152 RALPH S. LILLIE. 



are often obscured by irregularities in the rate of action, due 

 presumably to lack of uniformity in the zinc layer (local interrup- 

 tions, etc.). Platinum wires coated with copper in an electro- 

 lytic bath also make interesting demonstrations; such a wire 

 shows no formation of filaments in a solution of K 3 FeCye and 

 NaCl if the coating of copper is continuous; but if it is scraped 

 away at any region so as to expose the underlying platinum, the 

 copper near this region soon puts out filaments, and the process 

 extends for a distance of some centimeters from the area of 

 exposure. Such experiments are instructive as exemplifying the 

 nature of the effects that may follow local alteration in the electro- 

 motor character of a surface; and they may be used to illustrate 

 by analogy such physiological phenomena as the initiation of 

 growth-processes or regeneration in living organisms by incision, 

 amputation, or similar treatment. 



The reverse type of experiment, in which the formation of 

 filaments from one metal is inhibited or prevented by contact 

 with another metal of higher solution-tension, is equally readily 

 performed. Such an effect is illustrated in the just cited experi- 

 ment with zinc-plated iron wire; the exposed iron surface de- 

 velops no filaments; their formation is evidently prevented by 

 the adjacent zinc, which forms with the iron a couple in which 

 the zinc is anode; this, it may be added, is the reason why such 

 wires do not rust. The inhibitory influence of zinc upon the 

 formation of ferricyanide filaments from iron may be shown in a 

 more striking manner as follows; a straight piece of thin bright 

 iron wire (e. g., Baker's C. P.). some centimeters long, one end 

 of which is wound about a small strip of zinc, is placed in a 

 2 per cent. KsFeCye solution in dilute egg-white. Filaments put 

 forth rapidly from the zinc, especially near the iron, but the 

 iron itself remains perfectly bright and bare, and may show no 

 development of filaments for hours. If then the wire be cut in 

 two by scissors, the part remaining in connection with the zinc 

 remains unchanged, while the isolated part quickly develops the 

 characteristic blue-green filamentous growth of ferrous ferri- 

 cyanide. Evidently this development had previously been re- 

 pressed by the influence of the zinc; when the connection is 

 severed the iron reacts as usual. This experiment is even more 



