216 Dr. S. W. J. Smith on the Weston Cell 



surface of the 18 per cent, amalgam is continuing to fall. 

 The surface of the 17 per cent, amalgam has become 

 practically a two-phase system. 



(v.) At 45° C, the limiting percentages are about 8*8 and 

 16 5. The surface of the 20 per cent, amalgam remains 

 practically unchanged ; but, unexpectedly as before, the 

 surface percentage in the 19 per cent, amalgam is now 

 slowly falling. The decrease at the surface of the 18 per 

 cent, amalgam continues. 



(vi.) The amalgams were now cooled to 0° 0. After six 

 weeks at this temperature (last row of Table A) the surfaces 

 of all the amalgams containing more than 14 per cent. Cd 

 (excluding the irregular 16 per cent, amalgam) had returned 

 practically to the state in which they w T ere when the measure- 

 ments at 15°, as in (i.), were made. 



Table IX. (/. c. p. 269), described as typical, can be 

 analysed (by comparison with Table VIII.) in exactly the 

 same way as Tables I. and II. In connexion with this 

 Table the author writes : — ' ; At temperatures near to but 

 below the first transition temperature the diffusive processes 

 in an unstable amalgam are no doubt accelerated, and the 

 outer shell becomes richer in cadmium with a corresponding 



increase in the E.M.F. of the cell " No doubt rise of 



temperature will accelerate the diffusion ; but it is to be 

 remarked that, as shown in Table A ; an " unstable " amalgam 

 which has stood for some time at the ordinary temperature 

 can be raised through 20° or 30° C. without measurable 

 increase in the surface percentage of cadmium, and that 

 the first noticeable effect of temperature rise is a surface 

 decrease of an unexpected kind. The same effect is shown 

 in Table IX. 



Sometimes (e. g., I. c. pp. 260, 261, and Conclusion 1, 

 p. 274) Mr. F. E. Smith writes as if an unstable amalgam 

 may consist of one central solid mass surrounded by a shell 

 of lower concentration. It seems to me, however, that this 

 state of affairs must be very exceptional. 



§ 7. The probable structure of frozen amalgams. — It is a 

 well-established characteristic of crystallization in general, 

 that it proceeds around nuclei distributed more or less 

 uniformly throughout the cooling material. The uniformity 

 of distribution of the nuclear growths will be affected in the 

 present case by the fact that the solid grains are of less 

 density than the fluid out of which they separate. The first 

 grains to form must tend to rise. On account of their 

 sniallness they will not rise rapidly. As crystallization 



