SURFACES 35 



Hitherto we have only regarded the formation of surface skins at 

 the interface fluid/gas. Such skins may be formed, however, at 

 the interface fluid/fluid or fluid/solid, provided only that the sub- 

 stance in question diminishes the surface tension of the water with 

 reference to the other fluid or the solid phase. J. ZIEGLER has in- 

 formed me (in a private communication) that on shaking benzol, 

 toluol, etc., with water containing albumin or gelatin, the benzol 

 or toluol forms above the water an emulsion which contains the 

 colloid, and that with repeated shaking, the major part of the 

 colloid may be removed from the aqueous solution. Shortly after 

 this communication, there appeared a publication by WINKELBLECH * 

 which not only confirmed these facts but called attention to the fact 

 that through the formation of an emulsion mere traces of colloids 

 could be detected. This phenomenon has long been recognized as a 

 very disturbing factor by organic chemists. On shaking reaction 

 mixtures with ether or benzol, such emulsions frequently form and 

 are very difficult to separate. We know now that these emulsions 

 are to be attributed to the formation of colloidal reaction products. 



H. BECHHOLD and J. ZIEGLER used the method of shaking out 

 the foam for the separation of albumoses (Witte's peptone) into 

 their components. They shook a 10 per cent aqueous solution of 

 Witte's peptone with ether, separated the ether foam from the 

 aqueous solution and again shook it out with ether. Then the 

 ether was permitted to evaporate from the foam, and the residue was 

 dissolved in ten times its volume of water, and this solution was 

 again shaken out with ether. After thus treating the solution from 

 three to five times, two substances were obtained, one of which re- 

 mained in the water in clear solution and became turbid when treated 

 with 24 to 25 per cent of ammonium sulphate. By this procedure a 

 separation of two components was obtained, but it is a question 

 whether the water-insoluble portion was present in the original solu- 

 tions or was formed by the shaking, like METCALF'S peptone skins. 

 The slight diminution in concentration is in favor of the first view. 

 By "shaking out the foam " a separation of the slightly water-soluble 

 hetero-albumoses and the remaining albumoses was accomplished. 



This spreading of colloids and the formation of colloid films at 

 the interface between two fluids is a phenomenon very frequently 

 observed. G. QUINCKE * 2 showed that gum collects at the interface 

 between oil and a gum arabic solution. Pharmaceutical emulsions 

 accordingly consist of oil spheres surrounded by a film of gum. 

 And when oil is emulsified with albumin, oil spheres surrounded by a 

 film of albumin are formed (ASCHERSON *). I have attributed the 

 so-called "serum films surrounding the globules in milk" to the for- 



