GAS BATTERY. 



257 



liquid, and the absence of any necessity of touching the 

 electrolyte with the fingers. On the other hand, its disadvan- 

 tages are the difficulty of examining the gases after experi- 

 ment, and the impossibility of doing so during experiment 

 without changing the electrolyte, as in order to examine the 

 gases the whole apparatus must be immersed in a water- 

 trough, and the cover with the attached tubes taken off while 

 the jar and the ends of the tube are under water. 



Fig. 4 represents a cell of the second form ; b, c, d, e is a 

 parallelepiped glass or stoneware vessel, such as is com- 

 monly used for the outer cells of nitric acid Fig. 4. Fig. 5. 

 batteries ; the tubes are cemented into 

 pieces of wood, a b, a c, and can with 

 the wood be separately detached from 

 the trough, as shown in fig. 5. At the 

 aperture or space, a a, between the tubes 

 there is just room for a finger to enter, 

 close the orifice of either tube, and thus 

 detach it from the apparatus. In this 

 figure the platinum foil is turned up 

 round the edge of the tube, instead of being attached to a 

 wire sealed into the glass, and instead of a mercury-cup there 

 is a binding-screw connexion ; but it is obvious that this part 

 of the arrangement may be interchanged with the other ap- 

 paratus, or varied ad libitum. This apparatus I have found 

 in practice to be very much more convenient than the former, 

 from the facility of detaching either tube so as to discharge 



Fig. 6. 



some of the gas, if it be desir- 

 able to alter the level of the 

 water-mark ; or to examine or 

 change the gas in any of the 

 tubes. On the other hand, it 

 has the disadvantage of requir- 

 ing the finger to be immersed 

 in the electrolyte, which, when 

 the latter is of an active chemi- 

 cal character, is unpleasant and 

 in some cases injurious. In fig. 6 a battery of five cells of this 

 construction is represented as when charged with oxygen and 



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