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The Smee Battery

Fig. 121, consists of two plates of amalgamated zinc, between which is placed a silver plate coated with platinum, the object of the platinum being to fill the surface of the plate with inumerable fine points which aid in discharging the bubbles of hydrogen which would cling closely to it if the plate were smooth and thus polarize the battery. This battery is charged with a solution of one part sulphuric acid to seven of water. The plates are connected to the clamp and placed in jar. In this battery, above all, the precaution of amalgamating the zinc should never be neglected. With an unamalgamated zinc the results are very unsatisfactory. The voltage of the Smee, when not in action, s 1.09 volts; when in action it runs down to .482 volts; this is caused by the hydrogen clinging to the plate as described. This was the form of cell generally used before the introduction of dynamos for electrotyping and other heavy work, and it is still used to a large extent. It emits fumes of hydrogen when in action, but it is a single fluid battery and when working in large sizes, plates 12x12 inches in size are suspended in a large tank of acidulated water, first a plate of zinc, then a plate of platinized silver, then another of zinc and so on alternately, zinc and platinum, to the end. This gives great facility in handling, as any number of plates to suit the work may be placed in the tank. As there is but one tank and the plates may be placed close together or far apart as required, the resistance may be easily made to balance that in the depositing tank, and thus the work will be performed under the most favorable conditions. In working the Smee, or any other battery for that matter, large tanks are better than small ones, provided that the plates are kept close together so as to reduce internal resistance of the battery. In the large Smee, if plates 12x12 are worked in a tank say 15x15x30, it will not be long before the sulphate of zinc, which forms and falls to the bottom, will soon commence to rise in the tank, thus shutting off the acid from a portion of the plates and reducing the quantity of current. If the same plates were worked in a tank 24x24x30, the tank might be permitted to become half full of zinc sulphate before the action would be impaired at all, and thus a much more even and constant current would be maintained; this is generally done in practice. In a gravity battery, however, the tank ought not to be deep, because the two elements should not be more than eight inches apart on account of the increased resistance caused by the separation. The tank, however, may be made large enough in length and width to contain elements of the desired size, or a number of standard zincs and coppers, if such an arrangement seems desirable, either to increase the facility of handling or to reduce the cost of a large number of jars, wires, connections, etc. We have seen a number of tanks made of wood, lined with lead, 10x10x60 inches, in which a single large copper element was placed at the bottom and a number of zincs hung as required from an insulated copper bar across the top. It seemed to work well and was convenient.

A few words as to coupling batteries may be of service. It should be born in mind that the quantity of current flowing in any circuit is the quotient resulting from dividing the voltage by the total resistance in that circuit and that the resistance may be increased or diminished by increasing or dimishing the distance between the elements of the battery and between the anode and cathode in the plating vat; also that the resistance varies inversely, as the surface of the elements immersed. Thus a plating surface of one square foot in the plating vat will offer four times as much resistance as four square feet. It thus becomes possible by increasing or diminishing the voltage of a current to keep the current flowing in the desired quantity, and by keeping the resistance in the battery about equal to that in the vats the highest economy is obtained.

For example, let us take eight cells, having a voltage of 1, and giving say 1/2 ampere per cell on short circuit. If we now couple then -, +, -, +, -, +, -, +, we shall have the voltage of 8 and the amperage of one cell of the same size with a voltage of eight, in other words, the same amount of current and eight times the strength of the single cell, as in Fig. 122. This is termed coupling in series, and would be used in solutions having a high resistance and small amount of surface immersed. If, on the other hand, the solution had a low resistance and large surface exposed, so that the voltage of one cell was ample to force the current through the circuit, they should be connected +, +, +, +, +, +, +, +, and -, -, -, -, -, -, -, -, giving the quantity of eight cells and the voltage of one, which amounts to nearly the same thing as if a single battery having eight times the surface of the single cell were used. This is termed coupling in multiple, Fig. 123. Similarly, if they were coupled +, -, +,-, +, -, +, -, and +, -, +, -, +, -, +, and those two were joined as in Fig. 124, we should have the equivalent of a battery possessing a voltage of four, and elements twice the size of the single cell. This would be spoken of as a battery of eight cells in series of four. Also four multiples, in series of two, might be arranged to give a voltage of two and quantity due to cells of four times the size of a single cell, as shown in Fig. 125. As the amperes of current passing per second depends upon the voltage, divided by the number of ohms resistance, in the circuit, it will be seen that the current can be controlled by coupling and by manipulating the resistance.