524 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM 



of equivalents in galvanic decompositions, it appears that we ought to 

 multiply these equivalents by the numbei- of pairs of plates necessary to 

 effect the decomposition. This would perhaps be the true measure, for 

 after all it is necessaiy to consume a great number of atoms of zinc, in 

 order to decompose a single atom of any other substance less decompo- 

 sable. In what relates to the difference between quantity and intensity, 

 caloric offers analogies ; and in judging of a quantity of gas, we 

 ought always to know its volume and its density. I must here quote 

 another observation of Mr. Faraday, which is found in the Seventh 

 Series, art. 853. He is speaking of a current which is, he says, " pow- 

 erful enough to retain a platina wire j^^ of an inch in thickness red 

 hot in the air during the whole time" (3| minutes) ; and he adds in a 

 note : " I have not stated the length of wire used, because I find by ex- 

 periment, as would be expected in theory, that it is indifferent. The 

 same quantity of electricity which, passed in a given time, can heat an 

 inch of platina wire of a certain diameter red hot, can also heat a hun- 

 dred, a thousand, or any length of the same wire to the same degree, 

 provided the cooling circumstances are the same for every part in both 

 cases," &c. This is quite correct, but we may add that it would be ne- 

 cessarj' to multiply the number of pairs of plates in the same proportion 

 with the length of the wire to obtain a current of the same quantity. 



In short in order to heat a wire of 1000 inches to the same degree 

 to which a wire of a single inch would be heated by a single pair of 

 plates, it is necessary to disengage 1000 quantities of gas, proceeding from 

 the same number of pairs. I have thought it right not to suppress this 

 remark, considering that in the practical employment of the voltaic 

 pile oeconomy is requisite. 



16. 



Tlie foUomng is the table of experiments which I have made upon the 



deviation of the needle with relation to the quantity of gas developed 



at the surface of the negative plate of a voltaic pair of plates of silver and 



amalgamated zinc. The specific gravity of the sulphuric acid was 1-25. 



The bubbles of air rising rogidaily enough to serve as a meeisure, I 



