0° 4.525 21° 18.505 1° 4.867 22° 19.675 2° 5.231 23° 20.909 3° 5.619 24° 22.211 4° 6.032 25° 23.582 5° 6.471 26° 25.026 6° 6.939 27° 26.547 7° 7.436 28° 28.148 8° 7.964 29° 29.832 9° 8.525 30° 31.602 10° 9.126 31° 33.464 11° 9.751 32° 35.419 12° 10.421 33° 37.473 13° 11.130 34° 39.630 14° 11.882 35° 41.893 15° 12.677 36° 44.268 16° 13.519 37° 46.758 17° 14.409 38° 49.368 18° 15.351 39° 52.103 19° 16.345 40° 54.969 20° 17.396 When a gas is in contact with water the aqueous vapor is diffused throughout the mass, and the pressure to which the mixture is subjected, is partly neutralized by the tension of the water vapor. The real pressure to which the gas, whose volume is to be determined is subjected, is therefore diminished by that tension. If for instance a gas in contact with water show a volume of thirty-five cubic centimeters at 22° and 740 millimeters barometric pressure its volume is really greater than if it were perfectly dry. How much greater can be determined by inspecting the table, for at 22° the tension of water vapor is 19.675 millimeters of mercury. The real pressure to which the volume of gas is subjected is therefore 740 - 19.675 = 720.325 millimeters. If, therefore, in the example given, the nitrogen were in contact with water, the calculation would proceed as follows: 32.18 × 720.325 V′ = ----------------- = 30.5, 760 and 30.5 × 1.25456 = 38.26. Hence, 38.26 milligrams of nitrogen correspond to 7.65 per cent, when half a gram of substance is taken for the combustion. =165. Aqueous Tension in Solutions of Potassium Hydroxid.=—Even in strong solutions of potassium hydroxid the tension of aqueous vapor is not destroyed, but is reduced to a minimum, which is negligible in the calculation of the percentage by weight of the nitrogen in a sample of fertilizer. When dilute solutions of a caustic alkali are used however, the neglect of the tension of the aqueous vapor may cause an error of some magnitude. In such cases the strength of the solution should be known and correction made according to the following table:[137]