410 TENTH ANNUAL REPORT OP 



The secondary current thus obtained has an electro-motive force 

 which exceeds that of the primary current in proportion as the pairs 

 of plates of the secondary battery are more numerous. On the other 

 hand, the entire chemical effect which the secondary current produces. 



in the voltameter is only - (if the secondary battery consists of w pair 



n 



of plates) of that which the primary current had previously produced 

 in each separate cell for chargino^ the plates. For, while 6 cubic cen- 

 timetres of explosive gas were collected in the voltameter in the above- 

 mentioned experiment, 6 cubic centimetres of this gas had. to unite 

 to form water in each of the four cells of the charging battery, and 

 this quantity of gas was first released from the water by the action 

 of the primary battery. Therefore by the action of this battery in 

 the 4 cells together, the water of 6 X 4 = 24 cubic centimetres of 

 gas must be electrolyzed per minute, in order that 6 cubic centimetres 

 may be released in the voltameter. 



Without the pole-changer and by the direct action of the simple 

 battery in the four cells, (which in this combination represent a large 

 pair of plates,) not over 0.1 cubic centimetre of gas would be evolved, 

 because the gas, which appears at the first moment of the passage of 

 the current, i)roduces at onse a polarization of the plates, in conse- 

 quence of which only an exceedingly feeble current can circulate ; 

 but by the pole-changer this polarization is immediately removed, and 

 thus an undiminislied action of the chargitig cells is rendered possible. 



The platinum plates, of which Poggendorfif constructed his sec- 

 ondary battery, were platinized. If the secondary current is to be 

 tolerably strong, this is very necessary ; at least the negative plates 

 of the secondary battery must be platinized, i. e. those at which the 

 primary current has evolved oxygen, and to which the secondary 

 current carries hydrogen. The influence of platinizing appears from 

 the following experiments made by Poggendorff : 



In five minutes a battery of two pairs of platinum plates connected 

 with a small Grove's element and the pole-changer yielded the follow- 

 ing quantities of gas : 



1. All the plates uncoated 1 c. c. (a little over.) 



2. The positive plates platinized 1,5" 



3. The negative " " 13 to 14 c, c. 



4. All the plates platinized 13 to 14 " 



The positive plates are those at which the original current evolves 

 hydrogen. 



This is not due to the platinized plates being more strongly polar- 

 ized, for in fact they are less so than the naked ones ; but, in Pog- 

 gendorff' s opinion, the action of the platinum coating consists in favor- 

 ing the combination of the oxygen, separated at its surface by the 

 primary current, with the nascent hydrogen evolved in consequence 

 of the secondar)^ Much might be said in opposition to the modus 

 operandi as explained by Poggendorff; but this is not exactly the 

 place for the discussion, 



Poggendorff has successfully used plates of Bunsen's carbon in con- 

 structing secondary batteries. A battery of two pairs of such plates 



