Platina Electrodes of a Voltaic Battery. 383 



then making a communication with the galvanometer, the 

 needles moved to 30°. 



Exp. 9. The galvanometer being removed, the zinc rod 

 was immersed as in Exp. 7, and the hydrogen given off' col- 

 lected in separate tubes. 



In the tube over plate A was found 4*20 inches = 1*0 



B. 5*15 =1-23 



Exp. 10. The cup A was connected to the negative and B 

 to the positive side of the battery : decomposition of water was 

 allowed to proceed for 5 minutes; the wires were then re- 

 moved, the basin emptied of its contents, and repeatedly rinsed 

 out with cold water. It was then refilled with dilute sulphuric 

 acid, the rod of amalgamated zinc immersed, its wires dipping 

 into the cups A and B : the hydrogen evolved was collected 

 and measured. 



In the tube over the plate A was found 1 "3 inches =? 1 '0 



B 1-7 = 1-3 



Exp. 11. The basin of the apparatus was filled with the 

 dilute acid, connected with the battery for 20 minutes, 

 emptied, washed out with cold water, refilled with acid and 

 connected with the galvanometer ; again placed in communi- 

 cation with the battery for the same time, emptied, and 

 washed out with boiling water : this was repeated, the plates 

 of platina being washed with a solution of potass, and in a 

 fourth experiment with nitric acid ; the basin being always 

 refilled with the same dilute sulphuric acid before being con- 

 nected with the galvanometer. The deviations produced 

 were — 



After washing the electrodes with cold water 80° 



> boihng water 73° 



— ^ solution potass .,, 45° 



— . — ■ ■■■■ ■ — -'■'— nitric acid ,. 4° 



Exp. 12. The basin of the apparatus was filled with a 

 solution of pure potass, sp. gr, r064 and connected with the 

 battery during 5 minutes as in the preceding experiments. 

 On then dipping the galvanometer wires into the cups A and 

 B, the needles deviated to 45°. The basin was then emptied, 

 washed out with cold water, and refilled with the alkaline 

 fluid : on making connexion with the galvanometer, the needles 

 only indicated 5°. 



Exp. 13. The basin filled with the solution of potass was 

 again connected with the battery as in the last experiment; it 

 was then emptied, filled with dilute sulphuric acid and con- 

 nected with the galvanometer : the needles instantly deviated 

 to 90° tsoith considerable velocity. 



In all these experiments the direction of the deviations was 



