UGANDA STANDARD  
      US ISO 9831
First Edition
   2009 -09-04
 
Reference numbe r 
  US ISO 9831:1998
 © UNBS 200 9 
  
Animal feeding stuffs, animal products, and faeces or urine — 
Determination of gross calorific value — Bomb calorimeter 
method 
 US ISO 9831:1998  
 
© UNBS  2009 – All rights reserved Compliance with this standard does not, of itself confer immunity from legal obligations 
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct application  
© UNBS 2008  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, in cluding photocopying and microfilm, without prior written 
permission from UNBS. 
Requests for permission to reproduce this document should be addressed to 
The Executive Director 
Uganda National Bureau of Standards 
P.O. Box 6329 
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Uganda 
Tel: 256 41 505 995 
Fax: 256 41 286 123 
E-mail: unbs@infocom.co.ug
   US ISO 9831: 1998  
© UNBS  2008 - All rights reserved National foreword 
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry  of Tourism, Trade and 
Industry established by the Act of Parliament of 198 3, of the Laws of Uganda.  UNBS is mandated to co-
ordinate the elaboration of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex A limentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT/SPS Agr eements of the World Trade Organisation (WTO). 
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is established to deliberate on standards in a gi ven field or area and consists of representatives of 
consumers, traders, academician s, manufacturers, governme nt and other stakeholders. 
Draft Uganda Standards adopted by the Technical Committ ee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council. 
This Uganda Standard, US ISO 9831:1998,  Animal feeding stuffs, animal products, and faeces or urine —
Determination of gross calorific value — Bomb calorimeter method, is identical with and  has been
reproduced from an International Standard ISO 9831:1998,  Animal feeding stuffs, animal products, and faeces
or urine — Determination of gross calorific value — Bomb calorimeter method, and has been adopted
as a Uganda Standard . 
Wherever the words, "International Standard" a ppear, they should be replaced by "Uganda Standard." A Reference numbe r
ISO 9831:1998 (E)INTERNATIONAL
STANDARDISO
9831
First edition
1998-08-01
Animal feeding stuffs, animal products, and
faeces or urine — Determination of grosscalorific value — Bomb calorimeter method
Aliments des animaux, produits d'origine animale et excréments ou
urines — Détermination de la valeur calorifique brute — Méthode à la
bombe calorimétriqueISO 9831:1998(E)
©   ISO 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying andmicrofilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
iiContents
1Scope............................................................................................... 1
2Normative references...................................................................... 1
3Definitions........................................................................................ 2
4Principle........................................................................................... 2
5Reagents and materials................................................................... 2
6Apparatus........................................................................................ 3
7Sampling.......................................................................................... 4
8Preparation of test sample and test portion..................................... 4
9Procedure........................................................................................ 5
10Corrections...................................................................................... 7
11Expression of results....................................................................... 9
12Precision.......................................................................................... 10
13Test report....................................................................................... 11
Annex A (normative)  Determination of the effective heat capacity of
the calorimeter................................................................................. 12
Annex B (normative)  Special procedures for preparation of the test
sample............................................................................................. 14
Annex C (informative)  Method of checking that the average deviation
of the rate of change of temperature is within the specified limit..... 16
Annex D (informative)  Examples of calculating the results of calorific
determinations................................................................................. 18
Annex E (informative)  Results of interlaboratory tests.......................... 22
Annex F (informative)  Bibliography....................................................... 23© ISO ISO 9831:1998(E)
iiiForeword
ISO (the International Organization for Standardization) is a worldwide
federation of national standards bodies (ISO member bodies). The work ofpreparing International Standards is normally carried out through ISOtechnical committees. Each member body interested in a subject for whicha technical committee has been established has the right to be representedon that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collab-orates closely with the International Electrotechnical Commission (IEC) onall matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an InternationalStandard requires approval by at least 75 % of the member bodies castinga vote.
International Standard ISO 9831 was prepared by Technical Committee
ISO/TC 34,
 Agricultural food products , Subcommittee SC 10,  Animal
feeding stuffs .
Annexes A and B are an integral part of this International Standard.
Annexes C to F are for information only.INTERNATIONAL STANDARD   © ISO ISO 9831:1998(E)
1Animal feeding stuffs, animal products, and faeces or urine —
Determination of gross calorific value — Bomb calorimeter method
1   Scope
This International Standard specifies a method for the determination of the gross calorific value of animal feeding
stuffs, animal products and faeces or urine at constant volume in an adiabatic, an isothermal, or a static bombcalorimeter.
