Barometer Readings to 0 C Temperature

The apparatus should be assembled as shown in Fig. 2. If desired, the carboy may be mounted in a thermostat bath if so it must be clamped securely to overcome buoyancy. The manometer is an open tube manometer, one side of which is open to the atmosphere the pressure that it measures is therefore the difference of pressure from atmospheric pressure. A suitable liquid for the manometer is dibutyl phthalate, which has a density of 1.046 g cm at room temperature (20°C). To convert manometer readings (millimeters of dibutyl phthalate) to equivalent readings in millimeters of mercury (Torr), multiply by the ratio of this density to the density of mercury, which is 13.55 g cm at 20°C. To find the total pressure in the carboy, the converted manometer readings should be added to atmospheric pressure as given by a barometer. It is unnecessary to correct all readings to 0°C, as all pressures enter the calculations as ratios. 

The following corrections are used to reduce the reading of where h is the observed column height in mm and t the Celsius a mercury barometer with a brass scale to 0 °C. The number in temperature. This relation is based on thermal expansion coeffi-the table should be subtracted from the observed height of the cients of 181.81(T for mercury and 18.4-10" °C for brass, mercury column to give the true pressure in mmHg (ImmHg =... 

The mercury barometer (Fig. 10-11) indicates directly the absolute pressure of the atmosphere in terms of height of the mercuiy column. Normal (standard) barometric pressure is 101.325 kPa by definition. Equivalents of this pressure in other units are 760 mm mercury (at 0°C), 29.921 iuHg (at 0°C), 14.696 IbFin, and 1 atm. For cases in which barometer readings, when expressed by the height of a mercuiy column, must be corrected to standard temperature (usually 0°C), appropriate temperature correction factors are given in ASME PTC, op. cit., pp. 23-26 and Weast, Handbook of Chemistty and Physics, 59th ed., Chemical Rubber, Cleveland, 1978-1979, pp. E39-E41. 

A balloon 20 m in diameter is filled with helium at a gauge pressure of 2.0 atm. A man is standing in a basket suspended from the bottom of the balloon. A restraining cable attached to the basket keeps the balloon from r ing. The balloon (not including the gas it contains), the basket, and the man have a combined mass of 150 kg. The temperature is 24 C that day, and the barometer reads 760 mm Hg. 

The barometer is an 800-mm or longer tube which is sealed at the upper end, filled with mercury (Fig. 3-la), and inserted into a pool of mercury. If it has been filled in such a way as to avoid having air trapped in the upper end (e.g., by distilling in the mercury under a good vacuum), the height of the mercury column above the pool gives the atmospheric pressure. A temperature correction is usually applied, so that the readings correspond to that of a mercury column at 0°C. The open-end manometer (Fig. 3-1/ ) is closely related to the... 

The diffusivity of toluene in air was determined experimentally by allowing liquid toluene to vaporize isothermally into air from a partially filled vertical tube 3 mm in diameter. At a temperature of 39.4°C, it took 96 x iff sec for the level of the toluene to drop from 1.9 cm below the top of the open tube to a level of 7.9 cm below the top. The density of toluene is 0.852 gm/cm , and the vapor pressure is 57.3 torr at 39.4°C. The barometer reading was 1 atm. Calculate the diffusivity and compare it with the value predicted from (16-3). Neglect the counterdiffusion of air. 

It is advisable to have barometers checked occasionally against a standard instrument so that the corrections to be applied at various readings may be known. Aneroid barographs should be calibrated in the same way. These instruments — which generally have an accuracy of not more than 0-5 mm — are provided with charts running either for a day or a week. The charts should be fUed, in order that the atmospheric pressure at any time can be subsequently found. Aneroid barographs are as a rule compensated for errors due to temperature in the range of —40° to +40 °C by bimetallic strij).s. 

Barometer reading and temperature of the barometer. The observed barometric pressure shall be corrected by reference to standard tables and reported in terms of millimetres of mercury at 0 C. 

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