. By 

 longer contact with water they are dissociated, and form again liquid 

 oleic acid and neutral oleates or soap-solutions. 



When small quantities of neutral oleates are placed in contact with 

 water between the cover-glass and the slide, and are examined by a micro- 

 scope with polarised light, they are found to be covered with thin films 

 of oleic acid. This film dissolves oleate and water, and the diQ"usion of 

 both substances will bring water to the soap inside the oil-film of oleic 

 acid, and oleate to the water outside the oil-film. The volume of the soap 

 inside the oil-film is increased, the soap-solution foi-med on the common 

 surface of oil and water is spread out, and now the vortices, excited by the 

 spreading, attract the matter, the soap, and the liquid. In this way are 

 produced very curious forms called myeline by Virchow, who first observed 

 them in putrefied brain. These myeline forms — crystals of soap (with 

 water of crystallisation, covered with the thin oil-films and showing a 

 smooth surface) — are doubly refractive. 



The ' liquid crystals ' observed by Professor Lehmann, of Karlsruhe, in 

 fused benzoylcholesterine and fused azoxyanisol are also doubly refracting 

 crystals, covered with a thin film of oily matter formed in the liquid by 

 the fusion. 



