Dr. Hare on De Butts’ new Voltaic ee 131 
15. N ote. sipiiitondon to the letter of Foafheen Robert Hare 
to the Editor ‘on some a de forms of the Galvanic 
Difermer” pa. 99. Vol. VIII. sa, 
Since this letter was published, I find that my tania Dr. 
De Butts of Baltimore, has, in one apparatus, availed him- 
self of that ciulalate Se surfaces, that omission of insulation, 
which I had first used in one of my Calorimotors ;* in another 
ore numerous series of smaller reierd he employs the prin- | 
ciple of simultaneous immersion, originally used, with respect 
to an extensive series, in my Deflagrator. His plates differ 
— mine, in being semicircular—and there are more 
n the series, and — large plates in each pair, than in the 
Galosiaiantes In his apparatus, the plates by a quarter revo- 
lution enter the acid: in mine, a similar averadiausiin: the 
trough throws the sid on the plates. 
I often contemplated the mode which he has eek as 
it seemed sufficiently convenient; but for several r 
preferred the methods which I have employed. Cutting thee? 
sheets semicircularly, is ig wasteful of the metal—and aa 
have never seen sheet zinc for sale inthe circular form, nor 
copper either, unless tor’ bottoms: which are too heavy and 
expensive. Plates of castzinc cannot be used advantageously, 
as they are too heavy for large apparatus, and are soon a 
rough by corrosion, eee diminishes thee energy; where 
the rolled zinc may be eaten down as thin as paper, and still 
be efficient. The Satie wy "of this difference, is to be fou 
in the crystalline texture of the cast zinc, which rolling de- 
stroys. ‘Thatsolution, to a certain extent, tends to exposethe 
angles of crystals, has been fully shown, in the decrystalli- 
zation of alum, first observed, I believe, by Mr. Daniels. I 
have er seen it siriknialg exemplified . 
Experience demonstrates the im portance, of encasing each 
zinc sie especially if uninsulated, in me copper - the pair, 
* ae al which a plate is given at the end of the book, 
nsider as for i ins stance . one surface 
ue sper and one surface of zinc, when associa ated by metallic contact, or a 
8 veral 
sheet ts ©: of zine, Jeseodh several 0 copper; one metallic commaniontion uniting all 
another uniting all the copper shee 
