49 



IV On the Fusion of Metals by Voltaic Electricity. 



By J. P. Joule, F.R.S., &c. 



[Read March 4th, 1856.] 



The attention of practical scientific men has of late been 

 much occupied with the question, how far it is possible to 

 forge large masses of iron, without destroying the tenacity 

 and other valuable qualities of the metal^ employed. In 

 welding iron, the metal is raised to the high temperature at 

 which it assumes a soft and incipient viscid consistency. 

 Two pieces of iron in this condition will adhere together 

 slightly, if merely placed in contact with one another. That 

 a firm junction cannot be made in this way is simply owing to 

 the fact that few particles are brought into contact, and that 

 the metallic continuity is only established at those points. 

 The hammer is, therefore, employed to cause the entire 

 surfaces to meet together. The same end has also been 

 attained by the employment of great pressure ; and probably 

 we shall ultimately see large masses of forged iron formed by 

 simply subjecting a bundle of smaller pieces, raised to the 

 welding temperature, to the operation of great pressure. To 

 succeed in the latter process, it would however be requisite to 

 press clean unoxidized surfaces together. Indeed the im- 

 portance of presenting clean surfaces together in ordinary 

 welding cannot be too strongly insisted on ; for, if oxide of 

 iron be present, a portion of it will not fail to remain at, or in 

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