INST. OF STAND &

PUBUCATJONS BEFEffiiCE

1

ICO

NBSIR 73.158

Standard Reference Materials for

Combustion Calorimetry

George T. Armstrong and Walter H. Johnson

Thermochemistry Section

Physical Chemistry Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

July 1973

Interim Report

repared for

iffice of Standard Reference Materials

lational Bureau of Standards .

, D. C. 20234

NBSIR 73-158

STANDARD REFERENCE MATERIALS FOR

COMBUSTION CALORIMETRY

George T. Armstrong and Walter H. Johnson

Thermochemistry Section

Physical Chemistry Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

This report is prepared as a presentation for the Fourth International

Conference on Chemical Thermodynamics, Baden, Austria, 3-7 September

1973. The complete description of the experiments will be presented

in future publications which will receive general distribution.

Please consult the NBS Office of Technical Information and Publications

to obtain the proper citations.

July 1973

Interim Report

Prepared for Office of Standard Reference Materials

National Bureau of Standards

Washington, D. C. 20234

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Standard Reference Materials for Combustion Calorimetry

George T. Armstrong and Walter H. Johnson

Abstract

Combustion measurements using a rotating bomb adiabatic aneroid

calorimeter have been used to make a preliminary evaluation of ten

substances as potential thermochemical reference materials for combustion

of organic compounds containing CI and F. p-chlorobenzoic acid,

p-f luorobenzoic acid, and urea are recommended for acquisition,

certification, and distribution. Thianthrene may also be suitable.

For the ten substances including in addition to the above: o- and

m-chlorobenzoic acids, o-f luorobenzoic acid, nicotinic acid, acettanilide, and creatinine, typical combustion data are given, showing

corrections applied; and mean thermodynamic functions at axe

given together with error estimates. The results are compared

with other work. Recommendations and a discussion of the role of

standard reference materials for thermochemistry are given.

Table of Contents

Page

Abstract i

1.0 Introduction 1

2.0 Calorimeter 5

3.0 Experimental Studies 7

4.0 Substances Studied 13

4.1 Fluorobenzoic acids 13

4.2 Chlorobenzoic acids 13

4.3 Acetanilide 14

4.^ Urea (carbamide); ((NH2)2CO) 14

4.5 Nicotinic acid (pyridine-3-carboxylic acid;

(NC^H.COOH) 14

5 4

4.6 Creatinine (HN =C-N(CH^)-CH2-Co5h) 15

4.7 Thianthrene ((C,H, )^S„) 15

O 14- / Z 5.0 Recommendations 15

STANDARD REFERENCE MATERIALS FOR COMBUSTION CALORDETRY

GEORGE T. ARl'ISTRCR^G AND WALTER H. JOHNSON

Iherniochemistry Section

Physical Chemistry Division^ Institute for I-laterials Research

National Bureau of Standards, Washington, D.C. 20234 U.S.A.

1.0 Introouction

Standard reference materials (SRM's) for combustion calorimetry serve

two principal purposes. (1) A primary standard reference material provides

a means of calibrating a calorimeter using a process similar to those

vjhich are to be studied with the calorimeter. The value for the energy

of combustion determined in a national standardizing laboratory provides

the experimentalist with a scale of measurement consistent with the energy

scale of the measurement system. In the case of energy measurements this

is the joule as established in the International System of Units. (2) A

secondary standard reference material provides a well characterized

material of a particular class of substances, which can be studied in many

different laboratories. As the material is the same in all measurements,

observed differences are due either to differences in technique or to

differences in the calorimeters. If the experimental problems of measurement have been worked out by competent research workers in the field

recommended procedures for use of the material may also be available.

Such a material can be used by the experimentalist with some degree of

confidence to establish his capability of making accurate measurements on substances of this class. The possibility of differences in performances

of calorimeters may not be neglected. This is a less pronounced problem

in .bomb calorimetry than in some other calorimetric processes.

