Sulphation of Plates.—During discharge a storage cell deteriorates on account of the formation of lead sulphate over the surface of the plates. This lead sulphate is the product of the chemical combination of active material with the electrolyte. It is a non-conductor, white in color and of greater volume, in proportion than the active material. When the discharge is over prolonged, sulphation is evidenced by the electrodes becoming lighter in color, because of the sulphate which lessens the active surface.
Figs. 1,165 and 1,166.—Oil Insulator; [fig. 1,165], general view; [fig. 1,166], sectional view. Whenever a number of open cells are in use, unless precautions be taken, electrical leakage between the cells invariably occurs. This leakage is due chiefly to the semi-conducting nature of the thin layer of moisture which frequently covers not only the glass containing cells, but the unimmersed parts of the elements, and even the shelves on which the cells rest. To prevent this waste of energy, the outside of the cells should occasionally be well cleaned and thoroughly dried. A little vaseline or tallow may then be rubbed over them to advantage. The shelves or supports for the cells, should either be well varnished or coated with paraffin wax. Electrical leakage is greatly reduced if each cell be mounted on a glass or earthenware insulator, as shown in the illustrations. The insulator here shown is in two parts and of a mushroom shape. The lower cup contains a small quantity of some non-evaporating oil, and as the conducted moisture cannot bridge across this, a nearly perfect insulating medium is obtained. These insulators are made in various sizes and may be obtained in earthenware or glass. Those made of glass are found to give the best results.
Ques. Name some causes of sulphation.
Ans. It is sometimes caused by a too weak or too strong acid solution, but more generally by continued over discharging, or too rapid discharging of the batteries, or by allowing them to remain uncharged for long periods of time.
Ques. What is the effect of sulphation?
Ans. It tends to cause shedding of the active material, buckling of plates, loss of capacity, increase of resistance and consequent reduction of efficiency, and increase of temperature with flow of current. A sufficient amount of lead peroxide and sponge lead must be retained on the plates to reduce this resistance, otherwise the charging current cannot flow through the active material and regenerate the battery.