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The essential requisite of a voltaic battery for medical purposes is that the current of electricity which it supplies should not only be continuous but constant-should not vary appreciably in power during the application. Any battery which does not fulfil these requirements should be unhesitatingly rejected.
The Becker-Muirhead Battery is a modification of . Daniell's, and is that usually employed for telegraphic purposes. Its tension is low, but its action is very uniform. The elements consist of an un
amalgamated zinc plate (fig. 2, z), and of a thin copper plate, c. The copper plate is immersed in a solution of sulphate of copper contained in a porous cell, h; the zinc plate is immersed in water only, contained, with the porous cell and its contents, in
The Becker-Muirhead Battery as arranged at the National Hospital
for the Paralysed and Epileptic. a quadrangular porcelain vessel. The porcelain vessels are constructed in couples, each couple holding two pairs of elements, and five of these couples are packed in a strong oak box. The arrangement of the battery adopted at the National Hospital, as least complex, is shown in fig. 3, in which ten boxes containing one hundred pairs of elements are placed upon a simple open stand. The pairs are grouped in sets of five, and the terminal wires of these sets are attached to buttons in rear of two revolving disks, numbered respectively from 5 to 45, and from 50 to 100. By turning the disks the operator, without detaching the conducting wires with which the excitors are connected with the instrument, can bring into play the current from as many sets of cells as he desires. When in daily use the cells require to be re-charged and the zincs cleaned every two months, and new zinc plates are needed about every three years. This battery was designed by Mr. Becker, of the firm of Messrs. Elliott Brothers, 449 Strand, and it is supplied by them.
Mr. Becker has added to it, as a means of ascertaining its state of action, and as a guide to the operator, an ingeniously constructed tangent galvanometer. The battery when freshly charged and all connections cleaned is in its most effective state, but as the strength gradually diminishes it is essential for the medical practitioner to be able to ascertain at any given time the degree of diminution, so that he may determine the number of cells to be used in any given case.
The terminals of the galvanometer coil are connected with a simple commutator, so that the current may be made to traverse the galvanometer or not. When the battery is in perfect action it has been found that
5 cells give 45° deflection of the needle of the galvanometer. 10
Should five cells only give 22° deflection, the battery would be half its strength (if for the sake of illustration we take the angles for the expression of the strength instead of the tangents), and a higher number of cells should be placed in action, where before five were sufficient.
This battery has been in use at the National Hospital, and in my own private residence for several years. With ordinary watchfulness of its state of action, and care and regularity in re-charging and cleansing, it has proved a very effective and trustworthy instrument, and from the simplicity of its construction it can be cleaned, re-charged, and repaired with facility by an ordinarily intelligent artisan. Giving off no fumes or odours, it may be placed in any room without hesitation, never becoming offensive. In my own house the battery is placed in a closet on the area floor, and the conducting wires are brought into the consulting room and attached to the disks there. To clean and re-charge it, all that is necessary is to scrape the zinc plates, which become very foul, and to wash them, as well as the copper plates and porous cells, in cold water, to refill the porous cells with a saturated solution of sulphate of copper, and the porcelain vessels with fresh water. The porous cells, which are very cheap, occasionally become clogged, when it is better to replace them, for which purpose a few spare cells should be kept on hand. In very hot weather, when evaporation is rapid, it may be well to add a little fresh water without dismounting the battery, but this is very seldom required. If residing in town it is better to contract with the maker to do the recharging, of which the cost is about a sovereign. The price of a 100-cell battery is 251.—of a 50-cell battery, 151. 158.
All connections, binding screws, &c., of electrical instruments must be kept scrupulously clean, and to do this nothing is better than to rub them occasionally with a bit of very fine emery paper.
The single drawback to Muirhead's battery is that it is not portable. In every other respect it far surpasses any with which I am acquainted. Portability of a battery is of importance from facilitating the use of electricity as a means of diagnosis and in the treatment of cases not admitting of easy removal. M. Foveaux, of the firm of Messrs. Weiss & Co., 62 Strand, has designed and constructed a portable batvery which is unsurpassed for efficiency of action, and compactness consistent with efficiency.
Foveaux's Portable Battery is formed of pairs of