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An aneroid calorimeter for specific and latent heats
June, I917.]
U.S.
769
BUREAU OF STANDARDS NOTES.
There is no indication that the temperature within the helix is higher than on the outside o.f the turn. A difference in temperature of 2oo ° would be required to account for the observed difference in brightness of 9 ° per cent.; whereas pyrometric, thermal conductivity, and other measurements pl'ace this temperature difference at less than 5 ° . Although the quality of the radiation has been modified by multiple reflection within the helix, it is not sufficiently similar to that of black-body radiation to permit its use in exact temperature measurements by sighting an optical pyrometer within the turns of the helix.
AN ANEROID
CALORIMETER
FOR SPECIFIC
AND
LATENT
HEATS.*
By Nathan S. Osborne.
[A~ST~ACT.] THE principle of the unstirred or "aneroid" type of calorimeter has been embodied in an instrument especially designed for determinations of the specific heat and latent heat of several substances in general use as refrigerating media. Heat developed electrically in a coil located in the central axis of the cylindrical shell comprising the calorimeter is distributed by conduction to the calorimeter and contents, whose initial and final temperatures when in thermal equilibrium are measured by a platinum resistance thermometer. Heat from other sources is 'excluded by enveloping the calorimeter with a metal jacket separated from it by an air space and keeping this jacket during measurements at the same temperature as the calorimeter surface, using multiple thermocouples to indicate this equality. The calorimeter is adapted for use between - 5 °0 C. and + 5°o C. and for pressures up to 7 ° atmospheres in experiments where the measured heat added is used either to change the temperature of the contents or to evaporate a portion of the contents withdrawn as superheated vapor: in the first case the * Scientific Paper No_3o-Ii .
.
VOL. I83, No. IO98--No. 55
.
.
.
.
.
.
.
.
.
.
.
770
U.S.
BUREAU OF STANDARDS NOTES.
[J. F. I.
specific heat and in the second the latent heat of vaporization being obtained when proper corrections are made. Such experimen,ts are described in separate papers, this paper being devoted to the description of the instrument and its calibration. Several features to which special attention has been given are : I. Refinements to reduce errors in the evaluation of thermal leakage. These refinements include the following details: (a) Location of the heater in the central axis of the calorimeter so that abrupt thermal irregularities produced by the heat developed therein m.ay be subdued before affecting the surface. (b) Distribution of metal connections between calorimeter and jacket in such a way that the lead conduction is unaffected by inequalities in the surface temperature of the calorimeter. (c) Protection by means of superficial copper sheaths of the calorimeter surface from abrupt variations in temperature such as may occur within during calorimetric measurements. (d) Method of indicating relative mean surface temperatures of calorimeter and jacket by means of multiple integrating thermocouples, which permits the evaluation of, and usually the annulment of, the thermal leakage. 2. Provision, by means of a system of radial metal vanes, for the distribution of heat throughout the contents. 3. Provision for insuring the dryness of vapor withdrawn by means of baffle plate system. 4. Installation in the calorimeter of a strain-free type of platinum resistance thermometer selected to give requisite accuracy. 5. Devices for rapid cooling of the calorimeter, consisting of a copper ring which can be moved within the jacket so as to thermally short-circuit the insulating air space and permit the escape of heat to the cooled jacket. 6. Thermo-regulated bath for keeping the temperature of the isothermal envelope or jacket always under control of the observer in order to avoid any unmeasured heat increments by thermal leakage. Many other details are described which have a bearing on the convenience or accuracy in the use of the instrument. The method of manipulation in making measurements of heat capacity is described and the results are given of an extended
June, I917.]
U . S . BUREAU OF STANDARDS NOTES.
77 I
series of observations in the temperature range from - 5 °o C. to + 5°o C. to determine the heat capacity of the empty calorimeter. WAVE-LENGTHS
OF T H E S T R O N G E R L I N E S IN T H E H E L I U M SPECTRUM.* By Paul Vq. Merrill.
[ABSTRACT.]
WAVE-LENGTHS of 2I of the stronger helium lines have been carefully measured photographically by means of the Fabry and Perot type of interferometer, using several separations. Nine of the lines were compared directly with the standard cadmium line 6438.4696A, the remaining lines being referred to these. The accuracy attained is nearly o.oorA, so that the lines will become available as convenient standards for many purposes. The fact is well known that the separation of the effective reflecting surfaces of the interferometer usually appears to be slightly different for different colors. The possibility is noted of elimin'ating the effect on measured wave-lengths by taking differences of orders and of thickness from large and small interferometers. The Kayser and Runge formula for spectral series with constants derived frmn three consecutive lines will not reproduce accurately even the next member of any one of the six series. T H E R E L A T I V E S E N S I B I L I T Y OF T H E A V E R A G E E Y E T O L I G H T OF D I F F E R E N T C O L O R S A N D S O M E P R A C T I C A L APPLICATIONS TO RADIATION PROBLEMS.? By W. W. Coblentz and W. B. Emerson.
[ABSTRACT.]
IN the present investigation the methods are practically the same as used by previous experimenters. In the visual measurements the spectral light was compared with a standard white light by means of a flicker photometer and also an equality-ofbrightness photometer. The source of white light was a standardized vacuum tungsten lamp. A cylindrical acetylene flame was used as a source of spectral light. The distribution of energy * Scientific Paper No. 302.
