256 Dr. Faraday's Experimental Researches in Electricity. 



The 

 e mach 



Fig. 4. 



platina wires, as in fig. 4. The wire m was connected with 

 the prime conductor of the machine, the wire t with the dis- 



charging train, and the wires r and s entered into the course 

 of the electrical current by means of the pieces of moistened 

 paper : they were so bent as to rest each on three points, n, r 9 p ; 

 n 9 s,p, the points r and s being supported by the glass, and 

 the others by the papers, the three terminations/?,/?,^ rest- 

 ed on the litmus, and the other three n, n 9 n on the turmeric 

 paper. On working the machine for a short time only, acid 

 was evolved at all the poles or terminations p 9 /?, p, by which 

 the electricity entered the solution, and alkali at the other 

 poles ?i, n, n, by which the electricity left the solution. 



322. In all experiments of electro-chemical decomposition 

 by the common machine and moistened papers (316.), it is 

 necessary to be aware of and to avoid the following important 

 source of error. If a spark passes over moistened litmus and 

 turmeric paper, the litmus paper (provided it be delicate and 

 not too alkaline,) is reddened by it; and if several sparks are 

 passed, it becomes powerfully reddened. If the electricity 

 pass a little way from the wire over the surface of the moist- 

 ened paper, before it finds mass and moisture enough to 

 conduct it, then the reddening extends as far as the ramifica- 

 tions. If similar ramifications occur at the termination n, on 

 the turmeric paper, they prevent the occurrence of the red 

 spot due to the alkali, which would otherwise collect there; 

 sparks or ramifications from the points n will also redden 

 litmus paper. If paper moistened by a solution of iodide of 

 potassium (which is an admirably delicate test of electro-che- 

 mical action,) be exposed to the sparks or ramifications, or 

 even a feeble stream of electricity through the air from either 

 the point/? or n, iodine will be immediately evolved. 



323. These effects must not be confounded with those due 

 to the true electro- chemical powers of common electricity, 

 and must be carefully avoided when the latter are to be ob- 

 served. No sparks should be passed, therefore, in any part 



