252 RALPH S. LILLIE AND EARL N. JOHNSTON. 



I 



filaments which run along the surface of the solution. The 

 manner of formation of zinc filaments, described in detail below, 

 presents one of the most interesting rhythmical phenomena seen 

 among any of the precipitation-structures. The rhythmic motion 

 at the end of the filament is no doubt the cause of the regularly 

 striated surfaces. These effects can scarcely be seen in a mic- 

 rophotograph on account of the coarse, thick walls of the fila- 

 ments. In Fig. 13 some of the larger zinc filaments are shown. 

 Some of these are very regularly and evenly striated. The en- 

 larged place in one of the filaments is an instance of a broadening 

 and flattening effect produced when a filament comes to the 

 surface of the solution. Filaments in all cases are circular in 

 cross section while entirely submerged in the solution. 



Branching is a common feature of these large slowly growing 

 zinc filaments. The entire outline of these structures is very 

 irregular (Fig. 14); apparently there is a tendency to give off 

 branches all along the course of growth. 



Fig. 15 shows a part of an extremely large zinc ferricyanide 

 filament which gave off many lateral branches. It reached a 

 length of about 2.5 centimeters. These very large filaments 

 grow so slowly that the deposit of precipitate can scarcely be 

 seen under the low power of the microscope. The example 

 shown was photographed after 24 hours in the solution. Branch- 

 ing can also be produced in these large growing filaments by 

 puncturing with a fine pointed needle. 



3. Cobalt. In minute structure the cobalt ferricyanide pre- 

 cipitation-fijaments resemble those formed from zinc. They 

 develop best in a 2 per cent, egg-albumin solution containing 

 4 per cent. K 3 FeCy 6 and I per cent. NaCl, and when the cobalt is 

 in contact with copper or some other nobler metal. They re- 

 semble zinc filaments in the coarseness of the precipitate, which 

 imparts a granular appearance and irregular outline to the fila- 

 ments. There is also much non-coherent precipitate scattered 

 along the sides of the filaments. Fig. 16 shows the character- 

 istic structures. The manner of formation of the filaments 

 seems to be the same as for iron filaments, an even outflow of 

 solution and regular deposit of precipitate. When the Co-Cu 

 combination is put into a weaker solution (2 per cent, egg albu- 



