We did this. One balloon with plain air. One with pure hydrogen. One with 50/50 hydrogen and air. The one with pure hydrogen popped closer in magnitude to the pure air than it was to the 50/50 mix.

ETA: I may be misremembering, the more I think about it, the more I recall that we did not use air, we did use pure oxygen. Not like it was hard to get (and we had lots more interesting stuff than that in the lab, this was the 80s...). But the outcome I do remember. The entire point of the experiment was to examine the difference between the individual pure elements and the mix. We expected the pure hydrogen to be far more interesting than it turned out.