GAS BATTERY. 263 



of the gases which enter into solution, and are unaffected by 

 the platinum until in solution. This battery so charged gave 

 a very trifling action indeed ; it would not decompose iodide 

 of potassium, and but slightly affected a highly sensitive 

 galvanometer ; but when a little gas was added, so as to 

 expose the platinum to the gaseous atmosphere, a consider- 

 able current was developed, and a single pair decomposed the 

 iodide. 



If, again, a battery of this description (fig. 10) be charged 

 so that the water-mark is below the upper edge of the 

 platinum, and the ends are connected in closed circuit, the 

 liquid rises in both tubes until that in the hydrogen tube has 

 reached the top of the platinum, and then there is no farther 

 rise. This experiment decides the question as to what is to 

 be considered the working portion of the battery, but it does 

 not positively decide whether solution and electrolysis are 

 contemporaneous or successive, as it may be said that even 

 what I have termed the exposed parts of the platinum are 

 covered with a film of liquid. I should myself hesitate for 

 the present to express a decided opinion on this point ; my 

 first impression was, that there would be, as it were, three sets 

 of points in contact, but I have not been able to devise an 

 experiment definitely to settle this point* 



I aimed next at farther establishing the analogies of this 

 battery with the ordinary voltaic battery, i.e. regarding the 

 hydrogen tube as analogous to the plate of zinc or other 

 oxidable metal at the anode. I wished to see how far this 

 relation was borne out. It was beautifully shown in 



Experiment 4, where a single pair was charged with 

 oxygen and hydrogen, and a second with hydrogen in one 

 tube, the other being filled with dilute sulphuric acid ; when 

 the hydrogen of the second was metallically connected with 

 the oxygen of the first, and the liquid of the second with the 

 hydrogen of the first, as in fig. n, bubbles of gas rose from 

 the platinum, which proved, as I anticipated, to be hydrogen. 

 In short, though it required four pairs to decompose water 



* I have sometimes remarked, that when mixed oxygen and hydrogen have 

 been collected in one tube of the gas battery over distilled water, the addition of a 

 little sulphuric acid causes the gases rapidly to disappear. 



