224 Miss C. A. Raisin. On certain Structures formed 



As we add a larger amount of the salt solution, the following effects 

 were produced: first, the crystallised bodies all became larger; 

 more crystal-shaped grains formed, instead of the rounded blebs,* 

 and then, beyond an irregular, clear space around each, the ground 

 was occupied by a more distinctly dendritic deposit, which faintly 

 depolarised. In a more watery medium, the ovoid grains are more 

 marked. From a mixture of vermilion in a solution of the salt, the 

 results are similar, but the vermilion is in clots or lumps, or scat- 

 tered granules, with intervening, irregularly shaped spaces. In one 

 slide the clear spaces are rather definitely shaped and angular, 

 almost as if dominated by crystallising force, yet the crystallising salt 

 has formed only small, ovoid grains, clustered rather more thickly 

 near the central part of the space. 



The formation of spherulitic structures has been described by 

 several authors. Good examples were obtained in these experiments 

 with sodium phosphate mixed with gelatin. A weak solution, or a 

 solution of the salt without the gelatin, gave spherulitic structures, 

 though these were small and scattered. From a stronger mixed 

 solution the deposit consisted of rounded, gelatinous-looking globules, 

 more or lesa aggregated, which, with crossed nicols, showed radiate 

 structure and a black cross. Radial tufts of acicular crystals of 

 calcium sulphate are well known among microchemical tests ;f 

 these were obtained from pure solutions of the salt, or from mix- 

 tures with " mud," or with gelatin. One small isolated drop (J inch 

 across) of a mixture of calcium sulphate solution and vermilion, 

 which dried on another slide, J exhibited spherulitic spheres or hemi- 

 spheres (their centres being on, or just within, the circumference of 

 the drop), clustered like those which have been obtained in a sheet of 

 glass which had been raised to a high temperature and then cooled. 



In other drops, where definite crystals were formed, the crystals 

 projected inwards, often with branched, almost dendritic, or skeleton, 

 growth. || If in certain spherulites a radial ingrowth of crystallites 

 takes place, as seems probable, it would be somewhat analogous to 

 this result of shrinkage or skin tension in the drop. 



In certain examples, where a rather concentrated solution was 



* Cf. H. Vater, ' Zeits. fur Kryst./ vol. 27, p. 489. 



f " Notes on the Micro-chemical Analysis of Rock-making Minerals," by 

 Lieut.-General C. A. McMahon, F.G-.S. (' Min. Mag.,' vol. 10, p. 110). 'Manual 

 of Micro-Chem. Anal.,' Professor II. Behrens, p. 71. 



% I failed to reproduce this structure again, although many variations in the 

 conditions were tried. 



" Address of President," by Professor T. GK Bonney, ' Quart. Journ. Geol. 

 Soc.,' 1885, vol. 41. p. 63. ' Roy. Soc. Proc.,' 1885, vol. 39, p. 103, by D. Her- 

 mann and F. Rutley. 



|| For the mode of growth and general form of the crj'stals, compare Lehmann 

 in ' Zeits. fur Kryst.,' 1877, vol. 1, PL 21, figs. 49, 50a PL 22, fig. 84. 





