444 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



was conducted across the cell so freely, that the discharge was as good as if a wire 

 had been used. A ray of polarized light was then transmitted through this solution, 

 directly across the course of the electric current, and examined by an analysing 

 plate ; but though it penetrated seven inches of solution thus subject to the action of 

 the electricity, and though contact was sometimes made, sometimes broken, and 

 occasionally reversed during the observations, not the slightest trace of action on the 

 ray could be perceived. 



953. The large electrodes were then removed, and others introduced which fitted 

 the ends of the cell. In each a slit was cut, so as to allow the light to pass. The 

 course of the polarized ray was now parallel to the current, or in the direction of its 

 axis (517.) ; but still no effect, under any circumstances of contact or disunion, 

 could be perceived upon it. 



954. A strong solution of nitrate of lead was employed instead of the sulphate of 

 soda, but the results were equally negative. 



955. Thinking it possible that the discharge of the electric forces by the successive 

 decompositions and recompositions of the particles of the electrolyte might neutralize 

 and therefore destroy any effect which the first state of tension could by possibility 

 give, I took a substance which, being an excellent electrolyte when fluid, was a 

 perfect insulator when solid, namely, borate of lead, in the form of a glass plate, and 

 connecting the sides and the edges of this mass with the metallic plates, sometimes 

 in contact with the poles of a voltaic battery, and sometimes even with the electric 

 machine, for the advantage of the much higher intensity then obtained, I passed a 

 polarized ray across it in various directions, as before, but could not obtain the 

 slightest appearance of action upon the light. Hence I conclude, that notwithstand- 

 ing the new and extraordinary state which must be assumed by an electrolyte, either 

 during decomposition (when a most enormous quantity of electricity must be tra- 

 versing it), or in the state of tension which is assumed as preceding decomposition, 

 and which might be supposed to be retained in the solid form of the electrolyte, still 

 it has no power of affecting a polarized ray of light ; for no kind of structure or ten- 

 sion can in this way be rendered evident. 



956. There is, however, one beautiful experimental proof of a state of tension 

 acquired by the metals and the electrolyte before the electric current is produced, and 

 before contact of the different metals is made (915.) ; in fact, at that moment when 

 chemical forces only are efficient as a cause of action. I took a voltaic apparatus, 

 consisting of a single pair of large plates, namely, a cylinder of amalgamated zinc, 

 and a double cylinder of copper. These were put into a jar containing dilute sul- 

 phuric acid*, and could at pleasure be placed in metallic communication by a copper 

 wire adjusted so as to dip at the extremities into two cups of mercury connected 

 with the two plates. 



* When nitro-sulphuric acid is used, the spark is more powerful, but local chemical action can then com- 

 mence, and proceed without requiring metallic contact. 



