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The effusion method of determining gas density
N O T E S FROM T H E U. S. B U R E A U
OF S T A N D A R D S . *
THE E F F U S I O N METHOD OF D E T E R M I N I N G GAS D E N S I T Y ) By Junius David Edwards.
[ABSTRACT.]
THE effusion method of determining gas density, which is based upon the fact that the times required for the escape of equal volumes of two gases under the same pressure through the same small orifice are approximately proportional to the square roots of the densities of the gases, was investigated in order to determine the accuracy of the method and its sources of error. In co6peration with 'a. number of men employing this method in the natural gas industry, a series of experiments was made, using their apparatus under field conditions. It was found that results in error by more than Io per cent. were not unusual. The theory of the effusion process was studied in order to determine the influence of the numerous variables affecting the apparent specific gravity. The effect of differences in physical properties upon the relative rates of effusion of air and hydrogen, argon, methane, and carbon dioxide at different pressures was determined. A more detailed treatment of the theory in the light of these results will be given in ano.ther paper. The facts observed in this study, together with the observations made on the effect of the effusion pressure, the confining medium, and the sh~ape and size of the orifice, have been used in determining the most favorable conditions of operation for this method. It is very important that the orifice be of the proper size and shape. Recommendations have been made as to the most suitable type and form of apparatus for use and specifications given to guide in the construction of the orifice. * Communicated by the Director. 1 Technologic Paper No. 94.
767
768
U . S . BUREAU 0V STANDARDS NOTES.
[J. F. i.
It has been shown that the apparent specific gravity as determined by this meechod can be varied within rather wide limits by changing the conditions. However, by the observance of certain precautions in the construction and use of apparatus, it is possible to secure results accurate to about 2 per cent. The greatest precision is obtained where the physical properties of the gas tested show the least difference from those of air. Some further increase in accuracy, and particularly in reliability, can be gained by standardizing the apparatus as recommended.
T H E E M I S S I V I T Y OF S T R A I G H T A N D H E L I C A L F I L A M E N T S OF T U N G S T E N . * By W. W. Coblentz.
Isr the present investigation data are given on the radiation from the inside and the outside of the turn of a helically wound tungsten filament in an atmosphere of nitrogen. The intensity of the radiation from within the turn of the helix is from 9° to IOO per cent. greater than from a similar area on the outside of the turn. This is accounted for on the basis of multiple reflection within the helix. This modifies the quality of the light so that it is redder than the light from the outside of the turn. The observed infra-red measurements on the radiation from within the helix and the computed values (obtained on the basis of nmltiple reflection and the reflectivity of tungsten) are in close agreement, which is further evidence that the phenomenon is the result of multiple reflection. Tests were made with a Nicol prism, which showed that the light from within the filament is highly polarized, indicating that the quality of the light is quite different from that of a black body. The infra-red energy measurements also indicate that the quality of the radiation emitted differs from that of a black body. Computations of the radiation constant of tungsten indicate, as found in previous investigations, that the Wien equation is not applicable to the radiation from tungsten. * Scientific Paper No. 300.
OF S T A N D A R D S . *
THE E F F U S I O N METHOD OF D E T E R M I N I N G GAS D E N S I T Y ) By Junius David Edwards.
[ABSTRACT.]
THE effusion method of determining gas density, which is based upon the fact that the times required for the escape of equal volumes of two gases under the same pressure through the same small orifice are approximately proportional to the square roots of the densities of the gases, was investigated in order to determine the accuracy of the method and its sources of error. In co6peration with 'a. number of men employing this method in the natural gas industry, a series of experiments was made, using their apparatus under field conditions. It was found that results in error by more than Io per cent. were not unusual. The theory of the effusion process was studied in order to determine the influence of the numerous variables affecting the apparent specific gravity. The effect of differences in physical properties upon the relative rates of effusion of air and hydrogen, argon, methane, and carbon dioxide at different pressures was determined. A more detailed treatment of the theory in the light of these results will be given in ano.ther paper. The facts observed in this study, together with the observations made on the effect of the effusion pressure, the confining medium, and the sh~ape and size of the orifice, have been used in determining the most favorable conditions of operation for this method. It is very important that the orifice be of the proper size and shape. Recommendations have been made as to the most suitable type and form of apparatus for use and specifications given to guide in the construction of the orifice. * Communicated by the Director. 1 Technologic Paper No. 94.
767
768
U . S . BUREAU 0V STANDARDS NOTES.
[J. F. i.
It has been shown that the apparent specific gravity as determined by this meechod can be varied within rather wide limits by changing the conditions. However, by the observance of certain precautions in the construction and use of apparatus, it is possible to secure results accurate to about 2 per cent. The greatest precision is obtained where the physical properties of the gas tested show the least difference from those of air. Some further increase in accuracy, and particularly in reliability, can be gained by standardizing the apparatus as recommended.
T H E E M I S S I V I T Y OF S T R A I G H T A N D H E L I C A L F I L A M E N T S OF T U N G S T E N . * By W. W. Coblentz.
Isr the present investigation data are given on the radiation from the inside and the outside of the turn of a helically wound tungsten filament in an atmosphere of nitrogen. The intensity of the radiation from within the turn of the helix is from 9° to IOO per cent. greater than from a similar area on the outside of the turn. This is accounted for on the basis of multiple reflection within the helix. This modifies the quality of the light so that it is redder than the light from the outside of the turn. The observed infra-red measurements on the radiation from within the helix and the computed values (obtained on the basis of nmltiple reflection and the reflectivity of tungsten) are in close agreement, which is further evidence that the phenomenon is the result of multiple reflection. Tests were made with a Nicol prism, which showed that the light from within the filament is highly polarized, indicating that the quality of the light is quite different from that of a black body. The infra-red energy measurements also indicate that the quality of the radiation emitted differs from that of a black body. Computations of the radiation constant of tungsten indicate, as found in previous investigations, that the Wien equation is not applicable to the radiation from tungsten. * Scientific Paper No. 300.