Another useful application of electric heat is in the welding of metals. Instead of heating the pieces to be welded in a forge, their ends are simply butted together and the electricity--generally from an alternating-current transformer--turned on. The heat developed by the “contact resistance” between the pieces quickly softens the metal so that the pieces may be forced together, forming a perfect weld in a few minutes without any hammering. Fig. 5 is a view of one form of electric welding-machine in which this is accomplished. The electric process can weld certain metals that cannot be joined securely by ordinary welding methods, and is used in several special arts. Welding is also performed by the heat of a special electric arc-lamp, which a workman holds in his hand like a blow-pipe or torch. This process is especially useful in joining the edges of sheet-steel, in making tanks for electric “transformers,” etc. The workmen have to wear smoked glasses in order to protect their eyes from the intense glare of the arc. [Illustration: _=Fig. 5=_] Electric Car-heaters Perhaps the simplest and best-known application of electric heat is the electric car-heater, consisting of coils of high-resistance wire--such as iron or German-silver wire--mounted on an insulating, non-combustible frame which is placed under the seats of the car. Part of the current from the trolley wire or third rail passes through the resistance-coils, heating them up and thereby warming the air in the car. Household Uses Nowadays electric heat is being more and more widely utilized in what are known as household electric heating-appliances. One of the most useful of these is the electric flat-iron, shown in Fig. 6. This flat-iron is designed to do away with the use of a hot stove of any kind, and is internally heated by means of a resistance-coil of peculiar shape placed in the bottom of the iron close against its working face. The iron is connected to an electric-light socket by means of an attaching plug on the end of a long, flexible cord. It takes only a few minutes to get hot, and its use saves much time and labor. The list of special heating-appliances that are now made includes curling-iron heaters; heating-pads, for taking the place of hot-water bags in the sick-room; cigar-lighters, in which a little grid “resistance” is made incandescent by pressing a button; foot-warmers; and radiators to dry wet shoes or skirts on rainy days. For industrial use there are glue-pots, for bookbinders and pattern-makers; large flat-irons, for tailor-shops and laundries; and electric ovens, for drying certain parts of electrical machines and for cooking various kinds of “prepared foods.”