NATIONAL BUREAU OF STANDARDS REPORT

3^31

High -Temperature Thermodynamics

Technical Report n

Edited by A. M. bass

Division of Heat and Power

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

ized research, development, and engineering in the field indicated by its title. A brief description

of the activities, and of the resultant reports and publications, appears on the inside of the back

cover of this report.

Electricity. Resistance and Reactance Measurements. Electrical Instruments. Magnetic

Measurements. Electrochemistry.

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Technology. Length. Engineering Metrology.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenic Physics. Engines

and Lubrication. Engine Fuels. Cryogenic Engineering.

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and Scale. Capacity, Density, and Fluid Meters. Combustion Control.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

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Standards. Microwave Standards.

^Office of Basic Instrumentation ^Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT July 9, 195^ NBS REPORT

0301-20-2671* 3^31

High -Temperature Thermodynamics

Technical Report II

Edited by A, M. Bass

Division of Heat and Power

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, repri APP rove d for public release by the

unless permiiiion is oi Director of the National Institute of

25,d.c. Suchpermi Standards and Technology (NIST)

cal ly prepared If tha On October 9, 2015

par t, Is prohibited

dards, Washington

rt has been speclflort for Its own use,
«
Work of the Heat and Power Division

National Bureau* of Standards

in High Temperature Thermodynamics

Foreword

For a number of years several groups in the Heat and Power Division of

the National Bureau of Standards have been actively engaged in a program of

research in the field of high temperature physics and chemistry. It has

been the aim of this program to study the thermometric and thermodynamic

properties of matter at elevated temperatures in as great detail as possible

to provide the basic information that is needed in present-day technology

of high temperature systems.

The first progress report on this program was issued in August 1951

(NBS Report 1123, ’’High Temperature Thermodynamics Technical Report1 ’;. This second report summarized the progress and accomplishments of the

several groups involved in this program from that date until March 1954.

The main topics discussed in this report are: studies of radiation from

high temperature equilibrium and non-equilibrium systems; development of

the noise thermometer; the work of the pyrometry laboratory in high temperature measurement; measurement of thermal conductivities and heat capacities

at high temperatures. A number of the papers included herein have been

submitted for publication in scientific journals and they are reported here

for the sake of giving a complete picture of the program.

The work in this reporting period has been supported by several

agencies including the National Bureau of Standards, Office of Naval Research

Office of Ordnance Research (Army), Wright Air Development Center (Air Force)

National Adivsory Committee for Aeronautics, and the Atomic Energy

Commission.

A later report will describe studies of infrared radiation from hot

gases which has been carried on as part of this program under the sponsorship

of the WADC.

Dr. F. G. Brickwedde, Chief

Division of Heat and Power

A. 7. Astin, Director

National Bureau of Standards
TABLE OF CONTENTS

1 9 Introduction, A.* Bass and R#< D. Arnold 1

2. A. High Temperature Absorption Tube Furnace. R. D. Arnold 6

3. Design and Construction of a "Blackbody" and its use in the

Spectral Intensity Calibration of a Grating Monochromator.

G. T. Lalos, R. J. Corruccini and H. P. Broida 2?

4. A Survey of Flame Spectra. N. H. Kiess 43

5. The X4050 Group of Cometary Spectra in the Acetylene-Oxygen Flame

N. H. Kiess and A. M. Bass 68

6. The Decomposition of CF/j. in Flames. B. E. Squires 74

7. Ultraviolet Absorption Spectroscopy of Spark Ignited,

Low Pressure Explosions.

H. P. Broida, A. J. Everett and G. J. Minkoff 91

8. Use of a Vacuum Spectrograph for Combustion Study.

W. R. S. Garton and H. P. Broida 102

9. Development Work on the Noise Thermometer. E. W. Hogue 104

10. The Pyrometry Laboratory. J. P. Evans m

11. Thermal Conductivities at High Temperatures.

D. C. Ginnings and R. L. Nut tall X13

12. Heat Capacities at High Temperatures.

T. B. Douglas and E. D. West 115
1. Introduction - Radiation Studies of Systems at High Temperatures

A. M. Bass and R. D. Arnold

The High Temperature Laboratory of the Temperature Measurements Section

was established in 1949 to investigate methods of determining temperatures,

the accuracy of such methods, and the meaning of such temperatures in hot

gases (above 1000°C). As a direct corollary to investigations of this kind,

studies of non-equilibrium processes and the chemical kinetics involved in

the combustion of hydrocarbon and other gaseous fuels have been of great

interest. In August 1951 there was issued "Technical Report on High Temperature Thermodynamics - NBS Report 1123" which summarized the status of the

program to that date.

Since that time the high temperature research program has proceeded in

the direction outlined in the 1951 report. For the period since the appearance

of the first report it is possible to summarize the progress made in this program

in several categories.

1. The Molecule OH as a Thermometer

On the question of whether the radiation from OH in flames is of thermal

or chemiluminescent origin, there are indications that in the inner cone of the

acetylene-oxygen flame the radiation of OH( *ET * ) is, to a large extent che iluminescent [6]. It has also been found that in the outer cone of flame'- at

atmospheric pressure diluted with He, or A, and also in electrodele

discharges through water vapor, the rotational distribution is abnorma. [13,15]

.

These studies show that not only is the OH (^X+

) foraed in a non-thermal

distribution, but that the abnormal distribution of rotation is quite persistent

(~ 104 collisions). The theoretical calculations of the vibrational and rotational distributions in which OH is formed in certain elementary chemical

reactions, using the method developed by Golden, x^as coded for SEAC computation,

and two sample computations have been made.

In attempting to use the emission spectrum of OH as a temperature indicator,

it is known that one must exercise considerable care in interpreting the results

obtained. In this connection the effects of self-absorption on apparent rotational

temperatures of OH in flames have been studied both theoretically and experimentally. The conditions were determined under which the errors caused by this

effect are minimized [14]. Also the rotational distribution in OH in flames was

found to be dependent upon the vibrational state of the emitter [11]. This is

probably an indication of the effect of vibration-rotation interaction on the

rotational transition probabilities which were calculated by Dieke and Crosswhite

without regard to this interaction. Both the ground state (absorption) and the

excited state (emission) have been investigated.
2. Studies of Other Molecules

An investigation of the use of the CH rotational intensity distribution

has led to the conclusion that this molecule is unreliable as a temperature

indicator [12]. In the inner cone the rotational distribution indicates that

the excited CH is formed by a nonthermal process. The CH concentration in

the outer cone is too small for the CH spectrum to be observed.

In addition to the visible and ultraviolet measurements described above,

the program of infrared studies, as outlined in the preceding report, was

continued. The detailed results will be presented in a later report, but

a few items of interest may be mentioned here. The infrared emission of HF

in a hydrogen-fluorine flame was observed and consistent vibrational temperatures of 4000± 100°K were measured. Rotational temperatures were erratic

because of self-absorption effects [10]

A new infrared band system of FeO has been discovered and analyzed.

The band extends from 0.7 to 1.4 microns and probably arises from a resonance

transition of the molecule [7].

Measurements and analyses have been made on carbon dioxide and water

vapor absorption in the infrared at temperatures up to 400°C and pressures up

to 50 atmospheres. Observed integrated absorption coefficients are in order

of magnitude agreement with calculated values. High resolution spectra in

emission and absorption of water vapor and carbon monoxide have been measured

and analyzed completely for several regions of the infrared [8, 9, 26].

3. Flame Structure and Combustion Reactions

Along with measurement of temperature, observations have been made leading

to better understanding of flame structure and to mechanism of combustion.

Polyhedral flames were obtained in burning hydrogen and oxygen and propane and

oxygen diluted with argon, nitrogen, or helium. The observations tend to

support the theory that cellular structure in flames is caused by spatial

variation of mixture composition brought about by differential diffusion [4].

A photographic survey of the spectra of flames of various fuels (including

fluorocarbons), mixture ratios, and dilutions has been completed. The purpose of

the survey was to disclose flame conditions and spectral regions in which more

detailed spectrophotometric studies would most likely be fruitful. The survey

led directly to the first observation of the cometary bands of the C~ molecule

in hydrocarbon flame spectra. The details of these studies are given later

in this report [21, 24].
- 3 -

Spectroscopic studies by Broida and Gaydon at Imperial College have shown

that the probable mechanism for the formation of excited OH, CH, and HCO in

flames is by secondary chemical reaction rather than by dissociation of larger

molecules [19]* Evidence for the intermediate reaction of carbon monoxide and

atomic oxygen to form excited carbon dioxide also was found [16].

A detailed study has been made of the radiation emitted by atonic flames -

i.e. reactions between fuels and excited species formed in electrical discharges.

The optical spectroscopic data has been correlated with chemical and mass spectrometric data and the details of this study have been described in NBS Report

#3384 [27].

4. Instrumentation

Construction of the high temperature absorption tube furnace was completed,

and is described in detail in this report.

Several stainless steel gas sample containers have been constructed for use

in measurements of infrared absorption of gases. The vessels are designed for

temperatures to 1000°C and for pressures in excess of 100 atmospheres. They

provide a variety of path lengths from a few mm to about 15 cm.

Several apparatuses have been constructed for the purpose of studying

atomic flames. These have provision for production of atoms by both high

voltage discharge between aluminum electrodes, and high frequency electrodeless discharge. With the apparatus it is possible to sample the flame reaction

optically by studying the emitted radiation, and chemically by extracting

reaction products for chemical and mass spectrometric analysis.

A low pressure burner has been constructed in which it has been possible

to observe the combustion of acetylene and oxygen at pressures as low as a few mm of Hg (corresponding to an altitude greater than 100,000 ft.). The burner

has fused silica windows 5 inches in diameter so that it may be used for studies

of emission and absorption of radiation by the molecules in the flame over the

wavelength range 2000 A to 3*5 microns.

The Perkin-Elmer spectrometer has been converted to double-pass grating

operation, using a grating ruled with 7500 lines/inch. With this arrangement

a resolving power of 6000 (0.6 cm”l at 3600 cm“l) has been achieved. Also

the Leeds and Northrup grating spectrometer is being modified for infrared

operation and in preliminary tests has shown a resolving power of 10,000 at

1.4 microns.

The more recent results of this program, as well as of related high

temperature research in the Heat and Power Division, are presented in the

balance of this report.
- 4 -

Publications of the High Temperature Program Since August 1951

[1]

. Rotational Temperatures of OH in Methane-Air Flames.

J. Chem. Phys. 19 . 1383 (1951), H. P. Broida.

[2]

. Combustion in Bunsen Flames.

Ind. Eng. Chem. 2731 (1951), F. R. Caldwell, H. P. Broida and

J. J. Dover.

[33* Kinetics of OH Radicals, IV; Hydrogen-Oxygen Flame.

J. Chem. Phys. 20, 168 (1952), H. P. Broida and K. E. Shuler.

[43. Polyhedral Flames in Hydrogen and Hydrocarbons.

J. Chem. Phys. 20, 1042 (1952), W. R. Kane and H. P. Broida.

[53* Rotational Temperatures of OH in Several Flames.

J. Chem. Phys. 20 . 1466 (1952). H. P. Broida and G. T. Lalos.

[63* Kinetics of OH Radicals, V; Acetylene-Oxygen Flame.

J. Chem. Phys. 20 . 1383 (1952), K. E. Shuler and H. P. Broida.

[73. A New Infrared Band System of FeO.

Astrophys. J. 116 . 652 (1952), A. M.- Bass and W. S. Benedict.

[83* Precise Measurements in the Infrared Spectrum of CO.

J. Chem. Phys. 20, 175 (1952) E. K. Plyler, W. S. Benedict,

and S. Silverman.

[93. Absorption Spectrum of H^O between Ufi and 13 *5#.

J. Res. NBS 42, 91 (1952J, W. S. Benedict, H. H. Claassen, and J. Shaw.

[103. Infrared Emission of the Hydrogen-Fluorine Flame.

Phys. Rev. 87 . 213A (1952), W. S. Benedict, B. W. Bullock, S. Silverman,

and A. V. Grosse.

[113. Effects of Vibrational State on Rotational Intensity Distributions in OH.

J. Chem. Phys. 21, 173 (1953)* A. M.' Bass and H. P. Broida.

[123* Rotational and Vibrational "Temperatures” of CH in Flames at Atmospheric

Pressure.

J. Chem. Phys. 21, 340 (1953), H. P. Broida.

[133. Rotational "Temperatures” of OH in Diluted Flames.

J. Chem. Phys. 21, 347 (1953), W. R. Kane and H. P. Broida.

[143. Effects of Self-Absorption on Rotational "Temperatures" of OH in Flames.

J. Chem. Phys. 21, 1165 (1953), H. P. Broida.
- 5 -

[153.

[ 16].

[17].

[183.

[19]

.

[ 20

]

,

[ 21].

[ 22 ].

[23]

.

[24]

.

[25]

.

[ 26

]

.

[273.

Rotational Intensity Distributions of OH and 0D in an Electrodeless

Discharge through Water Vapor.

Phys. Rev. 82, 1053 (1953), H. P. Broida ana W. R. Kane.

The Luminous Reaction between Carbon Monoxj.de and Atomic Oxygen.

Trans. Farad. Soc. ^2, 1190 (1953), H. P. Broida and A. G. Gaydon.

Use of a Vacuum Spectrograph for Combustion Study.

Fuel 32 . 519 (1953). W. R. J. Garton and H. B. Broida

A Spectrophotometric Atlas of the ~

^rr Transition in OH.

N.B.S. Circular No. 541 (1953), A. M. Bass and H. P. Broida.

The Mechanism of Formation of OH, CH, and HCO in Flame Spectra, Using

Deuterium as Tracer.

Proc. Roy. Soc. A218 . 60 (1953), H. P. Broida and A. G. Gaydon.

Note on the Ultraviolet Spectrophotometry of Spark Ignited Low Pressure

Explosions

.

Fuel 22, (1954), A. J. Everett, G. J. Minkoff, H. P. Broida.

The Decomposition of CF, in Flames.

J. Chem. Phys. 22 . 348 (1954), H. P. Broida, D. E. Mann, B. E. Squires.

The Herzberg Bands of O

2 in an Oxygen Afterglow and in the Night-Sky,

Spectrum.

Proc. Roy. Soc., A222, 181 (1954), H. P. Broida and A. G. Gaydon.

The Forbidden ^ Z + ^ Z

~ Emission Bands of 0^.

J. de Physique (1954). H. P. Broida and A. G. Gaydon.

The \4050 Group of Cometary Spectra in Acetylene-Oxygen Flames.

J. Chem. Phys. 22. 569 (1954), N. H. Kiess and A. M. Bass.

Energy Transfer in Hot Gases.

N.B.S. Circular No. 523 (1954), Edited by A. M. Bass.

This volume contains

a. High-Resolution Studies of Infrared Flame

Emission, W. S. Benedict and E. K. Plyler.

b. Distribution of OH Rotational Temperatures

in Flames. H. P. Broida.

The Flame Emission Spectrum of H~0; I. The l,9u Region.

J. Res. N.B.S. j>2, 161 (1954), W. S. Benedict, A. M. Bass, and E.K. Plyler.

Atomic Flames: Spectra, "Temperatures”, and Products.

N.B.S. Report No. 3384 (1954), R.F. Ferguson and H. P. Broida.
- 6 -

2. A HIGH TEMPERATURE ABSORPTION TUBE FURNACE

R. D. Arnold.

1. Introduction

As a part of a program of research on the intensity of emission and

absorption spectra of flames and hot gases being carried out in the Heat

and Power Division of the National Bureau of Standards [1], the high temperature absorption tube furnace described in this report has been designed

and constructed.

While the object of the program is the application of spectroscopy to

studies of the physical and chemical processes occurring in flames , it is

advantageous to be able to observe the same molecules as are found in flames

but under more controlled conditions. In even the best controlled flames

there are temperature and concentration gradients, and there is uncertainty

as to concentration, temperature, optical path length, and as to the degree

of non-equipartition of molecular energy. For the determination of molecular

properties such as transition probability and line broadening it is therefore

preferable to observe molecules under known conditions of temperature, con- centration, optical depth, and thermal equilibrium. In an absorption tube

furnace these quantities can be much better determined than in flames.

The distinguishing features of the particular furnace described in this

report are the high temperature obtainable (2000°K) and the fact that the

windows of the chemically inert absorption tube are in the hot zone. Much

higher temperatures (3000°K) are of course possible if a carbon tube heater

is used as the aosorption tube [2,3»^]* out such a furnace is limited to

applications in which it is allowable to have solid carbon in equilibrium

with the gas under observation and in which the absence of windows (to limit

the optical path to the hot zone) is permissible. Temperatures slightly

higher (2200°K) than obtainable with the present furnace can be accomplished

by eliminating hot-zone windows [3*6] which again leads to a reduction in

versatility.

In short, the present furnace has most of the advantages of a quartz

tube aosorption furnace but at higher temperature. The exceptions are

l) the sample gas must be flowed through the tube, whereas a quartz tube

may be sealed off, 2) the window diameter is limited and 3) the furnace

is not designed for high-pressure samples.
- 7 -

2. The Absorption Tube

2.1 Hot Windows

The materials used in the construction of the absorption tube are high

purity alundum tubing (Norton Company Mixture RA 7232) and artificial white

sapphire windows. As soon as quartz is abandoned as the absorption tube

material the principal problems become the sealing on of the windows and the

sealing on of the gas access connections.

The window seal has been accomplished by grinding a slight taper on the

edge of the window and a corresponding taper in the end of an alundum tube.

Between the two is placeda one mil platinum foil (Detail "A", Fig, 2,1, At room temperature the seal is very poor but as it is heated the sapphire

expands slightly more than the alundum and so improves the seal. The co- efficients of expansion of the two materials are only slightly different.

The sapphire window is a crystal of AI2 O

3 and the RA 7232 alundum is approximately 99$ A^O-j. Were the coefficients of expansion too different the

expanding window would crack the tube. The platinum foil acts essentially

as a gasket.

Placing the windows on probe tubes entering either end of the gas

sample container (See Figs. 2,1, 2.2, 2.3) has the following advantages over simply placing windows on either end of an alundum tube sample container.

a) The sample container is easily filled through the annular space

between probe and container tubes. Seals for the gas connections are outside

of the furnace and can be effected with ordinary de-Khotinsky type cement.

b) Window seals of the type used are not completely tight even at high

temperature and it is therefore necessary to pump continuously on the space

outside of the windows so that none of the sample gas will be in the optical

path outside of the hot zone. The probe tube arrangement makes the pumping

simpler and also causes the pressure differential across the window to press

the window more firmly into place.

