79 



VI. — Effect of Zinc on Iron. 



A piece of galvanized iron of good quality, which when 

 cold several times resisted bending to and fro at right angles 

 to itself, was raised to a red heat with such rapidity that 

 only a small portion of the coating of zinc was vaporised. 

 On then attempting to bend it, it broke off sharp, the frac- 

 ture being short and crystalline. When cold, this piece 

 broke with all its former toughness, the fracture showing a 

 long fibre. The same piece was then heated till all the 

 coating of zinc was driven oiF; it was then found impossible 

 to break it. This clearly shows that the iron was not red 

 short except when rendered so by the zinc. 



The same experiments were tried with iron coated with 

 lead and with tinned iron, but without the above results. 



Some kinds of iron do not appear to be rendered red short 

 by zinc. 



Possibly the above phenomenon may have some connec- 

 tion with the fact that zinc forms an alloy with iron at a 

 red heat, containing from 2 per cent to 6 per cent of iron, 

 and having a melting point which is higher as the propor- 

 tion of iron is greater, while lead and tin do not alloy with 

 iron at this temperature. But still the iron appears to 

 absorb the liquid zinc in a similar way to that in which 

 it appears to take up acid on immersion in it, and with 

 similar results. 



Hitherto I have spoken of iron absorbing and occluding 

 acid as though this something which increases the weight 

 of the iron, alters its tensile strain, &c., had been definitely 

 proved to be acid ; but in the face of my having been unable 

 to obtain any reaction to test paper, this is very uncertain. 

 Though the fact that the immersion of iron which has been 

 soaked in an alkaline fluid greatly hastens its restoration to 

 its original state, and the rusting of the surface of iron 

 soaked in acid when heated in a confined space, all lead to 

 the belief that acid is absorbed, though other bodies, such 

 as gases, may be occluded at the same time. 



