812.  Charcoal was used as the positive electrode in both sulphuric and muriatic acids (808. 810.); but this change produced no variation of the results.  A zinc positive electrode, in sulphate of soda or solution of common salt, gave the same constancy of operation.

813.  Experiments of a similar kind were then made with bodies altogether in a different state, i.e. with fused chlorides, iodides, &c.  I have already described an experiment with fused chloride of silver, in which the electrodes were of metallic silver, the one rendered negative becoming increased and lengthened by the addition of metal, whilst the other was dissolved and eaten away by its abstraction.  This experiment was repeated, two weighed pieces of silver wire being used as the electrodes, and a volta-electrometer included in the circuit.  Great care was taken to withdraw the negative electrodes so regularly and steadily that the crystals of reduced silver should not form a metallic communication beneath the surface of the fused chloride.  On concluding the experiment the positive electrode was re-weighed, and its loss ascertained.  The mixture of chloride of silver, and metal, withdrawn in successive portions at the negative electrode, was digested in solution of ammonia, to remove the chloride, and the metallic silver remaining also weighed:  it was the reduction at the cathode, and exactly equalled the solution at the anode; and each portion was as nearly as possible the equivalent to the water decomposed in the volta-electrometer.

814.  The infusible condition of the silver at the temperature used, and the length and ramifying character of its crystals, render the above experiment difficult to perform, and uncertain in its results.  I therefore wrought with chloride of lead, using a green-glass tube, formed as in fig. 72.  A weighed platina wire was fused into the bottom of a small tube, as before described (789.).  The tube was then bent to an angle, at about half an inch distance from the closed end; and the part between the angle and the extremity being softened, was forced upward, as in the figure, so as to form a bridge, or rather separation, producing two little depressions or basins a, b, within the tube.  This arrangement was suspended by a platina wire, as before, so that the heat of a spirit-lamp could be applied to it, such inclination being given to it as would allow all air to escape during the fusion of the chloride of lead.  A positive electrode was then provided, by bending up the end of a platina wire into a knot, and fusing about twenty grains of metallic lead on to it, in a small closed tube of glass, which was afterwards broken away.  Being so furnished, the wire with its lead was weighed, and the weight recorded.

815.  Chloride of lead was now introduced into the tube, and carefully fused.  The leaded electrode was also introduced; after which the metal, at its extremity, soon melted.  In this state of things the tube was filled up to c with melted chloride of lead; the end of the electrode to be rendered negative was in the basin b, and the electrode of melted lead was retained in the basin a, and, by connexion with the proper conducting wire of a voltaic battery, was rendered positive.  A volta-electrometer was included in the circuit.