2.2 Evacuation of Probe Tubes

On the outside end of each probe tube is cemented a brass piece on the

end of which is affixed a quartz window with an O-ring seal. A side arm is

provided to take a 5/8 in. i. d. rubber hose which connects through a dust

trap to a 1 GFM mechanical vacuum pump. There is a separate pump for each

end of the furnace.

2.3 Support of Probe Tube

Each probe tube is supported by a brass piece sealed to and supported

by an end of the sample tube. Additional support (not shown in drawing) is
- 8 -

provided near the outer end of the probe tube. This outer support is adjustable

so that the probe tubes may be optically aligned, using the inner support as a

pivot. Inlet and outlet sample gas access tubes, in the form of quarter inch

copper tubing, are provided in the brass supports.

As the furnace was assembled, and as is shown in Fig. 2.1, the optical path in

the sample gas is ten inches. This length can be varied somewhat by telescoping

the probe tubes, but such a change requires breaking and remaking the seal at the

inner support and moving the outer support of the probe tube.

3. The Furnace

3.1 Heating Element

The heating element of the furnace consists of 0.050 inch diameter raolyb—

denum wire wound directly on the outside of the gas sample tube. There are 100 turns in the 16 inches of the winding, 23 turns over the central 4—3/4 inches

spaced at 0.19 inches per turn, 25 turns over each of two 4 inch sections adjacent to the center and spaced at 0.16 inches per turn, and 12.5 turns over each of two 1

5/8 inch outer sections spaced at 0.13 inches per turn. The diameter of the winding is 1-7/8 inches. Over the windings is a layer of Norton

HA 1148 alundum cement, a high purity fused alumina cement which matures at

1300°C and is rated at 1800°C maximum temperature.

3.2 Support and Gas Seals

Surrounding the gas sample tube with an annular gap of about 3/8 of an

inch, is another tube of RA 7232 alundum. This tube supports the gas sample

tube by means of a brass piece cemented to either end. The outer tube is 28

inches long and the sample tube 30 inches long. In operation the inner of

these two tubes is hotter than the outer and therefore expands more. To allow

for this differential expansion the seal between the inner tube and the brass

piece on one end is made by means of rubber sheet attached by an all-purpose

liquid cement, rather than by de-Khotinsky type cement as are the other metalto-ceramic seals. The four brass supports are water-cooled by quarter inch

copper tubing soldered to their outside circumferences and each of the cement

seals is cooled by an air blast.

3.3 Inlets for Electrical Power and Protective Atmosphere

Each of the two brass supports joining the ceramic tubes is pierced by

two quarter-inch copper tubes. One of these is to give a protective atmosphere access to the space surrounding the heater and the other admits the

heater wire itself. There are no electrical joints inside the furnace; the

molybdenum wire is brought unbroken out through the copper tubes on either

end. The gas seals on these tubes are effected by means of commercial (Conax)

glands in which powdered talc is compressed about the molybdenum wire. These

glands, the ends of which are pipe-threaded, are joined to the copper tube by
- 9 -

a suitable string of adapters. (Glands and adapters are not shown in the

drawing.) Ceramic tubes inside of gland, adapters, and copper tube, insulate

the wire electrically from the brass support pieces.

Protective Atmosphere

The purpose of the protective atmosphere is to prevent oxidation of the

molybdenum winding at high temperature. While an inert atmosphere or a vacuum

would accomplish this if all traces of oxygen could be excluded, an atmosphere

containing a large excess of hydrogen can compensate for oxygen contamination.

The protective atmosphere may be hydrogen, forming gas or, as is presently

employed for this furnace, cracked ammonia. Ammonia is passed through a tube

containing steel wool and heated to 900°C by a Nichrome-wire furnace, shown

next to the absorption tube furnace in Fig. 2^3. At the exit end of the large

furnace, the cracked ammonia passes through a device which may be used to determine its ammonia content, is bubbled through water to maintain its pressure

at slightly above atmospheric and is then fed into an exhaust duct.

3-5 Thermal Insulation

The outer ceramic tube of the furnace fits into the annular transite end

faces of a sheet metal cylinder 10 inches in diameter. Powdered alumina

(120 mesh) fills the space between ceramic tube and metal cylinder. Glands

packed with asbestos fiber prevent leakage of the powder where the tube passes

through the transite faces. Leakage at the junctions of the metal cylinder

with the transite faces was stopped by painting these places with Insulate

cement. No cooling is provided for transite or sheet metal.

Imbedded in the alumina insulation is a stock ceramic furnace core which

is supported by grooves on the inner faces of the transite end pieces. This

is to hold a pair of platinum-rhodium windings far enough out from the center

of the furnace that the platinum-rhodium alloy would not be above its melting

point with the furnace center at 2000°C. The purpose of the outer windings

is to attempt to control the temperature gradient along the axis of the

furnace. They are independently manually controlled by Variacs. In practice

these windings have not been used since attaching them to the laooratory

power system caused interference with the bridge circuit which controls the

main molybdenum winding. This effect is due to electrical conduction through

the insulating parts of the furnace when these are hot.

3.6 Electrical Characteristics and Power Requirements

The electrical resistance of the furnace winding as a function of temperature is plotted in Fig. 2,4, (curve R) . Resistance is measured by the control

system (see S^f.2) and the temperature was measured by a mercury-in-glass

thermometer up to 400°C and by an optical pyrometer between 800 and 1500°C.

Molded ceramic forms resting on the bottom of the absorption tube, out of the

direct line -of sight through the furnace out visible from off the axis, were
- 10 -

used. as targets for the pyrometer. These forms have small deep holes in them

to act as black oodies.

Curve "I" in Fig. 2.4 shows the current drawn when the furnace has reached

equilibrium at the given temperature. Higher currents, up to about 30

amperes, are drawn while the furnace is heating up. Equilibrium power (W)

and voltage (V) curves are derived from R and I.

For the extrapolations above 1500°C, the R-curve was taken from the

known resistance versus temperature behavior of molybdenum, and the W-curve

from a linear extrapolation of W versus temperature on a log log plot.

This plot is close to linear over the range 250“C to 15Q0?C f following the

equation,

W = 0.066 t1 *^ Watts (1)

t in °C

In the extrapolated region V and I are derived from R and W.

4, Furnace Centrol System

4.1 System Type

Control of the furnace is based upon using the main heater winding as a resistance thermometer. An electro-mechanical, time-modulated, proportional reset (integrating) type of control system adjusts the input power to

maintain the furnace resistance at a value set by the operator.

4.2 Resistance Measurement

The oasic control-loop circuit is shown schematically in Fig. 2.5. u

detailed electrical diagram of the chassis called "Thermoregulator'1 is shown

in Fig. 2.6 and Fig. 2,7 in a photograph of the control rack.) A Wheatstone

bridge with a 1000 to 1 ratio between its two sides contains the furnace as

one of its four arms. The other arm on the low resistance side is made up

of Advance ribbon (l/2 in. wide by .010 in. thick, 0.0480 ohms per foot).

It has a resistance of 0.51 ohms and a very low thermal coefficient of re- sistance. This resistor may be seen in Fig. 2 below the furnace table on

the left hand end. The ribbon is wound back and forth over pieces of ceramic

tubing set in an open frame. A fan at the opposite end of the table

(see Fig. 3) blows air through a chute and out over the resistor. The loops

are cooled by air blowing through the ceramic tubing. Use of the fan keeps

the resistance of this resistor constant within 0.2£ with current up to

40 amperes.

The high resistance side of the bridge is located partly in the thermoregulator chassis and partly in the recorder. This is a modified Rrown

strip-chart recording potentiometer. The 20 ohm resistor is the slidewire
- 11 -

which comes with the instrument. Since subsequent circuitry in the control

loop is arranged to make the midpoint of this slidewire the balance position

for control, then at balance 10 ohms of the slidewire belong to the lower

right hand arm of the bridge and 10 to the upper. The 10 ohms added to the

500 ohm resistor shown make the bridge ratio 1000 to 1. There are three

decades of 10 ohms, 100 ohms and 1000 ohms per step in the decade resistor.

The knob on the 10 ohm per step decade is set to read 10 ohms greater than

the actual resistance to allow for the 10 ohms in the slidewire. Thus, at

balance, the decade knobs read exactly 1000 times the resistance of the

furnace winding.

When the winding resistance changes the bridge unbalance signal causes

the balancing motor in the recorder to move the slidewire to reduce the bridge

signal to zero. This happens in a time short comparai to the time constant of

the overall control loop, so the bridge may be considered always in balance

and the instantaneous v/inding resistance may be read from the decade knobs

and the position of the recorder pen, which follows the slider. The value of

that must be added to the decade reading Rjj when the pen is separated from

the center of the scale by a fraction "a" of full scale is

The following modifications were made in the recorder. Since the bridge

signal is A. C, the converter was removed and the bridge signal applied

directly to the input transformer of the amplifier. In order to get a sufficient voltage for heating the furnace it is necessary to operate it from

two outer arms of the laboratory wire, 3-pbase A.G. power system (see pig, 2,4).

Now for correct phasing of the recorder amplifier with the bridge signal it is

necessary to use the same two terminals of the power system, and since this is

too high a voltage for the recorder, a step—down transformer is used. The

amplifier "ground”, separate from the power input, is connected to the neutral

(N) terminal of the laboratory system, since this is a true ground. It is

apparent from this arrangement that even when the bridge is balanced there

will be a potential difference between the primary and secondary windings of

the amplifier input transformer. This potential is only weakly coupled

capacitatively to the amplifier but is large enough to cause considerable

trouble if uncompensated. The in-phase part of the pick-up is compensated by

Since "a" is never larger than 0,5 and Rp is never larger than 0,04Rp, we may set the last factor above equal to unity and get that the furnace

resistance is
- 12 -

the action of the balancing motor and causes an error in the resistance reading

but this error is quite small due to the very large true bridge signal. The outof-phase part of the pick-up, however, is completely -uncompensated and gets large

enough to swamp the amplifier. It is therefore necessary to compensate by adding

into the secondary of the transformer an adjustable voltage 90° out-of-phase with

the bridge supply voltage. This is supplied from arms N and 2 (the bridge is on

1 and 3) of the laboratory supply. The amplified signal is brought out to an oscilloscope for monitoring the out-of-phase bucking. This same arrangement

also bucks out the out-of-phase signal due to the inductance of the furnace

winding.

4.3 Control of the Input Power

Up to this point we have a shaft position (pen and slidewire) proportional

to the difference between the true and desired furnace resistance. We want to

operate on the power Variac (50 B-G2) in such a manner as to reduce this difference to zero. There is no electrical error signal since the bridge is selfbalancing.

A proportional error signal in the form of a shaft rotation in the thermoregulator is generated from the shaft rotation in the recorder in the following

way. The two 1000-ohm potentiometers, one in the recorder and one in the

thermoregulator, and the amplifier and balancing motor in the thermo regulator

form a shaft rotation follower system. The shaft of the second potentiometer

assumes such a position that the input to the amplifier is zero, that is, the

departure of the second slider from its midpoint is proportional to the departure of the first from its midpoint. The constant of proportionality is equal

to the ratio of the voltage on the first potentiometer to that on the second

and may be varied from zero to about five by the Variac marked "Prop. Control"

in Pig. 2.6. The first potentiometer is geared to the recorder so that it is at

its midpoint when the pen is at midscale and is at one end when the pen is at a corresponding end of the scale. We now, therefore, have a shaft rotation in

the therraoregulator proportional to the furnace resistance error. The constant of proportionality may be set by the operator and is independent of the

oridge voltage. A low proportionality constant makes a loose, slow control

and a wide proportional band, though not wider than full scale on the recorder.

A high proportionality constant makes a fast, tight control and a narrow

proportional band.

Notice that a proportionality constant greater than unity may cause the

second potentiometer to attempt to overrun its end. This is prevented by

microswitch #3 (Pig. 2.6) which is opened when the potentiometer reaches either

end and thus reduces the proportionality constant to zero. The potentiometer

therefore "bounces" against the end but does not overrun it.

To complete the control loop it remains to cause the power Variac to move upward or downward at a rate proportional to the resistance error.
- 13 -

Connected, to the Variac shaft is a reversible, constant speed motor. Control of

the motor is by means of three wires which are designated R, W and B in Figurep

2.5 and. 2.6. .When R is shorted to W the motor goes downward and when to B, upward. The switching between W and B is accomplished by relay #1, which is con- trolled by microswitches #1 and #2. A momentary depression of microswitch #1

causes the relay to pull up and hold up. Then a momentary depression of microswitch #2 will cause the relay to drop down and stay down, etc. Each microswitch

is depressed momentarily every 6 seconds by a synchronous motor cam. Now one microswitch is fixed in position while the other rotates with the "error shaft"

of the thermo regulator. The moving microswitch is originally positioned so that

when the error shaft rotation is zero (recorder pen at midscale) this microswitch

is diametrically opposite the fixed microswitch.

It follows from the above arrangement that at zero error the power Variac

is driven upward for 3 seconds and downward for 3 seconds, thus having a net rate

of zero. During the three seconds the Variac brush moves over about two windings.

If there is a negative error signal (resistance less than decade setting) the

upward phase of the cycle will become greater than 3 seconds and the downward

phase less than 3 seconds. The net rate of the Variac will then be upward and

proportional to the error signal. As has been pointed out by Nurse and Welch [71

the time modulation control of a Variac allows a continuous, rather than stepwis^

variation of the average power output. When the correct control point is between two Variac windings, the brush will spend appropriate times on adjacent

windings to make the average correct.

Two additional features of the system are the programmed temperature

raiser and the ceiling control. The former is simply a motor-driven 10,000

ohm helipot which may be switched in to replace the decade resistor. It is

raised at the rate of 1,000 ohms per hour which causes the furnace resistance

to be raised at the rate of one ohm per hour. Thus the furnace is raised from

room temperature to 1500°C in about four and one-half hours.

The ceiling control is shown in Fig. 2.6. It serves as a safety device to

prevent the Variac from being driven above some preset voltage in case something

goes wrong with the control. The Variac voltage is rectified and applied to a relay winding in series with a variable resistor. When the voltage reaches a certain point, determined by the setting of the resistor, the relay pulls up.

This opens the "B" line in the Variac control circuit and thus prevents further

voltage rise. The event is marked by a signal light and buzzer. Because of the

hysteresis of the relay normal operation is restored only by opening the relay

(SW 1, fig, 2.6) even though the voltage has dropped below the critical value after

the relay operates. Standard procedure is to set the ceiling slightly above the

voltage required to maintain the desired operating furnace temperature.

Manual control of the Variac motor is provided by SW2 and SW3. When SW3

(Manual-Automatic) is in the "Manual" position then SW2 can be used to run the

Variac upward or downward or to hold it stationary.

307304 0 - 54 -2
- 14

Microswitch #4 on the timing mechanism of the thermo regulator has no function in the control of the absorption tube furnace but is merely a periodic

interrupter (operated by the cam on the synchronous motor) for the Sym-ply-trol

pyrometer which is used to control the ammonia-cracking furnace.

5. Assembly

5.1 Thermal Insulation

Several phases of the assembly of the furnace require special attention.

The large diameter 28" long ceramic tube was placed in its proper position in one of the transite end faces and the asbestos gland was packed and closed.

This assembly was supported vertically and the sheet metal cylinder was attached

to the transite. Then the ceramic core bearing the platinum windings was placed

in its groove in the transite. Into the two concentric annular spaces so formed

was poured and tamped the alumina powder. Then the other transite face was attached and the other gland packed and closed. The assembly could then be

placed horizontally in its cradle. The two holes on top of the sheet metal can

at either end were used only for replacement of powder that leaked out before

the Insulate cement was applied to the junction of the can and the transite

faces.

5.2 Heater Winding

The wire used in the heater winding is too stiff to wind directly onto

the absorption tuoe. It was first wound on a mandril of diameter slightly

smaller than that of the absorption tube and into which had been cut grooves

of proper spacing. It was then heated with a torch to dull red heat ( as suggested in Reference 8). When the tension was released it sprang out to a diameter between that of the mandril and that of the tube. These two were

then placed end to end and the winding was transferred from one to the other

by sliding turn by turn, worm fashion. This resulted in a snug fit on the

tube

.

5.3

Window Seal

In preparation for installing the sapphire windows in the probe tubes,

the polished windows were cemented to the ends of brass rods of diameter

approximately equal to that of the windows. Internal tapers were ground in

the probe tubes to a depth of l/8 inch, the window thickness. Then, without

changing the taper setting of the grinder, external tapers were ground in the

window-brass rod assemblies until the outer faces of the windows would penetrate about l/32 inch below the outer edge of the tubes. This amount of

penetration was about right to bring the windows back to flush with the tube

ends with the 0.001 in platinum foil in place. Platinum foil of width greater

than l/3 inch was wrapped around the window-rod assembly and fixed to the rod.

This assembly was then placed in the probe tube and the excess foil was cut

off. The rods were heated until the cement softened and the rods dropped off,
- 15 -

leaving the windows in place. Cement left on the windows was rubbed off with

sandpaper.

6. Operation

6.1 Heating Program

The furnace is heated slowly (4 l/2 hours to 1500°C) by means of the

programmed temperature raiser in order to minimize thermal shock in the ceramic

parts. Operation is almost entirely automatic and only general safety monitoring is required of the operator except that the out-of-phase bucker must be

occasionally readjusted. Also it is a safe practice to keep the Variac ceiling

control set not far above present voltage, resetting in small increments as the

alarm sounds. This is because if the voltage v/ere to run away while the furnace temperature is low (and therefore the winding resistance is low) a very

large current would flow, resulting in a very high rate of temperature rise.

6.2 Protective Atmosphere

The flow of protective atmosphere should be started while the furnace is

still cold to flush out air which may have got into the system between runs. Entrance of air is minimized by running a neutral gas (e.g. dry nitrogen)

through the system while the furnace is cooling after a run.

6.3 Probe Tube Pumps

It has been found advantageous to start the pumps on the probe tubes before the temperature is high enough to seal the sapphire windows. This causes

the windows to be pulled firmly into their seats and seems to make the seal

occur sooner after the windows are hot. At a furnace temperature of about 400°C

the seals close up except for a small residual leakage which remains at all

temperatures. Despite this leak the pumps used are able to maintain a probe

vacuum of 75 - 300 microns at high furnace temperatures.

6.4 Temperature Profile

A rough measure of the temperature profile has been made by sighting with

an optical pyrometer on black-body hole targets spaced along the bottom of the

absorption tuoe. At a furnace temperature of 1500°C the temperature difference between the center of the furnace and the position of the windows is

40 degrees. The positions midway between the center and the windows is down

5 degrees from the center.

