276 M. De la Rive's Researches 



mity to a plate of platina immersed in the same liquid ; the two 

 steel plates were inserted in the cork stopper belonging to the 

 flask in such a manner that the upper extremity of each passed 

 through the cork into the air. The portion of the two plates 

 immersed in the liquid remained perfectly intact ; at the end of 

 three years their surfaces had not lost any degree of polish ; 

 and in this respect there was no difference between them, not- 

 withstanding that one of them, in consequence of its contact 

 with platina, ought, according to the theory of Volta, to have 

 become oxidated, and that so much the more readily as the so- 

 lution of potash is a conductor of electricity ; but the part of 

 the plate which was inserted in the cork, and passed through 

 it into the air, was covered at the end of three years with a 

 very thick coat of oxide ; the insulated plate was also oxidated 

 at the same points, but in a much less degree, and it is worthy 

 of notice that the exterior of this plate presented a globule of 

 oxide of iron of the size of a pea, exactly similar in miniature 

 to those globules which are formed in iron tubes used for the 

 conveyance of water. From the preceding it follows that oxi- 

 dation must have commenced in order to the existence of an 

 electric current; the current produced by this oxidation de- 

 composes water, and in consequence determines a stronger oxi- 

 dation upon the steel plate in communication with the platina, 

 and this oxidation, in its turn, increases the energy of the cur- 

 rent; in this experiment, the water, which, produced by eva- 

 poration, moistened the cord, being mixed with a great deal 

 of air, performed at the same time the office of the exciting 

 body and the conductor. 



I have indicated the causes which may determine a chemical 

 action when two heterogeneous bodies are placed in contact 

 without making use of a liquid, and I have ascertained that if 

 their occurrence be prevented no electric effect is obtained. 

 To avoid these sources of error Messrs. Pfaff and Becquerei 

 employed a condenser of which one of the plates was of copper 

 and the other of zinc, between which a metallic communication 

 was established by means of an insulated arc of copper. The 

 first of these physicists placed the two plates of his condenser 

 in a vacuum in hydrogen, or in azote carefully dried ; the se- 

 cond gilt the copper plate, and covered the plate of zinc with 

 a thin coating of lac-varnish ; but notwithstanding these pre- 

 cautions they obtained a development of electricity by the con- 

 tact of the two metals. Can it be said that there was no chemical 

 action in their experiments ? It may easily be proved that in 

 the medium in which M. Pfaff placed his plates sufficient at- 

 mospheric air always enters to produce a slight oxidation of the 

 surface of the zinc ; and that in M. Becquerers experiments the 



