290 BECKER AND DAY 



as sealing wax, under torsion moves in planes at right angles 

 to the axis of torsion in such a way that each plane after torsion 

 remains a plane. On the other hand, in a solid mass even of 

 very feeble rigidity, surfaces originall}- plane and at right 

 angles to the axis of torsion become warped or otherwise dis- 

 torted surfaces after torsion. A prism of fine soapsuds was 

 -experimented upon by laying a fiber of silk around the per- 

 iphery at right angles to the axis and then twisting the mass. 

 The silk fiber immediately assumed the warped outline charac- 

 teristic of solids and showed that, in this respect at least, the 

 foam had the properties of a solid body. 



After some qualitative trials, it seemed worth while to make 

 at least an effort at measurement upon a solid of this character, 

 one principal reason being that distinctl}" finite displacements 

 (amounting to 30 or 40 per cent.) could very readily be obtained 

 with it. 



Plateau's solution was at first thought to offer the most promis- 

 ing material with which to prepare the pseudosolid, but we did 

 not find it as serviceable for this purpose as it has proved to be 

 for some others. We made up the solution from various olive 

 oil soaps, then from " C. P." sodium oleates furnished by 

 dealers, and finally with 2 preparations of very pure oleate 

 made in the chemical laboratory of the Geological Survey. 

 We were unable to verify Plateau's conclusion that increased 

 purity produced increased tenacit}- of film ; on the contrary, a 

 plain solution of yellow soap mixed with glycerine in random 

 proportions produced quite as rugged films. It was our experi- 

 ence, however, that all these films lost their toughness upon 

 being beaten into foam, and that the prisms of such foam de- 

 teriorated so rapidly that no measurements could be made upon 

 them. 



We next turned to the white of egg, with which we attained 

 a considerable measure of success. The white of a fresh egg 

 (it is imperative that it be very fresh), in which about an equal 

 volume of powdered sugar has been completely dissolved, can 

 be beaten to an extraordinarily fine homogeneous foam from 

 which prisms can be cut, mounted, and measurements covering 

 several minutes made upon them without any considerable 