The result obtained by this method is the gross calorific value of the test sample at constant volume, the water of
the combustion products being condensed to liquid at the calorimeter temperature.
NOTE    The international reference temperature for thermochemistry of 25 °C is used as the reference temperature for calorific
value, although the temperature dependence of the calorific value of the materials to which this International Standard appliesis small (about 1 J·g
21·K21).
2   Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject torevision, and parties to agreements based on this International Standard are encouraged to investigate thepossibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintainregisters of currently valid International Standards.
ISO 651:1975, 
Solid-stem calorimeter thermometers.
ISO 652:1975, Enclosed-scale calorimeter thermometers.
ISO 1770:1981, Solid-stem general purpose thermometers.
ISO 1771:1981, Enclosed-scale general purpose thermometers.
ISO 1928:1995, Solid mineral fuels — Determination of gross calorific value by the bomb calorimeter method, and
calculation of net calorific value.
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods.
ISO 6496:— 1), Animal feeding stuffs — Determination of moisture and volatile matter content.
ISO 6498:— 2), Animal feeding stuffs — Preparation of test samples .
                             
1)   To be published. (Revision of ISO 6496:1983)
2)   To be published. (Revision of ISO 6498:1983)ISO 9831:1998(E) © ISO
23   Definitions
For the purposes of this International Standard, the definitions given in ISO 1928 apply.
4   Principle
Combustion of a weighed portion of the test sample in oxygen in a bomb calorimeter under standardized conditions.
Calculation of the gross calorific value from the temperature rise of the water in the calorimeter vessel and the meaneffective heat capacity of the calorimeter. Allowances are made for the heat released by the ignition fuse, forthermochemical corrections and, where appropriate, for heat losses from the calorimeter to the water jacket.
5   Reagents and materials
Use only reagents of recognized analytical grade.
5.1   Water, complying with at least grade 3 in accordance with ISO 3696.
5.2   Oxygen, at a pressure capable of filling the bomb to 3 MPa and free from combustible matter.
NOTE 1    Oxygen manufactured by an electrolytic process may contain up to 4 % of hydrogen and is therefore unsuitable.
NOTE 2    1 MPa = 1 MN/m 2.
5.3   Fuse, comprising the following.
5.3.1   Firing wire , nickel/chromium wire (0,16 mm to 0,20 mm in diameter), or platinum wire (0,06 mm to 0,10 mm
in diameter).
5.3.2   Cotton thread , white cellulose.
5.3.3   Polyethylene strip , thin film of dimensions 30 mm by 5 mm.
5.4   Polyethylene bags , of dimensions 68 mm by 110 mm.
5.5   Polyethylene bags , of dimensions 50 mm by 55 mm, and mass approximately 170 mg.
5.6   Silica gel , chromatographic-grade powder.
5.7   Sodium hydroxide solution , standard volumetric solution, c(NaOH) = 0,1 mol/l.
5.8   Screened methyl orange indicator solution , r = 1 g/l.
Dissolve 0,25 g of methyl orange and 0,15 g of xylene cyanol FF in 50 ml of 95 % ( V/V) ethanol and dilute to 250 ml
with water.
5.9   Benzoic acid , thermochemical standard, certified by a national testing authority.
Drying or any treatment other than pelleting shall not be carried out.The gross calorific value at constant volume of the benzoic acid, listed in the certificate for the conditions of use,
shall be adopted in calculating the effective heat capacity of the calorimeter (see annex A).© ISO ISO 9831:1998(E)
36   Apparatus
Usual laboratory apparatus and, in particular, the following.
6.1   Bomb, capable of withstanding safely the pressure developed during combustion.
The design shall permit complete recovery of all liquid products.
The construction materials shall resist corrosion by the acids produced by the combustion.
CAUTION — Inspect bomb parts regularly for wear and corrosion. Pay particular attention to the condition
of the threads of the main closure.
6.2   Calorimeter vessel , made of metal, highly polished on the outside and capable of holding sufficient water to
cover completely the flat upper surface of the bomb while the water is being stirred.
The vessel shall be provided with a console to centre the bomb in the vessel and to obtain water circulation below
the bomb.
6.3   Stirrer, driven at a constant rotational speed.
The stirrer shaft shall contain a non-conducting section below the cover of the water jacket to minimize the
transmission of heat to or from the system. If a cover is used for the calorimeter vessel, the non-conducting sectionshall be above this cover.
For isothermal and static bomb calorimeters, the rate of stirring shall ensure that the length of the main period
(see 9.6) in determinations of effective heat capacity using benzoic acid (see annex A) does not exceed 10 min.
