Bernard E. Jones

Electric Primary Batteries - a Practical Guide to Their Construction and Use Bernard E. Jones

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ... and evaporation. The cell, with a jar 8 in. high, has a capacity of 300 ampere hours. Practically all the remarks made in connection with the EdisonLalande apply in this case also. CHAPTER VII SILVER-ZINC AND PLATINUM-ZINC CELLS The De la. Rue Battery THE original form of the De la Rue battery utilises a fairly stout silver wire to form the negative element, around which is cast a cylinder of fused chloride of silver. A zinc rod forms the other element, and the pair are placed in a glass jar or other receptacle. The exciting solution is a saturated solution of common salt (sodium chloride). The chemical action is briefly thus:-----The zinc and salt react and yield sodium and a zinc salt containing two molecules of chlorine. The sodium thus produced, in the presence of water, immediately oxidises and becomes soda, liberating hydrogen. Hydrogen in its turn combines with the chloride of silver, with the result that metallic silver and hydrochloric acid are produced. The latter then combines with the previously liberated soda, and the result is ordinary salt and water. Thus the chemical energy is at the expense of zinc, and the silver salt is used up to thicken gradually the silver element. The cell gives 1'3 volts when in best condition, but owing to high internal resistance the current output is limited unless the cells are cumbersome and expensive. The cells are sometimes used for worldng small medical coils, but seldom where larger currents are required such as for lighting purposes. These cells were used in 1868 by Warren de la Rue and Miiller to ascertain the nature of electric discharges in rarefied gases. No less than 14,400 small cells were used, coupled in series, to determine the striking distance of the spark in air. Gaiife's cell is very simi...