Specific heat at constant pressure of hydrogen, nitrogen, and the mixture N₂ + 3H₂; variation with pressure up to 200 atmospheres
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Abstract
The experiments were carried out at a mean temperature
of about 60°C. and the following results obtained:
(1) C increases regularly with increase of pressure in each case studied, and the variations are represented by the following equations: [P. Represents absolute pressure in atmospheres.] • Hydrogen, Cₚ = 3.418 + 4.27 x 10⁻⁴P • Nitrogen, Cₚ = 0.2475 + 2.45 x 10⁻⁴P • Mixture, Cₚ = 0.804 + 3.00 x 10⁻⁴P
These are accurate to 0.3% in the case of Hydrogen and to 0.5% in the other cases. The formulae are in terms of gram atmospheres and calories. These equations may be written in terms of atmospheres and C.H.U. per 1000 cubic ft. free gas at 20 °C. viz., • Hydrogen 17.87 + 2.23 x 10⁻³P • Nitrogen 18.01 + 1.78 x 10⁻²P • Mixture 17.78 + 6.65 x 10⁻³P
(2) Within the range and accuracy of the present work the values are additive for mixtures of nitrogen and hydrogen.
(3) The following values are obtained from the equations above:
. . Pressure . . | . . . . . . . Specific Heat. . . . . . .
Abs. | Gauge | Hydrogen | Nitrogen | Mixture.
0 | -- | 3.418 | .2475 | .804
1 | 0 | 3.418 | .2477 | .804
51 | 50 | 3.439 | .2600 | .819
101 | 100 | 3.461 | .2722 | .834
151 | 150 | 3.482 | .2845 | .849
201 | 200 | 3.503 | .2968 | .864
(4) As a "control ", determinations of Cₚ for air were made from time to time and results agreeing well with those of Holborn & Jakob were obtained. This agreement was found at the lowest pressures, studied so that the present work has cleared up the discrepancy between the value of 0.237 obtained at ordinary pressure by Witkowski and others by the Regnault method, and the value of 0.241 obtained by Holborn and Jakob and others by the Callendar method. In the present experiments a modified Regnault apparatus was used, and agreement was obtained with the figures from the Callendar method.
(1) C increases regularly with increase of pressure in each case studied, and the variations are represented by the following equations: [P. Represents absolute pressure in atmospheres.] • Hydrogen, Cₚ = 3.418 + 4.27 x 10⁻⁴P • Nitrogen, Cₚ = 0.2475 + 2.45 x 10⁻⁴P • Mixture, Cₚ = 0.804 + 3.00 x 10⁻⁴P
These are accurate to 0.3% in the case of Hydrogen and to 0.5% in the other cases. The formulae are in terms of gram atmospheres and calories. These equations may be written in terms of atmospheres and C.H.U. per 1000 cubic ft. free gas at 20 °C. viz., • Hydrogen 17.87 + 2.23 x 10⁻³P • Nitrogen 18.01 + 1.78 x 10⁻²P • Mixture 17.78 + 6.65 x 10⁻³P
(2) Within the range and accuracy of the present work the values are additive for mixtures of nitrogen and hydrogen.
(3) The following values are obtained from the equations above:
. . Pressure . . | . . . . . . . Specific Heat. . . . . . .
Abs. | Gauge | Hydrogen | Nitrogen | Mixture.
0 | -- | 3.418 | .2475 | .804
1 | 0 | 3.418 | .2477 | .804
51 | 50 | 3.439 | .2600 | .819
101 | 100 | 3.461 | .2722 | .834
151 | 150 | 3.482 | .2845 | .849
201 | 200 | 3.503 | .2968 | .864
(4) As a "control ", determinations of Cₚ for air were made from time to time and results agreeing well with those of Holborn & Jakob were obtained. This agreement was found at the lowest pressures, studied so that the present work has cleared up the discrepancy between the value of 0.237 obtained at ordinary pressure by Witkowski and others by the Regnault method, and the value of 0.241 obtained by Holborn and Jakob and others by the Callendar method. In the present experiments a modified Regnault apparatus was used, and agreement was obtained with the figures from the Callendar method.
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