6.5 Optics

Por absorption measurements a light source is focussed on the entrance

quartz window by a mirror that subtends at least as much solid angle as does the

outside end of the exit probe tube, which is therefore the aperture stop.
- 16 -

A lens just outside the exit quartz window refocusses the image on a spectrometer slit at such a distance from the lens that the light fills the aperture

of the spectrometer.

6.6 Light Source

The most satisfactory source for ultraviolet absorption measurements has

been a Hanovia high-pressure xenon arc lamp. It gives adequate intensity at

3000 A for the Leeds and Northrup mono chroma to r*[ 9] despite the very small

^“Loaned to the N.B.S. High Temperature Laboratory by the Research Department,

Leeds and Northrup Company on a field trial basis.

aperture of the furnace. There are sometimes fluctuations in intensity,

seemingly caused by jumping of the arc, which are too large to allow quantitive

absorption measurements. However, there are also periods of smooth operation,

of long enough duration to allow data to be taken.

6.7 Sample Spectrum

A sample spectrum of absorption in the furnace is shown in Fig. 2_8* J*or

this measurement oxygen was bubbled through water at room temperature and the

saturated mixture was flowed through the absorption tube. The furnace temperature was 1500°C and the absorption path length was 10 inches. The xenon lamp was the light source and the spectrometer was the Leeds and Northrup photoelectric recording monochromator. Shown in the spectrum is the 0,0 band head

of the ultraviolet transition in OH at A.

Mr. 0. D. Beale, Jr. of the High Temperature Laboratory did much of the

construction and assembly, and many of his suggestions were incorporated

into the design of furnace and control.
- 17 -

References

1. N.B.S. Report 1123

2. King, A. S. Astrophys. J. 28, 300 (1908)

3. King, R. B. Astrophys. J. 108 . 429 (1948)

4. Brewer, L. , Gilles, P. W. & Jenkins, F. A. J. Ghem. Phys. 16, 797 (1948)

5. Burrows, G. & Clark, F. L. , J. Sci. Instr. 10, 248 (1933)

6. Garton, W. R. S. & Feast, M. W. Nature 165, 282 (193°)

7. Nurse, R. W. & Welch, J. H. J. Sci. Instr. 2£, 97 (1930)

8. Cohn, W. M. Z. Techn. Physik 2, HO (1928)

9. Broida, H. P. and Shuler, K. E. J. Chem. Phys. 20, 168 (1932)
18 -

Figures

2.1. Drawing of absorption tube furnace.

2.2. Front view of absorption tube furnace.

2.3. Rear view of absorption tube furnace.

2.4. Electrical characteristics of the furnace.

2.5* Schematic of Furnace Control Circuit.

2.6. Schematic of Thermo regulator.

2.7. Control Rack.

2.8. Sample Absorption Spectrum.
SHEET

METAL

Figure
figure

2.2
'igure

2.3
o

400

800

1200

1600

2000
208

—

O

RECORDER
TO

PYROMETER

<T> O tO C\J in ro

<r CD

0,0 BAND HEAD OF 2 S - 2

I1

TRANSITION OF OH

IN ABSORPTION.

FURNACE TEMPERATURE I500°C

ZERO

ilgure 2.8
- 27 -

3, DESIGN AND CONSTRUCTION OF A "BLACKBODY" AND ITS USE IN THE

SPECTRAL INTENSITY CALIBRATION OF A GRATING MONOCHROMATOR*

C. T. Lalos, R. J. Corruccini and H. P. Broida

ABSTRACT

A "blackbody" constructed of graphite was inductively heated in an atmosphere of helium to a maximum temperature of 2700 degrees K. This "blackbody"

was used as a source of radiation of known intensity as a function of temperature and wavelength in the spectral intensity calibration of a grating

monochromator. The calibration was made over the spectral range of 2600 A to

3800 A in the second order and of 3300A to 7550 A in the first order.

Relative intensities were measured with an accuracy estimated to be of the

order of 9fa in the regions 2600 A to 2800 A in the second order and 7200 A to

7600 A in the first order, and of 5$ in the regions 2800 A to 3800 A in the

second order and 3300 A to 7000 A in the first order.

Submitted for publication in The Review of Scientific Instruments
- 28 -

1. IMRODUCTION

Instruments that are used to measure intensity distributions accurately

over large spectral ranges must be calibrated with a source of radiation of

known intensity distribution over the desired spectral range. By far the best

known source for this purpose is a "blackbody", i.e. a hollow cavity having its

walls at a uniform temperature. This source of radiation has been studied

extensively both theoretically [l] and experimentally [2], and is considered

the primary standard of radiation, i.e. a source whose intensity distribution

is known as a function of temperature and wavelength.

An inductively heated ''blackbody" was constructed and used to calibrate

a grating monochromator. Two tungsten-fi lament lamps also were calibrated to serve as secondary or working standards.

2. BLACKBODY

It can be shown theoretically that an enclosure of any arbitrary con- figuration and made of any material whose walls are at a uniform temperature

emits radiation whose intensity as a function of temperature and wavelength

is given by Planck? s blackbody distribution equation, i.e.

( 1)

where

^

is the radiancy in ergs per second per unit area of the source at

wavelength X and temperature T, c, is the first radiation constant, and C£

is the second radiation constant.

Radiation from such an enclosure may be utilized if a small opening is made

in one of its walls. This radiation is essentially blackbody radiation in

nature if the dimensions of the opening are small relative to the internal dimensions of the enclosure. As the opening is made larger the nature of the

radiation departs more and more from blackbody radiation. For clarity we have

adopted the convention of using quotation marks, i.e. "blackbody", when we refer to an enclosure containing an opening in order to utilize the radiation.

This merely signifies that true blackbody radiation is not realized, and that

therefore a,n emissivity is associated with a "blackbody" for each wavelength

and temperature.
- 29 -

Fig. 3.1 is a cross-sectional drawing of the "blackbody" that was constructed.

The inner t\ibe or "blackbody" proper is made of graphite and was machined as shown in detail in Figure 3 . 2 . This particular geometrical configuration was chosen because of its relative simplicity, ease of maintaining a uniform temperature, and high emissivity. Emissivity of a simplified "blackbody" of this

general shape, i.e. an open-end cylinder as a function of the emissivity of the

material of which it is made, is given by the expression [3 ]

[1 (1 - Xx) (s/S - sin2©) ] ZX“nr~B7S)"+ s/S ( 2 )

where X-^B is the emissivity of the "blackbody", Xx the emissivity of the

material of which the "blackbody" proper is made which is a function of temperature and wavelength, s is the area of the opening, S is the area of the enclosure,

and © is one-half of the angle subtended by the opening. It is evident from the

form of this expression that X. does not depend critically on the value of Xx,

especially if the ratio s/S is small. Calculations show that the percentage

change in due to a variation of Xx from 0.6 to 0,8 and a variation of s/S

from 0,03 to 0,025 is only of the order of 1-1/2 These assumed variations in

Xx and s/S are larger than would be expected to be found in the use of the

"blackbody" shown in Figures 3.1 and. 3*2. Therefore, the calculated emissivity is

not critically dependent on the assumed value of the emissivity of graphite at

the operating temperature and on the physical dimensions used in the construction

of this "blackbody."

The tlackbody" proper is surrounded with lampblack which serves as thermal

and electrical insulation. Lampblack was chosen as the insulation after an unsuccessful attempt was made using ZrC^. At the high temperatures which the

"blackbody" was operated, impurities in the ZrX^ fused and formed a slag of

high electrical conductivity which destroyed ios use as an insulator. A fused

silica tube approximately 6 inches in diameter supports the "blackbody" proper

and the lampblack insulation. Water-cooled copper induction-coil leads are insulated electrically from the water-cooled metallic outer shell by means of a polystyrene window. These coils are spaced j/h of an inch from the 6 inch

silica tube to prevent electrical breakdown between the coils and the tube.

A polished quartz viewing window is located at the open end of the "blackbody"

(see Figure3.3). A shutter located directly behind the quartz viewing window

serves to shield the window from the high-intensity radiation during the time

that the "blackbody" is being brought up to its operating temperature and after

a run during the cooling off period. The shutter is made of metal and is hand

operated from the outside of the "blackbody". A small 0-ring is located on the

part of the shutter handle that extends out of the "blackbody" in order to keep

the outside metallic shell air-tight. Helium gas regulated at a gauge pressure

of a few pounds per square inch was used as the inert atmosphere and served to

keep atmospheric oxygen from oxidizing the hot graphite tube. An inlet for the

helium gas is located in the neck that houses the quartz viewing window. Thus

the helium serves to partially keep carbon vapor from depositing on the window.

307304 0 - 54-3
- 30 -

The power supply used to heat the "blackbody" was a 20 KW, 450 KC Westinghouse Radio Frequency Generator designed for industrial induction heating

applications requiring up to 20 KW of radio-frequency energy. Temperature

control was attained by regulating the power to the "blackbody". This was accomplished by an automatic controller [4] and an auxiliary fine power indicator

and adjuster. Fig. 3.^ shows the working assembly including the induction

generator, power regulator, glass system for regulating the flow of helium into

the "blackbody", "blackbody", grating monochromator and its associated electronics,

and the intensity recorder.

3. GRATING MONOCHROMATOR

The grating monochromator* that was calibrated has been described in detail

elsewhere [ 5 ]. Briefly (see Fig* 3»5) the radiation from the source S is

focused by the front-surfaced mirrors and L2 on the entrance slit A, is then

reflected and collimated by the front surfaced spherical mirror M, is diffracted

by the plane reflection grating G, is then again reflected and focused by the same mirror M onto the exit slit B. The spectral energy is gathered behind the

exit slit by a specially selected 1P28 photomultiplier tube P, Scattered light

in this monochromator is very low; for example with a low pressure mercury

discharge, scattered light in the vicinity of the ^^61 A green line is less

than one part in 105 of the intensity of the 5l±6l A line. The photomultiplieramplifier combination is known to be linear within a few percent.

* The monochromator was constructed by the Research Department of Leeds and

Northrup Company and loaned to the Heat and Power Division of the National

Bureau of Standards on a field trial arrangement.

The need for calibrating this monochromator results from (1) selective

transmission of the external optics, (2) selective reflectance of the mono- chromator mirror and the grating and (3) spectral sensitivity of the photomultiplier tube.

4. CALIBRATION

A response calibration of the monochromator was made from 2600 to 7550 A.

The short wavelength limit was set by the limited amount of ultra-violet energy

available at the operating temperature and by the blaze of the grating

(specified with a blaze near 3000 A in the second order). The long wavelength

limit was set solely by the limit in sensitivity of the photomultiplier tube.

Radiation was viewed in the first and second order of a 3 inch 30,000 lines

per inch plane reflection grating using an entrance slit width of 20 microns
- 31 -

(0.4 A in the first order), and an exit 3lit width of 30 microns. The region

2600 to 3800 A was viewed in the second order and the region 3300 A to 7350 A

in the first order. This arrangement results in an overlap region of 500 A.

The temperature of the "blackbody" during the calibration was 2435°K.

The apparatus for calibrating the grating monochromator is shown in

Pig. 3.5- S is the "blackbody", W is the quartz window, and Lg are concave front-surfaced mirrors, F are optical transmission filters, and E is

the grating monochromator. The "olackbody", two front-surfaced mirrors Iq_ and

L£, and the grating monochromator all have an aperture of E:10.

Various combinations of Corning glass filters were used to filter out

overlapping orders and to decrease scattered light. Intensity measurements in

the 2nd order from 2600 to 33°0 A were made using a Corning #9863 filter. This

filter acted as a cut-off for the superimposed 1st order 5200 to 6600 A

radiation. Measurements of intensity in the 2nd order from 3300 to 3800 A were

also made using the #9863 filter but in this range the #9863 filter transmits

as much as 40$ of the superimposed 1st order radiation. This may possibly

result in a lowered accuracy in the calibration in the 2 nd order from 3300 to

3800 A.

In the 1st order intensity measurements from 3300 to 4100 A were made

with a #9863 filter in order to reduce the effects of scattered light beyond

4500 A. No filters were used in the region 4100 to 6200 A. The superimposed

2nd order radiation 2 O 5O to 3100 A was comparatively much smaller because of

the nature of the blackbody radiation curve, and also because of the response

characteristics of the apparatus. First order intensity measurements in the

regions 6200 to 6600 A, 6600 to 7000 A, and 7000 to 7550 A were made using

Corning filters #2412, #2403, and #2030 respectively. Each of these three

filters served as a cut-off filter for the superimposed 2nd order radiation

and also reduced scattered light from shorter wavelengths. Transmissions of

all the filters were measured at each wavelength with the filters in the

position they were to have for the calibration of the monochromator and just

prior to the intensity measurement at that wavelength. It had been observed

earlier that the transmissivity depends very critically on the angle of

incidence of the radiation. The filters also were air-cooled to room temperature since temperature affects the transmissivity, especially on the low wavelength cut-off side [ 6 ], The transmissivity of the quartz window of the

"blackbody" was measured before and after the calibration. Temperatures of

the "blackbody" were measured with a precision optical pyrometer calibrated

at the National Bureau of Standards.

A relative spectral intensity calibration was obtained by viewing the

radiation emitted by the "blackbody" with the grating monochromator over the

desired spectral range and comparing these measurements with values calculated

from the blackbody expression multiplied by the appropriate emissivity values

as calculated from equation 2 , and by the transmissivity of the quartz window

of the "blackbody". Measured intensities must be multiplied by the reciprocal
- 32 -

of the transmissivity of any filter that is used. The multiplication factor

is obtained from the ratio of the calculated intensity to the measured intensity at each wavelength and must be applied to all intensity measurements

made with the grating monochromator. This multiplication factor is a function

of the "transmissivity" of the grating monochromator, the reflectivity of the

two mirrors L]_ and Ig, and the sensitivity of the photomultiplier tube.

An investigation of the nature of the emission of the "blackbody" was made preparatory to the actual calibration, at a time when nitrogen rather than

helium was used as the inert atmosphere in the "blackbody". This was done by

scanning continuously the spectral interval over which the calibration was to

be made. Records thus obtained showed the smooth form of the "blackbody"

radiation curve and the high wavelength cut-off of the photomultiplier. In

addition these records showed that some absorption was present. On closer

examination a strong absorption at about 3900 A was identified as the 0,0 band

of the — 221 electronic transition of CN with a head at 3883 A. Two

very strong absorption lines at 3890 and 5896 A indicated the presence of

sodium as an impurity in the graphite. Various other absorption lines and

bands also were observed. With the exception of the sodium lines the absorption was eliminated by substituting helium for nitrogen as the inert atmosphere in the "blackbody".

Intensity measurements during the actual calibration were taken at intervals of 200 A in the 1st order and every 100 A in the 2nd order. Temperature

readings were made after each 3 readings, i.e. approximately every ten minutes.

figure 3*6 is a plot of the multiplication factor on a logarithmic scale

versus wavelength for the grating monochromator. The multiplication factor

increases from an arbitrarily assigned value of unity at 4900 A to approximately

60 at 2600 A and 25,000 at 7550 A. The shape of the curve at longer wavelengths is determined primarily by the response of the photomultiplier while

that at the shorter wavelengths by the blaze of the grating.

The accuracy of an intensity response calibration over a large wavelength

interval is limited by several possible sources of error - the temperature of

the "blackbody", transmissivity of filters, wavelength, linearity of the photomultiplier or associated electronics, and scattered light in the monochromator.

Temperature of the "blackbody" is the largest single source of error. For a small change in temperature, Z\T, the relative change in intensity from a blackbody in the region of the Wien Law approximation is C2AT/ A T where C£ is the

second radiation constant, A the wavelength and T the absolute temperature.

At 4850 A and 2435°^ a one degree change or error in temperature causes a l/2^

change in the intensity. During the course of the calibration the temperature

of the "blackbody" was held within a slowly fluctuating ±6°C and corrections

were made for changes in temperature. The transmissivity of the filters is

known to better than 1^. Since the wavelength interval is less than 1 A and

the wavelength is known to better than 1 A, there is only a negligible error in

the present calibration (at 7000 A an error of 1A causes less than 0. IJl error

in the calculated intensity). Scattered light caused no error except in those
- 33 -

regions of very low liglit intensity. Also the linearity of the electronics

caused no error except for the highest amplification (i.e. low light intensity)

The accuracy of the calibration was estimated to be of the order of 5# in

the region of 2800 to 3800 A in the 2nd order and in the region 3300 to 7000 A

in the 1st order. A somewhat lower accuracy of the order of 9/6 is estimated

for the region 2600 to 2800 A in the 2nd order because of the low energy available. In the 1st order from 7200 A to 7550 A the accuracy is probably of the

order of 9% because of the low sensitivity of the phototube in this region.

The high wavelength cut-off of the 1P28 photomultiplier tube occurs at approximately 7800 A. At the shorter wavelengths the low accuracy can be improved by

operating the "blackbody" at a higher temperature and by using a grating with

a more appropriate blaze, and at longer wavelengths by using a detector of

relatively higher sensitivity in this region.

Measurements of the ratio of intensity of the "blackbody" at two arbitrarily chosen wavelengths (4000 A and 5200 A) using three different slit widths

(10 to 80 microns) resulted in the same value of the ratio. This observation

indicates that the calibration is independent of the slit width of the monochromator, and that therefor the slit width can be changed subsequent to the

calibration without changing the multiplication factor. A similar test was made with the temperature of the "blackbody" as the variable instead of the

slit width of the monochromator. Results of this test indicated that the

calibration of the monochromator is independent of the temperature of the

"blackbody" during the actual calibration.

Two tungsten-filament lamps to serve as secondary or working standards

also were calibrated. The procedure used essentially was to measure the

intensity as a function of wavelength of a lamp at some measured temperature

with the monochromator and to correct these readings by the proper multiplication factor from Fig. 3.6. The result was the spectral energy emitted by the

lamp at that temperature. Comparison of these corrected values of intensity

with the blackbody distribution curve at the same temperature is a measure of

the emissivity of tungsten thus obtained between 2800 and 7400 A agree within

2$ to the corresponding values given in reference 2. This close consistency

indicates that our accuracy was considerably better than that estimated from

the various possible errors.
- 3^ -

5. CONCLUSIONS

With the present response calibration of the monochromator in conjunction

with the known spectral ©mission characteristics of the calibrated tungsten

strip lamps it will be possible to compare and to accurately measure radiation

intensities over a broad spectral range. An effort will be made to use these

known response characteristics to determine the vibrational transition

probabilities of molecules such as C2 » CH and OH,

The "blackbody" will be useful for calibrating response characteristics

in other spectral regions and as soon as the instrumentation is completed, an infra-red secondary standard will be calibrated. It is planned also to use

the "blackbody” to calibrate total radiation pyrometers.
- 35 -

6. REFERENCES

[l] Forsythe, W. E,, The Measurement of Radiant Energy, McGraw-Hill.