For many years benzoic acid has been available as a primary SRM. It was Available for this purpose as early as 1911 from the U.S. National

Bureau of Standards, Stratton (1911), and it, as well as other substances,

had been used by Stohman, Kleber, Langbein, and Offenhaver (1893). Technologically the principal use of this standard has been for calibrating

bomb calorimeters to be used in laboratories testing foods and other agricultural products, fuels, as well as other combustible materials and

tenergy sources. The standard has permitted rapid, inexpensive determinations of heating values of moderate accuracy. ^ However this particular

SRM was found to be of good enough quality even for the most precise

scientific studies of combustion energies, and its use throughout the

''"This paper is available as NBS Internal Report 73-158.

1
vjorlc in determining energies of combustion of pure substances has cause-l

0 lar^e fraction of t5;e total thermochemica 1 data base to be derived from

the certified energy of combustion.

Almost from the beginning^ the desirability of secondary SRM's was

recognized, but these materials have never been provided by a national

standardizing laboratory to the extent requested. The subject was

reviewed by Waddington (1956).

The reason secondary standard reference materials have not previously

been provided is probably in large part an economic matter. NBS standard

reference materials are sold at a price to compensate for their production,

certification, and sale. An SRM of a general character, such as benzoic

acid has a large enough market to permit sale at a very moderate price.

However, despite the fact tliat a number of laboratories have a very

urgent need for secondary SRM's, the actual number of potential users is

quite small. The estimated number of users in any year may be of the

order of ten for a particular standard reference material as specialized

as a thermochem.ical standard. The great benefit to the thermochemical

community and the improvement of the validity of thermochemical data are therefore important factors in justifying a series of materials.

Materials already in use for combustion calorimetry standards, and

materials previously proposed for combustion standards are listed in

Table 1, including both primary and secondary standards.

One purpose of a secondary SRM in thermochemistry is to give the user confidence in his ability to make accurate measurements after having

calibrated his apparatus. This seems to be primarily a didactic use or a reassurance. The novice training to do bomb calorimetry would be reassured

if, after calibrating his apparatus, he could then make measurements on a simple, straightforward process and obtain results that he could compare

with known correct values. This is the primary argument used for anotherC, H, 0 compound such as succinic acid. A possible variation of such a material from benzoic acid is a significantly different specific enthalpy

of ccsnbustion. The hydrocarbon, 2,2,4-trimethylpentane, gives the user an opportunity to test his skill at handling a volatile hydrocarbon. In

this respect it is partially satisfactory, but still fails to cope with

an important problem in petroleum test laboratories: the changing heat

value of a volatile fuel mixture on standing, due to fractional vaporization of the more volatile components. ^

2
Substance

hydrogen

methane

2 ^ 2

, 4 - trime thy 1 pentane

naphthalene

benzoic acid

sucrose salicylic acid

succinic acid

acetanilide

hippuric acid

urea nicotinic acid

THMA.M*

thianthrene

thioglycolic acid

sym-diphenyl thiourea

sulfanilamide

benzotrif luoride

p-f luorobenzoic acid

pentaf luorobenzoic acid

m-trif luoromethylbenzoic

acid

trichlorophenol

m-chlorobenzoic acid

p-chlorobenzoic acid

o bromobenzoic acid

m-iodobenzoic acid

triphenylphosphine oxide

H2(g)

^s^is^-^)

^lO^S^^)

C^H^O^Cc)

Cl2«22°ll(^)j

C^H^03(c)

CgHgNO(c)

CgHgN03(c)

CH^N20(c)

CgH^NO^Cc)

C^H^^NO^Cc)

^12^8^2

C^3H^2^2^(c)

C^HgN^O^SCc),

flow calorimetry

flow calorimetry

volatile hydrocarbon

formerly available

transfer standard

formerly available

C, 0- compound

N-compound

S- compound

C^E^O^dc)

y F-compound

C^HO^F^Cc)

C^H30Ci3(c)

C^H^O^CKc)

C^H^O^CKc)

C^H^O^BrCc)

C^H^02l(c)

