Dr. Hare onDe Bulls'' new Vollaic Batleries. IBl 



15. JVoie or addendum to the letter of Professor Robert Hare 

 to the Editor " on some improved forms of the Gahanic- 

 Dejlagrator.^'' pa. 99. Vol. VI If. 



Since this letter was published, I find that my friend Dr. 

 De Butts of Baltimore, has, in one apparatus, availed, him- 

 self of that alternation of surfaces, that omission of insulation, 

 which I had first used in one of my Calorimotors ;* in another 

 more numerous series of smaller plates, he employs tlie prin- 

 ciple of simultaneous immersion, originally used, with respect 

 to an extensive series, in my Deflagrator. His plates differ 

 from mine, in being semicircular — and there are more pairs 

 in the series, and fewer large plates in each pair, than in the 

 Calorimotor.f In his apparatus, the plates by a quarter revo- 

 lution enter the acid: in mine, a similar movement in the 

 trough throws the acid on the plates. 



I often contemplated the mode which he has adopted, as 

 it seemed sufficiently convenient ; but for several reasons, 

 preferred the methods which I have employed. Cutting the 

 sheets seraicircularly, is very wasteful of the metal — and I 

 have never seen sheet zinc lor sale in the circular form, nor 

 copper either, unless for bottoms, which are too heavy and 

 expensive. Plates of cast zinc cannot be used advantageously, 

 as they are too heavy for large apparatus, and are soon made 

 rough by corrosion, which diminishes their energy; whereas 

 the rolled zinc may be eaten down as thin as paper, and still 

 be efficient. The rationale of this difference, is to be found 

 in the crystalline texture of the cast zinc, which rolling de- 

 stroys. That solution, to a certain extent, tends to expose the 

 angles of crystals, has been fuUy shown, in the decrystalli- 

 zation of alum, first observed, I believe, by Mr. Daniels. I 

 bave recently seen it strikingly exemplified. 



Experience demonstrates the importance, of encasing each 

 zinc plate, especially if uninsulated, in the copper of the pair, 



* Of which a plate is 2;iven at tlie end of the book, 



1 1 crinsid-;r two h'»tpro^eneou? metnllic surfaces, as for instance, one surface 

 of CO)'; pr ami one si" face of zinc, when associated by metallic contact, or a 

 in*>'p.l!;c strap passing from one to the other, as a Galvanic Pair — whether the 

 sur'ctces be in one sheet of zinc, and one sheet of copper, or, consist of several 

 sheets of zinc, snd severe) of copper ; one metallic communication uniting all 

 the zinc sheets — and another uniting all the copper sheets. 



