312. A much more convenient and effectual arrangement for chemical decompositions by common electricity, is the following. Upon a glass plate, fig. 43, placed over, but raised above a piece of white paper, so that shadows may not interfere, put two pieces of tinfoil _a, b_; connect one of these by an insulated wire _c_, or wire and string (301.) with the machine, and the other _g_, with the discharging train (292.) or the negative conductor; provide two pieces of fine platina wire, bent as in fig. 44, so that the part _d, f_ shall be nearly upright, whilst the whole is resting on the three bearing points _p, e, f_ place these as in fig. 43; the points _p, n_ then become the decomposing poles. In this way surfaces of contact, as minute as possible, can be obtained at pleasure, and the connexion can be broken or renewed in a moment, and the substances acted upon examined with the utmost facility. 313. A coarse line was made on the glass with solution of sulphate of copper, and the terminations _p_ and _n_ put into it; the foil _a_ was connected with the positive conductor of the machine by wire and wet string, so that no sparks passed: twenty turns of the machine caused the precipitation of so much copper on the end _n_, that it looked like copper wire; no apparent change took place at _p_. 314. A mixture of equal parts of muriatic acid and water was rendered deep blue by sulphate of indigo, and a large drop put on the glass, fig. 43, so that _p_ and _n_ were immersed at opposite sides: a single turn of the machine showed bleaching effects round _p_, from evolved chlorine. After twenty revolutions no effect of the kind was visible at _n_, but so much chlorine had been set free at _p_, that when the drop was stirred the whole became colourless. 315. A drop of solution of iodide of potassium mingled with starch was put into the same position at _p_ and _n_; on turning the machine, iodine was evolved at _p_, but not at _n_.