  As gaseous detectors are operated at high rates of primary ionisation, ions
created in the detector have a considerable impact on the performance of the
detector. The upgraded ALICE Time Projection Chamber (TPC) will operate during
LHC Run$\,3$ with a substantial space charge density of positive ions in the
drift volume. In order to properly simulate such space charges, knowledge of
the ion mobility $K$ is necessary.
  To this end, a small gaseous detector was constructed and the ion mobility of
various gas mixtures was measured. To validate the corresponding signal
analysis, simulations were performed.
  Results are shown for several argon and neon based mixtures with different
$\textrm{CO}_2$ fractions. A decrease of $K$ was measured for increasing water
content.
