172 Galvanic Batteries. 



to be used in connexion with the battery before the latter is put into 

 action. 3d. The trough is put into readiness for use in an instant, a 

 single jug of dilute acid being sufficient for the charge of one hundred 

 pairs of four inch plates. 4th. On making the trough pass through 

 a quarter of a revolution, it becomes active, and the great advantage 

 is obtained of procuring for the experiment the effect of the first con- 

 tact of the zinc and acid, vi^hich is twice or sometimes even thrice that 

 which the battery can produce a minute or two after. 5th. When the 

 experiment is completed, the acid can be at once poured from between 

 the plates, so that the battery is never left to waste during an uncon- 

 nected state of its extremities ; the acid is not unnecessarily exhaust- 

 ed ; the zinc is not uselessly consumed ; and, besides avoiding these 

 evils, the charge is mixed and rendered uniform, which produces a 

 great and good result ; and, upon proceeding to a second experiment, 

 the important effect of first contact is again obtained. 6th. The sa- 

 ving of zinc is very great. It is not merely that, whilst in action, the 

 zinc performs more voltaic duty, but all the destruction which takes 

 place with the ordinary forms of battery between the experiments is 

 prevented. This saving is of such extent that I estimate the zinc in 

 the new form of battery to be thrice as effiective as that in the ordinary 

 form. 7th. The importance of this saving of metal is not merely that 

 the value of the zinc is saved, but that the battery is much lighter and 

 more manageable ; and also that the surfaces of the zinc and copper 

 plates may be brought much nearer to each other when the battery is 

 constructed, and remain so until it is worn out : the latter is a very 

 important advantage. 8th. Again, as, in consequence of the saving, 

 thinner plates will perform the duty of thick ones, rolled zinc maybe 

 used ; and I have found rolled zinc superior to cast zinc in action ; a 

 superiority which I incline to attribute to its greater purity. 9th. An- 

 other advantage is obtained in the economy of the acid used, which 

 is proportionate to the diminution of the zinc dissolved. 10th. The 

 acid also is more easily exliausted, and is in such small quantity that 

 there is never any occasion to return an old charge into use. Such 

 old acid, whilst out of use, often dissolves portions of copper from 

 the black flocculi usually mingled with it, which are derived from the 

 zinc ; now any portion of copper in solution in the charge does great 

 harm, because, by the local action of the acid and zinc, it tends to 

 precipitate upon the latter, and diminish its voltaic efficacy. 11th. By 

 using a due mixture of nitric and sulphuric acid for the charge, no 

 gas is evolved from the troughs ; so that a battery of several hundred 

 pairs of plates may, without inconvenience, be close to the experi- 

 menter. 12th. If, during a series of experiments, the acid becomes 

 exhausted, it can be withdrawn, and replaced by other acid with the 

 utmost facility ; and after the experiments are concluded, the great 

 advantage of easily washing the plates is at command. And it ap- 

 pears to me, that in place of making, under different circumstances, 

 mutual sacrifices of comfort, power, and economy, to obtain a desired 

 end, all are at once obtained by Dr. Hare's form of trough. 



" But there are some disadvantages which I have not yet had time 

 to overcome, though I trust they will finally be conquered. One is 

 the extreme difficulty of making a wooden trough constantly water- 



