NBS SPECIAL PUBLICATION 260-1 01

NBS

PUBLICATIONS

U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards SRM 1970: Succinonitrile Triple

Point Standard — A Temperature

Reference Standard

Near 58.08 °C

QC

100

U57

260-101

1986

C- 2

100 Boiling Point of H2 0

- - 58.08 SCN Triple Point

39.30 Rb Triple Point 37.0 Body Temperature

29.772 Ga Melting Point
Tm he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The m Bureau's overall goal is to strengthen and advance the nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a

basis for the nation's physical measurement system, (2) scientific and technological services for industry and

government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is performed by the National Measurement Laboratory, the National Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials Science and Engineering

The National Measurement Laboratory

Provides the national system of physical and chemical measurement;

coordinates the system with measurement systems of other nations and

furnishes essential services leading to accurate and uniform physical and

^chemical measurement throughout the Nation's scientific community, in- dustry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Basic Standards2 Radiation Research Chemical Physics

Analytical Chemistry

The National Engineering Laboratory

Provides technology and technical services to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement

capabilities; provides engineering measurement traceability services; develops

test methods and proposes engineering standards and code changes; develops and proposes new engineering practices; and develops and improves mechanisms to transfer results of its research to the ultimate user. The

Laboratory consists of the following centers:

Applied Mathematics

Electronics and Electrical Engineering2 Manufacturing Engineering

Building Technology

Fire Research Chemical Engineering2

The Institute for Computer Sciences and Technology

Conducts research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and economy in Government

operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing

the Federal Information Processing Standards Program, developing Federal ADP standards guidelines, and managing Federal participation in ADP

voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and provides the technical foundation for computer-related policies of the Federal Government. The Institute consists of the following centers:

Programming Science and

Technology Computer Systems

Engineering

The Institute for Materials Science and Engineering

Conducts research and provides measurements, data, standards, reference

materials, quantitative understanding and other technical information funda- mental to the processing, structure, properties and performance of materials; addresses the scientific basis for new advanced materials technologies; plans

research around cross-country scientific themes such as nondestructive

evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and nondestructive evaluation; and broadly disseminates generic technical information resulting from

its programs. The Institute consists of the following Divisions:

Ceramics

Fracture and Deformation 3 Polymers

Metallurgy Reactor Radiation

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Gaithersburg, MD 20899.

: Some divisions within the center are located at Boulder, CO 80303. 'Located at Boulder, CO, with some elements at Gaithersburg, MD.
NB3 RESEARCH INFORMATION CENTER Standard Reference Materials:

SRM 1970: Succinonitrile Triple-Point

Standard—A Temperature Reference

Standard Near 58.08 °C

B. W. Mangium

Temperature and Pressure Division Center for Basic Standards

National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899 Samir El-Sabban

National Institute of Standards

Cairo, Egypt

Sponsored by: Office of Standard Reference Materials National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

Issued March 1986

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
Library of Congress Catalog Card Number: 86-600505

National Bureau of Standards Special Publication 260-101

Natl. Bur. Stand. (U.S.), Spec. Publ. 260-101, 21, pages (Mar. 1986)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1986

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
Preface

Standard Reference Materials (SRM's) as defined by the National Bureau of Standards (NBS) are well-characterized materials, produced in quantity and certified for one or more physical or chemical properties. They are used to assure the accuracy and compatibility of measurements

throughout the Nation. SRM's are widely used as primary standards in many diverse fields in science, industry, and technology, both within the United States and throughout the world. They are also used extensively in the fields of environmental and clinical analysis. In many applications,

traceability of quality control and measurement processes to the national measurement system is carried out through the mechanism and use of SRM's. For many of the Nation's scientists and technologists it is therefore of more than passing interest to know the details of the measurements

made at NBS in arriving at the certified values of the SRM's produced. An NBS series of papers, of which this publication is a member, called the NBS Special Publication - 260 Series , is reserved for this purpose.

The 260 Series is dedicated to the dissemination of information on different phases of the preparation, measurement, certification and use of NBS SRM's. In general, much more detail will be found in these papers than is generally allowed, or desirable, in scientific journal articles. This enables the user to assess the validity and accuracy of the measurement processes employed, to judge

the statistical analysis, and to learn details of techniques and methods utilized for work entailing

the greatest care and accuracy. These papers also should provide sufficient additional information

not found on the certificate so that new applications in diverse fields not foreseen at the time the SRM was originally issued will be sought and found. Inquiries concerning the technical content of this paper should be directed to the author(s). Other questions concerned with the availability, delivery, price, and so forth, will receive prompt attention from: Office of Standard Reference Materials National Bureau of Standards Gaithersburg, MD 20899

Stanley D. Rasberry, Chief Office of Standard Reference Materials

iii
OTHER NBS PUBLICATIONS IN THIS SERIES

Catalog of NBS Standard Reference Materials

(1984-85 edition), Catherine H. Hudson, ed., NBS

Spec. Publ. 260 (February 1984). $5.50* SN003-

003-02558-5.

Michaelis, R. E., and Wyman, L. L. Standard

Reference Materials: Preparation of White Cast

Iron Spectrochemical Standards. NBS Misc. Publ. 260-1 (June 1964). COM74-1 1061**

Michaelis, R. E., Wyman, L. L., and Flitsch, R., Standard Reference Materials: Preparation of NBS Copper-Base Spectrochemical Standards. NBS Misc. Publ. 260-2 (October 1964). COM74-

1 1063**

Michaelis, R. E., Yakowitz, H., and Moore, G. A., Standard Reference Materials: Metallographic

Characterization of an NBS Spectrometric LowAlloy Steel Standard. NBS Misc. Publ. 260-3 (October 1964). COM74-1 1060** Hague, J. L. Mears, T. W., and Michaelis, R. E., Standard Reference Materials: Sources of

Information, NBS Misc. Publ. 260-4 (February

1965). COM74-11059

Alvarez, R., and Flitsch R., Standard Reference

Materials: Accuracy of Solution X-Ray Spectrometric Analysis of Copper-Base Alloys. NBS

Misc. Publ. 260-5 (March 1965). PB168068**

Shultz, J. I., Standard Reference Materials: Methods for the Chemical Analysis of White

Cast Iron Standards, NBS Misc. Publ. 260-6

(July 1965). COM74-11068**

Bell, R. K., Standard Reference Materials: Methods for the Chemical Analysis of NBS

Copper-Base Spectrochemical Standards. NBS

Misc. Publ. 260-7 (October 1965). COM74-

1 1067** Richmond, M.S., Standard Reference Materials: Analysis of Uranium Concentrates at the

National Bureau of Standards. NBS Misc. Publ. 260-8 (December 1965). COM74-1 1066** Anspach, S. C, Cavallo, L. M. Garfinkel, S. B. Hutchinson, J. M. R., and Smith, C. N., Standard Reference Materials: Half Lives of Materials Used in the Preparation of Standard Reference Materials of Nineteen Radioactive Nuclides

Issued by the National Bureau of Standards NBS Misc. Publ. 260-9 (November 1965). COM74-11065**

Yakowitz, H., Vieth, D. L., Heinrich, K. F. J., and

Michaelis, R. E., Standard Reference Materials: Homogeneity Characterization of NBS Spectrometric Standards II: Cartridge Brass and LowAlloy Steel, NBS Misc. Publ. 260-10 (December

(1965). COM74- 11064**

Napolitano, A., and Hawkins, E. G., Standard Reference Materials: Viscosity of Standard

Lead-Silica Glass, NBS Misc. Publ. 260-11 (November 1966). NBS Misc. Publ. 260-11** Yakowitz, H, Vieth, D. L., and Michaelis, R. E., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards III: White Cast Iron and Stainless Steel Powder Compact, NBS Misc. Publ. 260-12

(September 1966). NBS Misc. Publ. 260-12**

Spijkerman, J. L., Snediker, D. K., Ruegg, F. C,

and DeVoe, J. R., Standard Reference Materials: Mossbauer Spectroscopy Standard for the Chemical Shift of Iron Compounds, NBS Misc. Publ. 260-13 (July 1967). NBS Misc. Publ.

260-13**

Menis, O., and Sterling, J. T., Standard Reference

Materials: Determination of Oxygen in Ferrous

Materials - SRM 1090, 1091, and 1092, NBS

Misc. Publ. 260-14 (September 1966). NBS Misc.

