ADVANTAGES OF HARE'S TROUGH. 267 



the great advantage of arranging an apparatus to be used in connexion with the bat- 

 tery before the latter is put into action, iii. The trough is put into readiness for use 

 in an instant, a single jug of dilute acid being sufficient for the charge of 100 pairs of 

 four-inch plates, iv. On making the trough pass through a quarter of a revolution, 

 it becomes active, and the great advantage is obtained of procuring for the experi- 

 ment the effect of the Jirst contact of the zinc and acid, which is twice or sometimes 

 even thrice that which the battery can produce a minute or two after (1036. 1150.). 

 v. 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 unconnected state of 

 its extremities ; the acid is not unnecessarily exhausted ; the zinc is not uselessly 

 consumed ; and, besides avoiding these evils, the charge is mixed and rendered uni- 

 form, which produces a great and good result (1039.) ; and, upon proceeding to a 

 second experiment, the important effect oi Jirst contact is again obtained, vi. The 

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

 more voltaic duty (1128. 1129.), 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 

 effective as that in the ordinary form. vii. 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 (1 148.). viii. Again, 

 as, in consequence of the saving, thinner plates will perform the duty of thick ones, 

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

 a superiority which I incline to attribute to its greater purity (1144.). ix. Another 

 advantage is obtained in the economy of the acid used, which is proportionate to the 

 diminution of the zinc dissolved, x. The acid also is more easily exhausted, 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 

 fiocculi 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 

 (1 145.). xi. By using a due mixture of nitric and sulphuric acid for the charge (1 139.), 

 no gas is evolved from the troughs ; so that a battery of several hundred pairs of plates 

 may, without inconvenience, be close to the experimenter, xii. If, during a series of 

 experiments, the acid becomes exhausted, it can be withdrawn, and replaced by other 

 acid with the utmost facihty ; and after the experiments are concluded, the great 

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



