Heating by electricity
The heating element in an ordinary radiant electric fire is a length of resistance wire which becomes raised to a temperature of about 900 DC when current is passed through it. The wire is supported on a fireclay rod or bar or coiled inside a fused silica tube. The alloy from which the wire is made is a mixture of nickel and chromium which resists oxidation in air when red hot.
In the convector type of heater the element is raised to a temperature of only about 450 DC. This is popularly known as black heat, and the elements in this case are not designed to radiate but only to warm the air, which circulates through the heater by either free or forced convection. In another method of space heating current is passed through iron wires embedded in the concrete of floors and the plaster of walls and ceiling. Storage heaters use cheap electricity during the night and store up internal energy in fireclay blocks which subsequently is given out as heat.
Many domestic electric appliances contain heating elements. The kettle, laundry iron, toaster, and electric blanket are examples which readily come to mind, and the reader will be able to think of at least a half a dozen others. Whenever electricity is used for raising the temperature of water or other liquids the element is well insulated and enclosed in a metal tube or sheath. It is important not to let the element come into direct contact with water, otherwise the latter will become live and therefore dangerous.The elements of laundry irons are made of strip instead of wire, so that they are as flat as possible and also present a large surface for conducting away heat into the ole of the iron. Elements of this type are wound on mica and sandwiched between two thin sheets of the same material. Mica is a mineral which can be readily cleaved into thin sheets or laminae. It is not only highly insulating but can also withstand high temperatures.