Pure or nearly pure iron is readily weldable at a white heat. Malleable, or nearly pure wrought iron, is known as weld iron. The range of temperature in which it can be welded is very wide: it runs from the imperfect weld at cherry-red, to dazzling white, when the welding property is lost just before the iron melts. According to Pouillet, the different colors of heated metals are represented approximately by the temperatures given:

Deg. C

Incipient red ................................

525

Dark red ........................................

. 700

Incipient cherry ...........................

. 800

Clear cherry-red .....................

. 1000

White...........................................

. 1300

Dazzling white...................................

1500

Melting..........................................

155o

Wrightson1 states that he found iron to increase in volume as much as 7 per cent, when passing into the plastic stage.