92 



SCIENCE PROGRESS 



phosphate (in the gelatin) and various calcium salts, which 

 gives extremely fine and occasionally very complicated periodic 

 deposits of tricalcium phosphate.^ Sections through two 

 specimens are illustrated in Fig. 3. This is a reproduction 

 of an actual photograph, on which the zones of clear gel be- 

 tween the bands have been coloured black ; the white spaces 

 are the precipitate. The breaks in some of the latter are 

 a curious and so far unexplained feature of the particular 

 reaction. Apart from them, the two halves of the preparation 

 — ^which was cut in the axial plane of maximum slope — show 

 slight asymmetry, but this is hardly sufficient to permit definite 

 conclusions. In view of the quantitative results described 



Fig. 3 



above, it appears at least improbable that the diffusion velocity 

 varies with the varying degree of compression, and any anomalies 

 in the stratifications would therefore have to be ascribed to 

 the effect of deformation on one or more of the^ — numerous 

 and in part obscure^ — factors which influence it under normal 

 conditions. 



An experiment similar to those in gelatin cylinders has been 

 described by W. A. Richardson in a paper to which my attention 

 was drawn only quite recently (" The Relative Age of Concre- 

 tions," Geol. Mag., Iviii, p. 121, 1921). It was directed to 

 ascertaining the effect of unequal stresses on the formation 

 of the silver chromate bands of the original Liesegang reaction, 



1 E. Hatschek, " Eine Reihe von abnormen Liesegang'schen Schichtungen," 

 Koll.-Zeitschr., xxvii, 225, 1920. 



