6 PROTOPLASM 



physics in which I set myself to dabble, the experiments 

 would perhaps have never been undertaken. 



Various fruitless attempts were made first with different 

 kinds of emulsions, which led to no satisfactory results, since 

 they were not to be deprived of the character of an emulsion, 

 i.e. of minute drops suspended in a relatively abundant fluid 

 matrix. A foam of fine structure was, however, for the 

 first time successfully produced by the mixing of two fluids. 

 Without describing here the previous experiments that gave 

 110 result, I will proceed to make a few remarks on the 

 attempts that were first successful. If a very thick solution 

 of commercial soft soap (potash soap) be shaken up thoroughly 

 with benzin or xylol, a fine emulsion is formed, since the 

 benzin distributes itself in the soap solution in drops 

 varying in size from those of moderate fineness to the very 

 minutest. If this emulsion be then left to stand, the lighter 

 benzin droplets rise to the surface, and become arranged, 

 through the thinning out of the layers of soap solution 

 between them, into a fine froth, just as bubbles of air rising 

 to the top of a soap solution collect gradually on its surface 

 into an ordinary lather. The description and explanation 

 given by Plateau for the latter case is without doubt also 

 suitable for the froth here described. The whitish foam, 

 in which benzin plays the part of air in an ordinary 

 soap lather, attains to a considerable degree of fineness, but 

 is not to be compared in this respect with the froths which 

 I obtained later in another way. I have not taken any 

 measurement of the average size of its meshes, since such 

 benzin foams are difficult to investigate, but they stand 

 somewhere on the boundary between the macroscopic and 

 the microscopic, since at least their larger meshes are visible 

 with the naked eye or with a weak lens. Nevertheless the 

 durability of froths of this kind is striking. I have kept 

 such a froth for two years now in a tightly-stoppered bottle 

 without its having essentially altered. Perhaps in the course 

 of time its meshes have become somewhat coarser, but its 

 original character has been completely retained. 



Experiments of various kinds, especially electrical, which 

 I performed upon such benzin froths did not lead to definite 



