A photo of an old electric Ziff-O-Lec immersion heater. From what one understands, this device has an enameled outside and would be immersed in a container of water to heat it. The heater has a twisted-wire power cord with cloth covered wires and the plug is fitted with an Edison screw base adapter so that the heater can easily be powered from a light bulb socket. From information elsewhere, the Ziff-O-Lec heater may have been patented in the 1920s and produced by the Ziff Electric company of Los Angeles, California.