Portable Bat

battery chiefly in cases in which the interrupted Foveaux's voltaic current has been required to be used for tery. diagnostic purposes. It is an exquisitely made instrument, and fully supplies a long felt want.

tery.

Stöhrer's Battery with Lifting Apparatus.-Stöhrer Stöhrer's Batof Dresden has constructed a very excellent battery for medical purposes. The elements, consisting of carbon and zinc, are attached in pairs to a wooden rail, and project into glass vessels, which serve for the reception of diluted sulphuric acid, and which are so arranged in the completed apparatus, that they can be moved vertically up and down, and fixed in either position. By this arrangement the acid can be brought into contact with the zinc and carbon, or by shutting down the cells be excluded from them altogether. In the latter case the acid will only fill the lower third of the glass, and it is hardly possible that it can be spilt. Should, however, such an accident be apt to occur, a small stopper of caoutchouc at the left side of the base must be pulled out, and the instrument slightly inclined, that the acid may run out. The conducting cords are attached, as shown in figs. 7 and 8, to a simple and easily adjusted slide running in a groove upon the bar that supports the elements, and at its lower surface being in metallic connexion with them. By the movement of the slide any desired number of cells can be brought into operation; and on its upper surface is an ingeniously devised commutator, by

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Stöhrer's Bat- turning which to the right or left, the current admits of being reversed without removal of the conductors. The bar is marked from left to right with cyphers corresponding with the number of the elements, and their points of attachment, and it is of importance that the centre of the slide should be placed in a

in use.

line with this attachment, as shown in fig. 7, in which fourteen, and in fig. 8, in which ten cells are If this rule is neglected, rapid decomposition with development of gas, weakening of the current and general fouling of the instrument will result. In frequent use, re-amalgamation of the zincs will be required about once in six months, or whenever during use effervescence of the acid is perceived.

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

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.

C

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Stührer's Bat- 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 connexions 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 67. to 157. 158.

Pulvermacher's Chain Battery.

Pulvermacher's Chain Batteries.-As before stated, the fundamental requisite of a voltaic current for

macher'sChain

therapeutic application is its constancy. To ob- Pulver-
tain this property and at the same time a cheap Battery.
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 diagnosis, 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 prin-
ciple 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