and rendered uniform, which produces a great and good result (1039.); and, upon proceeding to a second experiment, the important effect of first 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 (1148.). 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.  The acid of old charges 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 (1145.). xi.  By using a due mixture of nitric and sulphuric acid for the charge (1139.), 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  If, during a series of experiments, the acid becomes exhausted, it can be withdrawn, and replaced by other acid with the utmost facility; and after the experiments are concluded, the great advantage of easily washing the plates is at command.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.

1133.  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-tight under the alternations of wet and dry to which the voltaic instrument is subject.  To remedy this evil, Mr. Newman is now engaged in obtaining porcelain troughs.  The other disadvantage is a precipitation of copper on the zinc plates.  It appears to me