Publ. 260-14**

Passaglia, E., and Shouse, P. J., Standard Refer- ence Materials: Recommended Method of Use

of Standard Light-Sensitive Paper for Calibrat- ing Carbon Arcs Used in Testing Textiles for Colorfastness to Light, NBS Misc. Publ. 260-15 (June 1967). (Replaced by NBS Spec. Publ.

260-41.) Yakowitz, H., Michaelis, R. E., and Vieth, D. L., Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards IV: Preparation and Microprobe Characterization of W-20% MO Alloy Fabricated by Powder Metallurgical' Methods, NBS Spec.

Publ. 260-16 (January 1969). COM74-1 1062** Catanzaro, E. J., Champion, C. E., Garner, E. L., Marinenko, G., Sappenfield, K. M., and Shields, W. R., Standard Reference Materials: Boric

Acid; Isotopic and Assay Standard Reference

Materials, NBS Spec. Publ. 260-17 (February

1970). Out of Print. Geller, S. B., Mantek, P.A., and Cleveland, N.

G., Standard Reference Materials: Calibration of NBS Secondary Standard Magnetic Tape (Computer Amplitude Reference) Using the Reference Tape Amplitude Measurement

"Process A," NBS Spec. Publ. 260-18 (November

1969). (See NBS Spec. Publ. 260-29.) Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measure- ments on the Vapor Pressure of Gold (Certifica- tion of Standard Reference Material 745). NBS

Spec. Publ. 260-19 (January 1970). PB190071**

Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measure- ments on the Vapor Pressures of Cadmium and

Silver, NBS Spec. Publ. 260-21 (January 1971). COM74-11359**

Yakowitz, H., Fiori, C. E., and Michaelis, R. E., Standard Reference Materials: Homogeneity

Characterization of Fe-3 Si Alloy, NBS Spec.

Publ. 260-22 (February 1971). COM74-1 1357**

Napolitano, A., and Hawkins, E. G., Standard

Reference Materials: Viscosity of a Standard

Borosilicate Glass, NBS Spec. Publ. 260-23 (December 1970). COM71-00157**

Sappenfield, K. M., Marineko, G., and Hague, J. L., Standard Reference Materials: Comparison

of Redox Standards, NBS Spec. Publ. 260-24 (January 1972). COM72-50058**

iv
Hicho, G. E., Yakowitz, H., Rasberry, S. D., and

Michaelis, R. E., Standard Reference Materials: A Standard Reference Material Containing

Nominally Four Percent Austenite, NBS Spec.

Publ. 260-25 (February 1971). COM74-1 1356** Martin, J. F., Standard Reference Materials:

National Bureau of Standards-US Steel Corporation Joint Program for Determining Oxygen and

Nitrogen in Steel, NBS Spec. Publ. 260-26

(February 1971). 85 cents* PB 81176620

Garner, E. L., Machlan, L. A., and Shields, W. R,

Standard Reference Materials: Uranium

Isotopic Standard Reference Materials, NBS

Spec. Publ. 260-27 (April 1971). COM74-

11358**

Heinrich, K. F. J., Myklebust, R. L., Rasberry, S. D., and Michaelis, R. E., Standard Reference Materials: Preparation and Evaluation of SRM's 481 and 482 Gold-Silver and GoldCopper Alloys for Microanalysis, NBS Spec. Publ. 260-28 (August 1971). COM71-50365**

Geller, S. B., Standard Reference Materials: Cali- bration of NBS Secondary Standard Magnetic Tape (Computer Amplitude Reference) Using

the Reference Tape Amplitude Measurement

"Process A-Model 2," NBS Spec. Publ. 260-29 (June 1971). COM7 1-50282 Gorozhanina, R. S., Freedman, A. Y., and

Shaievitch, A. B. (translated by M. C. Selby), Standard Reference Materials: Standard

Samples Issued in the USSR (A Translation from the Russian). NBS Spec. Publ. 260-30 (June

1971). COM71-50283**

Hust, J. G., and Sparks, L. L., Standard Reference

Materials: Thermal Conductivity of Electrolytic Iron SRM 734 from 4 to 300 K, NBS Spec. Publ. 260-31 (November 1971). COM7 1-50563** Mavrodineanu, R., and Lazar, J. W., Standard

Reference Materials: Standard Quartz Cuvettes, for High Accuracy Spectrophotometry, NBS

Spec. Publ. 260-32 (December 1973). 55 cents* SN0O3-OO3-01213-1 Wagner, H. L., Standard Reference Materials: Comparison of Original and Supplemental SRM 705, Narrow Molecular Weight Distri- bution Polystyrene, NBS Spec. Publ. 260-33 (May 1972). COM72-50526**

Sparks, L. L., and Hust, J. G., Standard Reference

Materials: Thermoelectric Voltage, NBS Spec. Publ. 260-34, (April 1972). COM72-50371**

Sparks, L. L., and Hust, J. G., Standard Refer- ence Materials: Thermal Conductivity of

Austenitic Stainless Steel, SRM 735 from 5

to 280 K, NBS Spec. Publ. 260-35 (April 1972.) 35 cents* COM72-50368**

Cali, J. P., Mandel, J., Moore, L. J., and Young, D.

S., Standard Reference Materials: A Referee Method for the Determination of Calcium in Serum, NBS SRM 915, NBS Spec. Publ. 260-36 (May 1972). COM72-50527**

Shultz, J. I. Bell., R. K. Rains, T. C, and Menis,

O., Standard Reference Materials: Methods of Analysis of NBS Clay Standards, NBS Spec.

Publ. 260-37 (June 1972). COM72-50692**

Richmond, J. C, and Hsia, J. J., Standard Refer- ence Materials: Preparation and Calibration of Standards of Spectral Specular Reflectance, NBS Spec. Publ. 260-38 (May 1972). COM72-

50528**

Clark, A. F., Denson, V.A., Hust, J. G., and

Powell, R. L., Standard Reference Materials: The Eddy Current Decay Method for Resistivity Characterization of High-Purity Metals, NBS

Spec. Publ. 260-39 (May 1972). COM72-50529**

McAdie, H. G., Gam, P.D., and Menis, O., Standard Reference Materials: Selection of Thermal

Analysis Temperature Standards Through a Cooperative Study (SRM 758, 759, 760), NBS

Spec. Publ. 260-40 (August 1972.) COM72-

50776** Wood, L. A., and Shouse, P. J., Standard

Reference Materials: Use of Standard LightSensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for Colorfastness to Light, NBS Spec. Publ. 260-41 (August 1972) COM72-50775**

Wagner, H. L. and Verdier, P. H., eds., Standard

Reference Materials: The Characterization of Linear Polyethylene, SRM 1475, NBS Spec. Publ. 260-42 (September 1972). COM72-

50944**

Yakowitz, H., Ruff, A. W., and Michaelis, R. E., Standard Reference Materials: Preparation and Homogeneity Characterization of an Austenitic Iron-Chromium-Nickel Alloy, NBS Spec. Publ. 260-43 (November 1972). COM73-50760**

Schooley, J. F., Soulen, R. J., Jr., and Evans, G. A.,

Jr., Standard Reference Materials: Preparation and Use of Superconductive Fixed Point

Devices, SRM 767, NBS Spec. Publ. 260-44 (December 1972). COM73-50037**

Greifer, B., Maienthal, E. J., Rains, T. C, and

Rasberry, S. D., Standard Reference Materials: Powdered Lead-Based Paint, SRM 1579, NBS

Spec. Publ. 260-45 (March 1973). COM73-

50226**

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and

Electrical Resistivity Standard Reference Materials: Austenitic Stainless Steel, SRM's 735 and

798, from 4 to 1200 K, NBS Spec. Publ. 260-46 (March 1975). SN003-003-0 1278-5* Hust, J. G., Standard Reference Materials: Electrical Resistivity of Electrolytic Iron, SRM 797, and Austenitic Stainless Steel, SRM 798, from 5 to 280 K, NBS Spec. Publ. 260-47 (February

1974). COM74-50176** Mangum, B. W., and Wise, J. A., Standard Refer- ence Materials: Description and Use of Precision Thermometers for the Clinical Laboratory, SRM 933 and SRM 934, NBS Spec. Publ. 260-48 (May 1974). 60 cents* SN003-003-0 1278-5 Carpenter, B. S., and Reimer, G. M., Standard

Reference Materials: Calibrated Glass Standards for Fission Track Use, NBS Spec. Publ. 260-49 (November 1974). COM74-51185

v
Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials:

Electrolytic Iron, SRM's 734 and 797 from 4 to 1000 K, NBS Spec. Publ. 260-50 (June 1975). $1.00* SN003-003-0 1425-7 Mavrodineanu, R., and Baldwin, J. R., Standard

Reference Materials: Glass Filters As a Standard Reference Material for Spectrophotometry;

Selection; Preparation; Certification; Use-SRM

930, NBS Spec. Publ. 260-51 (November 1975). $1.90* SN0O3-O03-01481-8

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials 730 and 799, from 4 to 3000 K, NBS Spec. Publ. 260-52 (September 1975). $1.05* SN003-003-

01464-8 Durst, R. A., Standard Reference Materials: Standardization of pH Measurements, NBS

Spec. Publ. 260-53 (December 1975, Revised). $1.05 SN003-003-01551-2

Burke, R. W., and Mavrodineanu, R., Standard

Reference Materials: Certification and Use of

Acidic Potassium Dichromate Solutions as an

Ultraviolet Absorbance Standard, NBS Spec.

