Durham tube

Durham tubes are used in microbiology to detect production of gas by microorganisms. They are simply smaller test tubes inserted upside down in another test tube. This small tube is initially filled with the solution in which the microorganism is to be grown. If gas is produced after inoculation and incubation, a visible gas bubble will be trapped inside the small tube. The initial air gap produced when the tube is inserted upside down is lost during sterilization, usually performed at 121 °C for 15 or so minutes. The method was first reported in 1898 by British microbiologist Herbert Durham.
External links.
1. http://www.vumicro.com/vumie/help/VUMICRO/Nitrate_Broth_with_Durham_Tube.htm
2. http://www.bd.com/ds/technicalCenter/inserts/L007459(07)(0506).pdf