A textbook of experimental physiology for students of medicine / by N.H. Alcock and F.O'B. Ellison ; with a preface by E.H. Starling.

  • Alcock, N. H. (Nathaniel Henry), 1871-1913.
Date:
1909
Catalogue details

Licence: In copyright

Credit: A textbook of experimental physiology for students of medicine / by N.H. Alcock and F.O'B. Ellison ; with a preface by E.H. Starling. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    BATTEEIES, COILS are acted on by the acid, and are largely converted into PbS04. When an electric current is sent through the cell, the plate by which the current enters, the anode, becomes oxidised to Pb02, according to the equation PbS04 + 2H20 + S04=Pb02 + 4H + 2S04 The plate by which the current leaves the cell, the kathode, becomes reduced to metallic lead— PbS04 + H2=Pb + 2H + S04 In this state the accumulator is said to be ' charged.' As the equations just given are reversible, it follows that, when the plates are connected-together, the accumulator acts as a battery. The plate coated with Pb now becomes the anode, that coated with Pb02 the kathode, and the positive current flows outside the cell from Pb to Pb02, until both plates are again changed to PbS04. The E.M.F. of an accumulator is 2-0 volts during the greater part of its discharge. The internal resistance is low, and a well-made accumulator can yield a very heavy current; but all accumulators require constant attention, and, as a rule, accidental short-circuiting buckles the plates, and renders the cell useless. The student must therefore take particular care not to connect the two terminals of an accumulator, unless there is sufficient resistance in the circuit to avoid this accident. Induction Coils.—It is often necessary for physiological purposes to use an electric current of a high potential, and apply this at a given moment of time. Both these ends can be attained by the use of an induction coil. The form in universal use is the modification of Buhmkorff's, devised by Du Bois Eeymond. This consists of a primary coil, composed of com- paratively few turns of thick wire, and a secondary coil of many turns of fine wire. A current of low E.M.F., taken from one of the cells just described, is sent through the primary coil; while this current is flowing steadily, no effect is produced in the secondary coil, but at the moment of make, and again at the moment of break, a current is induced in the secondary, the current at make being in the reverse direction to that of the primary, and the current at break being in the same direction.