12 NOMOS. 



rest each on three points, nrp, nsp, the points r and s 

 being supported by the glass, and the others by the 

 pieces of paper ; the three terminations ppp rest on 

 the litmus, and the other three nnn on the turmeric 

 paper. On working the machine for a short time 

 only, acid was evolved at the poles or terminations 

 ppp by which the electricity entered the solution, 

 and alkali at the other poles nnn, by which the 

 electricity left the solution."* If the direction of the 

 current be reversed in this experiment, the alkali 

 and acid immediately change places. Now in this, 

 and in all experiments intended to elucidate this 

 point, an important source of error must be guarded 

 against. The electricity must be made to pass 

 through the paper, for if it be allowed to pass over it 

 as a spark, some nitric acid is formed by the com- 

 bination of the nitrogen and oxygen of the atmo- 

 sphere ; and this acid will redden the litmus paper, 

 and prevent the appearance of the brown alkaline 

 stain upon the turmeric paper. This was first 

 pointed out by Cavendish. Such, indeed, is the 

 extent to which nitric acid may be formed under 

 these circumstances, that Dr. Faraday was soon able 

 to form touch-paper out of a piece of paper soaked 

 in solution of potass. This potass became converted 

 into nitrate of potass, or saltpetre, by combining with 

 the nitric acid, and thus the paper when dry became 

 touch-paper. 



It is said that ordinary electricity, like voltaic 

 electricity, has the power of decomposing water; 

 but this is not proved by the experiments which are 



* " Experimental Researches in Electricity," vol. i. p. 90. 



