The weight of a 2cc glass pharmaceutical flame sealed ampoule?
I grabbed 10 empty, unsealed ones and threw them on the analytical balance and got mean: 2.4071 g, s.d.: 0.01264 g for Wheaton amber glass pre-scored vials (part number 176796). The variation between vials isn't too bad, but I don't know if they can be filled and sealed consistently enough to determine gas density like that to any useful precision and other brands may be better or worse.