ElecirHc Co?iditio?i of Iron. 143 



Jan. Ist, 1839. A galvanic combination of iron and zinc 

 was put in communication with two poles of a differential 

 galvanometer ; a like-sized combination (or gal. pair) of copper 

 and zinc was connected with the other two poles of the cliff, 

 galvanometer : Deviation of needle in favour of the iron and 

 zinc pair = 25 degrees. 



Feb. 27, 1839. Experiments made on the comparative 

 power of two galvanic batteries fitted up on Wollaston's 

 plan (that is with the negative plate opposed to both surfaces 

 of the zinc or positive plate.) The size of the plates was the 

 same in both batteries, viz. zinc plate 2g- inch, by 2^ inch. 

 The number of pairs in each battery was ten. The only 

 difference between the two batteries was, that the negative 

 plates in one were of copper and in the other of iron. 



The exciting solution was dilute sulphuric acid, which was 

 not renewed during the experiment, but the experiment was 

 continued until the acid was exhausted. The power of each 

 battery was applied to the decomposition of water, and the gas 

 collected was the measure of the power. 



RESULTS. 



Battery of Copper and Zinc. 



The first cubic inch of gas obtained in 33 minutes. 

 Then one half cubic inch ... in 92 minutes. 



Acid was now exhausted. 1^ cubic inch in 125 minutes. 



Battery of Iron and Zinc. 



First cubic inch obtained in 7 minutes. 



Second — — — in 9 minutes. 



Third — — — in 26 minutes. 



Fourth — — — in 62 minutes. 



Acid now exhausted. 4 cubic inch, in 104 minutes. 



Iron battery with a measured quantity of acid gave 4 cubic 

 inches in 104 minutes. 



Copper battery with a like quantity of acid gave only l^- 

 cubic inch in 125 minutes. 



I have the honour to remain, 



Gentlemen, yours, &c. 



Dec. 16, 1839. Martyn J. Roberts. 



