i.L4 



EFFECT OF GAJ.VAN1SM. IN METAJ.MC ARBORIZATIONS. 



Erroneous 

 supposiiions. 



Another hy- 

 pethesb 



confuted by 

 experiment. 



^11 similar eases^ and not alone in that before us. Tjl}^y«f^ho 

 supposed in tbe lirst experiment, fig. 7, that the disoxigen- 

 ized metal was conveyed instantaneously from z to ;n, or 

 from the top downward; must necessarily admit, that in tlie 

 second experiment the metal, w, after having, ceded it§ qisJlt 

 gen, 0, to the zinc, «, which is at the bottom, must have 

 been carried from o toward m, that is, from the bottom up- 

 ward. But these two suppositions are diametrical\y opposite 

 to each other; and, besides, each is repugnant to th^ pi:im^ 

 law of chemical attraction, according to which tbe sphere of 

 perceptible affinity between bodies never extends beyond 

 the distance of apparent contact. The absurdity of these 

 hypotheses therefore is evident, and requires no further dis- 

 cussion. 



Sect, II. There is another way of explaining metallic 

 arborizations, more plausible indeed, but equally false. 



It may be supposed, that, in proportion as the metallic 

 particles of the solution are precipitated on the zinc, they 

 are raised up successively by those, that proceed to be de- 

 posited on it in their turn, to cede to it their oxigen» In 

 thi« case the first stratum of metal pr«cipitated must be 

 continually removing farther from that which acts iis the 

 precipitant; and all the various changes of form, must take 

 place solely in that part of the arborization, which imme- 

 diately covers the latter metal. But we (hall see the con- 

 trary to this demonstrated by experiment. If, for instance, 

 the extreme ramifications of the tree of Saturn, fig. 7, have 

 arrived as far as c, make a mark with ink opposite to (his on the 

 outside of the tube, and you will soon see, in a quarter of an 

 hour's attentive observation, fresh ramifications implant 

 themselves on those that before existed ;:the.iiew.ftCcr€tionsr 

 will, advance beyond the mark, but thfe extremity c^ cor- 

 responding toit, will remain fixed; and the ramifications 

 most remote from the zinc will be continually underg^jjjg' 

 changes of figure, , wh^le the part of the tree between -the 

 njark and the zinc; r^wiU, not e^sperience the lea ft change. 

 The hypothesis alluded to therefore is untenable, but from 

 t^eiobseryations made vye may i\>fer,; tjiaf, when a.istratwm 



th#fi^9h particl€»0f¥<*ked- Hiatal proereed^o aui'eh'IfiJen^fteat a"(liir-'" 

 taaucefroiB Uve iincrt^Js.i« the last^extTCteiti-s of the arbftriiaVKAi,"' 

 • • . of 



