  Modern detectors such as ATLAS use pressurized drift tubes to minimize
diffusion and achieve high coordinate accuracy. However, the coordinate
accuracy depends on the exact knowledge of converting measured times into
coordinates. Linear space-time relationships are best for reconstruction, but
difficult to achieve in the $E \propto \frac{1}{r}$ field. Previous mixtures,
which contained methane or other organic quenchers, are disfavored because of
ageing problems. From our studies of nitrogen and carbon dioxide, two mixtures
with only small deviations from linearity were determined and measured. Scaling
laws for different pressures and magnetic fields are also given.
