Mr. Arrott on some new Cases of Voltaic Action. 427 
When distilled, the tannin gave no indication either of pyro- 
gallic acid or of pyrocatechin. 
Catechin, which is the part of catechu insoluble in cold 
water, when distilled, yielded the pyrocatechin of Zwenger in 
considerable quantity. So far as I examined it, pyrocatechin 
appeared to possess the properties ascribed to it by that che- 
mist. 
In conclusion, I may mention that this is only the first of a 
series of papers on the astringent substances. 
Glasgow, Oct. 26, 1842. 
LXX. On some new Cases of Voltaic Action, and on the Con- 
struction of a Battery without the use of Oxidizable Metals. 
By ALEXANDER R. Arnott, Esg.* 
HAVING been for some time engaged in examining into 
certain remarkable voltaic actions occurring in cases 
hitherto unobserved, or at least not followed out so fully as 
their importance seems to demand, I am induced briefly to 
communicate the results of my inquiries, hoping they may not 
prove uninteresting to the Society. 
It is a fact known to every one who has carefully observed 
’ the phenomena attending chemical decomposition by means 
of electricity, that the electrodes immersed in the solution 
undergoing decomposition, acquire the power of producing a 
current in the opposite direction to that previously passing 
through them, when they are made to touch each other with- 
out being removed from the liquid. 
This effect has generally been ascribed to a power sup- 
posed to be acquired by the metals, of producing a current 
independently of any action of the liquids beyond that of 
simply completing the circuit, and has been called “ polariza- 
tion of the electrodes.” 
Becquerel was the first who advanced the opinion, that the 
effect was due to the alteration produced in the liquid by the 
current causing decomposition. He supposed that the current 
was a consequence of the combination of the acid and alkaline 
produced at the positive and negative surfaces; but it will be 
found that the most powerful acids and alkalies are incapable 
of producing a current, unless they readily undergo some 
other change than that which takes place when an acid and 
alkali combine as such. It has often been shown, that sul- 
phuric acid and potash, for example, are nearly or altogether 
* Communicated by the Chemical Society; having been read No- 
vember 15, 1842, 
