Sane

Hi everyone, first time here. I have no qualifications in physics what so ever. I am working on an experiment and would like to know if there is a device that can measure the MASS of AIR that is pumped into a container. Does it exist? What is it called? My whole experiment is based on the assumption that such a device exists (I do not want to use scales). I have searched high and low to no avail... If such a device does NOT exist,I have found out that there are AIR FLOW measuring devices (AFM) in the market. Which means I should be able to calculate the air MASS (kg) from the air FLOW (kg/hr). The device I am trying to build pumps air into 2 (air tight) containers until a given pressure is achieved i.e 2 Bars. The second container however, is NOT empty. Assuming that the second container is half full with a fluid or a solid, which of the following is true and WHY? 1. The FIRST container will take exactly DOUBLE the TIME to fill than the second one. OR 2. They will fill up at exactly the same time but the air flow on the FIRST container will be DOUBLE than the air flow on the second. My instinct tells me it's no. 2 but I am not sure. Can you help? Thanks.