L2] De Vos, J. C., The Emissivity of Tungsten Ribhon - The Tungsten Strip

Lamp as a Standard Source of Radiation, Ph.D. thesis,

Univ. of Amsterdam, Holland.

[3] Michaud, M. , Gompt Rend. 226, 999 (19^3).

[4] Theron, J. J, , Rev, Sci. Instr. 24, 281 (1953).

[5]

a-Fastie, W. G. , J, Opt. Soc. Am. 42, No. 9, 641 (1952).

b-Broida, H. P. and Shuler, K. E. , J. Chem. Phys. 2(3, 168 (1952).

fr [6] Gioson, S., Spectrophotometry, NBS Circular 484 (1949).
- 36 -

7. FIGURE LEGEND

3.1. "Blackbody" for monochromator calibration.

3.2. Detail of carbon tube for “blackbody”.

3*3. Photograph of front of tt blackbodyH

. I - leads to water-cooled copper

induction coil; S - shutter for protecting window; Q - quartz window.

3.4. Photograph showing end of monochromator, recorder and "blackbody*.

3.5» Schematic diagram of optical arrangement of calibration apparatus.

S - "blackbody"; W - quartz window; and Mg - front surfaced

aluminum mirrors; F - filters; A - entrance slit of monochromator;

M - spherical mirror; G - grating; E - exit; slit; P - photomultiplier

and E - monochromator housing.

3*6. Multiplication factor for the grating monochromator.
o

I-<

_J3

COo<

CD

CL

CO -i

LjJ

CD

LUHX

CL<

DC

CD

_

L ^

CD

_JOo

lx! Of

CD3 O bf<o 0 : O3Q — c: CO

c:

co

_joo

CD 0 : 0 :

LUX

CO

GC

LjJ

h-3O

O Ot ou

cfl

cS

<U LU

/* INI

Jtt? ,,Pr,A& V , mrmn,* * ' VjD

-OO

'C==D

///////////

'/////////////{mf/gt/flb ooo 33

CO< tb CD ^ 3 OOoo

LUX 3333

o-1

Figure

3.1


i’igare

3*^
I£
CALIBRATION

FACTOR

(Arb.

units)

Figure 3.6
- 43

4. A Survey of Flame Spectra

N. H. Kless

A photographic survey of flame spectra was undertaken for the purpose

of guiding more specialized study of the problems of combustion. A large

number of plates were taken. This report attempts to present the information on these plates in a systematic manner.

The spectra were photographed on Kodak plates. For each of the

following prints, the type of plate used and the exposure time are given.

In some cases it was necessary to mask the print in order to compensate for

the large gradient in plate blackening. The spectrograph used is the Hilger

E-2, with interchangeable glass and quartz optics. The dispersion of the glass

is about three times that of the quartz. Commercial grade tank gases - fuel

and oxygen, sometimes with an inert diluent - were burned on commercial

welding torches wnth port diameters ranging from 0.040 in. to 0.148 in. The

flows were regulated and measured to an accuracy of ± 2 per cent. The burner

port diameter, total gas flow, and fuel-to-oxygen ratio are given for each

figure. To express the latter, the parameter a is used, where

oxygen

fue]V

/ oxygen

Thus if a C/, the mixture is lean, while if a^/, the mixture is rich.

stoichiometri

c
- 44 -

Fig.

Fig.

Fig.

Fig.

Figure Legend

Acetylene - Oxygen Flame

..00: burner port diameter 0.041 in., total flow 35cc/sec.

4.1: quartz optics, plate type 33, exposure time 10 sec. The features

include OH extending with uniform intensity over the whole slit.

The 0,0 head is at 3064A and the 1,0 head is at 2811A. They also

include three CH systems appearing only in the inner cone. The

heads of these systems are at 4315A, 3871A, and 3143A. Some of the

bands of the C

? Swan system are visible before the plate sensitivity falls off at the long-wavelength end. These are the 1,0

sequence at 4737A and the 2,0 sequence at 4383A, the latter being

superimposed on a branch of the 4315A system of GH.

4.2: quartz, 33, 2 min. The increased exposure brings out the 0,1 and

2,0 sequences of OH, with heads at 3428A and 2608A, respectively.

The 1,1 and 1,0 bands of the 3871A CH system, with heads at 4025A

and 3628A, respectively, are present. The 0,0 sequence of the Cp

Swan system at 51&5A is strong, despite the lov; plate sensitivity

in this region. Between this and the 1,0 sequence appear the 0,1

band of the 4315A CH system, with. head at 4890A, and some of the

’•tail bands'* of the Swan system. The Deslandres-d* Azambuja system

of C appears, with the 0,0 head at 3852A. The 0,1 head at 4102A

is faint, as is the 1,0 head at 3607A. In the region of 3300A to

3700A, where the OH is w

r eak, there appear some of the SchumannRunge bands of 0^, with best contrast in the outer cone. Also in

the outer cone is a continuum at longer wavelengths.

4.3i quartz, 11-0, 30 min. It was necessary to mask the print because

of the several factors which cause the plate blackening to fall

off at short wavelengths. The most important of these is the

decrease in radiation from the flame, but absorption by air,

gelatine, and quartz also have an effect. In this region the

atomic carbon line at 2479A and the 4th positive system of CO are prominent features. The latter extends from about 2800A to 1000A.

The Schumann-Runge Op bands are in the outer cone, and overlap with

the 3,0 sequence of OH, whose head is at 2444A. At 2320A there is

a trace of the Mulliken system of C 2

.

4.4: quartz, 103-0-UV sensitive, 1 hour. No new systems are brought out,

but the 4th positive CO and the Schumann-Runge Op bands are extended

to the short-wavelength end of the instrument. The print was masked.
CH

and 5 Nu) <3- O oO ro

ro nO - — CO XO X

P-00

C\J

O

-r CO A CM

M- xC2

~Oroxo

c<o . im

v>x

cJ O ~ CO X CM O x I ~

o<->

<T> N O^CMXc

0)

•j§

O3 C'J 5

ro

** CM

CM

x o o

CM

ro

CMX

*°CM Q in I CD Q ro nX o

CD

CMCD

X roX

S2q I roio^s o x st ~ i CM o O

X M- O C°

O CD wgX CM O X

_ CM

307304 0 - 54 -4

CO4

1h

Positive
- 46 -

Fig. 4.

Fig. 4.

Fig. 4.

5: glass, II-F3, 10 sec. The CH bands at 3&71A and 4315A, and the

C2 Swan system, are shown with a dispersion approximately three

times that by using quartz optics. The 3S71A CH band is weak

because of the cut-off in the transmission of glass in that region.

The heads of the Swan bands are: 2,0 sequence, (superimposed on

CH), 43S3A; 1,0 sequence, 4737A; 0,0 sequence, 5165A; 0,1 sequence,

5636A; 0,2 sequence, 6191A; 0,3 sequence, about 6677A.

6: glass, I1-F3, 100 sec. More of the fine structure of the Swan

bands, as well as the ’'tail bands" of the Swan system, and the

4890A band, are brought out.

7: glass, I-N, 5 min. There is a complex band system on the long

wavelength side of the 0,3 sequence of the Swan system. Masking

was necessary because of the high intensity of the complex

structure.

- 48 -

a = Fig*

Fig.

Fig. 4

Fig. 4

.00: port diam. 0.041 in., total flow 45cc/sec.

4.8: quartz, 33, 10 sec. This exposure is to be compared with Fig. 4.1,

the corresponding exposure for a = 1.00. It is seen that the C

2

bands are stronger here, both the Swan system and the Deslandresd’Azambuja system. The 2,0 sequence of the Cp Deslandres-dT Azambuja

system, with head at 3400A appears. The 3143A GH system is enhanced,

as are the 4025A and 3628A bands of the 3871A CH system and the

’’tail bands” of the Swan system.

4 .

9

2 quartz, 33, 2 min. The increased exposure shows that the SchumannRunge O

2 bands are absent in this region.

.10: quartz, 11-0, 30 min. The Cp Mulliken bands are comparatively

strong in this flame. The atomic carbon line and the CO 4th

positive bands are strengthened, while the O

2 bands are faint in

this region. Masking was necessary.

.11: quartz, 103-0-UV sensitized, 1 hour. The CO 4th positive bands

are extended to the short wavelength end of the instrument (2100A).

Masking was necessary.
OH

0,0

CH

X3064 X

3871

Figure

4,3—

4.

IX
- 50 -

Fig.

Fig.

Fig.

4. 12: glass, II-F3, 10 sec. The Swan system is stronger with respect

to the GH bands than for a = 1.00.

4.13s glass, II-F3, 100 sec. The tail bands are brought out, along

with more fine structure.

4.14: glass, II-F3, 100 sec. The new features are the strong continuum,

which becomes stronger toward the red end, and the band systems in

the mantle. The C£ and CH bands, while much weaker than in the

inner cone, are nevertheless quite strong. The 4050A group appears

equally strong in the inner cone and in the mantle. CN appears

as an impurity (3883A). Masking was necessary.
O OJ

fO ooO (T) c fO c CO o <0 O <£) i in 3 in

to

x

C l£> 3 in s in

to

x

T3

C/) c ro O N- O X3 5 *

to

X

CM ro O fO 5 s}- LO X 0rn

figure

4.12-

4.14
a = Fig.

Fig.

Fig.

- 52 -

3.00: port diam. 0.041 in., total flow 55cc/sec.

4.15 • quartz, 33, 10 sec. This mixture bums with a luminous white

mantle around the inner cone. The features of the inner cone differ somewhat from those for a = 2.00. The OH bands are much

weaker and the CH bands are somewhat weaker, while the C£ bands

remain very strong. The 3143A CH band is now rather free from

overlapping OH. The mantle contains and CH, both much weaker

than in the inner cone, and OH. CN appears in the mantle alone,

the 0,0 head being at 3883A. This is the result of diffusion

of air into the flame. Also in the mantle is the "4050A group",

attributed to C,. It maintains uniform intensity in both the

inner cone and the mantle. At medium quartz dispersion it appears

as several broad, diffuse lines, one of which is at 4050A.

Masking was necessary.

4.16: quartz, 33, 2 min. The increased exposure brings out the 1,0

sequence of CN, head at 3590A, and the NH band at 3360A, both

resulting from diffusion of air into the flame. Because of the

weakness of the OH, a portion of the Fox-Herzberg bands of C 2

appears on the short wavelength side of 3064A. There is a strong continuum over the whole exposure. Masking was necessary.

4.17: quartz, 11-0, 30 min. In this region also there is a strong

continuum. The 2,0 sequence of OH is very weak. The Mulliken C2

bands are comparative^ strong, though not as strong as for

a = 2.00. The atomic carbon line and the CO 4th positive bands

are weak. Masking was necessary.
CN

0,0

X3

883

^4050

Group

oco

CO Icm O x

o-r- —— - co X CVJ O Xa

f"

(\l

A

xc

a> --

O

,2 ro ^ OJ CMX o

C'-

r-f•I

-d"Vua

"H
- 54 -

a = 0.400: port diam. 0.041 in., total flow 36cc/sec.

Fig. 4.18: quartz, 33, 10 min. The intensity of the flame as a whole is much

less than for a = 1.00. However, it is the intensities of the

bands with respect to each other that is of primary interest.

Relative to the OH bands, the Swan bands are much reduced in

intensity The 3143A CH system is also much reduced, as are the

higher transitions (1,0 and 1,1) of the 3871A CH system. The

0,0 bands of the 3871A and 4315A systems are slightly reduced.

The Deslandres-d t Azambuja system of C2 is absent. In the outer

cone, the Schumann-Runge 0^ bands appear with good contrast.

In the inner cone there is an extensive band system, between

4000A and 2500A, appearing as a wavy background. These are the ’’hydrocarbon flame bands”, believed to be emitted by CH0.

They begin to appear as the flame becomes lean, and are strong

in this flame.

Fig. 4.19: quartz, 11-0, 30 min. The increased exposure brings out the

OH, O2 , and hydrocarbon flame bands below 3064A.

Fig. 4.20: glass, 103-F3, 15 min. Because of the decrease in intensity of

the Swan bands, the CH band at 4890A stands out. Fine structure

at the long-wavelength end appears not to belong to the Swan

system. Schumann-Runge O

2 bands are in the outer cone, weak,

up to about 5000A. There is a fairly strong continuous background in both inner and outer cones, which extends to shorter

wavelengths.
Schumann -

Runge

O.

_

t'®

Ox o

CDCD X<* O x ~ Nc K)

5J- X

CO O

X

—

<Ch X o

°oX ro O X

O <fr 0u oo 1 ro O x

o. - —'“co X 00 O X

/K

C2Swan

1,0

CH

X4737

X4890
- 56 -

a = Fig.

a = Fig.

Fig.

).200: port diam. 0.088 in., total flow 54cc/sec.

4.21: quartz, 103-0, 10 min. There are no other band systems than the

hydrocarbon flame bands, OH, and CH. The latter two are highly

suppressed, while the former is now the prominent feature of

the flame.

).191: port diam. 0.072 in., total flow 40cc/sec.

4.22: quartz, 103-0-UV sensitive, 2 hours. The long exposure brings

out the hydrocarbon flame bands at shorter wavelengths than

2500A. There are no other OH bands than the 0,0 and 1,0.

4.23: glass, 103-D, 30 minutes. In this region there is only a slight trace of the Swan system - the 0,0 head at 5165A.

A weak, wavy structure between the CH bands at 4315A and 4890A

is the "carbon monoxide flame bands", the emitter of which is

believed to be CO2

. A continuous background is evident.
hydrocarbon

flame

bands
- 58 -

a = Fig.

a = Fig.

Fig.

(.126: port diam. 0.127 in., total flow 27cc/sec.

4.24: quartz, 103-0, 10 minutes. No outer cone appears. The only

diatomic bands are the 0,0 OH and the 4315A GH. These are very

weak. The rest is hydrocarbon flame bands.

Hydrogen-Oxygen Flame

1.12: port diam. 0.072 in., total flow 98cc/sec.

4.25: quartz, 103-0, 90 sec. The 0,0; 1,0; 2,0; and 0,1 sequences

of OH are strong. The 3,0 sequence, with head at 2444A, and

the 0,2 sequence, head at 3920A, are weak. There is a continuum at the long-wavelength end.

.331: port diam. 0.072 in., total flow 66cc/sec.

4.26: quartz, 103-0, 20 min. Strong OH, with O

2 mixed in.
OH

0,0

CH

X

3064

X43I5

X cm O x

oj o

o'TM

<T>

X ro O ^ — oo QOJ X ro O x

°'o X ro O X

<D-

"00 X CVJ O X o 00 ro x c\i o x

Figure

4.24-

4.2 6
- 60 -

a = Fig.

a = Fig.

a = Fig.

2.00: port diam. 0.041 in., total flow 35cc/sec.

4.27: quartz, 103-0, 20 min. This flame is comparatively weak in

overall intensity. ' The C bands are relatively stronger than

for a = 1.00. There is slight evidence of hydrocarbon flame,

bands.

Propane-Oxygen Flame

1.00: port diam. 0.041 in., total flow 24cc/sec.

4.28: quartz, 103-0, 20 min. The band systems here are all found in

the acetylene-oxygen flame. The difference is that the carboncontaining bands, especially C^, are relatively weaker compared

to OH than in the acetylene oxygen flame. This is true for all

values of a . Furthermore, the overall intensity is less. In

the inner cone is a trace of the hydrocarbon flame bands. There

is a continuum at longer wavelengths.

.261: port diam. 0.127 in., total flow 42cc/sec.

4.29: quartz, 103-0, 20 min. No Swan bands. OH and the hydrocarbon

flame bands are relatively strong. CH is relatively weak.
o -

CD XC\J O X

ro2; ro

x

X ro O x

ro X*

Oro

<d- <£> O

X ro O X o — — oo XOJ

o-*

!£?

X roX

rCDrox

O®

~8I CMX

CVl ingo

O ^ u

r*- o Q CD i m o x

307304 0 - 54-5

hydrocarbon

flome

bands
- 62-

a = Fig.

a = Fig.

a = Fig.

Methane-Oxygen Flame

2.00: port diam. 0.041 in., total flow 20cc/sec.

4 » 30 : quartz, 103-0, 1 hour. This flame is weak in overall intensity.

As in the rich flames of acetylene and propane, the bands are strong compared with the other bands, but here the Deslandresd

T Azambuja system of is very weak, only the 0,0 head at 3852A

showing.

1.00: port diam. 0.041 in., total flow 30cc/sec.

4.31: quartz, 103-0, 10 min. The overall intensity is much less than

that of the acetylene-oxygen flame of same a . Relatively, however, the OH remains strong, while the CH is weaker and the 0^ is very much weaker. There is a trace of the hydrocarbon flame

bands, and a continuum at long wavelengths.

.500: port diam. 0.041 in., 25cc/sec.

4.32: quartz, 103-0, 10 min. This flame differs from other hydrocarbon

flames of comparable values of a in that OH is by far the

strongest feature. The Swan bands are absent and the CH and

hydrocarbon flame bands are weak.
o„- “ 00 x oj o X

°~8

TMC0 X CM O X _ 00 -roj X ro O x

— CD °co X Jo o x

ro x!t

0,0X o *• o’ 10 Xo x o =

“00

XCM O X O CD X C\J O x ccv_<uXS

CT> X

in o <3- X

in

CM

x

O

inX o

o>GO x<t O x

O

c\T«o c®5 ro

co

x oo

o'* 10o

ID

ON— ro §5

figure

4.30-

4.32
- 64 -

Acetylene-Oxygen Flame Diluted with Carbon Dioxide

a = 2.00,

50% co

2 . port diam. 0.148 in., 54cc/sec.

Fig. 4.33 : quartz, 33, 8 min. Diatomic spectra^ hydrocarbon flame bands,

and carbon monoxide flame spectra are all present.

a = 1.00,

64% C02 : Fig. 4.34 : port. diam. 0.148 in., total flow 58 cc/sec.

quartz, 103-0, 2-1/2 min. The diatomic spectra are suppressed,

while the hydrocarbon flame bands are by far the strongest

feature. The characteristics of the carbon monoxide flamecontinuum and wavy band structure - are present.

a = .400,

50% co

2 . Fig. 4.35 : port diam. 0.148 in., 35cc/sec.

quartz, 33, 10 min. The outer cone is too weak to register.

Diatomic spectra are highly suppressed, while the hydrocarbon

flame bands show up with great strength and high contrast.
CO

flame

bands

rO

X

X

o<° °o

XfO O X

00 -CM X(0 o o

XSJ

q.Ofl

CDuoX~ o O _"S.

