. Dental electro-therapeutics. l by aconducting wire) the cell graduallyweakens, the polarization of the celltakes place faster than the depolariza-tion, and the flow of current getsgradually less. This kind of cell, however, has theproperty of recovering rapidly whenthe circuit is again broken, the man-ganese dioxide continues its action ofdepolarization until the cell is free fromthe collection of hydrogen gas on thenegative 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. l by aconducting wire) the cell graduallyweakens, the polarization of the celltakes place faster than the depolariza-tion, and the flow of current getsgradually less. This kind of cell, however, has theproperty of recovering rapidly whenthe circuit is again broken, the man-ganese dioxide continues its action ofdepolarization until the cell is free fromthe collection of hydrogen gas on thenegative 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 Wet Leelanche cell. 56 ELECT RO-PH YSICS 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 Ohms 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: VR1500 + amperes = 1 milliamp&re Fig. 8 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 p
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