A selection of electric heaters for laboratory use, c 1920s.

The use of electricity in laboratory heating could only become general after the introduction of widespread public power supplies at the end of the 19th century. The devices shown here are (left to right); a constant level water bath, a 'Red-rod' laboratory immersion heater, an Isopad 'isomantle' electric laboratory flask heater, sectioned to show internal construction and an Electrothermal electric bench heater. The latter is a radiant heater providing a small source of heat for experiments on a test tube scale.