6.4   Water jacket , which may be an adiabatic, isothermal or static type, enclosing the calorimeter vessel with an
air-gap of approximately 10 mm separating the vessel and water jacket.
The adiabatic water jacket shall have either electrode or immersion heaters capable of supplying energy at a rate
sufficient to maintain the temperature of the water in the jacket to within 0,1 °C of that of the calorimeter vessel afterthe charge has been fired. When in equilibrium at 25 °C, the temperature drift of the calorimeter vessel shall notexceed 0,000 5 °C/min.
NOTE 1    Special precautions are needed at high environmental temperatures.
The isothermal water jacket shall be provided with a means of maintaining it at a constant temperature to thenearest 0,1 °C.
The static water jacket shall have a thermal capacity great enough to restrict changes of temperature of the water in
it. From the time of firing the charge to the end of the after-period or during a period of 15 min, whichever is thegreater, with a cooling factor d = 0,002 0  min
21 (see 10.3), the rise in temperature of the water in the jacket shall be
less than 0,16 °C; with a cooling factor d = 0,003 0  min 21, the rise in temperature shall be less than 0,11 °C.
NOTE 2    For an insulated metal jacket, this can be ensured by making the capacity at least 12,5 l, contained in a wide annula r
jacket.
6.5   Temperature-measuring instrument , capable of indicating temperatures which, when corrected, have an
accuracy of 0,002 °C, so that temperature intervals of 2 °C to 3 °C can be determined with an accuracy of 0,004 °C.
It shall be calibrated against a known standard by a national testing authority, at intervals not larger than 0,5 °C over
the range of use or, for mercury-in-glass thermometers, over the whole graduated scale.
The following types of thermometer are suitable:
a) resistance thermometers comprising a platinum resistance, resistance bridge and galvanometer;b) mercury-in-glass thermometers which conform to ISO 651, ISO 652, ISO 1770 or ISO 1771.
A viewer with a magnification of about five times is required for reading the temperature to the required accuracy.ISO 9831:1998(E) © ISO
4A mechanical vibrator is recommended to tap the thermometer for a period of about 10 s before reading the
temperature, to prevent sticking of the mercury column. If this is not available, the thermometer shall be tappedmanually, for example with a pencil.
6.6   Crucible, of silica, nickel/chromium or platinum.
The crucible shall be about 25 mm in diameter, flat-based and not more than 20 mm high. Silica crucibles shall be
about 1,5 mm thick and metal crucibles about 0,5 mm thick.
For benzoic acid, either of the crucibles specified is suitable. If, after combustion, smears or unburned material
occur on the crucible, a small nickel/chromium crucible (for example 0,25 mm thick, 15 mm in diameter and 7 mmhigh) may be used.
6.7   Ignition circuit .
The electrical supply shall be 6 V to 12 V alternating current from a step-down transformer or direct current from
batteries. It is desirable to include a current-meter or pilot light in the circuit to indicate when current is flowing.
The firing switch shall be of the spring-loaded, normally open type.
6.8   Ancillary equipment , comprising the following.
6.8.1   Balance, capable of weighing at least 3 kg to the nearest 1 g.
6.8.2   Analytical balance , capable of weighing to the nearest 0,1 mg.
6.8.3   Briquette press .
6.8.4   Pressure regulator , to control the filling of the bomb with oxygen.
6.8.5   Pressure gauge , range from 0 MPa to 5 MPa, to indicate the pressure in the bomb.
6.8.6   Relief valve or bursting disc , operating at 3,5 MPa, installed in the filling line, to prevent overfilling the
bomb.
CAUTION — Equipment for high-pressure oxygen shall be kept free from oil and grease. Do not test or
calibrate the pressure gauge with hydrocarbon fluid.
6.9   Timer, fitted in a convenient place, indicating minutes and seconds.
It may usefully incorporate a device giving audible signals lasting 10 s starting at 1-min intervals.
7   Sampling
Sampling is not part of the method specified in this International Standard. A recommended sampling method is
given in ISO 6497 [4].
It is important that the laboratory receive a sample which is truly representative and has not been damaged or
changed during transport or storage.
8   Preparation of test sample and test portion
Prepare the test sample in accordance with ISO 6498.© ISO ISO 9831:1998(E)
58.1   Air-dry samples
8.1.1   Grind the laboratory sample so that it passes completely through a sieve with 1 mm apertures.
Mix the sample, preferably by mechanical means, immediately before the determination. By use of the briquette
press (6.8.3), press 0,5 g to 5 g of the test sample to form a pellet. The mass of the test portion depends on thecalorific value and the effective heat capacity of the calorimeter. The mass of the test portion should be such thatthe temperature rise due to combustion is between 2 °C and 3 °C.
