The weight of a 2cc glass pharmaceutical flame sealed ampoule? This is one of the flame sealed type whose neck is broken before use. There seems to be lots of info on dimensions but none with regard to weight.
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.