Publ. 260-54 (August 1977). $3.00* SN003-003-

• 01828-7

Ditmars, D. A., Cezairliyan, A., Ishihara, S., and

Douglas, T. B., Standard Reference Materials: Enthalpy and Heat Capacity; Molybdenum SRM 781, from 273 to 2800 K, NBS Spec. Publ. 260-55 (September 1977). $2.20* SN003-003-

01836-8 PoweU, R. L., Sparks, L. L., and Hust, J. G., Standard Reference Materials: Standard

Thermocouple Materials, Pt.67: SRM 1967, NBS

Spec. Publ. 260-56 (February 1978). $2.20* SN0O3-O03-0 18864

Cali, J. P. and Plebanski, T., Guide to United

States Reference Materials, NBS Spec. Publ. 260-57 (February 1978). $2.20* PB 277173

Barnes, J. D., and Martin, G. M., Standard Refer- ence Materials: Polyester Film for Oxygen Gas

Transmission Measurements SRM 1470, NBS

Spec. Publ. 260-58 (June 1979) $2.00* SN003-

003-02077 Chang, T., and Kahn, A. H. Standard Reference

Materials: Electron Paramagnetic Resonance

Intensity Standard; SRM 2601, NBS Spec.

Publ. 260-59 (August 1978) $2.30* SN003-

003-01975-5 Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., and Moody, J. R., Standard Refer- ence Materials: A Reference Method for the Determination of Sodium in Serum, NBS Spec.

Publ. 260-60 (August 1978). $3.00* SN003-003

01978-0

Verdier, P. H., and Wagner. H. L., Standard Refer- ence Materials: The Characterization of Linear Polyethylene (SRM 1482, 1483, 1484), NBS

Spec. Publ. 260-61 (December 1978). $1.70* SN003-003-02006-1

Soulen, R. J., and Dove, R. B., Standard Reference

Materials: Temperature Reference Standard

for Use Below 0.5 K (SRM 768). NBS Spec.

Publ. 260-62 (April 1979). $2.30* SN003-O03-

02047-8 Velapoldi, R. A., Paule, R. C, Schaffer, R. Mandel, J., Machlan, L. A., and Gramlich, J. W., Standard Reference Materials: A Reference Method for the Determination of Potassium in Serum. NBS Spec. Publ. 260-63 (May 1979). $3.75* SN003-O03-02068

Velapoldi, R. A., and Mielenz, K. D., Standard

Reference Materials: A Fluorescence Standard

Reference Material Quinine Sulfate Dihydrate (SRM 936), NBS Spec. Publ. 260-64 (January

1980). $4.25* SN003-O03-02 148-2 Marinenko, R. B., Heinrich, K. F. J., and Ruegg,

F. C, Standard Reference Materials: Micro- Homogeneity Studies of NBS Standard Reference

Materials, NBS Research Materials, and Other Related Samples. NBS Spec. Publ. 260-65

(September 1979). $3.50* SN003-O03-021 14-1 Venable, W. H., Jr., and Eckerle, K. L., Standard

Reference Materials: Didymium Glass Filters for Calibrating the Wavelength Scale of Spectro- photometers (SRM 2009, 2010; 2013). NBS Spec.

Publ. 260-66 (October 1979). $3.50* SN003-003-

02127-0

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel,

J., Murphy, T. J., and Gramlich, J. W., Standard

Reference Materials: A Reference Method for the Determination of Chloride in Serum, NBS Spec.

Publ. 260-67 (November 1979). $3.75* SN003-

003-02136-9 Mavrodineanu, R. and Baldwin, J. R., Standard

Reference Materials: Metal-On-Quartz Filters as a Standard Reference Material for Spectrophoto- metry-SRM 2031, NBS Spec. Publ. 260-68

(April 1980). $4.25* SN003-003-02 167-9 Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., Machlan, L. A., Garner, E. L., and

Rains, T. C, Standard Reference Materials: A

Reference Method for the Determination of Lithium in Serum, NBS Spec. Publ. 260-69 (July)

1980). $4.25* SN003-003-02214-4 Marinenko, R. B., Biancaniello, F., Boyer, P. A., Ruff, A. W., DeRobertis, L., Standard Reference

Materials: Preparation and Characterization of an Iron-Chromium-Nickel Alloy for Microanalysis, NBS Spec. Publ. 260-70 (May 1981). $2.50* SN0O3-O03-02328-1 Seward, R. W., and Mavrodineanu, R., Standard

Reference Materials: Summary of the Clinical Laboratory Standards Issued by the National Bureau of Standards, NBS Spec. Publ. 260-71 (November 1981). $6.50* SN003-003-02381-7

Reeder, D.J., Coxon, B., Enagonio, D., Christensen, R. G., Schaffer, R., Howell, B. F, Paule, R. C,

Mandel, J., Standard Reference Materials: SRM

900, Antiepilepsy Drug Level Assay Standard, NBS Spec. Publ. 260-72 (June 1981). $4.25* SN003-003-02329-9

vi
Interrante, C. G., and Hicho, G. E., Standard Refer- ence Materials: A Standard Reference Material Containing Nominally Fifteen Percent Austenite (SRM 486), NBS Spec. Publ. 260-73 (January

1982). $2.75* SN0O3-OO3-O2386-8 Marinenko, R. B., Standard Reference Materials: Preparation and Characterization of K-411 and

K-414 Mineral Glasses for Microanalysis: SRM

470. NBS Spec. Publ. 260-74 (April 1982). $3.50 SN003-003-023-95-7

Weidner, V. R., and Hsia, J. J., Standard Reference

Materials: Preparation and Calibration of First Surface Aluminum Mirror Specular Reflectance Standards (SRM 2003a), NBS Spec. Publ. 260-75 (May 1982). $3.75 SN003-003-023-99-0

Hicho, G. E. and Eaton, E. E., Standard Reference Materials: A Standard Reference Material

Containing Nominally Five Percent Austenite (SRM 485a), NBS Spec. Publ. 260-76 (August

1982). $3.50 SN003-003-024-33-3 Furukawa, G. T., Riddle, J. L., Bigge, W. G., and

Pfieffer, E. R., Standard Reference Materials: Application of Some Metal SRM's as Thermometric Fixed Points, NBS Spec. Publ. 260-77 (August 1982). $6.00 SN003-003-024-34-1

Hicho, G. E. and Eaton, E. E., Standard Reference

Materials: Standard Reference Material Containing Nominally Thirty Percent Austenite (SRM

487), NBS Spec. Publ. 260-78 (September 1982). $3.75* SN003-003-024-35-0 Richmond, J. C, Hsia, J. J. Weidner, V. R., and

Wilmering, D. B., Standard Reference Materials: Second Surface Mirror Standards of Specular

Spectral Reflectance (SRM's 2023, 2024, 2025), NBS Spec. Publ. 260-79 (October 1982). $4.50* SN003-003-024-47-3

Schaffer, R., Mandel, J., Sun, T., Cohen, A., and

Hertz, H. S., Standard Reference Materials: Evaluation by an ID/ MS Method of the AACC

Reference Method for Serum Glucose, NBS

Spec. Publ. 260-80 (October 1982). $4.75* SN003-

003-024-43-1 Burke, R. W., and Mavrodineanu, R. (NBS retired), Standard Reference Materials: Accuracy in Analytical Spectrophotometry, NBS Spec. Publ. 260-81 (April 1983). $6.00* SN003-003-024-8

Weidner, V. R., Standard Reference Materials: White Opal Glass Diffuse Spectral Reflectance Standards for the Visible Spectrum (SRM's 2015 and 2016). NBS Spec. Publ. 260-82 (April 1983). $3.75* SN003-003-024-89-9**

Bowers, G. N., Jr., Alvarez, R., Cali, J. P. (NBS

retired), Eberhardt, K. R., Reeder, D. J., Schaffer, R., Uriano, G. A., Standard Reference

Materials: The Measurement of the Catalytic

(Activity) Concentration of Seven Enzymes in NBS Human Serum SRM 909, NBS Spec.