Adequate precautions shall be taken to prevent uptake or loss of moisture by the test sample during mixing and
pelletizing, so that the moisture content of the test sample, recently determined as specified in 9.2, can be used infurther calculations. If this is not possible, the sample shall be exposed in a thin layer for the minimum timenecessary for the moisture content to reach approximate equilibrium with the atmosphere of the laboratorycontaining the bomb calorimeter.
8.1.2   For air-dry samples with a fat content exceeding 10 % ( m/m), and for air-dry samples which cannot be
pelleted easily, proceed as specified in B.1.
8.2   Liquid samples
Proceed as specified in B.2.
8.3   Samples of fresh materials
Proceed as specified in B.3.
9   Procedure
9.1   Determination of effective heat capacity of the calorimeter
If the effective heat capacity of the calorimeter is not known, or if the known value is questioned, and at intervals notexceeding 6 months, determine the effective heat capacity of the calorimeter as specified in annex A.
9.2   Determination of moisture content
For air-dry samples, determine the moisture content of the test sample in accordance with ISO 6496, at the sametime as the determination of the calorific value.
9.3   Preparation of the bomb
Place the test portion (clause 8) in the form of a pellet (see 8.1.1) or contained in a polyethylene bag (see 8.1.2, 8.2and 8.3), weighed to the nearest 0,1 mg, in the crucible (6.6) of the bomb.
NOTE 1    Normally 1 g of air-dry sample is an appropriate test portion (see also clause 8).
Connect a piece of firing wire (5.3.1) tautly across the terminals of the bomb. Tie a cotton thread (5.3.2) or a strip ofpolyethylene film (5.3.3), of known mass, to the firing wire. Arrange the ends of the cotton thread or polyethylenefilm so that they touch the sample.
NOTE 2    For convenience, a measured length of cotton thread of known mass per length may be used. The length used in
each determination of calorific value should be the same as was used in the determination of the effective heat capacity of thecalorimeter. The same applies to the polyethylene strip, if used.
Put 5 ml of water in the bomb (6.1). Assemble the bomb and charge it slowly with oxygen (5.2) to a pressure of
3 MPa without displacing the original air. If the bomb is inadvertently charged with oxygen above 3,3 MPa, discardthe test and begin again.ISO 9831:1998(E) © ISO
69.4   Preparation of the calorimeter vessel
Put sufficient water in the calorimeter vessel (6.2) to cover the flat upper surface of the bomb cap. This quantity of
water shall be the same, to within 1 g, as that used in the determination of the mean effective heat capacity of thecalorimeter (9.1).
If an isothermal calorimeter or static calorimeter is used, the initial temperature of the water shall be such that, at the
end of the main period [see 9.6 b)], the temperature does not exceed that of the water in the jacket by more than0,5 °C.
Transfer the calorimeter vessel to the water jacket (6.4). Lower the bomb into the calorimeter vessel and check that
the bomb is gas-tight. If gas escapes from the bomb, discard the test, eliminate the cause of leakage and beginagain.
For an adiabatic calorimeter, proceed in accordance with 9.5.For isothermal and static calorimeters, proceed in accordance with 9.6.
9.5   Procedure specific for an adiabatic calorimeter
Assemble and start up the apparatus. Use a constant rate of stirring, so that the predetermined interval (see A.4)
does not exceed 10 min. Select the setting of the bridge circuit that will result in the minimum drift in temperature ofthe calorimeter vessel at the final temperature.
After 10 min, tap the thermometer (see 6.5) lightly and read it to 0,001 °C. This is the firing temperature ( t
0). Fire the
charge, holding the switch closed only long enough to ignite the fuse.
CAUTION — Do not extend any part of the body over the calorimeter during firing, nor for 20 s thereafter.
After the predetermined interval, established in the determination (9.1) of the effective heat capacity of the
calorimeter, tap the thermometer again and read it to 0,001 °C. This is the final temperature ( tn). The observer
shall take care to avoid parallax errors when using the magnifying viewer (see 6.5) to read mercury-in-glassthermometers.
Proceed in accordance with 9.7.
9.6   Procedure specific for isothermal and static calorimeters
Assemble the apparatus. Start the stirrer and maintain in operation at a constant rate throughout the determination.
Stir for at least 10 min before starting to read the temperature to 0,001 °C and continue to do so at intervals of 1 minfor a period of 5 min.
