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To re-amalgamate the zincs allow each plate to remain for about a minute in diluted sulphuric acid (one part of strong acid to seven parts of

Fig. 8.

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Stöhrer's Portable Battery. water) for which purpose a common tumbler answers well. Hold the plate over a second empty tumbler, and pour upon it about a teaspoonful of quicksilver. Rub the quicksilver well over the plate with a piece of sponge until it is quite bright; replace the plate for a moment in the acid, and notice if any bubbles of gas are evolved ; if so, the amalgamation is imperfect, and more quicksilver will be required. If no gas is generated, rinse the plate for a moment in tepid water, and stand it aside to dry. At the same time the carbons should be soaked for about five minutes in tepid water (not hot), to dissolve the zinc salts with which they become encrusted. They may be also scrubbed with an old nail- or toothbrush. Clean all metallic connections with emery paper, and do not screw the carbons and zincs together again until they have been allowed to dry for twelve hours. Charge each cell with a solution of one part of strong sulphuric acid to nineteen of water, and put in each a pinch (about as much as a pinch of snuff) of sulphate of mercury, which will greatly contribute to preserve the amalgamation of the zincs. Dr. Stöhrer constructs this battery in several sizes, varying from thirteen to forty pairs of elements (fig. 7), adapted for hospital use; and in a portable form (fig. 8) of essentially the same construction, but smaller and lighter. It is a most efficient and serviceable instrument, and equal to all the requirements of electro-therapeutics. Its price is from 61. to 151. 158.

Pulvermacher's Chain Batteries. As before stated

the fundamental requisite of a voltaic current for therapeutic application is its constancy. To obtain this property and at the same time a cheap and portable instrument, has been for years the effort of manufacturers. The most ingenious arrangement of the largest number of elements in the smallest space is to be found in Pulvermacher's chains. But in action they are inconstant. Steeped in vinegar they yield currents of high tension, but their action rapidly declines, and they become much weakened in a very short time. They may in the absence of a better instrument be occasionally of use for purposes of diagnoses, employed with electrodes in the same way as other batteries ; but for therapeutical applications they are unsuitable, and worn upon the body as advocated by the inventor they exercise little or no benefit, except perhaps in some cases where they appear to act from their electrocutaneous excitation as counter-irritants. I am led to make these remarks and to describe these forms of battery from the very numerous letters of inquiry that I receive regarding them. The principle of their formation is that of the combination of a great number of elements, from 300 to 400, having but small surface. The original and best known forms of the chains are shown in figs. 9 and 10. The elements of which the chains are now constructed are formed of a cylinder of copper plate perforated with longitudinal openings, and within this cylinder is a cylinder of zinc without perforation. The zinc is separated from immediate contact with the copper by a few stout threads. An unbroken link which forms part of the copper cylinder serves as the means for joining the several segments. This construction permits the withdrawal and renewal of the zinc when

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Pulvermacher's Galvanic Chain. Another form of Pulvermacher's

Galvanic chain.
FARADISM.

The essential requisites for a faradic instrument are: 1. The possession of a primary and secondary coil, constructed after certain proportions of thickness and length of wire.* 2. A sufficient range of power. 3. An exact means of graduation. 4. Constant readiness for action, and capability of being placed out of action without trouble and loss of time.

*The distinction between the primary and secondary coil, therapeutically, is mainly a question of the greater tension of the current of the secondary coil, enabling its current to penetrate easily several thicknesses of muscle.

Duchenne's large Volta-faradic apparatus.—In this instrument the two coils forming the systems of induction are composed of two copper wires differing in diameter and length and covered with silk.

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The thicker and shorter of the two wires is rolled around a bundle of soft iron wire so as to form a coil (the primary coil). The ends of this wire terminate upon two small plates of platinum at the level of the knobs E, L, fig. 11, which are the positive

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