Flask is a British unit of mass or weight in the avoirdupois system, used to measure mercury.
[1][2][3][4][5] It is defined as 76 pounds (34 kg).
[1] Near room temperature, a flask of mercury occupies a volume of approximately 2.5451 litres (86.060 US fl oz; 89.575 imp fl oz).
[6] 1 flask (mercury) ≡ 76 lb[1] 1 flask (mercury) ≡ 34.47302012 kg