MORSE AND PIERCE. — SUPERSATURATION IN GELATINE. 



641 



another series, consisting 

 of fine, microscopic white 

 lines. According to Liese- 

 gang's description, when 

 the time came for the for- 

 mation of a new red line 

 one of the fine white lines 

 suddenly became yellow 

 and grew broader, until 

 it encompassed four of the 

 white lines and developed 

 into the dark red of sil- 

 ver chromate. Liesegang 

 observed, however, that 

 these white lines are not 

 necessary for the forma- 

 tion of the red ones and 

 are not present when 

 chromate diffuses into 

 gelatine impregnated with 

 silver. We are of the opin- 

 ion that these secondary 

 white lines are due to the 

 presence of impurities in 

 the gelatine, since they 

 appear with the same 

 distinctness when silver 

 nitrate diffuses into com- 

 mercial gelatine to which 

 nothing has been added. 

 They did not appear in 

 our purest electrolyzed 

 gelatine. The addition 

 of soluble chlorides, bro- 

 mides, or iodides in very 

 small quantities causes 

 the white rings to appear. 

 Figure 4 and Figure 5 

 show them between the 

 of silver 

 vol. xxxviii. — 41 



Figure 4. 



Precipitation in commercial gelatine, showing 

 fine white lines between the heavy dark deposits of 

 Ag 2 Cr0 4 . This is a section of a tube like Figure 

 2, magnified 10 diameters. 



larger lines 



Figure 5. 



Section of a plate like Figure 1, magnified 20 

 times, showing two sets of rings in commercial gel- 

 atine. The three heavy dark bands are Ag.,Cr0 4 . 



