1042. Weak and exhausted charges should never be used at the same time with strong and fresh ones in the different cells of a trough, or the different troughs of a battery:  the fluid in all the cells should be alike, else the plates in the weaker cells, in place of assisting, retard the passage of the electricity generated in, and transmitted across, the stronger cells.  Each zinc plate so circumstanced has to be assisted in decomposing power before the whole current can pass between it and the liquid.  So, that, if in a battery of fifty pairs of plates, ten of the cells contain a weaker charge than the others, it is as if ten decomposing plates were opposed to the transit of the current of forty pairs of generating plates (1031.).  Hence a serious loss of force, and hence the reason why, if the ten pairs of plates were removed, the remaining forty pairs would be much more powerful than the whole fifty.

1043.  Five similar troughs, of ten pairs of plates each, were prepared, four of them with a good uniform charge of acid, and the fifth with the partially neutralized acid of a used battery.  Being arranged in right order, and connected with a volta-electrometer (711.), the whole fifty pairs of plates yielded 1.1 cubic inch of oxygen and hydrogen in one minute:  but on moving one of the connecting wires so that only the four well-charged troughs should be included in the circuit, they produced with the same volta-electrometer 8.4 cubical inches of gas in the same time.  Nearly seven-eighths of the power of the four troughs had been lost, therefore, by their association with the fifth trough.

1044.  The same battery of fifty pairs of plates, after being thus used, was connected with a volta-electrometer (711.), so that by quickly shifting the wires of communication, the current of the whole of the battery, or of any portion of it, could be made to pass through the instrument for given portions of time in succession.  The whole of the battery evolved 0.9 of a cubic inch of oxygen and hydrogen in half a minute; the forty plates evolved 4.6 cubic inches in the same time; the whole then evolved 1 cubic inch in the half-minute; the ten weakly charged evolved 0.4 of a cubic inch in the time given:  and finally the whole evolved 1.15 cubic inch in the standard time.  The order of the observations was that given:  the results sufficiently show the extremely injurious effect produced by the mixture of strong and weak charges in the same battery[A].

[A] The gradual increase in the action of the whole fifty pairs of plates was due to the elevation of temperature in the weakly charged trough by the passage of the current, in consequence of which the exciting energies of the fluid within were increased.

1045.  In the same manner associations of strong and weak pairs of plates should be carefully avoided.  A pair of copper and platina plates arranged in accordance with a pair of zinc and platina plates in dilute sulphuric acid, were found to stop the action of the latter, or even of two pairs of the latter, as effectually almost as an interposed plate of platina (1011.), or as if the copper itself had been platina.  It, in fact, became an interposed decomposing plate, and therefore a retarding instead of an assisting pair.