156 Intelligence and Miscellaneous Articles. 



I employed fresh and well amalgamated Bunsen elemeuts ; the 

 experiment, not susceptible of great precision, on account of the 

 variations of the arc, gave the following values of the electromo- 

 tive force x of the differential current evaluated in Bunsen ele- 

 ments : — 



Lead. 



Iron. 



Oarbon. 



Copper. 



Zinc I. 



Zinc 2. 



Mercurv. 



2-5 



3-2 



5-0 



50-6 



66-2 



5*7 



103-7 



The first three substances are nearly equal ; the last three are very 

 active. Copper is equivalent to 50 bunsens ; zinc to 66 at the 

 commencement of the action, falling to 5. As to mercury, it pre- 

 sents an enormous and very constant value ; the differential current 

 has a mean electromotive force equivalent to 103-7 bunsens. The 

 same determinations conduct us to an estimation of the introduced 

 resistance. We have, in fact, 



._ .,_ 2/iA u_2/iA 

 1 " IT* ~ i^i'' 



B is in the inverse ratio of i—i'. 



Now the total resistance B was composed (1) of that of the wires 

 of the machine, (2) of that of the battery, (3) of that of the elective 

 arc. The last alone is variable, and increases or diminishes the 

 value of B ; it will therefore be the more the less i—i' is. Here 

 are the calculated values of i—i': — 



Carbon. 



Iron. 



Lead. 



Copper. 



Mercurv. 



Zinc 1. 



Zinc 2. 



0-406 



0-307 



0-283 



1-41 



0-89 



1-02 



0-56 



It would follow from these numbers that carbon, iron, and lead 

 offer the greatest resistance, copper and mercury the least. 



The differential current can only be explained in two ways — 

 either by a difference in the resistance, or else by inequality in the 

 inverse reactions of the arc in the one direction or the other. 



In order to ascertain if the resistance of the arc varies with the 

 change of direction, I caused a continuous current to pass, first 

 from the carbon to the mercury, afterwards from mercury to carbon. 

 A compass, placed in derivation, measured the intensity in the two 

 cases. I could not measure any appreciable difference. But these 

 experiments presented a remarkable peculiarity : when the current 

 passed from mercury to carbon, the arc had a very pronounced 

 green colour, and the volatilization of the metal proceeded vigo- 

 rously ; in the contrary case the arc was reddish, and there was a 

 less abundant production of vapour. This renders evident the 

 asymmetry existing in the two cases. Now, when the alternating 

 currents of a Gramme machine are directed through this burner, 

 the arc is green, which proves that the current going from mercury 

 to carbon predominates over that which goes in the opposite direc- 

 tion ; and as there is no difference in the resistance of the are. it is 



