254 Dr. Faraday's Experimental Researches in Electricity. 

 the other g, with the discharging train (292.) or the negative 



conductor; provide two pieces of fine platina wire, bent as 



in fig. 3, 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. 2 ; the points 



p 9 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 p, that it looked like copper wire; 

 no apparent change took place at n. 



314. A mixture of half muriatic acid and half water was 

 rendered deep blue by sulphate of indigo, and a large drop 

 put on the glass, fig. 2, so that p and n were immersed at op- 

 posite sides : a single turn of the machine showed bleaching 

 effects round p 9 from evolved chlorine. After twenty revolu- 

 tions no effect of the kind was visible at n 9 but so much chlo- 

 rine 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 9 but not at n. 



316. A still further improvement in this form of apparatus 

 consists in wetting a piece of filtering paper in the solution to 

 be experimented on, and placing that under the points p and 

 n, on the glass : the paper retains the substance evolved at 

 the point of evolution, by its whiteness renders any change of 



