Gas discharge tube

 

This apparatus contains a range of gas discharge tubes, and is likely unique as it was created specifically for the University of Canterbury. Designed purely as a teaching resource, it was made about 1964 in the Department’s workshops by technician Russell Gillard. It was rediscovered in 1986 and has remained in use since then. Used to teach Chemistry undergraduates the principles of emission of light - as well as more complicated physical chemistry concepts - the apparatus contains seven samples of different gases, each held in a small glass discharge tube.

The gas mixtures in the tubes are trapped between electrodes, and - when the machine is connected to a power source - they conduct electrical currents. After the gaseous atoms or molecules lose an electron from a high voltage spike, the gas mixtures will conduct a high amount of current for their size, and will emit light of a certain wavelength, which in the visible region of the electromagnetic spectrum we seen as coloured light. The apparatus demonstrates how the different gases produce light of different colours when current flows through them, and this helps students to visualise atomic structure and understand concepts such as absorption/emission.

Depending upon the gas, the mixtures inside the tubes have differences in voltage, discharge current, or the packaging type. These differences can be beneficial, as they give the gases a variety of uses, and they are found in settings ranging from telecommunication lines and alarm systems to surge protectors and medical electronics. Gas discharge tubes are also commonly seen in urban contexts, as the principle is applied in the neon lights used in many signs and advertisements. Usually, gas discharge tubes are filled with noble gases such as helium, neon and krypton, but tubes filled with hydrogen gas and sometimes even mercury vapour, as in this apparatus, exist also.

Text by: Connor O’Rourke

 

Gas dishcharge tube, c.1964