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Some improvements in psychrometry
356
U. S.
BUREAU
SATURATION
OF STANDARDS
SCALE FOR YELLOW
NOTES.
[J. F. I.
COLORS.
The relationship between calorimetric purity of the stimulus and saturation of the color evoked under specified observing conditions has been determined at the bureau for yellow colors by using the yellow series of Lovibond glasses. Two observers have selected glasses from this series requisite to produce a scale progressing by equal steps from white to yellow. These results have been compared with previous experimental results, and with two empirical relations. Glasses representing the four scales compared have been grouped together and judgments obtained from eight observers as to which group formed the most satisfactory scale with the result that the new experimental scale has been corroborated. This information is useful in developing a method of writing uniform color tolerances. SOME
IMPROVEMENTS
IN PSYCHROMETRY.
Air humidity is generally measured by noting the reading of a thermometer having a bulb encased in wetted cloth, and simultaneously measuring the temperature of the air with an ordinary thermometer. From the two readings so obtained, the air humidity can be found by means of a table or chart. This combination of a wet-bulb and a dry-bulb thermometer is called a psychrometer. With proper care in its use, the psychrometer will give rather accurate values of humidity under normal weather conditions. However, when it is either very hot or cold, or very dry or wet, rather large errors occur despite the best of care. The instrument simply does not function correctly under such conditions. By slightly modifying the conventional ventilated psychrometer, the Bureau of Standards has found it possible to correct these errors; the resulting instrument is quite accurate at all humidities up to go per cent. and up to at least 150’ F. air temperature. In studying the instrument, it was also tested and found accurate under reduced air pressures equivalent to altitudes up to 32,500 feet. A new chart for obtaining either relative or absolute humidity from the psychrometer readings has been developed.
Mar.,1933.1 U. S. BUREAU
OF STANDARDS
NOTES.
357
This chart is both simpler to use and more accurate than those previously available. VAPOR LOCK.
The computations of vapor handling capacities of the fuel systems in fifty automobiles on which vapor lock data were obtained by the bureau, have been completed. Using these values as a basis it has been possible to evaluate, with considerable accuracy, the permissible vapor pressures for freedom from vapor lock in these cars when operated under a variety of conditions on diverse types of fuels. This analysis of the vapor lock results indicates that changes in design of fuel feed systems so as to increase the vapor handling capacity may be very effective in increasing the freedom from vapor lock troubles. This procedure has, however, the disadvantage that fuel economy is decreased at the same time so that it is preferable to confine most of the efforts in It redesign towards lowering of the fuel line temperatures. is believed that a Reid vapor pressure limit of 8 pounds is satisfactory up to atmospheric temperatures of 37.7” C. (100' F.) and that a 12 pound gasoline may be used satisfactorily up to atmospheric temperatures as high as 23.8” C. (75” F.). Further work is being undertaken to verify these limits for different types of gasoline. The conclusions drawn from this analysis of the test data obtained in the vapor lock road tests were incorporated in a paper entitled “The Vapor Handling Capacity of Automobile Fuel Systems ” which was presented at the annual meeting of the Society of Automotive Engineers last month. STABILITY OF GREASES.
The Bureau is conducting an investigation of the effect of temperature on the bleeding of greases. It has been found that the change in the amount of bleeding, with increase in temperature, varies markedly for different types of greases. Thus, in some cases the amount of bleeding will increase as the temperatures increase, while in other cases the reverse is true. Believing that hardening of the grease due to loss of
U. S.
BUREAU
SATURATION
OF STANDARDS
SCALE FOR YELLOW
NOTES.
[J. F. I.
COLORS.
The relationship between calorimetric purity of the stimulus and saturation of the color evoked under specified observing conditions has been determined at the bureau for yellow colors by using the yellow series of Lovibond glasses. Two observers have selected glasses from this series requisite to produce a scale progressing by equal steps from white to yellow. These results have been compared with previous experimental results, and with two empirical relations. Glasses representing the four scales compared have been grouped together and judgments obtained from eight observers as to which group formed the most satisfactory scale with the result that the new experimental scale has been corroborated. This information is useful in developing a method of writing uniform color tolerances. SOME
IMPROVEMENTS
IN PSYCHROMETRY.
Air humidity is generally measured by noting the reading of a thermometer having a bulb encased in wetted cloth, and simultaneously measuring the temperature of the air with an ordinary thermometer. From the two readings so obtained, the air humidity can be found by means of a table or chart. This combination of a wet-bulb and a dry-bulb thermometer is called a psychrometer. With proper care in its use, the psychrometer will give rather accurate values of humidity under normal weather conditions. However, when it is either very hot or cold, or very dry or wet, rather large errors occur despite the best of care. The instrument simply does not function correctly under such conditions. By slightly modifying the conventional ventilated psychrometer, the Bureau of Standards has found it possible to correct these errors; the resulting instrument is quite accurate at all humidities up to go per cent. and up to at least 150’ F. air temperature. In studying the instrument, it was also tested and found accurate under reduced air pressures equivalent to altitudes up to 32,500 feet. A new chart for obtaining either relative or absolute humidity from the psychrometer readings has been developed.
Mar.,1933.1 U. S. BUREAU
OF STANDARDS
NOTES.
357
This chart is both simpler to use and more accurate than those previously available. VAPOR LOCK.
The computations of vapor handling capacities of the fuel systems in fifty automobiles on which vapor lock data were obtained by the bureau, have been completed. Using these values as a basis it has been possible to evaluate, with considerable accuracy, the permissible vapor pressures for freedom from vapor lock in these cars when operated under a variety of conditions on diverse types of fuels. This analysis of the vapor lock results indicates that changes in design of fuel feed systems so as to increase the vapor handling capacity may be very effective in increasing the freedom from vapor lock troubles. This procedure has, however, the disadvantage that fuel economy is decreased at the same time so that it is preferable to confine most of the efforts in It redesign towards lowering of the fuel line temperatures. is believed that a Reid vapor pressure limit of 8 pounds is satisfactory up to atmospheric temperatures of 37.7” C. (100' F.) and that a 12 pound gasoline may be used satisfactorily up to atmospheric temperatures as high as 23.8” C. (75” F.). Further work is being undertaken to verify these limits for different types of gasoline. The conclusions drawn from this analysis of the test data obtained in the vapor lock road tests were incorporated in a paper entitled “The Vapor Handling Capacity of Automobile Fuel Systems ” which was presented at the annual meeting of the Society of Automotive Engineers last month. STABILITY OF GREASES.
The Bureau is conducting an investigation of the effect of temperature on the bleeding of greases. It has been found that the change in the amount of bleeding, with increase in temperature, varies markedly for different types of greases. Thus, in some cases the amount of bleeding will increase as the temperatures increase, while in other cases the reverse is true. Believing that hardening of the grease due to loss of