^18«150P(=>

CI -compound

Br-compound

I-compound

P-compound

*tris (hydrox3niiethyl)aminome thane

3
Each additional element introduced into a compound also introduces

new problems. These problems include (a) obtaining completeness of com- bustion; and (b) obtaining a definite set of products. Thus, for instance a compound containing little hydrogen may smoke or char because

the flame is not hot enough to obtain complete combustion. This is a relatively simple problem in many cases, though troublescmie . The

techniques for obtaining more nearly complete combustion are well known

(higher oxygen pressure, promoters, lighter weight crucible and other

supports) ; also the techniques for determining that combustion is com- plete are known (CO^ determination, CO determination, odor of products,

absence of soot). Much more subtle problems are to establish the nature

of the products and to devise experimental conditions such that a con- sistent and analyzable set of products is obtained, when other elements

than C, H, 0 are present.

Typical problems are: (a) the formation of acid products when

group V, VI, and VII elements are present, (b) the formation of elements

in various oxidation states when multiple valency can occur. Acid

products can be determined by titration, but if more than one acid is

present the separate identification may be more difficult. Acid products may be corrosive to the calorimeter parts and side reactions may

therefore occur. Various oxidation states lead to other analytical

problems, as when Cl^ may be formed along with HCl from organic chlorine

compounds. The establishment of combustion conditions in which the

complexity of the products is minimized is a reasonable goal because it

simplifies the product analysis.

The problem of criteria for selection of suitable secondary reference materials does not have a simple answer. This becomes evident as . goon as one tries to choose a substance for a particular class —fluorine

compound—for example. Should the compound have a high proportion or a low proportion of fluorine? It turns out that if F is bound to C in the

compound, the probability of finding CF^ or other CF compounds in the

products is increased. As found by Good, Scott, Waddington (1956) the

amount of CF^ is determined by the ratio of H to F in the coirJbustion mixture--low H/F leading to high CF^. As CF^ is difficult to determine if

CO^ is also to be de'termined this presents a problem. One solution is tc select a high-as well as a low-fluorine sample. This approach leads to

conceptual difficulties because it increases the number of required samples and there is no discernable limit to such an increase. Any new set

of conditions could require a different reference material.

A possible solution to this dilemma is to set a criterion of difficulty for problems to be solved by the use of a standard reference

4
material. Thus an SRM for a given set of elements should exemplify a characteristic problem which must be solved in order to obtain satisfactory measurements.

An important function of reference materials is to help locate

errors in measurements by different individuals, different procedures and

different kinds of instruments. Thus too close adherence to a ritual

procedure and common design of calorimeter is shortsighted and likely to

obscure errors rather than reveal them.

Recognizing the importance of tracing errors in thermochemistiry and

of the important part reference materials may play in obtaining an internally self consistent set of thermochemical values inter-relating the

chemical substances, the National Bureau of Standards undertook the preparation of a series of thermochemical standard reference materials containing

the elements N_, F, CI, Br, I, S, and P, individually in organic compounds

This is a preliminary report of the investigations that have been carried

out in the study. The work involved collaboration between the Thermochemistry Section and the Office of Standard Reference Materials, which

provided samples for study and some financial support for the work. The

work that has been done is primarily a calorimetric study of the com- bustion energy of selected compounds which offer potentiality as standard reference materials.

2.0 Calorimeter

The calorimeter used in the experiments was designed , constructed and tested by Prosen and Johnson. It is an aneroid, vacuumjacketed calorimeter with adiabatic shield, and rotating bomb. The

calorimeter assembly is illustrated in figure 1. The bomb is shown in

f-igure 2. A principal problem in an aneroid calorimeter is to obtain

temperature distributions known well enough that heat transfer to the

surroundings does not create a large error. The laminated construction

is the design feature which solves this problem, when combined with the vacuum jacket and polished gold surfaces on bomb exterior and shield

interior.