Publ. 260-83 (June 1983). $4.50* SN003-003-024-

99-6

Gills, T. E., Seward, R. W., Collins, R. J., and

Webster, W. C, Standard Reference Materials: Sampling, Materials Handling, Processing, and

Packaging of NBS Sulfur in Coal Standard

Reference Materials, 2682, 2683, 2684, and 2685, NBS Spec. Publ. 260-84 (August 1983). $4.50* SN003-003-025-20-8

Swyt, D. A., Standard Reference Materials: A Look

at Techniques for the Dimensional Calibration of Standard Microscopic Particles, NBS Spec. Publ. 260-85 (September 1983). $5.50* SN003-003-

025-21-6 Hicho, G. E. and Eaton, E. E., Standard Reference Materials: A Standard Reference Material

Containing Two and One- Half Percent Austenite, SRM 488, NBS Spec. Publ. 260-86 (December

1983). $1.75* SN003-003-025-41-1 Mangum, B. W., Standard Reference Materials: SRM 1969: Rubidium Triple-Point - A Temperature Reference Standard Near 39.30 °C, NBS

Spec. Publ. 260-87 (December 1983). $2.25* SN003-003-025-44-5 Gladney, E. S., Burns, C. E., Perrin, D. R., Roelandts, I., and Gills, T. E., Standard Reference Materials: 1982 Compilation of Elemental

Concentration Data for NBS Biological, Geological, and Environmental Standard Reference

Materials. Spec. Publ. 260-88 (March 1984). $7.00* SN003-003-02565-8

Hust, J. G., Standard Reference Materials: A Fine- Grained, Isotropic Graphite for Use as NBS

Thermophysical Property RM's from 5 to 2500 K, NBS Spec. Publ. 260-89 (September 1984). $4.50* SN003-003-02608-5 Hust, J. G., and Lankford, A. B., Standard Reference Materials: Update of Thermal

Conductivity and Electrical Resistivity of

Electrolytic Iron, Tungsten, and Stainless Steel, NBS Spec. Publ. 260-90 (September 1984). $3.00* SN003-003-02609-3

Goodrich, L. F., Vecchia, D. F., Pittman, E. S., Ekin, J. W., and Clark, A. F., Standard Reference

Materials: Critical Current Measurements on an NbTi Superconducting Wire Standard Reference

Material, NBS Spec. Publ. 260-91 (September

1984). $2.75* SN003-003-02614-0

Carpenter, B. S., Standard Reference Materials: Calibrated Glass Standards for Fission Track Use (Supplement to NBS Spec. 260-49). NBS

Spec. Publ.. 260-92 (September 1984). $1.50* SN003-003-02610-7

Ehrstein, J., Preparation and Certification of Standard Reference Materials for Calibration of Spreading Resistance Probes, NBS Spec. Publ. 260-93 (January 1985). $2.25* SN003-003-02633-6

Gills, T. E., Koch, W. F. Stolz, J. W., Kelly, W. R., Paulsen, P. J., Colbert, J. C. Kirklin, D. R., Pei, P.T.S., Weeks, S., Lindstrom, R. M. Fleming, R. F., Greenberg, R. R., and

Paule, R. C, Methods and Procedures Used at the National Bureau of Standards to Certify Sulfur

in Coal SRM's for Sulfur Content, Calorific Value, Ash Content, NBS Spec. Publ. 260-94 (December 1984). $2.25* SN003-003-02629-8

Mulholland, G. W., Hartman, A. W., Hembree,

G. G., Marx, E., and Lettieri, T. R., Standard

Reference Materials: Development of a I ]\ m

Diameter Particle Size Standard, SRM 1690, NBS Spec. Publ. 260-95 (May 1985). SN003-003-

02665-4

vii
Carpenter, B. S., Gramlich, J. W., Greenberg, R. R., and Machlan, L. A., Standard Reference

Materials: Uranium-235 Isotopic Abundance Standard Reference Materials for Gamma

Spectrometry Measurements, NBS Spec. Publ. 260-96 (In Preparation). Mavrodineanu, R. and Gills, T. E., Standard

Reference Materials: Summary of the Coal, Ore,

Mineral, Rock, and Refractory Standards Issued by the National Bureau of Standards, NBS Spec.

Publ. 260-97 (September 1985). Hust, J. G., Standard Reference Materials: Glass Fiberboard SRM for Thermal Resistance, NBS

Spec. Publ. 260-98 (August 1985). SN003-003-

02674-3

Callanan, J. E., Sullivan, S. A., and Vecchia, D. F., Standard Reference Materials: Feasibility Study

for the Development of Standards Using

Differential Scanning Calorimetry, NBS Spec.

Publ. 260-99 (August 1985). SN003-003-02675-

Taylor, J. K., Standard Reference Materials: Handbook for SRM Users, NBS Spec. Publ. 260-100

(In Press). Mangum, B. W., Standard Reference Materials: SRM 1970, Succinonitrile Triple-Point Standard: A Temperature Reference Standard Near

58.08 °C, NBS Spec. Publ. 260-101 (In

Preparation). Weidner, V. R., Mavrodineanu, R., Mielenz, K. D., Velapoldi, R. A., Eckerle, K. L., and Adams, B., Standard Reference Materials: Holmium Oxide

Solution Wavelength Standard from 240- 650 nm, SRM 2034, NBS Spec. Publ. 260-102 (In Press). Hust, J. G., Standard Reference Materials: Glass Fiberblanket SRM for Thermal Resistance, NBS

Spec. Publ. 260-103 (September 1985). SN003-

003-02687-5 Mavrodineanu, R. and Alvarez, R., Standard

Reference Materials: Summary of the Biological and Botanical Standards Issued by the National Bureau of Standards, NBS Spec. Publ. 260-104 (November 1985). Mavrodineanu, R. and Rasberry, S.D., Standard

Reference Materials: Summary of the Environ- mental Research, Analysis, and Control

Standards Issued by the National Bureau of Standards, NBS Spec. Publ. 260-105.

* Send order with remittance to Superintendent

of Documents, US Government Printing Office Washington, DC 20402. Remittance from

foreign countries should include an additional one-fourth of the purchase price for postage. ** May be ordered from: National Technical Information Services (NTIS). Springfield

Virginia 22161.
SRM 1970 : Succinonitrile Triple -Point

Standard—A Temperature Reference

Standard Near 58.08 °C

B. W. Mangum

National Bureau of Standards, Gaithersburg, MD 20899 and Samir El-Sabban

National Institute of Standards, Cairo, Egypt

Accepted: August 8, 1985

Triple-point-of-succinonitrile cells have been tested and established as Standard Reference Material (SRM) 1970. Of the 115 cells tested, 109 were accepted as SRM 1970. Five of the 115 cells had triple-point temperatures lower than 58.0785 °C (the low-temperature limit established for SRM 1970) and, consequently, were rejected. One of the 115 cells broke during tests on it. The mean value of the triple-point temperatures

(obtained by freezing) of the 109 cells is 58.0796±0.0O15 °C, where the uncertainty is the total estimated

uncertainty relative to the International Practical Temperature Scale of 1968, Amended Edition of 1975. The

standard deviation of the triple-point temperatures is 0.48 mK. The purity of the succinonitrile of the SRM

1970 cells is estimated to range from 99.999,97% to 99.999,84%. The preparation of the cells, the various tests performed on them, and the procedure recommended for their use are described. Key words: SRM 1970; standard reference materials; succinonitrile; thermometry; temperature fixed point.

