8 ELECTRO-CHEMISTRY. 



The iron tube deposited in the tray was insulated 

 by inclosing it in a tube of glass, while the platina 

 wires which passed through the small perforations in 

 the side of the tray were encased in capillary tubes. 

 The extremities of the wires which projected beyond 

 the tray dipped into a small bent tube that contained 

 a solution of the iodide of potassium. In every 

 other respect the experiment was conducted precisely 

 as that which I had performed in 1849. In the 

 course of the experiment, I found that the solution 

 of the iodide of potassium was decomposed ; the 

 appearance of the iodide was first made manifest in 

 the limb of the tube into which the wire from the 

 tube containing the nitric acid was introduced. 

 From what source was the electricity derived by 



