PREPARATION OF OIL-FOAMS 11 



in this way, from olive oil and sugar or salt, and will forth- 

 with proceed to discuss the further experiments which were 

 performed in order to manufacture such foams, and to 

 explain their formation. 



The attempt to obtain similar drops of oil-froth with cod-liver 

 oil and common salt gave bad results, since only a defective foam 

 with large vesicles was formed. On the other hand, tolerably 

 good results were obtained with boiled linseed oil and common 

 salt. For certain reasons I experimented also on the behaviour 

 of a thick mixture made up with paraffin oil and common salt. 

 As was to be expected, no proper formation of foam took place 

 in the paraffin oil ; the salt, however, dissolved gradually with 

 formation of droplets, but very slowly. Hence diffusion of 

 water through the paraffin oil certainly takes place, although 

 very slowly. 



It has been already pointed out above, that the original 

 train of reasoning which led to the experiments upon the 

 formation of foam in oil was not, as a matter of fact, com- 

 pletely confirmed. I demonstrated that the particles of 

 the substances mixed with the oil were relatively coarse in 

 spite of the finest pulverisation ; hence it seems impossible 

 to ascribe the alveoli or foam vesicles of a successful oil- 

 foam of this kind, as a rule of extreme fineness, to the 

 drops of fluid produced by the solution of the enclosed 

 particles. For this reason some other source of the forma- 

 tion of the finest droplets of watery fluid must be present 

 in the oil. To clear up this point I instituted a series of 

 experiments, to enumerate which is of no further interest, 

 since they soon led to the result that even in pure olive oil, 

 placed in similar drops in H 2 under the cover-slip, numer- 

 ous very minute droplets of fluid very soon make their 

 appearance, causing it, at least in places, to become finally 

 quite opaque and 'of a minute foam-like structure. In a 

 few hours after setting up such a preparation, numerous 

 very fine droplets of fluid may be noticed in the oil ; these 

 drops increase continually in quantity, so that after one or 

 two days the drop has become quite turbid. In particular, 

 the lower edge of the drop, i.e. the edge of the surface by 

 which the drop rests on the slide, has then become quite 