1. Introduction

Accurate temperature measurements and control are necessary for many tests conducted in clinical and bio- medical laboratories in order to obtain accurate and

meaningful results which form the basis for the diagnosis and treatment of diseases. Temperature fixed points

at temperature values near those at which specific tests are conducted can be used as the reference temperatures

for those tests. This simplifies temperature measureAbout the Authors: B. W. Mangum is with the Temperature and Pressure Division in NBS' Center for Basic Standards where Samir El-Sabban served as a guest scientist.

ments and significantly improves the precision and ac- curacy of clinical measurements and results. The calibration of thermometers is performed, either directly or indirectly, through the use of temperature

fixed points. Because temperature fixed points provide

reproducible environments, they have been the basis for practical temperature scales, such as the International

Practical Temperature Scale of 1968, Amended Edition of 1975 (IPTS-68(75) and they are used in the cali- bration of thermometers on those scales. In addition to the defining fixed points of the scales, there are other

equilibrium states which are internationally recognized

as secondary reference points [2]. Those points may be

used for calibration of thermometers which do not operate over the entire range of the defining fixed points

' Numbers in brackets indicate literature references.
of the IPTS-68(75) and when a comparison calibration against a primary standard is not practicable. The feasibility of the use of the triple-point temperature of succinonitrile (SCN) as a temperature reference point near

58.08 °C has been investigated [3,4,5] and the quality of

this fixed point has been found to be very high, the point containing most of the features desired in a fixed point. Based on the previous work [4,5}, we have developed

an SCN triple-point Standard Reference Material (SRM). It is designated SRM 1970—the Succinonitrile Triple-Point Standard, and it is available from the Office of Standard Reference Materials (OSRM) of the National Bureau of Standards (NBS). These SRM devices

are easy to use and with them one can confidently ex- pect to achieve a calibration point with an uncertainty no greater than ±0.0015 K. The remainder of this publication describes SRM

1970, the tests performed on the cells of SCN, the conditions under which the cells were tested, the results obtained from testing 109 SRM 1970 cells, and the pro- cedure recommended for using the cells for calibration of thermometers.

2. Experimental Details

2.1 Preparation of SCN Triple-Poiut Cells

a) Cell Design Previous experience [4,5] with SCN led to the design shown in figure 1 for the triple-point cells constituting SRM 1970. These cells, sealed under vacuum, contain approximately 60 grams of high-purity SCN and are designed to be used with small thermometers, those not exceeding 4.5 mm (0.180 inches) in diameter. The ther- mometer well of a cell will accommodate most precision thermistor thermometers, many platinum resistance thermometers, and most diode thermometers.

b) Purification ofSCN and Filling of the Triple-Point

Cells The SCN used for SRM 1970 was purified by the zone-refining technique by Prof. M. E. Glicksman and

his students at Rensselaer Polytechnic Institute. The ap- paratus used for the zone-refining was a modified version of that described previously by M. E. Glicksman et

al. [3]. Three pyrex cells were attached to the zone-refining tube of the second stage of refining so that three cells could be prepared from the purest half of the purified material of that second stage. Each of the two stages of

purification consisted of at least 20 passes through the 6 zones of the zone-refining furnace. This amount of puri6.8 cm

12 cm

< I

1

7 mm O.D.

5 mm I.D. Thermometer—Well Extension Tube

6 mm O.D.15-25 mm

Thermometer Well

Succinonitrile 10 cm

1.7±0.2 cm i—r—

35 mm O.D.

Figure 1-Cross-sectional drawing of the succinonitrile triple-point

cell. fication had been determined previously by one of us (BWM) [6] to be the minimum required if three cells were to be routinely obtained from each zone-refined

lot. During the early part of the second stage of zonerefining, the three pyrex cells were washed several times with the purified SCN.

2.2 Testing of SCN Triple-Point Cells for SRM 1970 Using the inner-sheath technique, the freezing behaviors of 1 1 5 cells were studied in a well-stirred constant- tempeature oil bath maintained at 56.880 °C. Some pre- liminary tests were made prior to testing the cells to determine the optimum bath temperature to be used for the freezing experiments, consistent with a reasonable time for the freeze. The temperature selected was

56.880 °C. Prior to a freezing experiment, the SCN was melted by immersing the cell in a water bath at about 80 °C. When the material had completely melted, the cell was removed from the bath and its exterior dried. The cell was inverted several times to obtain a uniform distribu-
tion of any impurities present in the sample. Then a cold copper rod was inserted into the thermometer well, which contained a small amount of light mineral oil, to

initiate the growth of an SCN sheath around the well. When the sheath appeared to be 2 to 3 mm thick, the rod was removed. This sheath provided an inner liquid-solid interface which the thermometer sensed. Once the sheath had formed, the cell was placed in the constant- temperature oil bath and a thermistor thermometer was

inserted into the thermometer well. A second liquid- solid interface then formed along the outer wall of the

cell. After the cell was placed in the oil bath, temperature measurements were begun and they were made

at regular intervals until complete solidification of the SCN in the cell. These tests were made with groups of

three cells at a time.

2.3 Apparatus Used in the Realization of the Triple-Points of the SCN Cells

a) Constant Temperature Bath A constant temperature bath was used to study the

freezing behavior of all cells tested for suitability as SRM 1970. The bath has a 10.6-liter capacity; such baths

are commercially available. A light mineral oil (a di- methylpolysiloxane) with a 17-centistokes viscosity at 40 °C was used as a bath medium. The bath has both a cooling and a heating system and its temperature was

controlled by their combined effect. The cooling was

obtained by passing a stream of pressurized air at roomtemperature through the cooling coil. The heater, and

consequently the whole bath, was controlled by a commercially-available proportional controller with a thermistor as a sensing element. By this means, it was

possible to maintain a uniform bath temperature, constant to ±0.5 mK, for a time much longer than that needed for a freezing or a melting experiment. This high

level of temperature control, however, is not necessary

in the normal use of SRM 1970.

b) Thermometers

Bead-in-glass probe-type thermistor thermometers were used in this investigation. They were calibrated over the range 0 °C to 70 °C against a standard platinum

resistance thermometer (SPRT), all located in a copper

block immersed in a constant-temperature oil bath. The

copper block, a high-capacity, good thermal conductor, ensured thermal equilibrium among the thermistors and

with the SPRT, and damped any sudden temperature

fluctuations. The measurements of the SPRT re- sistances, from which the temperatures of calibration were obtained, were made with a Cutkosky 400-Hz

bridge [7] which, with a strip-chart recorder, has an

equivalent temperature resolution of about 1.5 /xK and

an inaccuracy of about 0.01 mK. The SPRT itself had

been calibrated previously on the IPTS-68(75) in the NBS Platinum Resistance Thermometer Calibration Laboratory using the same bridge. A constant-current source and high-quality 6j-digit digital voltmeter (DVM) were used for potentiometric measurements of

the thermistors. The uncertainty of the resistance measurements of the thermistor thermometers corre- sponded to about ±0.25 mK. By fitting the equation l/T=A +B log R +C(log R)2 +D(\og R)y (1)

to the data, where T is the temperature in kelvins and R

is the thermistor resistance in ohms at temperature T,

the constants A, B, C and D were determined. The

temperature value then derived from eq (1) for a measured thermistor-thermometer resistance agreed with

that measured with the SPRT to within ± 1 mK.

c) Temperature Measurement System The temperature measuring system used in testing the

cells for suitability as SRM 1970 was the same auto- mated one used in calibrating the thermistor thermometers and it consisted of a microcomputer, a 6j-digit DVM, a constant-current source, a standard resistor, and the calibrated thermistor thermometers [5].

3. Results and Discussion

3.1 Freezing Experiments

During previous work on SCN [4,5], it was found that the fastest and easiest way of producing a temperature

plateau for calibration of thermometers was by the freezing technique, using the inner sheath method,

rather than by the melting technique. Adopting this technique for testing the cells for suitability as SRM

1970, we conducted freezing experiments on a cell in the

oil bath maintained at 57.480 °C, 57.180 °C and

56.880 °C in order to ascertain a reasonable bath temperature at which to test all of the remaining cells. The

results for three freezes of cell A- 1/3 in a bath at 57.480 °C are shown in figure 2; those for the cell in a bath at 57. 180 °C are shown in figure 3; and those for the

cell in a bath at 56.880 °C are shown in figure 4. We

depict the combined results of these freezes of A- 1/3 in figure 5, which shows that although the times required

for the freezes vary with the temperature of the bath, as expected, the temperatures of the plateaus are unaffected by the bath temperature. Based on these results,

it was decided to test all cells in a bath maintained at 56.880 °C, a temperature that does not require an unrea- sonable amount of time for measurements.

