74f ON THE THEORY OF GALVANISM. 



only were oxld- learn from them that the action of the muriate of ammoniac 

 able by mur. upon copper is in a great meafure fufpended when the copper 



is in contact with zinc. 

 On the differ- 3. Before we can arrive at a perfect theory of the galvanic 

 at the ends of ' apparatus, it is neceflary to afcertain what is the eflential differ- 

 the pile. ence between the condition of the electric fluid, as it exifls in 



the two ends of the pile. It is eftablifhed decidedly by the ex- 

 periments of Van Marum, that the fluid exifls in the pofitive 

 fiate at what is called the zinc end, and in the negative at the 

 oppofite extremity. When the materials are arranged in the 

 order of filver, zinc, and card, it is evident that the end from 

 which the electric fluid is difcharged in the pofitive flate, is the 

 one contiguous to the oxidating furface of the zinc. It is not 

 altogether determined in what confifts the difference between 

 the pofitive and negative electricities, but it is generally fup- 

 pofed to depend upon the fluid being contained in bodies in a 

 greater or lefs quantity than their natural proportion. Let us 

 examine how far this takes place in the pile of Volta. We 

 may confider each pair of metallic plates with the interpofed 

 fluid as a complete apparatus for evolving and receiving the 

 electric matter; and to whatever extent the pile is increafed, 

 we fhall have merely a repetition of the fame action. Le*t Z, 

 jig. 3, plate 8, reprefent the plate of zinc, F the interpofed 

 fluid, and S the plate of filver. At the furface of the zinc, c d, 

 the electric matter is difengaged in confequence of the oxida- 

 tion of the metal ; this difengaged electricity is carried acrofs 

 the fluid, and enters the furface of the filver ef, and being then 

 diffufed through the body of this plate, the whole of the filver 

 acquires the pofitive flate, and confequently i becomes the po- 

 fitive and k the negative end of this little apparatus. Does the 

 plate of zinc in this cafe become abfolutely or only relatively 

 negative ? It might be fuppofed that no other part of the zinc 

 fliould have its electricity charged except that which is oxi- 

 dated ; yet from the experiments of Van Marum and others we 

 are led to conclude, that the zinc becomes abfolutely negative 

 through its whole fubftance. Dr. Van Marum informs us, that 

 when the wire of a Leyden phial was applied to the negative 

 end of his large pile, the infide of the jar became charged with 

 negative electricity ; and as there does not appear to have been 

 any connection between the external coating and the other end 



of 



