Use only enough dried silica gel to remove the moisture that you think is present. The gel will quickly turn dark as it loads up with NO2,
but it has much greater affinity towards adsorbing water than it does NO2. A quick puff of dry oxygen will flush most of the
NO2 out of the gel, while many minutes of flowing dry air would be needed to remove moisture to the same extent. Some residual nitrogen
will likely be left behind in the silica gel as nitric acid, and this will be hard to remove completely even with heat. |