But it would take an enormous volume of nitrogen to achieve significant positive buoyancy when the nitrogen is enclosed by much of anything. Air's mass is 28.97g/mol, vs. 28g/mol for N2. So, based on my vague recollection of chemistry, that means you only get 1g of container/cargo/engine for every 22.4L of gas enclosed.

> that means you only get 1g of container/cargo/engine for every 22.4L of gas enclosed.

For reference, the Hindenburg carried about 200 million liters of gas. A nitrogen craft would need approximately 1.52 million liters to carry a single 150#/68kg human being, not counting the additional gas needed for the craft itself.

So if you want to build a Hindenburg-size craft to carry about half a dozen people it might actually be plausible!