<o

r x 0 X — co 1 C\J O X o

o> E- X QJ o —

-co x C\J O X

in

x ro o o-X o roX O '3' 0-CD ° O X ro O X

ID Pjro O^-X _ r- X co O roX
- 66 -

fig. 36 : This graph gives estimates of the intensities of the principal

band systems in the acetylene-oxygen flame as a function of

The intensities are graded on a scale from 1 to 1000, and the

units are completely arbitrary. They are based on visual

impressions from examining and inter-comparing plate blackenings,

compensating, if necessary, for differences in exposure time and

plate type. They are intended to serve as a rough guide as to

what fuel to oxygen ratios to use to bring out these band

systems

.
Of

Figure k,36
- 68 -

5 . The ^4050 Group of Cometary Spectra in the Acetylene-Oxygen Flame*

Norman H. Kiess and Arnold M. Bass

(National Bureau of Standards, Washington, D. C.)

The group of emission hands which has been observed in spectra of comets

and late class N-stars, in the region of &+O 5O, has been produced recently

in the laboratory in a number of sources* Durie^ has observed the 14050

emission in the flame reaction of fluorine with organic compounds, but to the

best of our knowledge these bands have not been observed before in flames

burning in oxygen. We have recently observed a band emission in the 140 50

region in the radiation from the luminous zone of a fuel-rich acetyleneoxygen flame. This luminous zone appears at a fuel-to-oxygen ratio of about

2.6 times stoichiometric, and remains in the flame well beyond the ratio of

4 times stoichiometric. The low dispersion spectrum in this region shows a group of bands similar to that observed by Durie^ and Herzberg3. Figure 5.1

is a reproduction of the spectrum as photographed with a Hilger E-2 spectograph with glass optics. The source for this exposure was an acetylene-oxygen

flame, of fuel to oxygen ratio three times stoichiometric, burning on a welding torch with a port diameter of 1 mm. The exposure time was 1 minute on a spectrum analysis No. 1 plate. The bands of the A.4050 group are clearly

discernible as they extend unchanged over the whole slit, while the other

features of the spectrum (which are mostly CH) show a marked decrease in

intensity in going from the inner cone to the outer cone. Through the co- operation of the Spectroscopy Section of this Bureau, these bands were photographed in the second order of a 21 foot grating spectrograph with dispersion

of 0,88A/mm. The spectrum at this high resolution resembles that described

by Douglas^ as obtained in a discharge between carbon electrodes. Our spectrum

is much richer in lines, as would be expected by considering the much higher

temperature of our source. Fig* 5.2 is a reproduction of a densitometer tracing

of the spectral region between 4050 and 4075 4. This tracing was taken from a spectrum analysis No. 1 plate exposed for 4 l/2 hours by using as a source a three times stoichiometric acetylene-oxygen flame burning on a rectangular slot

burner of dimensions 56 min by .076 mm. The region of the flame selected for

this trace lies above the reaction zone.

Douglas has suggested that these bands may be explained as arising from a

X.-'Tr transition of a linear Cj molecule, and he has presented an analysis of

the rotational structure of the band which forms a head at 4050A. For most of

the lines of this band our measurements agree with those of Douglas to better

Submitted for publication in The Journal of Chemical Physics

1. For a recent complete review of this problem see B. Rosen and

P. Swings, Ann. d’Astrophys. , 16, 82 (1953).

2. R. A. Durie, Proc. Roy. Soc. , Lond. , A211 , 110 (1952)

3. G. Herzberg, Astrophys. J. . . 96. 314,(1942)

4. A. E» Douglas, Astrophys. J. 114 . 466 (1951)*
- 69 -

than 1 cm“^ in the spectral range in which the data overlap. Because of the

higher excitation temperature which we used, we have been able to extend the

analysis suggested by Douglas to higher rotational quantum numbers. The ex- tended analysis is presented in Table The lines for J less than 48 are omitted since the wavelengths which we measured are essentially the same as those reported by Douglas. For the type of transition postulated by Douglas, our measurements lead to the following constants:

These values for B M , B', and D* 1 are in very close agreement with those of

Douglas. For D' Douglas reports a value of 0.26 x 10“^ cm“l which is

considerably smaller than that which we found.

B" « 0.430 cm”1

D»' = 0.90 x 10”6 cm

l/ 0 = 24675.75 cm”1
J

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

77

79

81

83

85

87

89

91

93

95

97

99

101

103

105

107

109

111

- 70

TABLE 5.1

Extended analysis of the A405O band of C3

Wave number cm P(J) Q(J) R(J)

24598.61 24678.44

24637.45

94.20

34.59

77.09

89.58

31.58

75.96

84.90

28.51

74.63

80. 03

25.45

73.20

75.46

22.28

71.61

70.74

19.06

70.17

65.84

15.62

68.37

60.87

12.38

66.52

55.82

08.81

64.38

50.75

05.27

62.18

45.49

01.71

40.29

598.08

34.83

94.38

90.65

86.76

82.87

78.88

74.83

70.74

66.54

62.32

58.13

53.74

49.38

44.85

40.29

35.72'

31.11

26.22

21.60

16.60
- 71 -

Figure Legends

Figure 5.1. Emission spectrum of acetylene-oxygen flame as photographed

with Hilger E-2 glass prism spectrograph.

Figure 5.2. Densitometer trace of the M.050 band in emission from acetyleneoxygen flame. Original plate photographed with 21 foot grating

spectrograph, dispersion 0.88 A/mm.
Figure 5*1
40

50

60

figure

5*2
- 74 -

6 . THE DECOMPOSITION OF CF^ IN FLAMES

B. E. Squires

Recent studies of discharges through fluorocarbon vapours have led to the

discovery and partial analysis of several b^,nd systems ascribed to emission by

electronically excited CF and CF2 molecule

s

x~. The thermal decomposition of

CF^ in a graphite furnace has permitted the observation of the same band

systems in absorption^". It seemed of interest to explore other convenient

^Andrews and Barrow, Nature, 165 . 890 (1950).

^Laird, Andrews, and Barrow, Trans. Faraday 5oc. 46, 803 (1950).

3Venkateswarlu, Phys. Rev., 22* 676 (1950).

^Andrews and Barrow, Proc. Phys. Soc., 64, 481 (1951).

means for studying the breakdown of CF^. The admixture of the stream of the

vapour of this fluorocarbon in an acetylene-oxygen flame results in a manybanded spectrum in which new bands belonging to the previously found _ 2 _, transition of CF have been identified. The CF2 bands found in earlier work

do not seem to be present.

^Margrave and Wieland, J. Chem. Phys., 21, 1552 (1953).

Spectrograms were taken with a Hilger E-2 instrument using glass optics

from 8700 to 4000 A and quartz optics from 5000 to 2100 A. Eastman plates were used of emulsions 103 and I variously sensitized from 2100 to 9000 A. Iron

comparison spectra are shown on most plates. Because of the limited time,

photographs were first taken only when a flame showed visible changes by the

addition of fluorocarbons, either by the naked eye or with the use of a pocket

spectroscope. These boundaries were extended when it seemed desirable to

bring out some weak aspect of the spectra in the invisible portions of the

spectrum. The acetylene-oxygen flame was not photographed using glass optics.

Ordinary welding torches and a slot burner 5 cm. long and ,075 ° r .15 wide

were used. The prints in this report are those which show nearly all of the

observed spectra.

Introduction of CF24, deepens the color of the blue outer cone of the

acetylene-oxygen flames. For a fuel to oxygen ratio of 2.0, the 1-0, 0-0, 1-1,

0-1, 0-2, and 0-3 bands of the CF system A-X were observed in the inner cone. The 0-2 and 0-3 bands with heads at 2479 and 2559 A were not reported by

Andrews and Barrow^’3, and may have been missed because of overlapping by the

CF2 bands found in the discharge. The 0-4 and possibly the 0-5 bands also were present in the flame but were obscured by overlapping bands of CS, which were

strong in the region between 2494 and 2715 4. CC1 bands between 2 777 and 2790 A
- 75 -

also were prominent, and a few copper lines were observed. The usual acetylene

flame spectra of C2, CH, CN, CO, and OH were not appreciably altered (see

plates 6.1 to 6.10, 6.17 and Table 6.1).

The appearance of the A-X system of Cl1 seemed to be favored for a fuel to

oxygen ratio of 2.0. A lower fuel to oxygen ratio produced a flame slightly

brighter visibly but somewhat smaller and less favorable for the appearance of

the Cg Deslandres-D'Azambuja system. A higher ratio produced a flame less bright

visibly with a larger orange mantle and somewhat less stable. The amount of CF4

added was adjusted to produce the maximum intensity of the CF bands; greater

amounts apparently cooled the flame and lesser amounts reduced the population

of CF. A sharp band head was observed at 2781.9 A which has not been positively

identified; it is probably due to CC1. No evidence was found of the B-X2 tt

system attributed to CF; this is most probably due to the greater intensity of

the CO fourth positive system in this region.

The appearance of hydrogen-oxygen flames is markedly changed by the addition of CF4. The nearly colorless flame appears blue with a tinge of red. For

a fuel to oxygen ratio of 1.0, spectra due to the impurities Cu, CuCl, CuF, CuO,

K and Na were observed with the addition of CFn. The usual OH spectra of hydrogen-oxygen flames was not appreciably altered (see plates 6.11 to 6.16, Table 6.2).

An extensive system of bands was observed for wavelengths greater than 7000 A

but it has not been identified; it would require more extensive study than has

been made. Other than the usual OH bands, no radiation was observed below

3000 A with exposures as long as 1.5 hours.

The CuF bands (see plate 6J.3> have been observed in flames, probably for the

first time. Both the CuF and CuCl bands (see plate 605) were fairly intense

even with a few minutes exposure, showing several vibrational transitions not

listed in the compilation of Pearse and Gaydon. The copper as an impurity in

^Pearse and Gaydon, The Identification of Molecular Spectra, Second Edition,

Chapman and Hall, London (1950).

the spectra comes from the tip of the brass burner which showed definite signs

of erosion after several hours of use with these flames, particularly with

hydrogen. Possibly this erosion is caused by the action of atomic fluorine or hydrogen fluoride which may be formed in the lower portions of the flame,

although their spectra were not observed. The cooling of the burner also makes

possible the condensation of water and the consequent formation of hydrofluoric

acid if hydrogen fluoride is present. The chlorine is a known impurity in the

CF4 gas in the form of FCl2C:CCl2F in quantities up to 6 $0. The sources of sodium,

potassium, and sulphur are not known, but they are common impurities in flames.

It appears likely that a very small amount of CS2 was in the CF4, and also the

intensity of the CS bands were greater in the first sample of CF4 than in the

second.

This study of these spectra has encouraged us to investigate such "mixed"

flames, partly in order to search for new bands or spectra, and partly to

obtain spectra under higher resolution so that detailed analyses may be made.
- 76 - TABLE 6,1. Compilation of bands and lines observed in an acetyleneoxygen-carbon tetraf luoride flame. Intensities listed are relative,

estimated on a scale of 1000. Bands with an asterisk (*) are estimated

wavelengths and most probable assignments.

System Wave Length v

1 . v1 ’ Intensity

C£ Swan 5165.2 0,0 500

5129.3 1,1 300

5097.7 2,2 200

4737.1 1.0 900

4715.2 2,1 800

4697.6 3,2 800

^4684.8 ^.3 800

4382.5 2,0 500

4371.4 3,1 500

- 4365.2 4,2 700

Deslandres-D'Azambuja’

s

3852.2 0,0 200

3607.3 1,0 90

3592.9 2,1 90

3587.6 3,2 100

3399.7 2,0 80

CC1 2789.8 0,0 70

2788.3 1.1 70

2782.3 0,0 60

2778.8 0,0 70

2777.6 1.1 70

Cl1 A-X *2551.5 0,3 30

*2558.8 0,3 30

*2475.0 0,2 50

*2479.3 0,2 50

*2404.1 0,1 40

*2400.2 0,1 40

2331.8 0,0 10

2327.8 0,0 10

2308.7 1.1 10

2304.6 1.1 10

2242.2 1.0 10

2238.2 1.0 8

CH 4300 A 4312.5 0,0 1000
- 77 -

TABLE 6.1. (Cont.)

System Wave Length V* . V* * Intensity

CH 3900 A 3889.0 0,0 300

3871.1 0,0 400

3628 1,0 40

CH 3143 A 3143.4 0,0 1000

3156.6 1,1 100

CN Violet 3883.4 0,0 400

3871.4 1,1 200

3861.9 2,2 100

CO Fourth Positive 2311.5 7,16 8

2286.1 6,15 10

2261.7 5,14 9

2238.3 4,13 2

2221.5 7,15 9

2196.8 6,14 10

2173.0 5,13 9

2150.2 4,12 8

2137.0 7,14 2

2128.3 3,11 3

2113.1 6,13 4

2107.2 2,10 3

CS 2708.9 3,4 20

2693.2 2,3 20

2677.0 1,2 30

2662.6 0,1 30

2621.6 3,3 20

2605.9 2.2 20

2589.6 1,1 50

2575.6 0,0 60

2538.7 3,2 40

2523.2 2,1 30

2507.3 1,0 20

2493.7 5,3 8

NH 3360 0,0 200

307304 0 - 54-6
System

OH

Element

Copper

- 78 -

TABLE 6,1. (Cont.)

Wave Length v* . v

1

1

Intensity

3063.6 0,0 200

2945.2 3.2 10

2875.3 2,1 20

2811.3 1,0 60

Wave Length Intensity

3274.0 100

3247.6 100

2247.0 5

2242.6 4

2238.5 4

2236.3 4

2230.1 6

2227.8 2

2225.7 5

2214.6 2

2199.8 2

2199.6 2

2192.3 2

2181.7 4

2178.9 4

2169.5 1

2165.1 2
- 79 -

TABUS 6.2 . Compilation of bands and lines observed in a hydrogenoxygen—carbon tetraf luoride flame. Intensities listed are relative,

estimated on a scale of 1000. Bands with an asterisk (*) are estimated

wavelengths and most probable assignments.

System Wave Length v* . v

8

1

Intensity

CuCl "B" 4982.2 0,1 50

4881.5 0,0 500

4788.5 1,0 200

n Dii *4773 0,5 40

*4686 0,4 80

*4600 0,3 300

4515.9 0,2 500

4433.8 0,1 700

4353.9 0,0 900

4280.9 1,0 600

4211.0 2,0 300

*4146 3,0 100

*4745 0,5 40

*4658 0,4 70

*4575 0,3 300

4493.8 0,2 500

4412.4 0,1 700

4333.2 0,0 900

4258.9 1,0 600

4187.9 2,0 400

4119.9 3,0 100

*4157 4,0 50

CuF "A" 5694.3 0,0 100

5685.7 1,1 90

5677.2 2,2 80

*5669 3,3 50

*5660 4,4 30

*5652 5,5 10

*5644 6,6 5

"B" 506 I.I 0,0 200

5052.3 1.1 100

*5043 2,2 50

*5034 3,3 20
80 -

TABLE 6.2. (Cont.)

System Wave Length V* . V

1

1

Intensity

CtLP "C

4932.0 0,0 800

4926.8 1,1 600

4922 2,2 700

*4916 3.3 300

*4911 4,4 100

GuO 6161,5 1,1 100

6146.8 0,0 20

6059.3 2.1 40

6045.1 1,0 10

h2 ° 8097 400

7164.5 50

OH 3428.1 0.1 400

3184.8 2,2 700

3121.7 1,1 800

3063.6 0,0 1000

2945.2 3.2 400

2875.3 2.1 500

2811.3 1,0 600

2677.3 3.1 100

2608.5 2.0 200

Element

Copper 5105.6 400

3274.0 1000

3247.6 1000

Potassium 7699.0 1000

7664.9 1000

Sodium 5890.0 200

5895.9 200
- 81 -

Figures 6,1 - 6,10, 6.17

Spectrograms of an acetylene-oxygen-carbon tetrafluoride flame with a fuel

to oxygen ratio of about 2.0. Prints were made from type 103-0 and 103-0 U. V.

Eastman Kodak spectrographic plates with exposures ranging from 5 sec. to

50 minutes. Relative intensities are tabulated in Table 6,1.

Figures 6,11 - 6.14

Spectrograms of a hydrogen-oxygen—carbon tetrafluoride flame with a fuel

to oxygen ratio of about 1,0. Prints were made from type 103 F-3 and 1-N

Eastman Kodak spectrographic plates with exposures ranging from 2 to 20 minutes.

Relative intensities are tabulated in Table 6.2.

Figures 6.15, 6.16

Spectrograms of a hydrogen-oxygen-carbon tetrafluoride flame with a fuel

to oxygen ratio of about 1.0. Prints were made from type 103-0 Eastman

Kodak spectrographic plates with exposures ranging from 10 to 30 minutes.

Relative intensities are tabulated in Table 6.2.
4900

4500

4000
3200

3100

3000

2900

2800

ft
2400

O o

IL. O

o o

o o

Figure

6.5

-

6.6
2300

2200 o _

xO. o o oo

00

CM lOo —

oo

Figure

6.7
to—„

Ooj

to°i Oro

l^ro oo tn°r. ug

Oro

t0~„

Oo

</>*> Ooj

to't. om

(/>« oin

too. o-cn- oOoj

01*9“

6*9
8500

8000

7500

7000

6500

CuO

CuO

No

<nbs

Figure

6.11-

6.12
5500

5000

_ CD o —

_ OD o o

5

“

o — ° o'
4800

4500

4000

3700

x°i

Ocm

xo

'oo

x —

„

oo
o

o

OJ

<4^ 4°

.o —

,

<-><*
- 91 -

7 . ULTRA. VIOLET ABSORPTION SPECTROSCOPY OP

SPARK IGNITED, LOW PRESSURE EXPLOSIONS*

Uy

H. P. Broida^ A. J. Everett and. G. J. Minkoff ^

ABSTRACT

Preliminary studies have been made of the absorption of ultra-violet

radiation at selected wavelengths as a function of time by spark-ignited

explosions in low-pressure mixtures of hydrogen and oxygen, of methane and

oxygen, and of carbon-monoxide and oxygen. Plots of the logarithm of the

optical density versus frequency between 3000 A and 2100 A for the three

mixtures at various pressures were linear with a slope of 1.51 x 10“ cm

- ^ The results have been compared to previous work on determinations of

hydrogen peroxide formed by explosions in similar vessels. No evidence for

the existence of hydrogen peroxide in the gas phase was found. Also ozone

was not detected (less than 0.03 percent of the original free oxygen) in the

main reaction but some may have appeared about 10 milliseconds later. Pormic

acid was found during the main absorption. The present experiments in

cylindrical vessels did not permit a clear separation between absorption due

to the flame front and that due to the hot gases behind the flame.

