Therapeutic electricity and practical muscle testing.

  • Hedley W.S.
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Therapeutic electricity and practical muscle testing. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    not acted upon, but as the result of the decomposition of the electrolyte there is a tendency to evolve hydrogen at the negative plate; and if this be allowed to accumulate, the ability of the cell to furnish a current is materially decreased. And this decrease occurs not only because the film on the copper increases the internal resistance of the battery, but because the accumulation of hydrogen may for the moment be regarded as transforming the copper plate into a hydrogen plate, and hydrogen being electro-positive to zinc a current is set up opposing the original one; this is called a counter- electromotive force (C. E. M. F.). This accumulation of hydrogen is called polarisation, and when a cell gives out from this cause it is said to be polarised. Various forms of conducting substances, usually metals or carbon, are em- ployed for the couples. Zinc is usually the positive element, the negative being carbon, copper, lead, silver, or platinum. The Leclanche cell.—That primary cell which for medical purposes is most generally useful is the Leclanche (Fig. 4). Fig. 4.—A Leclanche cell. Here the elements are carbon and zinc, and the excitant is an aqueous solution of chloride of ammonium. The chemical energy which produces the E. M. F. is got in the combination between the zinc plate and the solution of ammonium chloride.