To show spectral lines of pure substances. These are glass tubes about 26cm long, central capillary portion about 9-10cm long with electrodes sealed at both ends and connected to lead wires protected by metal caps. Provided with loops welded to caps for electrical connection. Needs an induction coil 5cm spark, or or spectrum tube power supply.
Except for Neon and Helium, these can not be used as lamps. Length of capillary portion can be varied as required. For intermittent use.