AFMAN 24-204(I)/TM 38-250/NAVSUP PUB 505/MCO P4030.19H/ DLAI 4145.3 369 11 DECEMBER 2001 A26.5.   Properties  of  Common  Gases.   Figure  A26.5  is  a  list  of  the  molecular  weight  and  specific  gravity  of common gases. Figure A26.5.  Properties of Common Gases. GAS          SYMBOL   MOLECULAR           SPECIFIC                    WEIGHT                  GRAVITY Helium He            4.00          0.138 Argon                        A          40.00                1.377 Air                             -             29.00                        1.000 Oxygen                      O₂          32.00                        1.103 Nitrogen                    N₂          28.00                       0.966 Hydrogen     H₂            2.00                        0.0695 Nitric Oxide              NO          30.00                  1.034 Carbon Monoxide     CO          28.00                        0.965 Hydrochloric Acid    HCl          36.50                  1.256 Steam                         H₂O          18.00                0.623 Carbon Dioxide        CO₂          44.00                1.516 Nitrous Oxide           N₂O          44.00                        1.518 Sulfur Dioxide          SO₂          64.00                2.208 Ammonia                  NH₃          17.00               0.587 Acetylene                  C₂H₂          26.00               0.897 Methyl Chloride        CH₂Cl          50.50                1.738 Methane                    Ch₄          16.00                0.553 Ethylene                    C2H₄          28.00               0.967