280 Dr. C. R. A. Wright on the Determination of 



most extreme instances, were observable in each case with 

 different bright plates as compared with one another. On the 

 other hand, on comparing various electro-copper or amalga- 

 mated copper plates with one and the same zinc plate, or 

 various amalgamated zinc plates with one and the same copper 

 plate, the extreme ranges of fluctuation were found to be not 

 more than half those observed with bright plates, and usually 

 did not exceed + "001 as compared with the average. 



(4) As the ultimate average result of all the determinations 

 made, it Mas found that an amalgamated zinc plate gave, when 

 opposed to a given copper plate, an E.M.F. lower by *002 volt 

 than a bright zinc plate, and lower by "001 volt than an 

 electro-zinc plate. The actual differences in various experi- 

 ments ranged in the former case between +-006 and — -004, 

 the bright zinc plate sometimes giving a higher value, and 

 sometimes a lower value, than the amalgamated plate — more 

 frequently the former. (In the example emoted above, the 

 bright zinc plate gave a value lower by "0030 when opposed 

 to an electro-copper plate, and by -0037 when opposed to a 

 bright copper plate.) With electro-zinc as compared with 

 amalgamated zinc, the difference ranged between + '004 and 

 — '003, the electro-zinc sometimes giving a higher and some- 

 times a lower value than the amalgamated zinc, more usually 

 the former. 



(5) Similarly, the effect of substituting a bright copper plate 

 for an electro one in any given combination was uniformly to 

 cause an increase in the E.M.F. by an amount varying between 

 •001 and -010 volt, and averaging, on the whole, -006. (In the 

 example emoted above, bright copper gives a higher value 

 than electro-copper by *0075 when opposed to amalgamated 

 zinc, and by '0068 when opposed to bright zinc.) The effect 

 of amalgamating a copper plate was found to be, on the whole, 

 to give an E.M.F. lower by '001 than that given under the 

 same conditions by a freshly electro-coppered plate, the actual 

 difference ranging between +'002 and —'003, the amalga- 

 mated plate sometimes giving a higher value and sometimes a 

 lower one than the electro-plate, more frequently the latter. 

 It is worthy of notice that no sensible difference was obser- 

 vable whether the plate amalgamated were previously of bright 

 rolled metal or of electro-metal ; so that, on the whole, the 

 effect of amalgamating a bright rolled plate was to depress 

 the E.M.F. by "006 + -001 = -007. 



(6) The average results of all the experiments made are 

 contained in the following tabular statement : increase in 

 E.M.F. is indicated by the + sign, and diminution by the — 

 sign:— 



