STRUCTURES RESEMBLING ORGANIC GROWTHS. 15! 



at the surface of the metal, and somewhat later slender filaments 

 begin to grow out ; in a short time (half an hour or less) the metal 

 is covered with filaments and vesicular formations from one end 

 to the other. The first appearance of these structures is typically 

 near the contact with the copper; a gradient in the rate of 

 formation is thus apparent, with the most active region near the 

 copper. This accelerating influence of the nobler metal is clearly 

 perceptible at the extremity of the strip, i. e., for a distance of 

 some centimeters from the contact. A similar "control" piece 

 of zinc, without copper, shows only a few irregular and slightly 

 developed filaments at a time when the copper-bound piece is 

 completely covered with a luxuriant hypha-like growth. Plati- 

 num and iron w T ires have the same general effect as copper, only 

 with platinum the accelerating influence is distinctly greater, 

 and with iron less, than with copper. Carbon may also form the 

 substance of the cathodic area; a piece of zinc marked with 

 lead-pencil shows a rapid development of filaments, beginning at 

 the marked area and grading off from there. 



Striking experiments may also be performed with copper as 

 the filament-forming metal. In this case a higher concentration 

 of NaCl is required for the rapid formation of filaments ; beautiful . 

 structures develop after some minutes in a solution containing 

 4 per cent. K 3 FeCy 6 and 4 per cent. NaCl (with or without 

 egg-white). A piece of fine copper wire 3 or 4 cm. long, encircled 

 at one end with a platinum wire, or wound around a piece of 

 carbon, shows a highly characteristic development of filaments; 

 some of these within a few hours may reach a length of several 

 centimeters; such filaments, as already described, often exhibit 

 a very perfect and regular cross-striation where they run along 

 the surface of the solution. A similar piece of copper wire with- 

 out contact of nobler metal or carbon remains unchanged. 



Many variants of this type of experiment will readily suggest 

 themselves. Experiments with plated wires yield instructive 

 results. Pieces of "galvanized" (zinc-plated) iron usually show 

 the first development of filaments of zinc ferricyanide near the 

 cut surface where the iron is exposed, and gradients in the rate 

 of formation extending from this region along the wire are 

 frequent. It should be added, however, that these gradients 



