Caesofine gas

Caesofine gas, also known as Caesofine concentrate, was a volatile gaseous compound utilised by the Sontarans as a clone feed, serving a function analogous to amniotic fluid. Its composition was one part Bosteen, and two parts Probic 5.

In preparation of their 2009 invasion attempt of Earth the Sontarans manipulated humans to utilise ATMOS devices, seemingly a device to neutralise carbon dioxide emissions. However the true purpose of the ATMOS devices was to release caesofine gas into the atmosphere and thus turn the Earth into a clone world. Thanks to its combustibility, the gas was eliminated from the Earth's atmosphere by the Tenth Doctor with Luke Rattigan's atmospheric converter. (TV: The Sontaran Stratagem / The Poison Sky, The Last Sontaran)