The calorimeter is a comparison device, comparing the energy of com- bustion of the substance under study with the energy of combustion of the

reference substance, benzoic acid (NBS SRM 39i^. The certificate value,

26.434 ± 0.003 kJ«g was used for the energy of reaction of benzoic

acid. On the basis of calibration measurements the energy equivalent of

the calorimeter is about 2519 J'K the value being determined accurately

with an uncertainty (2 sdm) of about 0.005 percent for each series of

experiments.

''Standard reference materials listed with a number associated are available from the Office of Standard Reference Materials, National Bureau

of Standards, Washington, D.C. 20234.

5
Figure 1. Schenatic view

of calorimeter assembly.

(An early diagram) The

outer, room- temperature

y

evacuated box is shown,

with the rotating adia- -

batic shield. The shield

rotates on two axes following a pre-programmed routine. The bomb, (see fig.

2 for detail), is contained

within the adiabatic shield.

Figure 2. Cross section of aneroid calorimeter bcmb

(an early version) showing laminated construction.

Heat transfer is aided laterally by inner and outer

layers of high-conductivity metals, and hindered

radially by the laminated construction and by the

lower conductivity of the steel layer, which provides the necessary strength. From interior to

exterior the laminations consist of platinum liner

(about 1 mm), silver (about 12 mni)

steel (about 12 mm), silver (about

7 mm), gold plate. The bomb is

suspended within the adiabatic

shield by two axial pins inserted in

holes shown in top and bottom.

Temperatures are measured by a calibrated capsule-type platinumresistance thermometer inserted in the bomb wall. Temperature differences between calorimeter bomb and adiabatic shield are measured by

copper-constantan thermocouples. The output voltage is used to regulate

the adiabatic shield temperature in such a way as to minimize the tem6
perature difference. Small temperature drifts (due

to thermOTieter heat) are observed in the bomb temperature during the

rating periods, and these drifts are taken into account in calculating

the temperature rise. Temperature rise values ranged from about one kelvin to about three kelvins and were reported to 10 K. The energy equivalent of the standard calorimeter system was adjusted for variations in the average temperature of the experiments,

for heat capacities of minor components added to the calorimeter, and for

the heat capacities of the initial contents of the bomb. The first two

adjustments amounted to less than one J-K The heat capacities of the

bomb contents, accurately calculated in each experiment, contributed 15

to 20 J'K mostly due to the water added for dissolving acids formed.

The small energy equivalent of the calorimeter makes possible the use of comparatively small samples. Depending on the chemical constitution of the substance, samples of 0.1 to 0.7 g, releasing 2 to 8 kJ, are used to obtain the desired temperature increments of one to 3 K.

3.0 Experimental Studies

Typically a series of six experiments, with occasional variations of one or two in number, was made with each potential reference material.

The experiments are discussed briefly belcw for each substance. A

typical experiment is summarized for each substances in table 2. Data

listed for each substance are experiment number; observed total heat,

Q , ; correction for ignition energy, q. *, correction for decomposition

obs ° '

' ign'

of HNG^j q^^; Washburn correction, q^) correction for adjustment to standard final temperature, 'Irpj* energy of standard reaction, Uj-U^; mass of

, sample, m^ ; specific standard internal energy of reaction at selected

final temperature, Z^°(at Tf) . Special entries for some substances when

listed are mentioned in the paragraph relating to the substance.

The reaction^ carried out approximated the stoichiometric equations

listed in Table 3. The observed energy measurements were adjusted to

correspond to these reactions. In Table 4 are given average thermodynamic quantities and uncertainties of these quantities corresponding to

the equations in Table 3. The final temperature, Tf, to which the experimental reaction was referred, and the mean specific standard internal

energy of combustion .at Tf are given together with the number of

' c

'

experiments and the standard deviation of the mean. Also given are the

molar standard internal energy of combustion, ^°,the molar standard

enthalpy of combustion, and the molar standard enthalpy of formationj

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34

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COCM

12
^} at 25°C, for each substance, together with the respective uncertainties of these quantities.

In reducing the data atomic weights were taken from the 1969 table

of atomic weights. Enthalpies of formation of other substances were

taken from Wagman, et al (1968). Washburn corrections were made by com- puter program based on equations generally taken from appropriate chapters of Experimental Thermochemistry, Rossini (1956) and Skinner (1962).