? Scientific Paper No. 3o3.
U.S.
769
BUREAU OF STANDARDS NOTES.
There is no indication that the temperature within the helix is higher than on the outside o.f the turn. A difference in temperature of 2oo ° would be required to account for the observed difference in brightness of 9 ° per cent.; whereas pyrometric, thermal conductivity, and other measurements pl'ace this temperature difference at less than 5 ° . Although the quality of the radiation has been modified by multiple reflection within the helix, it is not sufficiently similar to that of black-body radiation to permit its use in exact temperature measurements by sighting an optical pyrometer within the turns of the helix.
AN ANEROID
CALORIMETER
FOR SPECIFIC
AND
LATENT
HEATS.*
By Nathan S. Osborne.
[A~ST~ACT.] THE principle of the unstirred or "aneroid" type of calorimeter has been embodied in an instrument especially designed for determinations of the specific heat and latent heat of several substances in general use as refrigerating media. Heat developed electrically in a coil located in the central axis of the cylindrical shell comprising the calorimeter is distributed by conduction to the calorimeter and contents, whose initial and final temperatures when in thermal equilibrium are measured by a platinum resistance thermometer. Heat from other sources is 'excluded by enveloping the calorimeter with a metal jacket separated from it by an air space and keeping this jacket during measurements at the same temperature as the calorimeter surface, using multiple thermocouples to indicate this equality. The calorimeter is adapted for use between - 5 °0 C. and + 5°o C. and for pressures up to 7 ° atmospheres in experiments where the measured heat added is used either to change the temperature of the contents or to evaporate a portion of the contents withdrawn as superheated vapor: in the first case the * Scientific Paper No_3o-Ii .
.
VOL. I83, No. IO98--No. 55
.
.
.
.
.
.
.
.
.
.
.
770
U.S.
BUREAU OF STANDARDS NOTES.
[J. F. I.
specific heat and in the second the latent heat of vaporization being obtained when proper corrections are made. Such experimen,ts are described in separate papers, this paper being devoted to the description of the instrument and its calibration. Several features to which special attention has been given are : I. Refinements to reduce errors in the evaluation of thermal leakage. These refinements include the following details: (a) Location of the heater in the central axis of the calorimeter so that abrupt thermal irregularities produced by the heat developed therein m.ay be subdued before affecting the surface. (b) Distribution of metal connections between calorimeter and jacket in such a way that the lead conduction is unaffected by inequalities in the surface temperature of the calorimeter. (c) Protection by means of superficial copper sheaths of the calorimeter surface from abrupt variations in temperature such as may occur within during calorimetric measurements. (d) Method of indicating relative mean surface temperatures of calorimeter and jacket by means of multiple integrating thermocouples, which permits the evaluation of, and usually the annulment of, the thermal leakage. 2. Provision, by means of a system of radial metal vanes, for the distribution of heat throughout the contents. 3. Provision for insuring the dryness of vapor withdrawn by means of baffle plate system. 4. Installation in the calorimeter of a strain-free type of platinum resistance thermometer selected to give requisite accuracy. 5. Devices for rapid cooling of the calorimeter, consisting of a copper ring which can be moved within the jacket so as to thermally short-circuit the insulating air space and permit the escape of heat to the cooled jacket. 6. Thermo-regulated bath for keeping the temperature of the isothermal envelope or jacket always under control of the observer in order to avoid any unmeasured heat increments by thermal leakage. Many other details are described which have a bearing on the convenience or accuracy in the use of the instrument. The method of manipulation in making measurements of heat capacity is described and the results are given of an extended
June, I917.]
U . S . BUREAU OF STANDARDS NOTES.
77 I
series of observations in the temperature range from - 5 °o C. to + 5°o C. to determine the heat capacity of the empty calorimeter. WAVE-LENGTHS
OF T H E S T R O N G E R L I N E S IN T H E H E L I U M SPECTRUM.* By Paul Vq. Merrill.
[ABSTRACT.]
WAVE-LENGTHS of 2I of the stronger helium lines have been carefully measured photographically by means of the Fabry and Perot type of interferometer, using several separations. Nine of the lines were compared directly with the standard cadmium line 6438.4696A, the remaining lines being referred to these. The accuracy attained is nearly o.oorA, so that the lines will become available as convenient standards for many purposes. The fact is well known that the separation of the effective reflecting surfaces of the interferometer usually appears to be slightly different for different colors. The possibility is noted of elimin'ating the effect on measured wave-lengths by taking differences of orders and of thickness from large and small interferometers. The Kayser and Runge formula for spectral series with constants derived frmn three consecutive lines will not reproduce accurately even the next member of any one of the six series. T H E R E L A T I V E S E N S I B I L I T Y OF T H E A V E R A G E E Y E T O L I G H T OF D I F F E R E N T C O L O R S A N D S O M E P R A C T I C A L APPLICATIONS TO RADIATION PROBLEMS.? By W. W. Coblentz and W. B. Emerson.
[ABSTRACT.]
IN the present investigation the methods are practically the same as used by previous experimenters. In the visual measurements the spectral light was compared with a standard white light by means of a flicker photometer and also an equality-ofbrightness photometer. The source of white light was a standardized vacuum tungsten lamp. A cylindrical acetylene flame was used as a source of spectral light. The distribution of energy * Scientific Paper No. 302.
? Scientific Paper No. 3o3.