In the present glass boxes properly arranged on accessible shelves, with only plugs or studs between the plates, clear vision through the cell in any direction is easy, and accidental obstruction not only very seldom occurs but if it does it can without difficulty be seen and removed. But it must be granted that these boxes are less compact than their predecessors, and for some purposes, such as locomotion, compactness is of the first importance.
We have spoken mainly of difficulties connected with the positive plates, and have said nothing concerning the negatives. It is not that these are not susceptible of improvement, but their faults have been of a less imperious and obtrusive nature. They are not perfect, but they do fairly well, and there has been little need to worry much about them until the extraordinary behaviour of positives had been taken in hand and checked. The time is coming to attend to these also. They fail not from exuberance, but from inertness. As they grow old they do not swell, and warp, and burst, and crumble, like the positives, but they grow quietly hoary, and serenely decay. The composition in a worn-out negative consists of white sulphate through and through, but the frame remains intact, and it consequently never falls to pieces, nor does it swell. Impurities in the acid used tell upon a negative plate - nitric acid is fatal. Acid much too weak or very much too strong is also deleterious, and idleness is bad. The difficulties connected with negatives mostly depend on their aggravating property of always requiring a quite opposite treatment to positives. The less a positive is formed and overcharged the better. A negative delights in complete formation and frequent overcharge.
In recognition of this it is now customary to form them separately and to give the negative a thorough dose of hydrogen without commencing the corrosion of the positive by an overdose of oxygen. When the discharge from a cell begins to flag, it is the resisting scum of sulphate that has formed over the negative plate which is responsible for the flagging. The true E.M.F. of a cell is wonderfully constant throughout the whole discharge; but the internal resistance is all the time increasing, at first very slowly, ultimately, towards the end, with a rush. One such run-down cell in the midst of a lot of others therefore obstructs the current terribly. If only a series of cells could, with certainty, be made to work together uniformly, if a series of cells could behave as well as some of the cells in it, no one would have cause to complain. - (Nature.')
Repeated experiments have shown that the capacity of a secondary battery cell varies with the rate at which it is charged and discharged. For instance, a cell, such as used on street cars, gave a useful capacity of 137. 3 ampere hours when discharged at the average rate of 45.76 amperes, and this same cell yielded 156.38 ampere hours when worked at the rate of 22. 34 amperes. At the commencement of the discharge the electro-motive force of the battery was 2.1 volts, and this was allowed to drop to 1.87 volts when theexperiment was concluded. The entire active material contained in the plates of one cell weighed 11*5 lb., therefore, the energy given off per lb. of active substance at the above high rate of discharge was 62*225 ft.-lb., and when discharging at the lower rate of 22.34 amperes, the available useful energy was 72.313 ft.-lb., or nearly 2.2 electrical H.P. per lb. of active matter. But this active substance has to be supported, and the strength or weight of the support has to be made sufficiently great to give the plate a definite strength and durability.
The support of the plates, inclusive of the terminals above referied to, weighs more than the active material, which consists of peroxide of lead and spongy lead, so that the plates of one cell weigh actually 26.5 lb.; add to this the receptacle and acid, and you get a total of about 41 lb. per cell when in working order. 70 of these cells will propel an ordinary street car for 4 1/2 hours, whilst consuming the stored energy at the rate of 30 amperes, or over 5.6 electrical H.P. The whole set of 70 cells weighs 2,870 lb., which is barely1/5\ of the entire weight of the car when it carries 40 adult passengers; therefore^the energy wasted in propelling the accumulator along with a car does not amount to more than 20 per cent, of the total power, and this can be afforded so long as animal power is the only competitor. From numerous and exhaustive tests with accumulator cars in this country and abroad, I have come to the conclusion that the motive power for hauling a full-sized 6treet car for 15 hours a day does not exceed 7s., and this includes fuel, water, oil, attendance, and repairs to engine, boiler, and dynamo.
We hare thus an immense margin left between the cost of electric traction and horse traction; and the last objection, that relating to the depreciation of the battery plates can be most liberally met, and yet leave ample profits over the old method of propulsion by means of animals. (Reckenzaun.)