VOLTAIC PHENOMENA. 303 



If a copper wire form the anode of a voltaic battery of 

 moderate power in dilute sulphuric acid, it is, as is well 

 known, gradually oxidated and dissolved. If the intensity of 

 the battery be increased, I have found that, at a certain point, 

 (varying with the voltaic combination employed), the action 

 is arrested, the copper is no longer dissolved, and a galvano- 

 meter interposed in the circuit gives little or no indication of 

 a current. Let the intensity be now farther increased, by 

 gradually adding to the voltaic series, and a very curious phe- 

 nomenon is exhibited : the copper is apparently disintegrated, 

 boiling off, as it were, in a very fine reddish-brown powder ; 

 the heat is intense, and the electrode rapidly worn away ; the 

 powder thus formed is partially dissolved, provided the acid 

 be not already saturated ; after saturation it subsides, and 

 may be collected and examined ; it proved to be the second 

 oxide, or copper 32 -f oxygen 8, called by some authors the 

 protoxide, by others the deutoxide. Besides employing the 

 usual chemical tests, I analysed it voltaically, by comparing 

 the weights lost from the anode with the hydrogen evolved 

 at the cathode; the following are three experiments taken 

 from my note-book, dated April 27, 1841 : 



Thermometer, 60 Fahrenheit. 



Exp. i. For 6 cub. in. of hydr. collected, anode lost 4*2 



n 2- ,, ,, 4'2 



> 3- 4'3 



3)i27_ 



4-23 

 Now, 47*2 : 32 ::6 : 4-07. 



This result was obtained with a common pair of scales, 

 and although too coarse for a very accurate determination of 

 the equivalent, was quite sufficient to prove that it was the 

 full oxide, which was all I required. 



The battery employed varied from I to 20 cells of the 

 nitric acid combination. I generally found that the intensity 

 at which the current was arrested was when from 5 to 10 cells 

 were employed 12 to 16 seldom failed to give the disinte- 

 grating effect. 



The points worthy of notice in this experiment are 



