28 Professor A. Crum Brown [Jan. 31, 



" I have frequently, however, seen him galvanise louis-d'or lent 

 him by persons present. To efltect this, he places the louis between 

 two pieces of pasteboard thoroughly wetted, and keeps it six or eight 

 minutes in the chain of circulation connected with the pile. Thus 

 the iouis becomes charged, without being immediately in contact with 

 the conducting wires. If this louis be applied afterwards to the crural 

 nerves of a frog recently prepared, the usual contractions will be 

 excited. I had put a louis thus galvanised into my pocket, and 

 Mr. Ritter said to me a few minutes after, that I might find out this 

 louis from among the rest, by trying them in succession upon the frog. 

 Accordingly I made the trial, and in reality distinguished among 

 several others a single one, in which the exciting quality was very 

 evident. This charge is retained in proportion to the time that the 

 piece has remained in the circuit of the pile. It is with metallic discs 

 charged in this manner, and placed upon one another with pieces of 

 wet pasteboard alternately interposed, that Mr. Ritter constructs his 

 charging pile, which ought in remembrance of its inventor to be called 

 the Bitterian pile. Mr. Ritter made me observe, that the piece of gold 

 galvanised by communication exerts at once the action of two metals, 

 or of one constituent of the pile ; and that the half which was next 

 the negative pole while in the circle became positive, and the half 

 toward the positive pole became negative." 



Brugnatelli * suggested that the polarisation of the plate which 

 during the electrolysis had given off hydrogen was due to a compound 

 of hydrogen with the metal of the electrode. But it was not until 

 Schonbein discussed the question in 18391 that a systematic attempt 

 was made to settle it by experiment. Schonbein's results were in 

 favour of the view that the polarisation is due to the formation, on 

 the surfaces of the electrodes, of thin sheets of the products of the 

 electrolysis. 



Now the old theories assume that if we begin with very small 

 electromotive force and gradually increase it, we have at first a state 

 of tension, the electromotive force so to speak pulling at the ions, 

 that this tension increases as the electromotive force increases till it 

 becomes sufficient to pull the ions apart. If this were so there should 

 be no current and no electrolysis till the electromotive force reaches 

 a certain amount, and then suddenly a very great current, and some- 

 thing like an explosive discharge of gas ; for many molecules would 

 be in the very same state of tension and all would give way at 

 once. 



When the electrolytic decomposition of water was first observed, 

 as it was (by Nicholson and Carlisle) immediately after the publica- 

 tion of Volta's first description of the pile, the great difficulty felt by 

 every one was that the hydrogen and the oxygen came oif at different 

 places which might be far apart. Grotthuss's theory no doubt 



* Brugnatelli, Gilbert's Annalen, xxiii. p. 202 (1806). 

 t Schonbein, Pogg. xlvi. p. 109 ; xlvii. p. 101 (1839). 



