IX] 



OF LIESEGANG'S RINGS 



427 



conostats, which are formed in the surface layer of the solution, 

 consist of a portion of a spheroidal calcospherite, whose upper 

 part is continued into a thin spheroidal collar, of somewhat larger 

 radius than the solid sphere ; but the precise manner in which 

 the collar is formed, possibly around a bubble of gas, possibly 

 about a vortex-like difiusion-current* is not obvious. 



Among these various phenomena, the concentric stria tion 

 observed in the calcospherite has acquired a special interest and 

 importance f. It is part of a phenomenon now widely known, and 

 recognised as an important factor in colloid chemistry, under the 

 name of "Liesegang's Rings J." 



Fig. 204. Conostats. (After Harting.) 



If we dissolve, for instance, a little bichromate of potash in 

 gelatine, pour it on to a glass plate, and after it is set place upon 

 it a drop of silver nitrate solution, there appears in the course 

 of a few hours the phenomenon of Liesegang's rings. At first the 

 silver forms a central patch of abundant reddish brown chromate 

 precipitate ; but around this, as the silver nitrate diffuses slowly 

 through th'e gelatine, the precipitate no longer comes down in 

 a continuous, uniform layer, but forms a series of zones, beautifully 

 regular, which alternate with clear interspaces of jelly, and which 

 stand farther and farther apart, in logarithmic ratio, as they 

 recede from the centre. For a discussion of the raison d'etre of 



* Cf. p. 254. 



f Cf. Harting, op. cit., pp. 22, 50: "J'avais cm d'abord qne ces couches 

 concentriques etaient produites par I'alternance de la chaleur ou de la lumiere, 

 pendant le jour et la nuit. Mais I'experience, expressement instituee pour 

 examiner cette question, y a repondu negativement." 



X Liesegang, R. E., Ueber die Schichtungen bei Diffusionen, Leipzig, 1907, and 

 other earlier papers. 