The adaptations were made by Shomate (for C, H, 0, N compounds), and

further modified by Armstrong, and by Prosen with respect to these com- pounds and to allow treatment of F compounds. The program for CI com- pounds was provided by Mansson. No computer program for the 3 compound was available so that the calculations were made following Hubbard, Scott^

and Waddington (1956).

4.0 Substances studied: characterization and observations.

The studies which were carried out were not performed on samples

that would form the proposed reference materials, but on materials already available. In some cases these were substances already certified

as standard reference materials for other purposes.

4.1 Fluorobenzoic acids

A sample of o-f luorobenzoic acid and a sample of p-fluorobenzoic

acid(i) obtained from W. D. Good (U.S. Bureau of Mines, Bartlesville)

and a commercial sample of p-f luorobenzoic acid(ii) (J. T. Baker, Ultrex

No. 4979) were tested as potential fluorine containing thermochemical

standards. The fluorobenzoic acids from Good were the same as used by

Good, Scott, and Waddington (1956). The results obtained on the orthoacid in this work and in the Bureau of Mines work do not differ significantly. The results on the two samples of the para-acid do not differ

significantly from each other or from the work of Cox, Gundry, and Head

(1964). They do not agree as well with the results of Good, Scott, and

Waddington (1956).

4.2. Chlorobenzoic acids

0-chlorobenzoic acid used was an NBS microana lytica 1 standard; the m- chlorobenzoic acid was a commercial sample (J. T. Baker, Ultrex No.

4976); and p-Chlorobenzoic acid was obtained frcm the Lund thermochemical

laboratory, and was the sample used by Hu, Sinke, Mansson and Ringner

(1972). Relatively large uncertainties are assigned by Cox and Pilcher

(1970) to the work of Smith, Bjellerup, Krook, and -Westermark (1953) on

0-, and m-chlorobenzoic acids. The present results are well within these error limits. Bjellerup and Smith (1954) and Hajiev and Agarunov (1968)

have reported measurements on p-chlorobenzoic acid which are in agree13
ment with each other and with the present work. More recently Hu^ Sinke,

Mansson, ^nd Ringner (1971) have reported three values determined in

different calorimeters and which are at the limits of the combined errors. In these experiments ^^2^3 used to reduce chlorine formed in

the combustion. The correction for this reaction of chlorine is listed

in Table 2 as q^^* A difficulty was encountered in these experiments

caused by the slow reaction of arsenious oxide with oxygen during the

period after loading the bcrnib and before performing the heat measurement.

This tended to cause an error in the determination of the amount of

arsenic oxide formed during the reaction. It was found to be catalyzed

by the platinum of the bomb lining in contact with the arsenious oxide

solution. This difficulty was overcome by placing the arsenious oxide

solution in a plastic container. A small correction,

'^Pt^ applied

for the formation of H2PtGlg during the reaction.

4.3 Acetanilide (C,H^NHCOCH_)

The sample measured was NBS SRM 141b, certified as a material for

microchemical analysis of C, H, and N. The sample is indicated by its

certificate to be 99.99 mole percent pure, and to be non-hygroscopic It had been purified by fractional crystallization from the melt. The

enthalpy of formation calculated from our combustion measurements is in

close agreement with the value obtained by Wadso (1962) on the basis of

the liquid phase reaction of acetic anhydride and aniline as calculated

by Cox and Pilcher (1970) but in less good agreement with the value calculated by Domalski from the same reaction using different auxiliary data

4.4. Urea (carbamide) ; ((NH2)2CO)

The sample used was NBS SRM 912*', a standard obtained from a commercial source and certified for use in clinical analysis procedures. The

observed enthalpy of combustion is in good agreement with that reported

by Huffman (1940), and Mansson and Skinner (1963). Urea requires an

igniter to obtain consistent combustion. Using benzoic acid for

this purpose, very good precision is obtained. The energy from this

small amount of benzoic acid is listed in Table 2 as q, . This sample ^Aux

had the best reproducibility of the samples tested.

