One method of providing evidence of the low atmospheric content of CO2 is to provide four, two-quart plastic juice bottles (1.89 L and about 85 g each) that have had their empty masses (cap included) adjusted to 102.24 g by the addition of about 15 g of masses and removal of pieces of the labels. Because the air in the 1.89 L container at 25oc has a mass close to 2.24 g, the mass over 100.00 g is the mass of the gas in the bottle. One of the bottles is sealed, thus containing air. The air in the remaining three bottles is displaced with nitrogen, oxygen, and CO2, respectively, and sealed. The bottles can then be weighed on an electronic centigram scale to sufficient precision that observations can be made and conclusions can be reached. The masses of the bottles will come out close to the values 2.24 g, 2.17 g, 2.48 g, and 3.41 g respectively for the air, nitrogen, oxygen, and CO2, The bottles will maintain their masses for many weeks although the CO2 bottle eventually will collapse. Consistent with expectations, the mass of the air comes out a little above the mass of nitrogen and between the masses of nitrogen and oxygen. The mass measurements demonstrate