74 Mr. J. Enright on Electrifications due 



and repeated the experiment. It again went off the scale. 

 I withdrew a considerable quantity from the needle, and 

 eventually reduced the sensibility of the instrument to such a 

 degree that the deflexion never amounted to 300 divisions. 



Fresh zinc and hydrochloric acid were now placed in the 

 dish. The spot rapidly went up to 130 on the scale, from 

 zero, and began to return. The " water-dropper " was then 

 quickly disconnected from the quadrants, and the spot stood 

 at 125. The dish was again supplied with fresh acid and 

 zinc and placed in position, and when I could see by the fumes 

 that the nozzle was enveloped in the escaping gas I again 

 connected the quadrants to the " water-dropper," when the 

 spot moved up the scale higher. This was repeated as long 

 as the spot could be forced to go higher. At 187 from zero 

 it only oscillated right and left to the extent of 3 or 5 divi- 

 sions, but could not be forced higher by the liberation of 

 hydrogen near the nozzle from fresh acid and zinc. I took 

 this number as measuring the potential above earth of the gas 

 as it escaped from the acid. 



The reason for changing the acid so frequently is to be 

 found in the fact, which I had already proved, that when 

 hydrogen passes through a solution of ZnCl 2 it comes off with 

 a negative charge ; and on this account, if the measurement 

 be not made when the gas is passing through at the first 

 stage of the reaction, the result cannot be correct. And, 

 indeed, no matter what precautions are taken the result must 

 be a little too small. 



Several preliminary experiments of this kind were made, 

 and when I was satisfied that the result was definite and con- 

 stant I made very carefully the three following determina- 

 tions. In each case the acid was changed nine times : — 



Zero. Deflexion. Division. 



(1) 362 552 190 



(2) 359 544 185 



(3) 358 545 187 



3)562 



187 

 I knew that I had reduced the sensibility of the electro- 

 meter very much, and when I proceeded to find the value of 

 the scale-divisions in volts 1 found that the standard Daniell 

 gave only a deflexion of from 3 to 6 divisions. Besides, this 

 being very small I could not be certain of it to within a divi- 

 sion, as the spot did not come precisely to zero. Of course, 



