Alkaline batteries In the year 1900, Thomas Edison in America and Valdemar Jungner in Sweden both invented storage cells using a solution of caustic potash as the electrolyte. Edison used iron for the negative plate and Jungner used cadmium. Both men used nickel hydroxide for the positive plate. Cadmium has certain advantages over iron, and present-day cells […]
Care of lead cells The level of the sulphuric acid in a lead cell should be inspected regularly and any loss from evaporation made up with distilled water only. Acid should never be added except in rare cases where spillage has occurred. Lead cells must be charged regularly, using the maker’s recommended charging current, and not left […]
The lead-acid cell Two plates of lead are immersed in a glass vessel containing dilute sulphuric acid, and a current of about 2 A is passed between them from a battery in series with a rheostat (page 406) and an ammeter. After a time the plate at which the current enters the cell turns a deep chocolate brown […]
Primary and secondary cells The cells already described in this chapter are known as primary cells. In them the current is produced as a result of non-reversible chemical changes taking place between their various components, When all the zinc has been used up the cell cannot be restored to its original condition by passing a charging current […]
The dry cell The dry cell is a form of Leclanche cell in which the ammonium chloride solution is replaced with a jelly composed of starch, flour and ammonium chloride (Fig. 34.6). The positive element consists of a carbon rod surrounded by a core of a compressed mixture of manganeseuv) oxide and carbon. This is placed inside […]
The Leclanche cell Following the discovery of the simple cell, came the invention of a number of different cells in which polarization was either reduced or eliminated. All these have long since passed into history, but one which survived until comparatively recent times was the Leclanche cell, invented by Georges Leclanche about 1865. It has an e.m.f of […]
To study the simple cell A plate of copper and a plate of zinc, each fitted with a terminal, are dipped into a beaker containing very dilute sulphuric acid, and both plates are carefully examined. So long as the plates are not allowed to touch, no action will be observed at the copper plate. Owing to local action, […]
Faults of a simple cell (1) Polarization When a simple cell is in use it is found that the current quickly falls to a very small value. This defect results from the formation of a layer of hydrogen bubbles on the copper plate and is called polarization. The hydrogen layer weakens the current for two reasons. First, the […]
Electromotive force Any device such as a cell or dynamo which is able to drive an electric current round a circuit is said to possess electromotive force (e.m.f.). Electromotive force which is measured in volts is defined on page 406. For the time being, however, we may regard the e.m.f. of a cell as being equal to […]
Conventional direction of an electric current When the simple cell was discovered in the year IgOO its action was not understood, and scientists had no way of finding out in which direction the current flowed. They therefore decided to adopt the convention of regarding the current as a flow of positive electricity from the copper to the […]