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fuffered to remain open, fo as to admit of a free circulation of air. A tube, with water, 

 and filver wires, was adapted to the extreme plates. 



This pile was introduced, without being moiftened, into a veflcl, provided with a 

 ftopper, filled with oxigenated marine acid gas ; but no perceptible galvanic aGion took 

 place. After two hours, no gas had formed in the tube, nor had any oxidation of the 

 zinc wire been produced *. The fame pile was now moiftened by immerfion in water. 

 Before and after it had been wiped, it fhewed no (igns of adtion in the atmofphere. It was 

 introduced into a veflel of oxigenated marine acid gas, opened as before in the atmofphere. 

 In a moment, the zinc wire, in the tube, began to oxidate with the greateft rapidity, whilft 

 gas was given plentifully from the filver wire. The procefs continued to go on till 

 the green colour had difappeared in the cylinder. 



This experiment not only arranges with the fa£l:s of Fabroni and Colonel Haldane, and 

 thofe I have before flated ; but likewife feems to prove that the chief ufe of the large 

 furface of water required in the pile of Volta is to oxidate a larger quantity of zinc : for 

 in this inftance very minute quantities of water connected the plates, and confequently 

 very minute quantities were fufficient to enable the eledlrical currents to form the circuit. 



I am at prefent engaged in endeavouring to afcertain by experiments whether any 

 differences exifl in the gafes evolved from water by the galvanic current, when different 

 oxidating fubftances form the medium of communication between the plates. When 

 thefe experiments are compleated, or at fome future time I fhall probably offer fome obfer- 

 vations on the peculiar affinities which enable iron, zinc, &c. to decompofe water only 

 when it holds in folution atmofpheric air, acids, or other bodies containing oxygen. On 

 the principles before laid down, nothing is more eafy than to explain the ufe of muriate 

 of foda, muriate of ammoniac, &c. in increafing the powers of the common pile. 



As the quantity of power in a pile is probably in proportion to the quantity of the 

 oxidation of the zinp, and the number of the feries of plates, the pile of Mr. Cruickfhank, 

 or that I have defcribed, will probably be moft ufeful for procefTes, in which much galvanic 

 power is required. In thofe proceffes, muriatic acid, or very diluted nitrous acid, may be 

 ufed as the oxidating fubflance : for they will enable the plates ^to a£l till all the oxidable 

 metal is deftroyed, without the common trouble of cleaning and rebuilding the pile. 



Anal'^ts of various FcJJils. 



Trommsdorff, who has lately been engaged in mineral analyfes, has found, that the 

 lapis obfidianus of mount Heckla in Iceland is compofed of 63 parts of filiceous earth, 

 20.5 parts of alumine, and 13.5 parts of oxide of iron. 



That the heliotrope of Bohemia contains 6& parts of filiceous earth, 15 of alumine, 

 1 of oxide of iron. 



• The metals of tlie pile had been afted upon in this experiment, and were warm at the con- 

 chifion of it. 



That 