3
58.084

244

Figure 2-Freezing curves of sample A- 1/3 obtained on different days, each time in an oil bath maintained at 57.480 °C.

Figure 3-Freezing curves of sample A- 1/3 obtained on different days, each time in an oil bath maintained at 57.180 °C.

58.074 Time (min.)

Figure 4-Freezing curves of sample A- 1/3 obtained on different days, each time in an oil bath maintained at 56.880 °C.

Time (min.)

4
58.082

58.080

58.078

58.074

Figure 5-Freezing curves of SRM

1970 cell A- 1/3 in constant temperature baths at three different temperatures. The data repre- sented by were obtained with

the cell in a bath at 57.480 °C, those data represented by A_ were obtained with the cell in a bath at 57.180 °C, and those data represented by were obtained with the cell in a bath at 56.880 °C. 244

Figures 2, 3, and 4 also show the irreproducibility of

the freezing curves of A-l/3. The spread among the

three curves of figure 2 is 0.7 mK, that for the curves of

figure 3 is 0.6 mK, and that for the curves of figure 4 is 0.8 mK. We see, however, that the plateaus of the indi- vidual curves in figures 2, 3, and 4 are fairly flat and that the freezing range of any given curve is about 0.5 mK.

The initial rapid rise in temperature indicated by the thermistor thermometer is due primarily to the temperature of the oil and thermistor in the thermometer

well of the cell rising to the temperature of the SCN

liquid-solid interface. The curvature at the ends of the

freezes is due mainly to the low thermal conductivity of

the SCN [8]. Also, the small but gradual increase in temperature during about the first two-thirds of any

given freeze is attributed to the low thermal conductivity of SCN. The small but gradual decrease in temperature during the last one-third of a freeze is attributed to the low thermal conductivity of SCN, to increased concentration of impurities in the liquid SCN due to rejection of those impurities at the solid-liquid interface

as the SCN solidifies, and to decreased effective im- mersion of the thermistor thermometer because of the way the outer solid-liquid interface progresses inward.

It can be seen from figure 5 that even with the temperature of the bath set 1.2 °C below the triple-point temperature of SCN, there is still a plateau lasting about

2 hours, a sufficient time for most calibrations. If longer

times are required for calibrations, the bath temperature must be set closer to the triple-point value of the SCN. As indicated in section 2, the column of the second

stage of the zone-refining apparatus normally contained enough SCN to fill three cells from the top half (the purest part and that which constituted a "lot") of the column. The cells were given a designation ending with

-1/X, -2/X or -3/3. The letter X represents either the

number 2, indicating that only two cells (-1/2 and -2/2) were filled from that lot, or the number 3, indicating that three cells (-1/3, -2/3 and -3/3) are in the lot. The first cell to be filled would normally be considered to be the purest of a lot, the second cell to be filled the next purest, and the third cell to be filled the least pure. In some

cases, however, one could envision cells designated -2/X being purer than cells designated -1/X due to the washing of the empty (contaminated?) cells and the impurity not being removed from the first portion of the SCN in the subsequent zone refining. The spread of the

triple-point temperatures of the cells of SCN of a given

lot is an indication of the relative purity of those cells. Figures 6, 7, and 8 show freezing curves of three groups

of cells, each group constituting a lot. All of the freezing curves were obtained at the same bath temperature us- ing the same technique of freezing. The behavior por- trayed in these figures is typical of all the lots of SRM

1970. Figure 6 displays freezing curves of cells L28-1/3, L28-2/3, and L28-3/3; these cells belong to lot L28. The

temperatures of the plateaus of these cells have a spread

of 1.3 mK. Figures 7 and 8 display the curves obtained during freezing of cells L25-1/3, L25-2/3 and L25-3/3, which belong to lot L25, and cells L34-1/3, L34-2/3 and

L34-3/3, which belong to lot L34, respectively. The

curves obtained during freezing of lot L25 show a spread of about 0. 1 mK while those of lot L34 have a spread of about 0.8 mK. We see that all of the curves of

figures 6, 7, and 8 are rather flat, with freezing ranges of about 0.5 mK, ranges which are due primarily to curvature near the ends of the freezes. These small freezing ranges indicate high purity. We see from figures 6, 7, and 8 that the differences in temperature values of the plateaus of the different cells of a given lot are small but the temperatures are, nevertheless, not exactly the same. This is primarily because

5
58.084

58.082

58.080

58.078

58.076

58.074

Figure 6-Freezing curves of the three cells of lot L28 obtained in a bath at 56.880 "C. represent

data for L28-1/3, A represent data for L28-2/3, and represent data for L28-3/3.

58.084

58.082

58.080

58.078

58.076

58.074

Figure 7-Freezing curves of the

three cells of lot L25 obtained in a bath at 56.880 °C. represent data for L25-1/3, A represent data for L25-2/3, and represent data for L25-3/3.

Time (min

58.084

58.082

|

58.078

58.076

58.074

24 64 84 Time (min.) 104 124

Figure 8-Freezing curves of the three cells of lot L34 obtained in a bath at 56.880 "C. • represent data for L34-1/3, A represent data for L34-2/3, and represent data for L34-3/3.
the cells were filled with SCN from different sections on

the same zone-refining column and the purity varies along the column. The results for the cells of lot L34, shown in figure 8, as well as the results for cells of lots L28 and L25, shown in figures 6 and 7, respectively, demonstrate that the purities of the cells belonging to a given lot have different values and that generally they

are in the sequence discussed above. The freezing curves of the three samples of lot L34, taken from the same zone-refining tube, clearly demonstrate how impurities affect the triple-point values of the SCN. It is seen in figure 8 that the first sample has a plateau during

freezing which has the highest temperature of any sample of that lot. The third cell, L34-3/3, was the last sample in that lot to be extracted from the column and

it has a plateau with the lowest temperature, while sample L34-2/3 is purer since it was the second sample to be

taken from the column. This distribution of temperatures of the plateaus is as expected from purification of a material by zone refining. The spread of the temperature values of the plateaus of the curves obtained during freezing of the cells of each of the 39 lots of SRM 1970 cells are shown in figure

9. This shows that the spread ranges from 0.1 mK to 1.3 mK. Only four lots, however, have a spread in temperature exceeding 0.9 mK, and those have a spread of

1.3 mK. These results indicate that the cells of SRM

1970 are of high purity.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Spread Per Lot (mK)

Figure 9-Histogram of the spread of the temperatures of the plateaus of the freezing curves of the cells of a given lot.

Our results indicate that in general, then, the purity of

the cells of a given lot is such that the first extracted sample (comprising the -1/X cell) is the purest, the sec- ond cell filled is the next purest, and the last cell (the third cell) will be the most impure. Histograms of the

triple-point temperatures for the cells labelled -1/X,

-2/X, and -3/3 are presented in figure 10. The highest plateau temperature measured for any cell was

58.0806 °C, as indicated in the histograms for cells la- belled -1/X and -2/X. Although the lowest temperature

indicated in the histograms is 58.0785 °C, five cells with

triple-point temperatures below that value were tested but were rejected as being unsuitable to qualify as SRM

1970. Consequently, they are not included in the histo- grams. The rjottom section of figure 10 shows that the values of the 39 cells with designations -1/X have the

E

=> 4

J3EI 4 % 2 o

I

'

1 1 1

I

1 1 1 1 I

'

1 1 '

I

LJ

ii

Freezing Point Temperature (°C)

Figure 10-Histograms of the triple-point temperatures obtained by

freezing of all of the SRM 1970 cells. The histogram at the bottom

of the figure is for cells designated -1/X; that in the middle of the

figure is for cells designated -2/X; and that at the top of the figure

is for cells designated -3/3.

