This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
In making connections, especially in electrical heating devices subject to high temperatures, it is out of the ques tion to use solder, since the tempera ture reached in the device would cause the solder to melt and run out. A convenient arrangement for welding the connections of flatirons, or any other fine wires, is shown in the illustration. The ends of the wires to be welded are twisted together, and the weld is completed by forming an arc, one electrode of which is the twisted connection and the other a piece of carbon. The resistance of the heating unit in the iron is sufficient to limit the amount of the current flow so that a short circuit does not result. - Contributed by G. Irving Davis, Albany, N. Y.
Ill: An Arc is Formed with a Piece of Carbon, to Weld the Twisted Ends of Wire Together