154 • W. A. Osborne.- 



bubbles in a liquid, when they are small, results from the equality 

 of hydrostatic pressure in all directions. But in a jelly suppose 

 a cavity of any arbitrary shape formed. In the jelly bounding it 

 there will be surface stresses due to the unequal pressure effects of 

 the surface tension acting on parts of the surface of different curva- 

 ture. If the jelly is weak enough it will begin to flow (like lead in 

 the manufacture of pipes), and will assume finally the spherical 

 form round the cavity. But if the jelly is too strong to flow quickly 

 enough the unequalites of stress will not be relieved rapidly. The 

 escape of gas may accentuate them, with the result that in a stiff 

 enough jelly the material begins to tear at the part of the original 

 arbitrary cavity, where the conditions are most favourable, and the 

 tearing will go on till no longer necessary. A slow flow of the 

 jelly w^ill round off the edges of the spreading cavity, and give it a 

 lenticular shape." 



The bubbles make all possible angles with each other, giving a 

 spangled appearance. This point I was particularly anxious to 

 investigate. In a recent number of " Science Progress,"! there is 

 a reference to an article by Hatschek in 1914. which apparently 

 dealt with this same subject — the formation of bubbles in jellies. 

 I have been unable through the war to get Hatschek's article in 

 the " Kolloid-Zeitschrift," and so cannot institute any comparison 

 l>etw€en his results and mine, but most certainly my observations 

 did not support the assumption that any particular angle was pre- 

 dominant amongst these disk-like bubbles. I was at first inclined to 

 regard these results as evidences of the absence of crystalline or 

 pseudo-crystalline arrangement ; but as lines of cleavage are 

 absent in certain substances most definitely crystalline, this view 

 can not be rigidly held. If, however, a vectorial characteristic is 

 present, the arrangement must be similar to that exhibited in 

 masonry composed of courses of uniform cubical bricks. 



Fracture and Regelation. 



If a solid cylinder of 5%-10% gelatine is broken transversely at 

 any point, and the fracture mended by warming the opposing sur- 

 faces and allowing to set, it will be generally found that the former 

 line of fracture is the seat of weakness. If a sti-aight piece of 

 combustion tubing filled with 10% jelly is heated between cork 

 guards at some point, and then allowed to stand over-night, it will 



1 S. C. Bradford. On the Gelation of the Natural Einulsoids. Soience Progress, July, 1917 

 p. 64. 



