SOAP PRESENT IN THE OIL 13 



to the ascending air-bubbles in a soap solution, or the earlier 

 described benzin droplets in a froth of soap and benzin. 



Drops of almond oil and cod-liver oil, which were brought 

 into water, behaved in just the same way as the olive 

 oil already investigated. Cod -liver oil especially became 

 turbid very quickly and intensely, and turned completely 

 into a fine frothy structure in the lower region. 



These experiments led me to suppose that the formation 

 of foam in oil-drops in water might depend on the presence 

 of small quantities of soap dissolved in the oil. The dissolved 

 soap strongly attracts water which diffuses into the oil, and 

 the watery solution of soap thus formed, not being soluble 

 in oil any longer, separates out in minute particles, which by 

 further absorption of H 9 become minute droplets. This 

 hypothesis appeared also very probable, if not certain, from 

 special experiments directed to the point. It was not found 

 possible to deprive olive oil of its property of becoming 

 gradually turbid and frothy in H 2 0, by heating it with 

 water and shaking it repeatedly ; indeed it is improbable that 

 oil can be thus completely deprived of such soap as it may 

 contain. On the other hand, the influence of soap in the 

 olive oil on the production of froth was shown very plainly, 

 when the amount of contained soap was increased by warm- 

 ing the oil for some time with Venetian soap, even though 

 the latter was not noticeably dissolved. A drop of such 

 oil, brought into water in the usual manner, begins to turn 

 frothy immediately; at the same time wave-like stream- 

 ing movements (superficial extension -currents) appear on 

 the surface, called forth by local extension -movements of 

 the soap. In a few hours the drop became quite frothy. 

 A similar result is obtained if a few particles of Venetian 

 soap are enclosed in a drop of pure olive oil, which is then 

 brought into H 2 under a cover-slip. Such drops also im- 

 mediately show lively wave -like extension-currents, and 

 minute droplets stream out on all sides from the particles 

 of soap into the surrounding oil. After a few hours the 

 oil-drop becomes finely frothy throughout, therefore white 

 and opaque. I have not followed out this method of pre- 

 paring such oil-lathers more accurately, so that I cannot 



