Spectrum Discharge Tube - Iodine

Spectrum tubes are glass tubes filled with a gas, usually that of an element or small molecule. Sealed metal electrodes are located at the ends of each tube. Depending on the gas, they MAY generate light by sending an electric discharge through the ionized gas, a plasma.

These tubes are made of glass 26 cm long overall and narrowed to capillary width for 8.5 to 10 cm of the length. Metal wires holding the electrodes are sealed through the ends and welded to metal caps, which have loops for connecting wires.