An introduction to physiology . UES 0 and 1 metre posts of the rheochord, the zero post and the slider to the capil-lary electrometer (Fig. 13). Turn the pole-changer to pass the battery current through thecopper sulphate solution or electrolyte. The cation (copper) will bepartially de-ionized atthe negative pole, orcathode, on which cop-per will be depositedin a fine film. The anion(sulphion, S04) will pass-~o) towards the positive pole,or anode, where it givesup its electric charge andbecomes the ordinary radical S04. This radicalcannot exist uncombined in water, but for
An introduction to physiology . UES 0 and 1 metre posts of the rheochord, the zero post and the slider to the capil-lary electrometer (Fig. 13). Turn the pole-changer to pass the battery current through thecopper sulphate solution or electrolyte. The cation (copper) will bepartially de-ionized atthe negative pole, orcathode, on which cop-per will be depositedin a fine film. The anion(sulphion, S04) will pass-~o) towards the positive pole,or anode, where it givesup its electric charge andbecomes the ordinary radical S04. This radicalcannot exist uncombined in water, but forms sul-phuric acid, setting free oxygen, which thereforeappears at the anode. The elements copper and oxygen depositedrespectively on the cathode and anode tend tofly back into the ionic state; and this ten-dency, taken in connection with the opposingosmotic force of the ions already in solution,sets up an electromotive force equal to thatwhich caused the de-ionization, but in an op-posite direction. Hence the polarization cur-. METHODS OF ELECTRICAL STIMULATION 53 rent. On cutting off the electrolyzing current,the polarization current may be measured. Note the position of the meniscus of the capil-lary electrometer. Turn the pole-changer so thatthe cell is cut off and the electrodes are broughtinto the electrometer circuit. The meniscus will indicate a current oppositein direction to the current from the cell. Dry Cell.—A dry cell is very convenientfor large classes. It usually consists of a zinccup, lined with plaster of Paris, saturated withammonium chloride, in the centre of which is acarbon plate surrounded with black oxide ofmanganese. When the cell is in action, the zincforms a double chloride of zinc and ammoniumwhile ammonia gas and hydrogen are liberatedat the carbon pole. These cells should never beused continuously for many minutes, for they arerapidly polarized by the accumulation of hydro-gen on the carbon plate. The unused cell re-gains its difference of potent
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