ELECTRIC HEATER. If a wire of more or less resistance is wound on a frame, and a current sent through, the resistance encountered by the current develops heat, and this is the principle of the electric heater. The hot wire or metal is surrounded by some non-inflam mable substance that is a good conductor of heat, as porcelain. In a well-known type a metallic paint is fired upon mica strips, which are formed into groups or sets, so that a heater can be built up of any size from these units. For heating an electric car some six sets of conducting wires are coiled around porcelain tubes, the current being supplied with the motor. The cost is stated at about 60 cents a car per day. The method of heating is waste ful where the source of heat is coal, and it cannot be generally substituted for house heat ing; but it is excellently adapted for small in dividual heaters, where the cost is less import ant than the convenience, as for flatirons, ket tles, saucepans, dinner plates, soldering tools, toasters, dishwashers and cookers. The indus
try of manufacturing such small heaters already runs into several million dollars annually in the United States. A recent new use for the electric heater is the stimulation of petroleum wells that are running dry. Heating coils are lowered into the well to melt out the heavy oil accumulation and cause it to flow freely. In the manufacture of armatures, time has been re duced by the use of electrically heated ovens to dry out the moisture. The temperature can be regulated so accurately that there is no danger of melting the solder. In enameling iron the electric heater has also found a field of use fulness, because it maintains a high and uni form heat. The same quality of uniformity has caused the manufacturers of linotype machines to make an electric heater for their melting pots.