GAS BATTERY. 265 



abated, the iodide was no longer decomposed, and the liquid 

 did not rise perceptibly in the tubes containing oxygen. The 

 solution when tested by ferrocyanide of potassium gave a 

 blue precipitate, indicating the presence of peroxide, but the 

 greater portion of this was probably formed at the expense of 

 the atmospheric air. 



In the last experiments and others I had observed that a 

 more decided effect was obtained when free hydrogen alone 

 was present than when oxygen was alone. In my former 

 paper I attributed this to the atmospheric air in solution ; and 

 for convenience of arrangement I have hypothetically assumed 

 this explanation in the commencement of this paper, but the 

 recent letter of Dr. Schcenbein induced me to look farther 

 into this point. Therefore, in 



Experiment 7, I charged two batteries, of two cells each, 

 with hydrogen and dilute sulphuric acid in the alternate cells. 

 When tested by iodide of potassium each battery gave notable 

 effects. One of these batteries was then placed, together with 

 a cup containing phosphorus, in a shallow vessel of water ; 

 the phosphorus was ignited and a large glass vessel inverted 

 over the whole ; the terminal wires of the battery, carefully 

 protected by thick coatings of cement, passed under the 

 edge of this vessel through the water, the exterior surface 

 of which was covered with oil, more effectually to prevent the 

 absorption of air. The terminal wires were then united and 

 left so. After two hours, when the oxygen of the surround- 

 ing atmosphere had been exhausted by the phosphorus, the 

 effect became more feeble, but continued throughout the 

 evening. The next morning, however, the enclosed battery 

 produced not the slightest effect upon the iodide ; the liquid 

 had risen in the hydrogen tubes about 0*2 cubic inch, but 

 no other effect was perceptible. On the other hand, in the 

 battery which had been placed by its side, charged in the 

 same way, and similar in every respect but in the fact of 

 being exposed to the atmospheric air, a very decided effect 

 was produced ; hydrogen had been evolved from one of the 

 platinums to the extent of 0*3 cubic inch in the cell contain- 

 ing liquid, and a decided effect was produced on the iodide. 

 The two batteries were left in this state for three more days ; 

 the decomposition and the evolution of hydrogen continued 



