172 APPENDIX. [No. VI. 



After explaining the difference between his battery and the two other 

 batteries, he finishes thus : 



" Professor Daniell's excellent invention being distinguished by its 

 constancy ; Mr. Grove's powerful battery, by its intensity ; and my own, 

 by the cheapness with which the quantity of electricity may be developed, 

 and by its simplicity. By some it (Smee's battery) has been too much 

 extolled, by others too much blamed. Notwithstanding the mis-state- 

 ments on both sides, it has fully stood the test of time, and has been 

 employed by the public in a manner which I had not even hoped. The 

 reason they prefer it for general and especially for manufacturing 

 purposes, appears to be, that it does not require the use of porous tubes 

 or of the strong acids, and that it does not give off poisonous fumes. It 

 usually continues in active operation for six, eight, ten, or more days, 

 when a sufficiency of acid is supplied to it. The zinc frequently demands 

 but one amalgamation; and the time required either for setting it in 

 action, or for maintaining its operation, is comparatively not worth a 

 thought ; and, lastly, the expense of working it is reduced to the lowest 

 possible amount, being exactly proportionate to the power obtained. 



" Although theoretically it is not absolutely constant, yet practically, for 

 the purposes of the electro-metallurgist, its constancy remains for two or 

 three days, or, in other words, until the battery is nearly exhausted ; and 

 then, to replenish the solution of zinc with a fresh supply of dilute acid 

 will not occupy more than half a minute. In recording my own experience 

 of its practical, though not of its absolute constancy, I can at the same 

 time conjoin the testimony of some of the most extensive manufacturers in 

 this country. By the practical manufacturer this instrument is re-charged 

 with acid, at intervals varying from three days to a fortnight, according 

 to the size of the vessel containing the acid. Whilst upon the use of the 

 battery, I may state that the platinum, with proper care, never wears off 

 the silver, and that the platinized silver never undergoes the slightest 

 change, or is affected by the slightest local action. 



" Perhaps I may be expected to give an approximation to the relative 

 cost of working the three batteries. In mine it is the cost of the zinc 

 dissolved by the acid : zinc + acid + a local action. In Daniell's battery, 

 it is zinc + acid + sulphate of copper + much local action. Each cell 

 of this, to do any given amount of work, would cost about twice as much 

 as mine. In Grove's battery it is zinc + acid H- nitric acid reduced by 

 the hydrogen -f- nitric acid combined with ammonia formed during the 

 action of the battery + extensive waste of the zinc = about three times as 

 much as mine." 



YI. 



ON THE PRODUCTION OF ELECTROTYPES. By ALFKED SMEE, 

 Esq., Surgeon. (' London and Edinburgh Philosophical Magazine and 

 Journal of Science,' April 21st, 1840.) 



THE mode of taking copies of medals by the galvanic current is de- 

 servedly occupying much of public attention, and each is striving to add 

 his mite to the perfection of this elegant and useful process. There are 