7
smallest spread of triple-point temperatures and a mean

value (58.0797 °C) which is slightly higher than that of

the other groups of cells (those designated -2/X and

-3/3). Also, no cell of the bottom portion of figure 10 has

a triple-point temperature below 58.0790 °C. The middle section of figure 10 shows that the 38 cells with

designations -2/X are spread over the entire range from

58.0785 °C to 58.0806 °C, with a mean value of

58.0796 °C, a value only slightly less than that for the group of cells designated -1/X. The top section of figure 10 shows the distribution of the 32 cells designated -3/3. These cells have triple-point temperatures ranging from

58.0785 °C to 58.0800 °C, with a mean value of

58.0793 °C. In order to demonstrate the reproducibility of the

triple-point temperatures observed for the SRM 1970

cells, we present four typical freezing curves in figures

11 and 12. In figure 11, we display two freezing curves

of cell D-3/3, obtained on different days in a bath at the same temperature and using the same thermistor ther- mometer. This shows the excellent reproducibility that

is obtainable with most of the cells comprising SRM

1970. In figure 12, the freezing curves characteristic of

cell K-2/3 are presented. As shown there, the curves did not reproduce exactly, but the spread was less than

1 mK. The results in figure 12 are typical of those for

cells with the greatest irreproducibility. All 109 SCN

cells accepted as SRMs were tested for reproducibility

in the manner just described. In figure 13, we present a histogram which indicates that each of the cells had

freezing curves which repeated to within a value lying between 0.0 mK and 0.8 mK. Figure 13 shows that 77%

of the cells, i.e., 84 cells, have a spread of <0.3 mK and

only 25 cells had freezing curves with plateaus that dif- fered by amounts ranging from 0.4 to 0.8 mK.

58.084

58.082

58.080

58.078

58.076

58.074

58.084

58.082

58.080

58.078

58.076 —

58.074

Figure 11-Freezing curves of cell D-3/3 obtained on different days

in a bath at 56.880 °C, showing

reproducibility.

Figure 12-Freezing curves of cell K-2/3 obtained on different days

in a bath at 56.880 °C, showing

reproducibility.

Time (min.

8
0.0 0.2 0.4 0.6 0.8 1.0 Spread of TTP per Cell (mK)

Figure 13-Histogram of the spread of the triple-point temperatures of each of the cells of SRM 1970, as determined from freezing curves.

As indicated previously, we obtained 115 cells of SCN to investigate for suitability as SRM 1970. Of

these, 109 were accepted as the standard reference material; five were rejected because the temperatures of the

plateaus of their freezing curves had values below

58.0785 °C, and one cell broke. The histogram shown in figure 14 represents the distribution of the triple-point temperatures of 111 of the 115 cells considered in our

study. It is shown that the triple-point values of the 111

cells are distributed over a temperature range of 2.6 mK,

i.e., from 58.0780 °C to 58.0806 °C, with the two cells having triple-point temperatures below 58.0785 °C being rejected as unsuitable for SRM 1970. All of the five

cells rejected for SRM 1970 belonged to the group des- ignated -3/3. The mean triple-point temperature of the 109 cells accepted as SRM 1970 is 58.0796 °C, with a standard deviation of 0.48 mK and a standard error of

0.04 mK.

3.2 Determination of Purity The reproducibility of the plateau of the freezing curve of a sample and the depression of the triple-point/ freezing-point temperature is a function of the purity of

that sample [9-11]. Similarly, the purity determines, in

Figure 14-Histogram of the triple- point temperatures of the 109

cells of SCN accepted as SRM

1970, plus those of two cells with temperatures below

58.0785 °C, which, consequently, were rejected as being unsuitable for SRM 1970.

t(°C)

9
a major way, the melting behavior of a sample [9-11]. Both of these methods, of course, are nondestructive and can be used for any SRM 1970 cell. In using melting curves to estimate the purity of the SCN used as SRM

1970, three cells were selected with triple-point temperatures distributed over the range of temperatures ob- served for the plateaus of all the cells. One sample chosen was L27-2/3, with a triple-point value of 58.0804 °C; another cell chosen was L20-2/3, with a triple-point temperature of 58.0787 °C; the third cell selected was

L26-2/3, which has a triple-point temperature of

58.0795 °C. Prior to the melting experiments from which the purities were to be determined, the cells were

prepared as follows. The SCN was completely melted by placing the cells in a water bath at about 80 °C. Then

the cells were removed, wrapped with paper towels, placed in dewars, and a slow stream of air directed into

their thermometer wells to cause the SCN to freeze slowly from inside outwards. This technique of freezing causes the impurities that have distribution coefficients with values less than 1.0 (impurities rejected on freez- ing) to be more concentrated on the outermost parts of

the cells. After the SCN had solidified and cooled to room temperature, the cells were immersed in a constant temperature bath, maintained at a temperature of

58.38 °C, and their temperatures monitored as the SCN

melted. Melting curves of the three cells are presented in figure 15. Assuming that the law of dilute solutions [12,13] is valid for our samples, the purity can be estimated by

using the equation [9] A(Tn -Tf2) [(1//D-0//2)]

where X is the total mole fraction of impurities in the sample, 7}, and T/2 are the temperatures when the frac- tions melted are f\ and fl, respectively, and A is the cryoscopic constant ( = 0.004318 K" 1 for SCN). The

constant A can be calculated from the equation ML

RTl

(i)

where R is the gas constant (8.314 J mol" 1 K" 1 ), AJJ is the latent heat of fusion (3703.45 J mol"' for SCN), and T0 is the melting-point temperature in kelvins. Although

the plateaus are not perfectly flat (i.e., there is a finite melting range), the temperature difference between the bath and the SCN is essentially constant, and thus the absorption of heat per unit time by the sample during

melting is nearly constant. Consequently, the fraction of SCN melted can be considered to be directly proportional to the time elapsed during the melting and eq (2) can be rewritten as A(Tn -T!2 ) [(l/M)-(l//2)] (4)

(2)

where fl and fl have been replaced by tl and tl, re- spectively. Since the three melting curves shown in figure 1 5 do

not have perfectly flat plateaus and since that for L20-2/3 has an odd shape, we selected various parts of each curve for possible use in estimating the impurity

content. The results of the calculations are given in table

1. Values of fl (or tl) greater than 0.8 were not used

58.085

58.083

58.081

58.079

58.077

58.075

Figure 15-Melting curves of cells L20-2/3, L26-2/3 and L27-2/3

obtained in a bath maintained at 58.380 °C. represent data obtained for cell L20-2/3, represent data obtained for cell L26-2/3, and represent data obtained for cell L27-2/3.

10
Table 1. Mole fraction of impurities for three cells (representative of all 109 cells of SRM 1970

certified to date), determined by using different parts of the melting curves.

(rl,r2) X

L27-2/3 L26-2/3 L20-2/3

(0.1,0.5) 0.000,000,162 0.000,000,593 0.000,001,510

(0.1,0.6) 0.000,000,207 0.000,000,725 0.000,001,553

(0.1,0.7) 0.000,000,302 0.000,000,755 0.000,001,61

(0.1,0.8) 0.000,000,394 0.000,000,888 0.000,001,627

(0.2,0.5) 0.000,000,288 0.000,001,151 0.000,001,870

(0.2,0.6) 0.000,000,388 0.000,001,424 0.000,001,941

(0.2,0.7) 0.000,000,604 0.000,001,450 0.000,002.054

(0.2,0.8) 0.000,000,805 0.000,001,726 0.000,002,071

(0.3,0.7) 0.000,000,906 0.000,002,491 0.000,002,718

(0.3,0.8) 0.000,001,242 0.000,002,900 0.000,002,692

Best estimates: of X 0.000,000,3 0.000,000,7 0.000,001,6 of Purity 99.999,97% 99.999,93% 99.999,84% because at values greater than that the temperatures of

the thermometers were already being influenced by the environment external to the cells. As indicated in table

1, 10 different sections of each curve were used to esti- mate the amount of impurity. In these determinations of

impurities, eq (4) is most sensitive over about the first 50% of the melt. Consequently, we gave that section of

the curves the greatest weight in estimating the amount

of impurities present. The measurements on the three samples, representative of all the SRM 1970 cells, then, lead to estimates of the purities ranging from

99.999,97% to 99.999,84%, as listed in table 1.

4. Recommended Procedure for Use of SRM

1970 in Calibration of Thermometers To obtain the best results in calibrating thermometers

using SRM 1970, the SCN should be totally melted, a

thin sheath of solid SCN prepared around the thermometer well, the cell placed in an appropriate constant- temperature environment, and the SCN slowly frozen while calibrating the thermometers. The constant-temperature environment should be a

well-stirred fluid bath (preferably containing a light purified mineral oil) maintained at a temperature between

56.88 ±0.05 °C and 58.02±0.05 °C. Since the SRM 1970

cells are approximately 18 cm long, the bath should be

at least 20 cm deep from the top level of the oil. The cell or cells should be mounted vertically in a suitable holder

in such a way that the cells are completely immersed below the level of the oil.

