254 RALPH S. LILLIE AND EARL N. JOHNSTON. 



is used, more filaments and fewer shell-like structures are formed, 

 but in general cadmium shows little tendency to form filaments. 



5. Copper. Precipitation-structures are not formed so readily 

 from copper as from Fe, Zn, and Cd and a few other metals. 

 The solution-tension of copper is low, hence the metal does not 

 readily enter into solution under the conditions of these expe- 

 riments. A fine copper wire in contact with a nobler metal (Pt) 

 or carbon, and immersed in a solution of 4 per cent. K 3 FeCy 6 

 in distilled water containing not less than 4 per cent. NaCl, 

 will in a short time form some filaments and numerous structures 

 having the appearance of a burr (Fig. 20). The filaments that 

 are formed are usually not large, are comparatively straight, 

 and their walls are smooth and finely granular; very little non- 

 coherent precipitate is formed. A few which run over the surface 

 of the solution show a very perfect cross striation. None of 

 these filaments show any tendency to branch. The burr-like 

 structures are vesicular with short spicular filaments radiating 

 out in all directions. They often exhibit a pulsating or rhythmic 

 motion, one or more of the spicules shooting out rather quickly 

 at each pulsation. On account of the darkness of color and 

 thickness of the walls of these structures no striations have been 

 detected, and few details can be shown in a photograph. 



6. Nickel. Strips of nickel in contact with copper or silver 

 in a 2 per cent, egg albumen solution containing 4 per cent. 

 K 3 FeCy6 and 4 per cent. NaCl soon form a great many winding 

 tortuous filaments, closely resembling those formed from cobalt 

 (Fig. 21). Some large, thick walled, irregular filaments also 

 grow out very slowly from the surface of the metal, and large 

 masses of amorphous precipitate are formed. Some of the 

 filaments on the surface of the solution exhibit a few irregular 

 cross striations. A few groups of small vesicular structures also 

 form from the surface of nickel; these have a rhythmic motion 

 during their formation and will be described later. 



Experiments similar to the above were performed with Cr, 

 Pb, Sn, Mn, Ag and Al, but no well defined precipitation-struc- 

 tures w r ere formed except in the case of Cr and Pb. These two 

 produced only a few very small filaments so small in fact that 

 they could not easily be studied under the high power of the mi- 