4.5 Nicotinic acid (pyridine-3-carboxylic acid); (NC H COOH)

1 b ^ The sample used was NBS SRM 148, certified for microde termination of

See footnote p. 5.

14
C, y^. Titrimetric assay indicates a purity of 99.99 r 0.08 percent.

No previous ceterninations have been mce of the combustion energy'. This

saniple gave clean reproducible conbustions vithout a promoter.

4.6 Creatinine (H::=<?.;(CH ) CiLCCl^H

1 The sample used was SB!-: 914^ certified for use in calibration

and standarization of procedures used in clinical analysis. Its com- position (percent) is stated to be: purity (99.8)^ volatile i::£.tter (0.03)^ chloride (0.07), ash (0.003), insoluble natter (0.001). The

sample required an igniter to obtain complete combustions. The reproducibility was substantially poorer than for the other nitrogen com- pounds tested and larger samples led to incomplete combustion. The

results were at about the limits of stated experimental error from those

reported by Huffman, Ellis, and Fox (1936).

4.7 Thianthren^ ((C,H, )„S„)

The sample was obtained commercially (Aldrich Chemical) and was zone refined with fifteen passes. The results were less reproducible than

most of the other substances, but had about the same reproducibility as previously reported work. These measurenients give an energy of combustion about midway between the results of Hubbard, Katz, and Waddington

(1954) and of Hu, Yen, and Ceng (1966) . They are in good agreement with

the results of Sunner (1963)

.

The thianthrene combustions led to a black finish on the platinum

crucible, which on ignition led to a clean matte finish. The problem.

which this poses is not understood. The correction in Table 2, labeled

q,., is the adjustnent of the final solution to the standard concen- ^diln

tration.

5.0 Recorw.ndations t The follcwing tentative recomnendations are made about the thermochemioal reference materials program: (1) In the selection of a thermochemical reference material for comparative studies a criterion of

difficulty should be used to insure that the reference material exem- plifies a difficult problem characteristic of the class of substances

it represents. (2) Urea is a reasonable reference material for nitrogen

COTipounds because it requires an igniter to achieve consistent

combustion, a problem characteristic of organic nitrogen compounds.

(3) while P-iChlorobenzoic acid and p-f luorobenzoic acid are lew in halogens, the amount of experimental comparison work already done on them

should be taken advantage of in selecting them as reference materials.

^See footnote p. 5.

15
(4) Because the demand for thermochemical reference materials is likely

to be light, the collection of reference materials certified for other

purposes seems to be a reasonable source for the materials needed.

(5) Certification of thermochemical reference materials containing special elements should include references to work done on the same substance (the same or other batches) in other places as v/ell as the standardizing laboratory. (6) Because the purposes of thermochemical refer- ence materials include the discovery of sources of systematic or random

errors, the use of rigidly defined procedures should not be overemphasized. Reasonable variations in procedures and instruments should be

encouraged. (7) Comparison of the results of measurements made in this

work with measurements made elsewhere on the same substances indicates

that differences between laboratories /samples /procedures lead to differences of 0.01 to 0.05 percent between well qualified scientists.

Absolute differences of 0.2 to 2 kJ«mol ^ are prevalent.

16
6 . 0 References :

Bjellerup, L., and Smith, L. (1954) Kgl. Fysiograph. Sa'llskap. Lund

Forh. 24, 21.

Cox, J, D., Gundry, H. A., and Head, A. J. (1964) Trans. Faraday Soc. ^ 60, 653.

Cox, J. D., and Pilcher, G. (1970) Thermochemistry of Organic and Organ- ometallic Compounds , Academic Press, London.

Domalski, E. S. (1972) J. Phys, and Chem. Reference Data 1, 221.

Good, W. D., Scott, D. W. , and Waddington (1956) J. Phys. Chem. 60, 1080

Hajiev, S. N. , and Agarunov, M. J. (1968) J. Organomet. Chem. _11, 415.

