Defines the nitrogen fraction of a breathing gas, given as a real number less or equal 1.0 in percent (of volume).
<mix>
<mix>
(see also <mix>)
<mix id="alfreds_nitrox">
    <name>my_nitrox</name>
    <!-- 37,5 % oxygen fraction -->
    <o2>0.375</o2>
    <!-- 62,5 % nitrogen fraction -->
    <n2>0.625</n2>
    <!-- no further components -->
    <he>0.0</he>
    <ar>0.0</ar>
    <h2>0.0</h2>
</mix>