ELECTRIC HEATER. A device for the conversion of electricity into heat for purposes of artificial heating. Electric heaters consist essen tially of eoils or circuits of some refractory metal through which the current is passed, these coils or circuits being surrounded by air or some insulating material. and the whole being placed in a metallic box or radiator. which throws off or radiates the heat produced. In the simplest form of electric heater exposed coils of wire or strips of metal are wound around insulating material or left surrounded by air. Another common form consists of wire or strips of metal imbedded in asbestos, either in the form of coils or in flat layers. A third elass of heater, to which belong the Leonard, Carpenter. Crompton, and other heaters. is made by imbedding the resistance wire in some fireproof insulation, such as enamel or glass. The Tommasi heater consists of a coil of wire imbedded in a material having great latent heat of fusion. such as crystallized acetate of sodium and hyposulphite of sodium. In these heaters the current is turned on until the desired temperature has been reached. and is then Writer] off and the latent heat allowed to dissi pate itself. It is claimed that. the heater re main: active about four hours after the current is shut off. The Prometheus system, extensively used in Germany. eonsists of fusing a broad strip of rare metal on to an enamel which forms the ide of t he passing the current through the metal strip or film. Tests have shown the etlieieney of this apparatus to be between SI and 87 per cent. The Le Boy system consists of sticks of crystallized carbon in glass tubes. In the Parville heater there are rods of metallic powder mixed with fusible clay. com pressed under a pressure of 2000 kilograms per square centimeter and baked at a temperature of 1350' C. 'l'he al(ove eonstruetions are used in electric cooking and heating apparatus. Elec tric heaters have their chief field of usefulness in supplying heat for cooking and for laundry irons and for warming electric ears. 'Unless elec tricity is produced at a very low cost, it is not commercially practicable for heating residences or large buildings. Nevertheless it is generally
considered that the electric heater has a field of application in heating small offices. bathrooms, cold corners of rooms, street railway waiting rooms, the summer villa on cool evenings, etc. It has the peculiar advantage of being instantly available and portable, and it does not vitiate the atmosphere or make dirt. For heating electric ears the electric heater commends itself for rea sons that are plainly obvious to all. For heating laundry irons it is commonly figured that elec trically heated and gas-heated irons are tut a par in economy when gas costs $1.25 per 1000 cubic feet and electricity eosts 1 cent per hors•-power per hour. Numerous tests and estimates of the efficiency of electric heaters for cooking purposes have been made, and the reader interested will tied them adequately summarized itt II. A. Fos ter's Electrical Engineer's Poeket-ltook (New York, 190)). Generally speaking, it may be con cluded that the efficiency of electric cooking ap paratus varies from CO per cent. to 90 per cent. for ovens), depending upon a Dll1nber of variable conditions. such as time, size, quantity to be heated. and temperature rise. The efficiency of an ordinary cooking-stove using solid fuel is only about 2 per cent.. 12 per cent. being wasted in obtaining a glowing lire. 70 per cent, going in the ehinmey, and It; per cent. being radiated into the room. In a gas-stove. considering that the number of heat units obtainable at a certain price is but small compared with solid fuel. the ventilating current required for the operation alone consumes at least SO per cent. of the heat units obtained by burning the gas. In the case of an electrical oven more than 90 per cent. of the heat energy can he utilized: and thus, al though possibly 5 to 6 per cent. only of the heat energy of the fuel is present in the electrical energy, 90 per cent. of this, or per cent. of the whole energy, actually goes into the food, and thus the electrical oven is practically twice as economical as any other oven, whether heated by solid fuel or by gas. See WELDING; ELECTRO