The isolation of hydrogen peroxide from liquid-air cooled, spark-ignited

explosions of hydrogen and oxygen has been reported by Egerton and Minkoff

(1947), who described U. V. absorption tests on the source of formation of the

hydrogen peroxide. When methane explosions were studied later in the same apparatus, hydrogen peroxide and ozone were isolated (Everett and Minkoff, 1949).

Further work on the U. V. absorption of the explosions (Everett, 1953) showed

that the results of Egerton and Minkoff were rendered doubtful by the presence

of condensed droplets on the windows. Another difficulty was due to the duration

of the flame travel, which was much shorter than had been expected (Egerton,

Everett and Minkoff, 1953). This meant that unless the explosions were accurately synchronised with very short explosures, the photographs with

absorption would receive so much light, extraneous to the explosion time, that

the absorption would be masked. It was therefore decided to investigate the

phenomenon by using photomultiplier detection.

^National Bureau of Standards, Washington, D. G.

^Chemical Engineering Department, Imperial College, London S.W. 7

*In preparing the manuscript for inclusion in this report, copies of the figures

were not available. The text is presented without the figures since the

procedures and results are of importance in studies of combustion. This paper

will be presented at the Fifth Symposium on Combustion, Pittsburgh, September 1954.
- 92 -

The method was to pass U. V. light axially through the cylindrical

explosion tube, and to allow a selected wavelength to fall on a photomultiplier. This gave a signal which was sent to a cathode ray oscillograph

and recorded as a single sweep, at a rate which produced a time-intensity

curve for the duration of the explosion.

One reference only has been found to the use of the photomultiplier

method of following the U. V. absorption of explosions. This briefly describes

the results obtained by Norrish, Porter and Thrush (1953) with flash ignited

explosions of acetylene-oxygen mixtures. The results obtained by Norrish and

Porter (1952) with a high-s'peed photographic technique on hydrogen explosions

have some relevance to the present work and will be discussed later. In the

infrared, .Bullock and Silverman (1953) have studied the progress of light

emission in a carbon monoxide-oxygen explosion, and they also report a few

absorption experiments. These results will be discussed in a later publication in connection with the U. V. emission of explosions.

Experimental

Apparatus . The spectrograph used was a large aperture, Raman-type

Hilger E- 5I8 with quartz optics, having a dispersion of 50 A/inm. at 3000 A,

30 A/mm e at 25OO A and 15 A/mrn. at 2100 A. With entrance and exit slits

set at 0.2 5 min., it was possible to resolve 12.5 A, 7.5 A and 3.8 A at the

corresponding wavelengths. The photomultiplier was a specially selected R.C.A.

type 1P28, with an ultraviolet transmitting envelope. It was enclosed in a light-tight housing mounted on a continuously moveable rack fitted with a fine

adjustment. The position could be read to ca.0.01 mm. with a vernier. Wavelengths were calibrated daily with a low-pressure mercury lamp, and were reproducible to approximately 0.03 mm.

A simple photomultiplier power supply was used, which consisted of four

small 300 volt batteries with a voltage divider giving any voltage between

300 and 1200 v. The very simple and robust circuit has been described elsewhere (Oldenberg and Broida, 1951)*

The cathode ray oscilloscope was a Furzehill instrument, type 1684/D with

blue screen and mark II camera. The instrument could be set for single-sweep

operation, the spot being kept just off the left side of the screen. When two

contacts were broken, the spot traversed the screen at velocity which had been

chosen according to the requirements of the experiment. The shortest duration

of the overall phenomena was such as to require the spot to cross the screen

in 6 - 7 milliseconds. It was then possible to resolve in time events

occurring in 2 percent of this, i.e. about 10”“^ secs.

The source of light was a M. S. Go. hydrogen arc, type HFWX, which was water-cooled and ran on 1 amp. The D. C. mains could not be used to supply

this (except in preliminary experiments) because the background light, instead

Kfe
- 93 -

of appearing as a straight line, had a strong, 150 c/s ripple superimposed. The

H.T. was therefore supplied by six heavy-duty 12V accumulators. Due to the

wandering of the arc, small fluctuations of intensity (not more than 3/Q were sometimes observed.

The reaction vessel consisted of a pyrex tube, 2 cm. wide and 30 cm. long,

with flanged ends on which quartz windows bad been fixed with Araldite cement.

The gas mixture was introduced through a stopcock, lubricated with silicone

grease, in a narrow glass tube which entered the vessel at a central position.

The electrodes were tungsten wires fused in pyrex capillaries so that only the

cross-section of the wire (0.1 mm.) was exposed to the hot gases. The l/4 inch

spark gap was situated in a small chamber fused to one side of the center of

the explosion vessel. This was designed to reduce light from the spark from

entering the spectrometer. In order to prevent the condensation of products

on the windows, the explosion vessel was surrounded by a steam jacket, which

kept the temperature at ca. 70°C. The spark itself was obtained by the rapid

opening of a switch in the primary of a 4000 V. transformer, the secondary of

which was connected to the electrodes. The firing switch also triggered the

oscilloscope sweep.

Optical Alignment . The light from the hydrogen arc was focused on the

slit of the spectrometer by one quartz lens, between the arc and the explosion

vessel. The reaction vessel was traversed by a slowly converging beam of light*

which reduced any errors due to reflection or chanelling inside the walls of

the vessels. Such errors were also diminished by using a stop on the lens, and

so confining the light to the central part of the tube. In order to test for

the possibility of changes in light intensity due to overall changes in refractive index of the gases (due to variation of temperature or of composition),

experiments were repeated using both parallel and diverging beams of light as well as convergent. However, there was no change in percentage absorption.

This does not eliminate the possibility of scattering of light by pockets of

burning gas, cellular flames, and similar phenomena which might reduce the amount

of light reaching the spectrometer.

Materials . Hydrogen and oxygen were of normal commercial purity. The only

impurity in methane, from Point of Ayr Colliery, was 2^ nitrogen. Commercial

carbon monoxide was freed of moisture and iron carbonyls by passage through

liquid nitrogen. The hydrogen content was shown to be not greater than 3 parts

in 10,000 by mass spectrometer analysis. Mixtures were made up in 5 flasks

at least one day before they were required, to ensure thorough mixing. The

compositions used were: 2 CO + O2 ; 1.6 H2 + O2 and CH4

+• 2 . 02 *

Procedure . The explosion vessel had been originally washed with dilute

hydrofluoric acid, rinsed and dried. Between explosions, the vessel was evacu- ated with a metrovac pump, to ca.0.01 mm, for one minute, and the gas mixture

then introduced; its pressure was measured with a mercury manometer, which was

then separated from the vessel by two stopcocks. Fifteen seconds after filling*

307304 0 - 54-7
- 94 -

the mixture was exploded. For absorption experiments the zero position was obtained on each photograph by opening the trigger

spectroscope slit closed.

The time scale was obtained on every 10th exposure by recording a 5^ c/s

signal at the same scanning speed. After developing, fixing and drying the

films each frame was projected, with tenfold enlargement, and both the explosion curve and the zero line were traced on a sheet of paper. The distance

from the explosion peak to the zero line represents the transmitted light (I),

while the distance from the zero line to the line traced out by the spot before

the explosion indicates the incident light (I Q

). These distances are illustrated in Fig. 6(a). The function which is used to describe all the absorption

results if the optical density (D) , given by log^C I

Q /l),

and firing switch with the

With each gas, several series of experiments were carried out. The

effect of pressure at one or two selected wavelengths was investigated, and

the dependence of optical density on wavelength was also observed at selected

pressures.

Results

Wavelength Dependence . The explosions of hydrogen-oxygen, carbon monoxideoxygen and methane-oxygen mixtures all showed absorption beginning below 3000 A

and increasing more rapidly as the wavelength decreased to 2100 A. It was found

that with all three gases, straight lines were obtained by plotting logqoD

against the frequency (wave number) of the absorbing light. The slopes of five

such lines, which include two pressures each of hydrogen and of carbon monoxide

and one of methane, are identical within the experimental error, as is shown

in Fig. 1, and have a value of 1.51x10" ^ cm

- -*-.

Fig. 1

The interpretation of these facts, and their relation to the detection of hydrogen peroxide, will be referred to in the Discussion. Although the slopes have

a common value, the amount of absorption depends both on the gas and on the

pressure. Thus, at 2300 A, at a pressure of 10 cm., hydrogen explosions had an optical density of 0.28, carbon monoxide 0.34, while methane had the strongest

absorption, with D = 0.65* If the absorbing species had a concentration which

was proportional only to the pressure (p) (for example, one of the reactants),

then plot of D/p against p should be straight lines parallel to the pressure

axis. A relation of this type was only exhibited by methane explosions above

4 cm. pressure. Hydrogen showed a slow, linear increase passing through the

origin, while carbon monoxide was associated w ith a steeper rise beginning at a higher pressure than hydrogen. (Fig. 2)
95 -

Absorption by OH . The comparatively low resolving power of the spectroscope made it impossible to attempt to resolve the banded absorption spectrum

of OH in the region 2900 - 3200 A. Nevertheless, by measuring the absorption

at 2900, 3000, 3100 and 3200 A, it was shown that absorption over this range

had a maximum value of 10$ at 3100 A, corresponding to the 3064 (0,0) band of

OH, This was observed in both hydrogen and methane explosions.

Absorption by Formaldehyde . This was only observed in the preliminary

experiments in which the vessel was not heated. The light received by the

photomultiplier appeared as a steady signal on the oscilloscope, and absorption was indicated by a transient movement of the line, which was observed

visually. There was then some indication, in the explosions of methane, of

aDsorption from 2800 A to ca. 3600 A, the region in which formaldehyde absorbs

most strongly.

Absorption Due to Formic Acid . Formic acid has a banded absorption

system with the most intense maxima at 2283, 2295* 2340 and 2400 A (Pearse

and 0-aydon, 1953). During the main part of the work, some evidence was obtained of the presence of absorption peaks at 2340 and 2400 A, v/ith optical

densities only about 0.06 above the values of the main absorption slope. In

the preliminary series of experiments to which reference has just been made,

peaks were detected at the four wavelengths corresponding to formic acid within

the accuracy of our measurements; there, however, the optical densities were much greater in relation to neighboring absorption, as is evident from

fig. 3, in which the observations in this part of the spectrum are plotted

on an extended wavelength scale.

Fig. 3

The discrepancy was not due to the effect of heating the vessel, since

the more intense absorption did not return when the heating was stopped.

Absorption by Ozone . Ozone has an aDsorption system with a maximum at

255O A (Fabry, 1950). Many readings were taken between 2350 and 2750 A with

explosions of both methane and carbon monoxide. Ho significant absorption

was found apart from the continuous absorption already described. The scatter

of the experimental points was such that a peak of density 0.03 would have

been just detectable. This would correspond to ca. 0.03$ of the original

free oxygen in a 2 00:02 mixture at 15 cm. pressure.

Although there was no evidence of ozone absorption in the main part of

the reaction zone, one series of experiments on the effect of pressure on

the absorption at 2500 A in methane explosions suggested that a small quantity

of ozone might be formed after the reaction was over, and the products were

cooling. This was shown by the presence of a small amount of absorption about

10 m sec. (shown in fig. 4) after the main absorption peak. Although this

phenomenon was not always reproducible, and, in some tests, was obscured by
- 96 -

Pig. 4

electronic noise, a linear relationship between the pressure (p, in cms.) and

the time (t, in milliseconds) which elapsed between the initial sharp rise in

absorption and the appearance of the second peak suggested that it was not

merely a random phenomenon. The equation of the straight line was

t = p + 4.0.

The optical density was of the order of 0.03, which would correspond to ca. 0.03^

ozone

.

Residual Absorption. In preliminary experiments with methane, the explosion

tube not being heated, the absorption increased to a maximum and fell to about a third of the peak value in a very short time (by visual observation); the

absorption then decreased to a steady value of about 10^ after several seconds.

This absorption was observed at wavelengths up to 4350 A, and it could be removed

by pumping. As droplets were seen on the windows, scattering by the condensed

products probably accounted for the observed absorption. Explosions of hydrogen

under these conditions exhibited an additional feature. The first peak in

absorption, which vanished above 2800 A, was very quickly followed by a second

peak, with subsequent decrease to a constant absorption which again persisted

to long wavelengths. This experiment will be referred to in the discussion of

the evidence for the detection of hydrogen peroxide.

Rates of Decay of Absorption . Although there were differences in the

appearance of the absorption, the rate of decay of the absorption after the peak

obeyed a kinetic law which v/as similar for explosions of hydrogen at 2200 A, of

carbon monoxide at 2300 A, and of methane at 2400 A. This was shown by plotting

log (D) against t, where the time t was measured from the instant when the rate

of decrease of absorption had reached a maximum value. The graphs obtained by

this procedure are shown in fig. 5* while the point t0 is indicated on fig. 6(a).

Fig. 5

The absorption associated with the GH radical at 3100 A was not sufficient for

the application of the method.

Duration and Shapes of Absorption Curves . Many of the explosion absorption

curves showed a composite character, which was revealed as the pressure was lowered. This is illustrated in fig. 6(c). As the effect was probably due to

the flame travel not being symmetrical about the center of the tube, no further

discussion of it will be made until more work has been done in spherical vessels.

A number of typical curves are shown in fig. 6. At some wavelengths at which

Fig. 6

light was both emitted and absorbed, an emission peak appeared prior to the

absorption one, as shown in fig. 6(b), for methane explosions, at 2700 A.
- 97 -

In any one set of conditions, the duration of emission was usually about half

the time which elapsed before the absorption had become vanishingly small. The

absorption and emission times obtained by the present method will be compared

in a later publication w ith the data yielded by high-speed cinematography of

the progress of the same flames, briefly, however, it may be said that for

hydrogen and methane explosions, the films indicate that the flames reached the

ends of the tube in just under 1 msec., while absorption lasted for ca. 10 msec. Carbon monoxide flames took 20-40 ms. to travel to the ends of the tube, while

absorption did not disappear for ca. 80 - 90 msec.

The time to reach maximum absorption did not appear to be related to the

time of flame travel in the same manner in all the explosions. Thus, in explosions of hydrogen and methane, the time to maximum absorption was approximately

twice that of flame travel, while in carbon monoxide explosions, the first

steep rise in absorption only lasted one half to one quarter of the time of

flame travel. Another distinction in appearance between the first two gases and

carbon monoxide was the absorption in the former began to decay very soon after

reaching the maximum absorption, while the carbon monoxide showed a much flatter

portion between increase and decrease in absorption. This is illustrated in

fig. 6(a) and (d) #

Discussion

The nature of the various absorbing species will be considered first, and

then the possibilities of the technique will be assessed. The first problem

is to attempt to identify the molecules or radicals responsible for the

absorption increasing to shorter wavelengths, which is found below 2800 A.

Although it might be due to hydrogen peroxide in the explosions of hydrogen and

of methane, the absorption is of comparable intensity in carbon monoxide

explosions in which the total hydrogen content is extremely small. Absorption

in the latter explosions and also some of that in methane explosions might on

the other hand, be ascribed to 'hot' carbon dioxide molecules, which have been

postulated to take in the oxidation of carbon monoxide (Dr. A. 0. Walsh,

priv. comm.). However, the observation that the relation between absorption

and wave number is identical for the explosions of the three gases studied

(fig. l) is an indication (though not a conclusive one) that the same absorbing substance is present in all three explosion mixtures. Clearly, the most

likely molecule is oxygen, which is believed to absorb at high temperatures.

Norrish and Porter, for example, found a very complex line absorption in the same region, with similar characteristics, when they flash-initiated hydrogenoxygen explosions. The same spectrum was found when they replaced hydrogen by

deuterium, bromine or chlorine, and they therefore concluded that oxygen was

the absorber. Until direct evidence is obtained, the tentative conclusion will

be made that hot oxygen was responsible for the main absorption observed in the

present work.

The increase in absorption with rising pressure in the explosions of
- 98 -

hydrogen and of carbon monoxide could now be interpreted as follows. The

intensity of absorption depends on the concentration of hot oxygen molecules,

which is itself directly governed by the pressure and by the temperature, and,

less directly, by the nature of the explosive gas. In addition, the temperature is known to affect the wavelength limit of the Schumann-Hunge emission

system, and the same is probably true of the absorption system. It might

therefore be possible, if the fine structure were resolved, to relate the

absorption quantitatively to the concentration of oxygen molecules and to the

temperature

.

The absorption by hot oxygen greatly increases the difficulty of attempting to detect hydrogen peroxide in explosions by U. V. absorption. If the

hydrogen peroxide which was isolated in the chilled experiments on hydrogen - had all been formed in the gas phase, the expected optical density at 2300 A

would have been 0.21 for an initial pressure (at room temperature) of 15 cm. The observed value was more than double this, i.e. 0.44. If hydrogen peroxide

were solely responsible, the only explanation would be that half of it decomposed before reaching the walls. The reverse situation was expected, however, since considerable amounts of the peroxide are probably formed on the

cold walls. Furthermore, the shape of the observed log D vs. cm“^ plot

differed' from the published values of Holt, McLane and Oldenberg (1948) and

of Urey, Dawsey and Rice (1929)* The measured slopes of the absorption in

the explosions (fig. l) suggest that the main absorber was not hydrogen

peroxide. However, the U.V. studies alone do not show conclusively the origin

of hydrogen peroxide and some other technique, such as infra-red spectroscopy,

must be applied.

Some indirect evidence of the formation of hydrogen peroxide is given

by the preliminary experiments in which no heating jacket was used. With

methane explosions, visual observation of the CRO trace suggested that up

to about 3000 A, the aDsorption very rapidly rose, fell by a third, then

slowly decayed to the residual value of ca 10% absorption. The latter was observed at all wavelengths. Hydrogen explosions showed an additional

feature, which consisted of a second absorption peak preceding the slow fall

to the residual value. The second peak, as well as the residual, was observed at wavelengths up to 4350 A. The final fall to a residual absorption has been shown to be due to the formation of condensate on the windows.

The observed facts could be explained by suggesting that the second peak in

hydrogen explosions is connected with the condensation of unstable hydrogen

peroxide, whose rapid decomposition on the windows leads to a change in drop

size and hence of the scattering of light. This is in agreement with the

observation that much of the hydrogen peroxide chilled out (to -80°C or below)

from hydrogen-oxygen explosions decomposes in less than a second, while no peroxide at all can be isolated if the reaction vessel is at room temperature

(Everett)

.
- 99 -

Absorption by other species . No evidence was found to suggest that more than 0 . 03 $ of ozone was formed during the main part of the explosion process.