Hu, A. T., Sinke, G. C, Mansson, M. , and Ringner, B. (1972), J. Chem.

Thermodynamics 4, 283.

Hu, J-H, Yen, H-K, and Ceng, Y-L (1966) Acta Chemica Sinica 32, 242.

Hubbard, W. N., Katz, C, and Waddington, G. (1954) J. Phys. Chem. 58,

142.

Hubbard, W. N., Scott, D. W. , and Waddington, G. (1956) in Experimental

Thermochemistry, F. D. Rossini, editor, Interscience Pub., NY, p. 75

Huffman, H. M. (1940) J. Am. Chem. Soc. 62, 1009.

Huffman, H. M., Ellis, E. L., and Fox, S. W. (1936) J. Am. Chem. Soc.

58, 1728.

Keith, W. A., and Mackle, H. (1958) Trans. Faraday Soc. 54, 353.

l^nsson, M. , and Sunner, S. (1963) Acta Chem. Scand. 17_, 723.

Rossini, F. D. (1956) Experimental Thermochemistry , Interscience

Publishers, New York.

Scott, D. W., Good, W. D., and Waddington, G. (1956) J. Phys. Chem.

60, 1080.

Skinner, H. A. (1962) Experimental Thermochemistry , Vol. II, Interscience Publishers, New York.

Smith, L., Bjellerup, L., Krook, S. and Westermark, H. (1953) Acta Chem.

Scand. 7, 65.

Stohman, F. , Kleber, C. Langbein, H. and Offenhaver, P. (1893>.

Stratton, S. W. (1911) The Standardization of Bomb Calorimeters , Circular Bur. Stand. No. 11, U.S. Government Printing Office,

Washington, D.C., p. 10.

Sunner, S. (1946) Svensk Kem. Tidr. 58, 71.

Sunner, S. (1963) Acta Chem. Scand. 17, 728.

Sunner, S., and Lundin, B. (1953) Acta Chem. Scand. 7, 1112.

Waddington, G. (1956) in Experimental Thermochemistry , F. D. Rossini,

editor, Interscience Publishers, Inc., New York, p. 287-295.

17
Wadso, I. (1962) Acta.Chem. Scand. 16, 471.

Wagman, U. D., Evans, W. H. , Parker, V. B., Halow, I., Bailey, S. M.

and Schumm, R. H. (1968) Selected Values of Chemical Thermodynamic

Properties , NBS Tech. Note 270-3, U.S. Government Printing Office,

Washington, D.C.

18
FORM NBS-n4A (1-71) U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA

SHEET NBSIR 73-158

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Standard Reference Materials for Combustion

Calorimetry

5. Publication Date

6 July 1973

6. Performing Organization Code

7. AUTHOR(S)

G. T. Armstrong and W. H. Johnson

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No. 3160275 and 3160110

11. Contract/Grant No.

12. Sponsoring Orgcinization Name and Address

Office of Standard Reference Materials

13. Type of Report & Period C ove re d Interim Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Combustion measurements using a rotating bomb adiabatic aneroid calorimeter

have been used to make a preliminary evaluation of ten substances as potential

thermochemical reference materials for combustion or organic compounds containing

S, CI and F. p-chlorobenzoic acid^ p-f luorobenzoic acid^ and urea are recommended for acquisition^ certification^ and distribution. Thianthrene

may also be suitable. For the ten substances including in addition to the above:

o- and m-chlorobenzoic acids, o-f luorobenzoic acid, nicotinic acid, acetanilide,

and creatinine, typical combustion data are given, showing corrections applied;

and me^n thermodynamic functions at 25 °C are given together with error estimates.

The results are compared with other work. Recommendations and a discussion of

the role of standard reference materials for thermochemistry are given.

17. KEY WORDS (Alphabetical order, separated by semicolons) Acetanilide ; bomb calorimetry; calorimetry;

chlorobenzoic acid; combustion; creatinine; f luorobenzoic acid; nicotinic acid;

reference materials; thermochemical; thermochemical standards; thianthrene; urea.

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