ALVEOLAR LAYER 



35 



The fluidity of the described froths naturally demands 

 that the so-called alveolar layer should also be fluid. 

 Although the distinctness and sharpness with which it 



hence parallel to one another. Under these circumstances the lines of section 

 ac and be, which the two tangential planes at the points of attachment (a and 

 b) of the two neighbouring radial lamelke produce with the plane of the 



a 



Fig. I. 



Fit:. II. 



paper, will form at their point of intersection an angle of 120, as follows at 

 once from the triangle abc. If, however, the surface is curved, the two 

 neighbouring radial lamella? will not be parallel, but will form an angle ]8 with 

 one another (see II.) Then it follows from the quadrilateral acbd, that the 

 angle which the two tangential planes include at c = 120-/3. Mutatis 

 mutandis, it follows in the same manner that with a concave curvature of the 

 whole surface, the angle included by the tangential planes = 120 + /3. But since 

 the transverse measurement of the alveoli ab evidently always remains nearly 

 the same (in any case it does not increase, but, if anything, becomes smaller), 

 then as the angle c diminishes the radius, of the segment of the circle described 

 in it becomes smaller, and hence the curvature stronger, and vice versa. 

 That with strong curvature of the surface the transverse measurement of the 

 alveoli must, as has just been pointed out, become less, but in no case greater, 

 follows from the following 'considerations. Since, as is well known, the sphere 

 is that body which, with the same volume, possesses the smallest surface, a 

 portion of froth imagined as limited by plane surfaces will continually 

 diminish its surface during the transition into the spherical form, from which 

 it follows that this change of form is not accompanied by any tendency to 

 widen out the alveoli of the alveolar layer, but that they would rather tend, 

 on the contrary, to become narrower. The same reasoning holds, however, 

 also in the spherical rounding off of a portion of the froth, the surface of 

 which presented various degrees of curvature. 



With regard to the question discussed here, it is of special interest to note 

 that Budde (Zeitschr. f. physik. Chemie, Bd. vii. 1891, p. 586) has recently 

 shown that fine emulsions of chloroform droplets, which arise by the 

 action of soda on a solution of chloral, show a distinct tension in relation to 

 the remaining fluid, and hence form a constant marginal angle with the wall 

 of the vessel. 