It is just possible that mercury vapour was responsible, since some mercury

lines appeared in emission in experiments carried out later; however, this is

not considered probable. No definite conclusion about the role of ozone in

explosions of carbon monoxide or of methane can be drawn, since it could be

argued that its stationary concentration remains very low. Had ozone been

detected, it might even have been an indication that it was an end product

rather than an active intermediate. Nevertheless, although a low stationary

concentration of intermediate is expected in a show reaction or below an explosion limit, the instantaneous concentration might have been expected to

increase during a branched chain explosion. This suggestion again is not

conclusive, since it cannot be made quantitative at this stage. However, if

the small additional absorption at 255O A observed after the main absorption

(fig. 4) can be proved to be due to ozone, formed by the recombination of

free oxygen atoms with each other or with oxygen molecules on cooling, then

the evidence presented in this communication may be taken to suggest that ozone does not play a major part in the explosive oxidation of carbon monoxide.

The role of formic acid in the explosion of methane will not be discussed

at this stage. It has been detected previously in the products of chilled

methane explosions (Everett and Minkoff). Lack of reproducibility of the

absorption of this compound is somewhat similar to the difficulties encountered

in attempts to identify methyl peroxide in the products of methane explosions

in vessels cooled to -180°C. It has not yet been possible to identify the

factors which determine whether or not a peroxide shall be found, under

apparently standard conditions. Although it is possible that the formic acid

is due to a reaction of ozone with formaldehyde, it is strange that the

absorption corresponds to a time of only a few milliseconds.

Finally, the potentialities of the method will be discussed. It has

clearly been shown that events lasting 6-10 milliseconds can easily be

followed and recorded, and that times of the order of 2$ of this, i.e 10

_z+ msecs., can be resolved. There is no reason to suppose that much shorter

times could not be followed, since the writing speed depends on the brightness

of the oscilloscope spot, and this was not used to its full extent. The

absence of timing marks Is not a good feature, but this could be easily

remedied in future work.

The shape of the reaction vessel used, i.e. a tube viewed axially with

one flame front travelling toward the spectrometer while the other flame

front travelled away from it, is not suitable for general studies. Wall

effects, including loss of heat, must have been considerable, although the

high extents of reaction (90-95$ in explosions of hydrogen and of methane,

and 80-90$ in those of carbon monoxide) suggest that quenching was not of

great importance. Nevertheless, it is clear that less equivocal information

would be obtained if the explosions were in a spherical vessel. The effects
100 -

of the walls could then be assessed by using cylindrical tubes of varying

diameters. The reason for using a cylindrical vessel in the present work

is that the studies of the formation of hydrogen peroxide in chilled explosions (Everett and Minkoff, 19^+8; Everett, 1953) showed that yields were extremely sensitive to changes of shape or of vessel size. The vessel

selected was therefore similar to those in which most of the previous work

had been done.

A general criticism of the method of viewing through a flame is that

only an average description is obtained of the various sections. The present

technique, however, can be used to distinguish whether a certain absorbing

species exists mainly in the flame front or in the hot gases left behind.

The concentration of species in the flame front would rise very quickly, as soon as the flame front is established, to a value which remains approximately constant. When the flame is extinguished on reaching the end of the

tube, the concentration would fall sharply to zero. If, on the other hand,

the species were related to the hot gases, then its concentration would rise

less rapidly, in a time of the order of magnitude of that of flame travel, and

then decay, probably exponentially, at a rate controlled by the cooling of the

gases. It is clear from the curves in Fig. 6(a) and (c), that the absorption

ODserved in the explosions of hydrogen and of methane are of this latter type.

The absorption of carbon monoxide explosions, Fig. 6(a) at first sight seems

to indicate aosorption connected with the flame front. This is not correct,

since the rate of decay is still exponential. The approximately flat portion

of the absorption trace is probably due to the much slower rate of movement

of the flame (Everett and Minkoff, 1953) » with the consequent absence of re- heating effects in the bulk of the gas.

In conclusion, the method has the great advantage of attempting to relate

quantitatively studies of absorption to such factors as pressure, composition,

etc. The most useful results would be obtained if extremely short exposures

of the whole absorption spectrum could also be recorded photographically, in

order to reveal the existence of any unexpected band systems.

One of us (H. P. B.) is grateful for the award of a John Simon

Guggenheim Memorial Fellowship.
- 101

REFERENCES

Bullock and Silverman, S., 1953* JOSA

Egerton, A. and Minkoff, G. J,, 19^2.

Egerton, A., Everett and Minkoff, 1953.

Everett, and Minkoff, G. J,, 19*^8.

Everett and Minkoff, G. J,, 19^9.

Everett, 1953.

Fabry, 1950.

Norrish, and Porter, 1952, Proc. Roy, Soc,

Norrish, and Porter and Thrush, 1953, Nature

Oldenberg, 0, and Broida, H. P. , 1950, JOSA 40, 381,

Urey, Dawsey, and Rice, 1929.
102 -

8, USE OS’ A VACUUM SPECTROGRAPH FOR COMBUSTION STUNT

W. R. S. Garton, Department of Astrophysics,

Imperial College, London

and

H. P, Broida,* National Bureau of Standards

Washington, D. C,

Since many hydrocarbon molecules have characteristic absorption spectra

and large absorption coefficients in the far ultra-violet, it might be possible

to investigate some reactions by following the concentration of one or several

species during combustion. Small concentrations of oxygen completely absorb

radiation below 1760 A and therefore it is necessary to use a vacuum spectrograph to obtain the shorter wavelengths, and in addition only those reactions

not involving molecular oxygen can be studied.

We have made some preliminary studies of flat diffusion flames of the

type investigated by Wolfhard and Parker (1952). It was hoped that changes

in the absorption spectra would be found by measuring the absorption from the

fuel side to the oxygen side of the flame, and from such changes to learn

something about the combustion process. These initial attempts have shown

that, while the far ultra-violet might be profitably applied to combustion,

much background study of hot gases will have to be completed before many

definite conclusions can be made.

A rectangular burner 14mm by 251am, with the inlet supply of gaseous

fuel separated by a thin metal barrier from the oxygen, was completely

surrounded by a stream of oxygen-free nitrogen and enclosed by a metal housing 30mm by 42mm with two lithium fluoride windows (transmitting to below

1200 A). One window was sealed over the slit of a vacuum one meter normal

incidence grating spectrograph, and the other to a large

Lyman hydrogen discharge tube. A one mm slit was used on the Lyman tube

to limit the aperture of the light beam going to the spectrograph slit.

The slits were parallel to the direction of the gas flow and to the flame.

Exposure times of 4 minutes were sufficient for the entire spectral region

from 1200 to 2550 4. The burner was mounted on a rack and pinion, moving

transversely across the light beam so that different portions of the flame

could be observed.
- 103 -

Flames with three different fuels were observed - town gas, ethylene and

hydrogen; all were burned with oxygen. In each case there was a continuous

absorption that extended as far as 1925 A; even as far as 9mm on the ethylene

side of the flame there was continuous absorption below I85O A which was not

caused by oxygen since Schumann-Punge system was not observed. On the oxygen

side of the flame this oxygen system was clearly evident. Near the flame

front the absorption extended to longer wavelengths than at either side. On

the fuel side of the flame with both town gas and ethylene, an absorption

consisting of fine structure extended from the continuous absorption to 2200 A,

the amount of absorption decreasing toward the center of the flame. In one plate taken with a flame of town gas and oxygen, the absorption bands of NO

between 2000 and 2200 A were detected. In the hydrogen flame a very weak group

of 6 absorption bands were found between 19^0 and 2200 A, but these were not

identified.

A careful check was made to determine the cause of the continuous absorption and to make certain that it was not due to some impurity in one of the

gases. For example, spectra observed of hydrogen and the surrounding nitrogen

showed that these gases did not absorb appreciably to the cut-off limit of

the windows. Oxygen showed the Schumann-Punge system and the continuous

absorption below 1760. The most probable cause of the observed continuous

absorption during the burning is absorption by water vapour. Water at room temperature is known to absorb below 1830 A and it is quite possible that

hot water would absorb to longer wavelengths.

We were surprised not to see any evidence of the "pyrolysis” continuum

such as that observed by Wolfhard and Parker-^-.in their experiments with

hydrocarbon flames. It is possible that our failure to detect this absorption is due to the Schlieren effect of the hot gas on the unfocused light

beam. However it might be well to emphasize the difficulty of measuring

continuous absorption near the short wavelength limit of a quartz spectrograph, which might cause the appearance of a stronger continuum than actually

exists

.

^Wolfhard and Parker, Proc. Phys. Soc., A 5 , 2(1952).
- 104 -

9. Development Work on the Noise Thermometer*

E. W. Hogue

The general objective of the project has been to design and construct a thermometer which will determine the ratio of two absolute temperatures by a method based on the noise thermometer of J. B. Garrison and A. W. Lawson

at the Institure for the Study of Metals, University of Chicago^; and to use

the thermometer to provide independent values accurate to three places for

temperatures in the region 1000°K to 1500°K for comparison with results

obtained by other methods.

The noise thermometer is a null device for determining the ratio of two

absolute temperatures by balancing the average values of the thermally

generated voltage fluctuation, obtained after amplification, from two resistor

elements maintained at the temperatures in question. (See fig. 9*1). In the

use of this device, the value of one resistor is adjusted until a null is

reached, indicating that the average value of the noise produced by it equals

that from the other resistor. Then if the electrical time-constants R^C-j_

and R2C2 of the two resistors and their total respective associated shunt

capacitances are made equal, the ratio of their temperatures is given by the

inverse ratio of their DC resistances.

The block diagram in figure 9*1 shows the principal components of the

noise thermometer. From the input (synchronous switch 1) to amplifier #4,

it is basically the same as the original noise thermometer of this type

built bjr Garrison & Lawson^, but the remainder was devised at MBS in an effort

to improve noise balance sensitivity by increasing both gain and averaging

time. Electronic circuits are used to balance the average value of the noise

fluctuation and to equalize the time constants of the resistor elements for

the condition of noise balance. These operations involve the amplification

of noise outputs from the resistors, the averaging of the separately amplified

noise voltages over a time interval of l/5 second; the subtraction of one average from the other; the averaging of the difference over a period of

approximately 8 minutes; and the exhibition of this average difference on a meter or strip chart recorder. The principal balance is obtained using an amplification band of from 10KC to 60KG, (amplifiers 1, 2, & 3); and the

equalization of time constants is carried out using a high-frequency, small

relative bandwidth amplifier 20KC wide at 450KC (amplifier #6 ). The first

three sections of the wide-band, low-frequency part of the thermometer

serve to amplify the noise from each resistor element in succession by being

rapidly switched (approximately 67 times per second by means of an electrically

driven vib rating-reed switch) between the two elements. This amplification

*This work was supported in part by ONR and the Office of Basic Instrumentation
- 105 -

raises the noise from approximately 2 microvolts rms to 20 volts average

fluctuation amplitude. Half-wave rectification is then carried out by a linear diode detector, and is the first step necessary in the averaging

process, producing a DC component proportional to the average amplitude of

the noise level from each resistor. A second vibrating switch, operating

in synchronism with the first, deposits charge through a common resistor R

in each of two capacitors C &and C^, so that the voltages maintained as the

capacitors are proportional to the average amplitudes of the noise voltages

from the two resistor elements. The large time constant (1/5 second) of

the charging resistor and each capacitor effectively filters out most of

the high frequency components, leaving slowly fluctuating voltages indicating

the average noise levels averaged over roughly 1/5 second. The difference

between the voltages on the capacitors is the unbalance signal, and will

average to zero over an infinite time for perfect balance. The precision

with which the noise balance can be made depends upon the length of time

over which this unbalance signal is averaged between adjustments of the

resistor element toward balance. The 1/5 second time constant gives

insufficient averaging time for the desired precision of 0 , 1% or better in

temperature measurement. Also, calculations show that the d.c. component

of V

g - for an unbalance equivalent to 0.1% in temperature is of the

order of only a few millivolts. To provide extra gain, and a longer

averaging time, a 67 cycle per second square-wave carrier having the

unbalance signal V

& - for its envelope is generated by switching the

high impedance input of amplifier #4 between C a and by means of synchronous switch #3. This amplifier raises the amplitude of the square-wave

carrier by a factor of 30 or so, after which its envelope is recovered by

a full-wave synchronous detector of the type shown in fig. 9«2, and is fed

to a feed-back type integrating circuit such as is used in analogue com- puters, (see fig. 9.3). As far as its effect on the signal is concerned,

this integrator behaves like a low-pass RC-filter having a time constant

of 8 minutes, followed by a d. c. amplifier leaving a gain of 650.

Because of a factor of two loss in the modulation-demodulation process,

the total gain added after the diode detector is approximately 10,000.

As a result, the unbalance signal corresponding to a 0 , 1% temperature

measurement error appears at the output of the integrator in about 8

minutes as a steady voltage of approximately 25 volts. Superimposed on

it is the random fluctuation remaining after passage of the initial 10

volt, 10 KC to 60 KC noise at the diode detector through the low-pass

filter RC a and RC^ and finally the very narrow low-pass "integrator".

The fulctuation amplitude reduction resulting from the bandwidth reduction

which follows the diode approximately equals the total gain following the

diode so that the random component at the integrator output about equals

that at the diode about 10 volts average amplitude.

Calculations, checked by experiment, indicate that for this noise

thermometer to achieve a temperature measurement precision of 0.1:1, a difference in the average value of the noise at the detector of one part

in 4000 must be detectable. The DC component at the detector is approximately 10 volts; therefore, at the integrator output a steady voltage of

10 x 1/4000 x 10,000 = 25 volts must be distinguishable in the presence

of 10 volt (average amplitude) fluctuations.
- 106 »

In operation, the integrator output is continuously recorded on a chart

to provide a record of the signal behavior during the averaging period. After

each average, the integrator is readjusted to zero (the center of the chart).

Several kinds of sensitivity measurements were made to determine what temperature measurement precision might be expected. The restiTts showed that the

circuit, exclusive of the first synchronous switch is capable of resolving

noise average-amplitude differences of the order of a part in four thousand.

This corresponds to a temperature measurement precision of 0.1% when the

amplifier noise equals that of the input resistor elements. The time required

to resolve such a small difference is 6 to 10 minutes. With the input synchronous switch in operation, it was impossible to achieve stability sufficient

for precision better than 0.3% to 0.5%. Experience with the electrically driven

synchronous switch system points to the necessity for mechanically driven

switches of special design.

The most serious fundamental limitation of this type of noise thermometer

for precise temperature measurements, is the requirement that the amplification

characteristic (gain, noise, and bandwidth) of the input stages be independent

of the source impedance presented to it. For example, if the reference resistor

is maintained at 0°C and the other resistor is used as a thermometer element to

measure temperatures near 1000°C, the impedance presented to the input stage

changes by a factor of 4. The gain and noise level of this stage must, however,

remain constant to better than one part in four thousand for measurement of

temperature to 0.1%. Because of the improbability that this final requirement

can be fulfilled, the method of noise thermometry just described has been

abandoned as a possible high-temperature absolute standard. If the comparison

resistor R-j_, which is maintained at the reference temperature, could be replaced

by a noise generator having an internal impedance identical with that of the

thermometer element this requirement would be eliminated. The result, would

then not be a self-calibrating absolute thermometer as was the case when a resistor was used as the noise source because the noise from the generator

would not be produced directly by thermal agitation. If, however, the meansquared value of the noise from the generator were a unique, simple, and

accurately known function of some easily and accurately measurable parameter

of the generator; and if the amplitude vs. frequency spectrum, and statistical

distribution of maxima of the generator noise were identical with that of

thermal noise, a calibration curve of the generator could be made. Une might

ask what would be the advantage of such a method over the resistance thermometer or thermocouple since a calibration curve is required for all three. The

answer lies in the nature of the function relating the measurable generator

parameter to the Kelvin temperature on the one hand, as compared with the

functions relating resistance and thermoelectric e.m.f. to Kelvin temperature

on the other, if the generator noise has the same characteristics as thermal

noise, then under conditions of noise thermometer balance, the mean-squared

generator noise will be an exact linear function of the Kelvin temperature of

the thermometer element; therefore, the form of the relationship between

Kelvin temperature and generator parameter will be exactly that of the function

relating mean-squared generator noise with generator parameter. It is felt

that it might be possible to build a generator which duplicates thermal noise
- 107

sufficiently well and for which this function can be specified exactly for

all values of generator noise by two or three calibration points; and therefore the relationship between generator measurable parameter and thermometer

element Kelvin temperature could be expressed as a simple function completely

determined for all temperatures by two or three calibration points. Because

the curve is specified exactly, absolute temperatures well outside the range

of calibration could be determined with certainty. This cannot be said for

the resistance thermometer and the thermocouple. The curves for these

devices are entirely empirical, dependent as they are on the physical properties

of matter, so that the uncertainty of a measurement increases rapidly outside

the range of calibration.

REFERENCES

1. "An Absolute Noise Thermometer for High Temperatures and High Pressures",

J. B. Garrison and A. W. Lawson, Rev. Sci. Instr. Vol. 20, No. 11, 765-794,

November, 1949.
- 108 -

Fig. 9.1

Noise Thermometer basic diagram.

Fig. 9.2

A synchronous detector.

Fig. 9.3

Miller integrator.
I

I

307304 0 - 54-8

Figure

9.1
MM

—

O

<ft>

Figure 9.2 - 9.3
Ill -

10 . The Pyrometry Laboratory

John P. Evans

A. Since September, 1951, research and development work in the pyrometry

laboratory has been centered around the projects listed below. These

projects, except for the development of a new base-metal thermocuple which

was sponsored by the U. S. Naval Engineering Experiment Station, were

unsponsored.

1. Tantalum Tube Furnace : A furnace for general laboratory use consisting of a resistively heated tantalum tube insulated by tantalum

and nichrome foil has been constructed. Provisions are made to operate

the furnace in a vacuum or in an inert atmosphere. During initial runs to

1700°C, oil from the diffusion pump condensed on the water cooled walls of

the furnace so that it was necessary to introduce a refrigerated baffle in

the system between the pump and the furnace. The furnace will be used to

determine the temperature-emf relations for high temperature thermocouple

materials. It is so designed that temperatures may be measured with an optical pyrometer. The furnace is designed to attain temperatures of

about 2500 'C.

2. Copper Black Comparator Furnace : A furnace, consisting of an electrically heated copper block containing a number of wells, has been constructed

for the intercomparison of platinum resistance thermometers and platinum versus platinum-rhodium thermocouples. The furnace is designed to operate in a vacuum

or with an inert atmosphere. .Longitudinal thermal gradients are minimized by

heated end blocks and temperature differences between the various wells are not more -than 0.01°C. The furnace has been operated to the freezing point of

antimony (630.5°C) and has proven satisfactory for the primary calibration of

themocouples.

