Advantages of Hare’s Trough. 119 
pers may therefore be dispensed with; and it is that circum- 
stance which principally permits of such other alterations in 
the construction of the trough as gives it its practical advan- 
tages. 
1132. The advantages of this form of trough are very nu- 
merous and great. i. It is exceedingly compact, for 100 pairs 
of plates need not occupy a trough of more than three feet in 
Jeneth. ii. By Dr. Hare’s plan of making the trough turn 
upon copper pivots which rest upon copper bearings, the latter 
afford fixed terminations; and these I have found it very con- 
venient to connect with two cups of mercury, fastened in the 
front of the stand of the instrument. These fixed terminations 
give the great advantage of arranging an apparatus to be used 
in connexion with the battery before the latter is put into ac- 
tion. 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 experiment 
the effect of the first contact of the zinc and acid, which is 
twice or sometimes even thrice that which the battery can pro- 
duce a minute or two after (1036. 1150.).  v. When the ex- 
' periment 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 ren- 
dered 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 a// the destruc- 
tion which takes place with the ordinary forms of battery be- 
tween 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 