A temperature controller capable of controlling the bath to ±0.02 °C is preferred, but one could use a bath

controlled to only ±0.05 °C, or even ±0.1 °C. The detailed procedure preferred for calibrating a thermometer through the use of an SRM 1970 SCN

triple-point cell is as follows: First, get a well-stirred oil bath to a temperature between 56. 88 ±0.05 °C and

58.02 ±0.05 °C and maintain it at that point. Melt the sample by immersing the cell in a water bath at about

80 °C. After the SCN has completely melted, remove

the cell from the bath and invert it several times to ensure a thorough mixing of the liquid material (SCN

and all impurities) inside the cell. Dry the cell, put a small amount of oil in the thermometer well, and insert a cold copper rod into the well. After the formation of what appears to be a 2-to-3 mm sheath of the SCN

around the thermometer well, put the cell into the temperature-controlled bath, using a holder to support

the cell. Insert the thermometer to be calibrated in the thermometer well of the cell, wait 10 to 15 minutes, then read the indication of the thermometer. The correct temperature of the thermometer at that time is the value

indicated on the SRM certificate. If more than one thermometer is to be calibrated, the second and succeeding thermometers should be allowed

5 to 10 minutes to reach thermal equilibrium with the freezing SCN in the cell before obtaining measurements on them. The smaller the mass of the thermometer and

the closer the temperature of the thermometer is to that of the fixed point, the shorter the length of time required

for equilibrium.

If the minimum recommended temperature of the en- vironment of the cell (56.88 °C) is used, there should be

11
a minimum time of about 90 minutes available for cali- bration from the time the SCN sheath is prepared. If more than about 75% of the SCN has solidified and if more calibrations are needed, remove the SCN cell, repeat the previous procedure to prepare a new inner

sheath, and put the cell back into the oil bath (or other

controlled environment) for further cahbration work. These consecutive freezing and melting processes may

be repeated as often as required.

5. Summary and Conclusions

In certifying cells of SCN for SRM 1970, 115 cells of

purified SCN were tested, 5 of them were rejected be- cause their freezing values were below 58.0785 °C, and

one was broken. The remaining 109 samples were ac- cepted as suitable for the temperature standard refer- ence material. The triple-point temperatures of all the

cells accepted for SRM 1970 ranged between

58.0806 °C and 58.0785 °C, with a mean value of

58.0796 °C, a standard deviation of 0.48 mK and a stan- dard error of 0.04 mK.

In realizing the fixed points of these cells, the freezing technique was found to be more convenient than that of

melting because of the greater flatness of the freezing

curves. Each of the cells showed a high degree of re- producibility, with the observed temperature values of

the plateaus differing by no more than 0.8 mK. These

properties make the cells very attractive as a temperature reference standard for the calibration of ther- mometers near 58.08 °C. The SCN used was of high purity; that is clear from

the fact that the spread of freezing - point - temperatures

values per lot did not exceed 1.3 mK. The amount of

impurities estimated to be present in the SCN of the 109 cells of SRM 1^70 has values ranging from 3 X

10" 7 to 1.6X 10" 6

, equivalent to a purity of the SCN

ranging from 99.999,97% to 99.999.84%. This is a very high purity for an organic material.

Thermometers with diameters no greater than 4.5 mm

may be calibrated in these SRM 1970 cells.

6. References

[1] The International Practical Temperature Scale of 1968, Amended Edition of 1975, Metrologia 12, 7-17 (1976).

[2] Bureau International des Poids et Mesures, Monograph, Sup- plementary Information for the IPTS-68 and the EPT-76,

Pavilion de Breteuil, F-92310 Sevres (1983).

[3] Glicksman, M. E.; P. W. Voorhees and R. Setzko, The triple- point equilibria of succinonitrile—its assessment as a temperature standard, in Temperature: Its Measurement and

Control in Science and Industry 5, American Institute of

Physics: New York, NY, 321-326 (1982).

[4] Mangum, B. W., The succinonitrile triple-point standard: a

fixed point to improve the accuracy of temperature measurements in the clinical laboratory, Clin. Chem. 29, 1380-1384 (1983).

[5] Mangum, B. W., Triple point of succinonitrile and its use in the

calibration of thermistor thermometers, Rev. Sci. Instrum.

54, 1687-1692 (1983).

[6] Mangum, B. W., private communication.

[7] Cutkosky, R. D., An ac resistance thermometer bridge, J. Res.

Natl. Bur. Stand. (U.S.) 74C, 15-18 (1970).

[8] Smit, W. M., Errors occurring in the determination of

temperature-heat content curves, Anal. Chim. Acta 17, 23-35 (1957).

[9] Smit, W. M., Melting curves (temperature-heat content curves)

as criteria for purity, Recuil Trav. Chim. des Pays-Bas. 75, 1309-1320 (1956).

[10] Furukawa, G. T.; J. L. Riddle, W. R. Bigge, and E. R. Pfeiffer, Application of some metal SRM's as thermometric fixed

points, Natl. Bur. Stand. (U.S.) Spec. Publ. 260-77, Supt. of Documents, U.S. Gov't. Printing Office: Washington, DC

20402 (1982).

[11] Riddle, J. L.; G. T. Furukawa and H. H. Plumb, Platinum

resistance thermometry, NBS Monograph 126, Supt. of Documents, U.S. Gov't Printing Office: Washington, DC 20402

(1973).

[12] Lewis, G. N., and M. Randall, Thermodynamics and Free Energy of Chemical Substances, McGraw-Hill Book Co.: New

York, NY, p. 238 (1923).

[13] White, W. P., Estimating impurities by means of the melting

point curve, J. Phys. Chem. 24, 393-416 (1920).

12
U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR REPORT NO. NBS/SP-260/101

2. Performing Organ. Report No. 3. Publication Date March 1986

4. TITLE AND SUBTITLE Standard Reference Materials:

SRM 1970: Succinonitrile Triple-Point Standard- Reference Standard Near 58.08 °C-A Temperature

5. AUTHOR(S)

B. W. Mangum and Samir El-Sabban

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered GAITHERSBURG, MD 20899

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP) Office of Standard Reference Materials

National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card No. 36-600505

I | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a si gnificant bibliography or literature survey, mention it here) Triple-point-of-succinonitrile cells have been tested and established as Standard Reference Material (SRM) 1970. Of the 115 cells tested, 109 were accepted

as SRM 1970. Five of the 115 cells had triple-point temperatures lower than 58.0785 °C (the low-temperature limit established for SRM 1970) and, consequently, were rejected. One of the 115 cells broke during tests on it. The mean value of the triple-point temperatures (obtained by freezing) of the 109 cells is 58.0796 ± 0.0015 °C, where the uncertainty is the total estimated uncertainty

relative to the International Practical Temperature Scale of 1968, Amended Edition

of 1975. The standard deviation of the triple-point temperatures is 0.48 mK. The purity of the succinonitrile of the SRM 1970 cells is estimated to range from

99.999,97% to 99.999,84%. The preparation of the cells, the various tests performed

on them, and the procedure recommended for their use are described.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons) SRM 1970; Standard Reference Materials; succinonitrile; temperature fixed point;

thermometry

13. AVAILABILITY

|~^| Unlimited

| | For Official Distribution. Do Not Release to NTIS

|~~y| Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

21

<TU.S. Government Printing Office: 198 6—491-07 0/4005 3 USCOMM-DC 6043-P80



Technical Publications

Periodical

Journal of Research—The Journal of Research of the National Bureau of Standards reports NBS research and development in those disciplines of the physical and engineering sciences in which the Bureau is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad

range of subjects, with major emphasis on measurement methodology and the basic technology underlying

standardization. Also included from time to time are survey articles on topics closely related to the Bureau's

technical and scientific programs. Issued six times a year.

Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with interested industries, professional organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies. Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and

technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide pro- gram coordinated by NBS under the authority of the National Standard Data Act (Public Law 90-396). NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published quarterly for NBS by

the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints, and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials, components, systems, and whole structures. The series presents research results, test methods, and perfor- mance criteria related to the structural and environmental functions and the durability and safety

characteristics of building elements and systems. Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject

area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies. Voluntary Product Standards—Developed under procedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized re- quirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private

sector standardizing organizations. Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological marketplace. Order the above NBS publications from: Superintendent of Documents, Government Printing Office, Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR 's—from the National Technical Information Service, Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the official source of

information in the Federal Government regarding standards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations). NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS

for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161, in paper copy or microfiche form.
U.S. Department of Commerce

National Bureau of Standards

Gaithersburg, MD 20899

Official Business

Penalty for Private Use $300