3. Black-body Radiation Source : The black-body radiator, consisting of an inductively heated graphite tu be insulated by lamp black, has been used to

determine the response of a photoelectric recording monochromator up to 2300°C.

A neutral atmosphere of argon was found to give the best results. An adapter

is being constructed to permit the calibration of total radiation pyrometers

up to a temperature of 2300°C. Incorporated in the adapter is a gas tight

chamber so that the effect of various types of atmospheres interposed in the

oath of radiation may be studied easily. Temperatures will be determined

with an optical pyrometer.

A. Modified 1913 Reference Tables for Iron-Constantan Thermocouples :

An investigation was made of the characteristics of iron-constantan

thermocouples typical of those being supplied to reproduce the standard temperature-emf relationship that was established commercially in 1913. Using the

calibration of the thermocouple that most nearly matched the 1913 reference

table over the range to which iron-constantan thermocouples usually are limited,

a slightly different temperature-emf relationship was derived which is more

nearly realizable by commercially available materials. [R. J. Rorruccini and

H. Shenker, J. Res. N.B.S. 50, 229 (1953)].
112 -

5. Development of a New Base-Metal Thermocouple ; Alumel wire, in

chromel-alumel thermocouples, has failed in applications in which it was

exposed to atmospheres containing sulfur or in which it was subjected to severe vibrations at high temperatures. Such failure has been ascribed to

intergranular corrosion. A material to replace the alumel wire of chromelalumel thermocouples was sought. It was found that a pencil-type chromelalumel thermocouple is suitable for use in atmospheres containing sulfur up

to 2000°F provided a silver shield is not used. A 310 stainless steel versus alloy 242 thermocouple is suitable for applications where severe vibrations

or atmospheres containing sulfur are encountered.

6. Annealing of Platinum for Thermometry : Experiments were performed

on the annealing of platinum wire in which the coefficient of resistance and

thermal emf were used as criteria of the physical state of the metal. It was found that the platinum wire of the highest purity almost completely

recovers its electrical properties at a temperature as low as 300°G, although

a slight further recovery occurs with increase of annealing temperature up

to 1A50°C. On quenching heated wires in various gaseous media, changes in

the electrical properties occur that are greater the more rapid the quenching

and that are similar to the effect of strain. The electrical properties of

dilute alloys of gold, silver, and copper in platinum were measured. Contrary

to prediction, the copper and silver alloys were thermoelectrically positive

to platinum at ordinary temperatures. Thus far, no impurity other than gold

has been found to lower the thermoelectric power of platinum. [R. J. Corruccini,

J. Res. N.B.S. 47, 94 (1951)].

B. Under consideration for future investigation are the following items. Only

preliminary work has been done and these items are listed to show the fields

in which interest lies.

1. High Temperature Thermocouples : The tantalum tube furnace described

above (A-l) will furnish a means for calibrating very high temperature thermocouple materials, such as iridium vs. iridium-rhodium. The temperature-emf

relationship for tungsten vs. tantalum and tungsten vs. molybdenum will be

investigated first, and these materials will then possibly be used as intermediaries in the calibration of the iridium vs. iridium-rhodium.

2. Photoelectric Pyrometer: A means of replacing visual observation

by photoelectric detection in the disappearing filament type optical pyrometer

has been studied and appears feasible. The field of view would be scanned by

a vibrating mirror and the image projected on a photomultiplier tube. The output signal of the tube would be used to detect a mismatch in brightness between

the standard pyrometer lamp and the target area. The detector unit would be

designed as an attachment to the laboratory standard optical pyrometer and

little modification in the present instrument would be required.
113 -

11 . Thermal Conductivities at High Temperatures

D. C. Ginnings and R. L. Nuttall

The thermal conductivity program consists of two parts, (1), the

measurements on gases up to 500°C and 100 atmospheres pressure and (2), the

measurements on liquids and solids up to 1000°C and one atmosphere pressure.

1. Gases; It was the purpose in these measurements to obtain as high an accuracy as possible at these high temperatures and pressures. The method

used longitudinal heat flow downward from a "hot plate” through a thin

(0.5mm) gas space to a "cold plate”. A "guard ring” was used to protect

the hot plate from heat flow other than to the cold plate. The heat transfer by radiation is accounted for by a

,rblank” experiment with the apparatus

evacuated. The use of bright silver surfaces throughout minimizes radiation

heat transfer. The apparatus used for these measurements has several advantages in precision work over other apparatus used in this field. First,

using linear heat flow downward avoids the possibility of convection errors which may exist in radial heat flow. Second, the use of platinum resistance

thermometers gives a temperature scale which is independent of the thermoelectric power of any thermocouples. Third, no spacer is used between the

hot plate and the cold plate, the spacing between the two plates being

determined in place by an absolute capacitance method.

The apparatus has been completed after many difficulties of which

probably the most troublesome has been contamination of the platinum resistance

thermometers in the blank experiments (evacuated) near 500°C. In spite of the

difficulties, satisfactory conductivity measurements have been completed on pure nitrogen gas up to 500°C and 100 atmospheres pressure. These measurements

are now being written up for publication. This program was supported initially

by the National Advisory Committee for Aeronautics and later by the National

Bureau of Standards.

2. Liquids and Solids : This program, sponsored by the Wright Air Development

Center, was intended originally for measurements on liquids at high temperatures

but because the apparatus was also suitable for measurements on solids, measurements have been made on two solids. The program can be divided into two parts,

(a) the measurements on liquids and solids having relatively high thermal con- ductivities . and (b), the measurements on liquids having moderately low thermal

conductivities.
- 114 -

a. Apparatus for high-conductivity liquids and solids .

This apparatus uses longitudinal heat flow downward through either a solid rod or a tube containing liquid. Heat is introduced electrically at

the top of the sample and the resulting temperature gradient in the sample

is measured by platinum vs. platinum-rhodium thermocouples. Radial heat

loss from the sample is minimized by (1) providing a "guard” surrounding

the sample with the same temperature gradient as the sample, and { 2 ),

providing as good insulation as possible between the sample and the guard.

If a liquid sample is to be used, it is contained in a tube and a

,rblank”

experiment must be made with no liquid in the tube to account for heat

flow down the tube. This apparatus has been used on two solids, namely

on molybdenum and molybdenum disilicide, the latter up to 800°C.

b. Apparatus for low thermal conductivity liquids

For these measurements, a radial heat flow apparatus is now under

construction. The heat will flow through a thin layer (,1/16"J of the

liquid which is contained between two coaxial silver cylinders. Calculations indicate that convection in this thin layer should be negligible.

Temperatures will be measured by platinum vs. platinum-rhodium thermocouples.

The upper temperature limit of this apparatus will be 9b(J°C.
- 115 -

12. Heat Capacities at High Temperatures

T. B. Douglas and E. D. West

1 . Method

The NBS program for the measurement of heat capacities at high

temperatures (up to 900°C, the limit of the present apparatus,) emphasizes

the highest accuracy compatible with the purity of the materials

measured. Using apparatus which was developed at this Bureau and which

is generally regarded as the most accurate of its type, the ’’drop” method

has been used here continuously for the past nine years.

These measurements of heat capacity have served several different

purposes. The results on aluminum oxide (synthetic sapphire) and n-heptane,

two of the materials recommended by the U. S. Calorimetry Conference as standards of heat capacity in the high-temperature range, will be described

in detail in publications to appear in the near future in Journal Research

NBS. In addition, accurate measurements have been made on a number of

materials that are useful as heat-transfer media at high temperatures (such

as liquid salt mixtures and liquid alloys), and on certain solids useful

because of their resistance to corrosion at high temperatures (such as molybdenum disilicide and several transition-metal alloys). Many of these results

have been used also to evaluate critically and correlate the thermodynamic

properties of these substances.

A previous report (NBS Report No. 1123, "Technical Report on High

Temperature Thermodynamics") describes some of the work done up to the date

of its publication, 1951. The publications listed below cover most of the

unclassified work done since. In addition, abstracts of a few examples are included.

2. Adiabatic Method

The apparatus at NBS for high temperature "drop" calorimetry is being

augmented by an adiabatic calorimeter designed to measure heat capacity and

heats of transition in the range 30 to 600°G with an accuracy of a few tenths

of a per cent. This calorimeter will be used for materials which do not easilj'

reach reproducible states at the ice point and are therefore difficult or Impossible to investigate with the drop calorimeter. It offers the advantage

that measurements can be made over small temperature intervals, permitting a more detailed determination of heats of transition and rapidly changing heat

capacities. The first work will be done on sulfur, which assumes various

solid states at 0°G, depending on the temperature of the liquid before

quenching.
- 116 -

The calorimeter consists of an inner sampleTbontainer of suitable material

screwed to a heavy silver ring which also supports three thin silver shields.

The shields reduce radiative heat transfer and attenuate temperature gradients

on the container so that the outer shield presents the same surface temperature

distribution to the surroundings whether the container is full or empty.

Heaters and thermocouples are attached to the silver ring. The absolute temperature is measured with a platinum resistance thermometer placed in the center

of the calorimeter.

The calorimeter is surrounded by a jacket consisting of a similar system

of four thin silver shields attached to a heavy silver ring whose temperature

is matched to that of the silver ring in the calorimeter by means of a ten

junction thermopile. The heat accounting method will depend not on eliminating

all significant temperature gradients but on matching in empty or "blank”

experiments the small gradients produced in the experiments with the container

filled. Since heat transfer in the experimental range is largely by radiation,

the apparatus will not be evacuated but will be operated in an argon atmosphere.

The bulk of the heat lost to the room will be supplied by ni chrome

heaters fixed in a closed aluminum cylinder surrounded by insulation.

The major parts of the apparatus have been built in the shop and

assembly has been started. Auxiliary equipment for measuring electric power,

time, and temperature and for evacuating the container has been set up. It

is estimated that assembly of the apparatus will be completed and measurements

made on sulfur in 1954.
- 117 -

Recent Publications

Heat capacity standards for the range 14 to 1200°K (D.C. Ginnings and G. T.

Furukawa) , Jour. Amer. Chem. Soc. 75, 522, 6359 (1953).

'““^Calorimetric determination of the half-life of polonium (D. C. Ginnings,

A. F. Ball, and D. T. Vier^), J. Research NBS j>0, 75 (1953).

“““‘Heat capacity of potassium and three potassium-sodium alloys between 0°

and 800°, the triple point and heat of fusion of potassium (T. B. Douglas,

A. F. Ball, D. C. Ginnings, and W. D. Davis^), Jour. Amer. Chem. Soc. 74,

2472 (1952).

'“The heat capacity of lithium fluoride from 0° to 900° C (T. B. Douglas and

J. L. Dever) , Wright Air Development Center Technical Report 53-201, Part 1

(1953).

-“““-A cryoscopic study of the solubility of uranium in liquid sodium at 97.8°C

(T. B. Douglas), AEC Document 3254 (1951); J. Research NBS (1954).

'“The heat capacity of anhydrous sodium hydroxide from 0° to 700°C (T. 3.

Douglas and J. L. Dever), Wright Air Development Center Technical Report

53-201, Part 2 (1953).

-

;;'The heat capacity of molybdenum disilicide from 0° to 900°C (T. B. Douglas

and W. M. Logan), Wright Air Development Center Technical Report 53-201,

Part 3 (1953).

Heat capacity of four alloys: Nichroine 7 and Stainless Steels types 347 and

446, 0° to 900° C; Monel, 0° to 300° C (T. B. Douglas and J 4 L. Dever), NBS

Report 2302 (1953).

“_x'Heat capacity of the eutectic mixture of lithium chloride and potassium

chloride from the eutectic temperature to 800°C (T. B. Douglas and J. L. Dever),

NBS Report 2303 (1953).

“““The heat capacity of lead from 0° to 900°, and the heat of fusion; the heat

capacity of the lead-bismuth eutectic alloy from 150° to 800°C (T. B. Douglas

and J. L. Dever), NBS Report 2544 (1953).

-“"*The heat capacity of lithium from 25° to 900°C; the heat of fusion and the

triple point; thermodynamic properties of the solid and liquid (T. B. Douglas,

L. F. Epstein^, J. L. Dever, and W. H. Howland^), NBS Report 2879 (1953).

“Sponsored by the U. S. Air Force, Wright Air Development Center.

““-Sponsored by the U. S. Atomic Energy Commission.

-4jOs Alamos Scientific Laboratory, University of California, Los Alamos, N. M.

2Knolls Atomic Power Laboratory, General Electric Co., Schenectady, N. Y.
118 -

Calorimetric Properties of Normal Heptane from 0° to 520°K .

T.3. Douglas, G.T. Furukawa, R.E. McCoskey, and A.F. Ball

Precise measurements of the heat capacity of solid and liquid n-heptane

from 20° to 523°K are described. An adiabatic calorimeter, with which was determined also the triple point and heat of fusion, was used from 20° to

370°K, whereas a drop method was used with a Bunsen ice calorimeter from

273° to 523°K. These two series of heat-capacity measurements and three

other series of independent values show a maximum difference of approximately

0.25 percent in the range 50° to 370°K. Besides the heat capacity, the

enthalpy, entropy, and Gibbs free energy of the solid and liquid at saturation

pressures from 0° to 520°K are derived and tabulated. The same properties of

the ideal gas from 298° to 470°K also are derived by making use of published

precise measurements of gaseous heat capacity, heat of vaporization, and the

normal boiling point. Interconsistency of the values of the various thermal

properties is shown by the fact that the vapor pressures calculated from these

values agree with those precisely measured by other investigators between 299°

and 372°K to within ± 0.1 percent.

The Heat Capacity of Sodium Hydroxide from 0° to 700°C

(Sponsored by the U. S. Air Force, Wright Air Development Center)

T. B. Douglas and J. L. Dever

Samples of sodium hydroxide, whose purity as indicated by analyses was approximately 99»3 percent, were sealed in pure silver. Cryoscopic measurements indicated a transition temperature of 293°0. Using a drop method and a Bunsen ice calorimeter, the enthalpy change between 0° and ea.ch of eleven

temperatures up to 700°C was measured. With reasonable simplifying assumptions, the thermal measurements near the freezing point were used to correct

for the impurity, giving values for the melting point and heats of transition

and fusion of the pure compound. The heat capacity derived for the liquid

is estimated to be correct within ± 2 percent. Values of heat capacity,

entropy, relative enthalpy, and relative free energy are tabulated at

regular intervals from 298° to 1000°K.
- 119 -

The Heat Capacity of Sodium Hydroxide from 0° to 700°C

(Sponsored by the U.S. Air Force, Wright Air Development Center)

T.B. Douglas and J. L. Dever

Samples of sodium hydroxide, whose purity as indicated by analyses was approximately 99.3 percent, were sealed in pure silver. Cryoscopic measurements indicated a transition temperature of 293°C. Using a drop method and a Bunsen ice calorimeter, the enthalpy change between 0° and each of eleven

temperatures up to 700° C was measured. With reasonable simplifying assumptions, the thermal measurements near the freezing point we re used to correct

for the impurity, giving values for the melting point and heats of transition

and fusion of the pure compound. The heat capacity derived for the liquid

is estimated to be correct within ± 2 percent. Values of heat capacity,

entropy, relative enthalpy, and relative free energy are tabulated at

regular intervals from 298° to 1000°K.

Thermodynamics of the Liquid System Sodium-Potassium from 0° to 800°C

T. B. Douglas

The available published data on the solid-liquid and liquid-vapor phase

equilibria are combined with heat-capacity data determined recently at the

National Bureau of Standards. From these are derived equations of moderate

accuracy for the free energy, heat content, and entropy of liquid sodiumpotassium solutions, relative to the pure liquid elements, at one atmosphere

pressure and over the temperature range 0° to 800°C. Numerical uncertainties

are estimated and assigned to the results. These properties can all be

derived simply from the equation

F - Fideal = 1201-18200/T - 0.692T)

- (1282 - 1.192T) N

k

+ (1183

- 1.102T) N

k

2

]

N

k ; which gives the free energy at T°K (in calories per gram-atom of solution) in excess of that of a hypothetical ideal solution of the same composition

(atomic fractions N

^ and N ) . The free-energy deviations from ideality, xWiich are positive throughout this temperature range, are fairly large near 0°C.

The calorimetrically measured values of one recent investigation elsewhere

agree closely with the calculated heats of solution.
- 120 -

Heat Capacity of Lithium from 25° to 900°C.

The Triple Point and Heat of Fusion . Thermodynamic Properties of the Solid and Liquid , (Sponsored by the U. S. Atomic Energy Commission)

T.B, Douglas, L.F. Epstein, J.L. Dever, and W.H. Howland

Lithium was distilled at 650°-70Q°C in vacuum and sealed in stainless

steel type 347. From chemical analysis the purity of the first sample was

99.98 atomic °/o and that of the second sample, obtained with the still in

vacuum, was approximately 99.99 atomic /o . The melting curves, which are consistent with these analyses, gave a triple point of 180.54°C. Using a Bunsen ice calorimeter and a drop method, the relative enthalpy was measured

from 0 to 900°, yielding values of the heat capacity of the liquid estimated

to be accurate to ± 0.3 percent. The observations were combined with adjusted

published low-temperature heat capacities and vapor pressures at high temperatures, with use of the Sackur-Tetrode equation, to determine the thermodynamic

properties of the solid and liquid from 298° to 1200°K. A value of 38800 cal.

per gram-atom was derived for the cohesive energy of the jnetal.

Thermodynamics of the Liquid System Sodium-Potassium from 0° to 800°C

T. B. Douglas

The available published data on the solid-liquid and liquid-vapor phase

equilibria are combined with heat-capacity data determined recently at the

National Bureau of Standards. From these are derived equations of moderate

accuracy for the free energy, heat content, and entropy of liquid sodiumpotassium solutions, relative to the pure liquid elements, at one atmosphere

pressure and over the temperature range 0° to 800°C. Numerical uncertainties

are estinated and assigned to the results. These properties can all be

derived simply from the equation.

F - Fideal = £(1201-18200/T - 0.692T)

(1282 - 1.192T) Nk + (1183

1.102T) Nk

2

J

N^ Nk, which gives the free energy at T°K (in calories per gram-atom of solution) in excess of that of a hypothetical ideal solution of the same composition

(atomic fractions N^ and Nk) . The free-energy deviations from ideality, which

are positive throughout this temperature range, are fairly large near 0°G. The

calorimetrically measured values of one recent investigation elsewhere agree

closely with the calculated heats of solution.

U. S. GOVERNMENT PRINTING OFFICE : O—1954


THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

c ummary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.