HISTORY OF GALVANISM. 97 



sparks were produced even in the nitric and sul- 

 phuric acids.* , 



I have given above some account of a paper of Branded 

 Erman's, in which he endeavours to show, that Erman, 

 certain bodies are what he calls Unipolar, that is, 1! 

 that they are conductors of one kind of electricity 

 only. Mr. Brande conceived, that the facts 

 brought forward by Erman might admit of a bet- 

 ter explanation upon a different principle, viz. that 

 some chemical bodies being naturally positive, and 

 others naturally negative, they would be attracted 

 to the surface of the pile in a contrary state to 

 their own, the positive to the negative, and the 

 negative to the positive surface. 



In order to submit his opinion to the test of ex- Experi- 

 periment, Mr. Brande procured two insulated me- m 

 tallic balls, one connected with the prime con- 

 ductor, and the other with the rubber of an electri- 

 cal machine ; and placing between them the differ- 

 ent substances under examination, he observed to 

 which of the balls they were attracted. He found 

 that the flame of a candle, which principally con- 

 sists of carbon and hydrogen, was attracted to the 

 negative ball ; while the flame of phosphorus, 

 which would contain a quantity of phosphoric 

 acid, was attracted to the positive side. Here the 

 bodies seemed to folio w the known laws of electro- 

 chemical attraction, according to the idea of their 

 inherent electrical states; and the other experi- 



f 



* Davy's Elements of Chemical Philosophy, p, 152. 

 H 



