Page:Popular Science Monthly Volume 44.djvu/55

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the iron is made in the form of a shallow tray into which the enamel is poured. The wire in the shape of a zigzag forms a fiat coil completely surrounded by this insulating compound. A hot plate suitable for heating a kettle of water or baking griddle cakes is made in the same way, and a grid or frame with gutter-shaped bars filled in with the enamel serves as an oven heater, a sufficient number of these grids being disposed at various parts of the oven. Operations such as the broiling of steak are performed on a modified form of broiler in which the ordinary wires give place to narrow inverted U-shaped bars. The heating wires are carried through the hollow space of these bars and imbedded in enamel. For the heating of water in special vessels, such as the ordinary kitchen boiler, the vessel is made with a bottom in the form of a hot plate. In all the utensils shown at the exhibition the enamel used is of the ordinary gray variety which requires firing, but an enamel for this purpose has been introduced in England which needs no baking. When it comes to heating either by direct radiation or through the medium of hot air, the form finally adopted is that of a coil of wire wound over a pottery or porcelain center and partially inclosed in an iron case. For car warming, heaters are placed under the seats, and located so that they can radiate directly into the car, wire guards being placed in front of them to protect the clothing of passengers. Such heaters have been introduced quite extensively into trolley cars, and are said to have been found economical when everything is taken

PSM V44 D055 Electric hot plate.jpg
Fig. 11.—Electric Hot Plate.

into consideration. They require no attention, and take up no room which would otherwise be occupied by passengers, both items of economic advantage in such a use. Heaters designed to take the place of the hot-air furnace are constructed in the same general manner as those for car use. The plan is to place a large primary heater in the cold-air box of the ordinary furnace, and then subsidiary heaters just inside the grating of registers, by means of which additional heat may be obtained when the main heater is insufficient. All classes of apparatus are made to be used with either an alternating or continuous cur-