. Dental electro-therapeutics. ct-ing wire) the cell gradually weakens,the polarization of the cell takes placefaster than the depolarization, andthe flow of current gets graduallyless. This kind of cell, however, has theproperty of recovering rapidly when thecircuit is again broken, the manganeseLedanehe dioxide continues its action of depolari-zation until the cell is free from thecollection of hydrogen gas on the nega-tive element. The chemical action of this cell ceases whenthe circuit is broken, so that its elements are not continuallyacted upon and it is a most lasting and economical cel
. Dental electro-therapeutics. ct-ing wire) the cell gradually weakens,the polarization of the cell takes placefaster than the depolarization, andthe flow of current gets graduallyless. This kind of cell, however, has theproperty of recovering rapidly when thecircuit is again broken, the manganeseLedanehe dioxide continues its action of depolari-zation until the cell is free from thecollection of hydrogen gas on the nega-tive element. The chemical action of this cell ceases whenthe circuit is broken, so that its elements are not continuallyacted upon and it is a most lasting and economical cell. A collection of these cells makes a very useful batteryfor dental purposes, if kept in a cabinet and the water andammonium chloride renewed when required, will remainactive for a number of years, requiring very little zincs are destroyed in time by chemical action butthey are readily replaced. When it is unnecessary to movethe battery about, as is the case in a dental surgery, thesecells are admirably Fig -Wet :cell. LECLANCHE DRY CELL 55 The electro-motive force (E) of the Leclanche cell volts; there is considerable internal resistance (r).The calculation of the current strength (c) can be readilycarried out according to Olnns law. it will be found thatone cell is inadequate for dental purposes with the body incircuit. Take, for example, the resistance of 1500 ohms for thebody and roughly ohm for internal resistance. Theequation then is: V R1500 + = ampere = 1 milliampere It is therefore necessary to collect the current from anumber of these cells by joining them in series in the formof a battery. Leclanche Dry Cell.—This cell is made on the same prin-ciple as the wet cell described. Instead of the glass jar, thecase of the cell is made of zinc which is used as the positiveelement; in the centre is the carbon nega-tive element surrounded with a layer ofmanganese dioxide as the electrolyte is a pasty subs
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