Prof. Thomson on the Mechanical Theory of Electrolysis, 443 



Electrolysis of Acidulated Water, 



Mean corrected tangent Hydrogen liberated ' 



of deflection. per second. 



1-7600 -001092 grain. 



To determine the strength of the current (7) in absolute 

 measure, which produces a deflection (S) of the needle in thg 

 tangent galvanometer, we have the equation 



7=oz:tan8, 



ATT 



where r denotes the radius of the circular conductor, and H the 

 horizontal component of the earth^s magnetic force, in absolute 

 measure ; since the magnetic axis of the needle will be drawn 

 from the magnetic meridian into a vertical plane containing the 

 resultant of the horizontal force H in the magnetic meridian, 



and the force — ^ perpendicular to the plane of the conductor, 



and consequently to the magnetic meridian. It is impossible 

 at present to assign with accuracy the values of the horizontal 

 magnetic force at Manchester at the times when the experi- 

 ments were made ; but according to data which Colonel Sabine 

 has kindly communicated to me, it must have been nearly 

 3*542 in 1846, and cannot probably at any time of observation 

 during that or the preceding year have differed by as much as 



^j-prpr of its value from that amount. Taking, therefore, 3*542 for 

 lUu 1 



H, and taking — for r (the diameter of the conductor being one 



rH 



foot), we have ^='28186; and consequently, for observa- 

 tions made with Mr. Joule^s tangent galvanometer at Manchester 

 in 1846, 



7= -28183 X tanS. 

 Hence from the preceding experimental results, we find for the 

 electro-chemical equivalent of zinc, 



*01508 ^_Q. 



*28183x*7345 -^^'Q^^^^- 

 and for the electro-chemical equivalent of hydrogen, 



•^^1^^^ or *002201. 



•28183x1*7600' 



From the mean results of a series of four experiments on the 

 electrolysis of sulphate of copper, communicated to me by Mr. 

 Joule, I have found for the electro-chemical equivalent of copper, 



•07052. 