Tap the thermometer (see 6.5) lightly for 10 s before each reading. Take care to avoid parallax errors when using
the magnifying viewer (see 6.5) to read mercury-in-glass thermometers.
Fire the charge immediately after reading the last temperature in the preliminary period [see a) below]. Hold the
switch closed only long enough to ignite the fuse.
CAUTION — Do not extend any part of the body over the calorimeter during firing, nor for 20 s thereafter.
Read the thermometer as follows.
a) Preliminary period:  If the average deviation of the values of the rate of change of temperature during this
period of 5 min exceeds 0,001 °C/min (see note 2), continue to read the thermometer at 1-min intervals until theaverage deviation is less than 0,001 °C/min for a period of 5 min. The last temperature of the preliminary periodis the initial temperature ( t
0) of the main period.© ISO ISO 9831:1998(E)
7b) Main period:  During the first few minutes of the main period, it will not be possible to read the thermometer to
0,001 °C, but resume readings to this precision as soon as possible and continue them to the end of the test.The main period does not necessarily end with the attainment of maximum temperature. The last temperatureof the main period is the final temperature ( t
n), which is the initial temperature of the after-period.
c) After-period:  This period begins at the first temperature after which for a subsequent 5-min period, the
average deviation of the individual values of the rate of change of temperature is not more than 0,001 °C/min(see note 2). This first temperature is the final temperature ( t
n).
NOTE 1    If the Regnault-Pfaundler cooling correction (see 10.3) is to be calculated, the procedure specified should be
adopted. If an alternative formula, which is equivalent and acceptable, is to be used, some of the temperature readings may notbe required and the procedure should be modified accordingly.
NOTE 2    A convenient method of checking that the average deviation of the rate of change of temperature during the
preliminary period and the after-period is within the specified limit is specified in annex C.
9.7   Assesment of the bomb contents
9.7.1   Remove the bomb from the calorimeter vessel, release the pressure and dismantle the bomb. Examine the
bomb interior and discontinue the test if unburned sample or a sooty deposit is visible.
9.7.2   When certain samples are tested, the residue in the bomb may contain detectable unburned sample. A
correction to be applied for such persistently incomplete combustion may be calculated from the amount ofunburned carbon, which may be estimated by the procedure described in 9.7.3.
9.7.3   The mass of unburned carbon in the crucible may be estimated as follows.
Transfer the contents of the crucible (not the lining) to a silica or porcelain dish and dry for 1 h at 105 °C. Leave to
cool, then weigh the dish and its contents to the nearest 0,1 mg. Heat at 550 °C for 1 h. Leave to cool and reweighto determine the loss in mass. The loss is taken to be unburned carbon.
Alternatively, the unburned carbon may be determined by one of the methods specified in ISO 609 [1] or
ISO 625 [2]. Should more than 6 mg of unburned carbon be determined, the correction will be invalid and thedetermination of gross calorific value should be repeated.
9.8   Determination of acidity
Wash the contents of the bomb into a beaker with water. Wash the underside of the bomb cap and the outside ofthe crucible with water. Add the washings to the beaker. Dilute to approximately 100 ml and boil to expel carbondioxide.
While the mixture is still hot, titrate the warm (not boiling) bomb washings with sodium hydroxide solution (5.7) using
the screened methyl orange solution (5.8) as indicator, to determine the total acidity.
10   Corrections
10.1   General
Apply the corrections given in 10.2 to 10.6 to the experimental observations.
10.2   Thermometer corrections
If a mercury-in-glass thermometer is used, apply the corrections specified in the certificate issued with thethermometer, to the observed firing temperature ( t
0) and to the final temperature ( tn).ISO 9831:1998(E) © ISO
810.3   Cooling correction
For an adiabatic calorimeter such as is specified, the heat loss to the water jacket is negligible and a cooling
correction is not necessary.
For an isothermal or static calorimeter, the heat loss to the water jacket may be compensated by an addition to the
temperature rise. This correcting addition may be calculated by the Regnault-Pfaundler equation or by any equationwhich is equivalent to it and which is accepted as such by a national standardizing body.
Calculate the cooling correction according to Regnault-Pfaundler by the equation:
t
c = (nvp 1 dZ)f
in which
dvv
tt=-
-ap
ap
() Zt t t n tin
iin
=++ −



==−
∑05
11
,0oop
where
tcis the cooling correction, in degrees Celsius, according to Regnault-Pfaundler;
nis the number of minutes in the main period;
dis the cooling factor, in reciprocal minutes, of the calorimeter, which shall be determined for each set of
conditions;
Zis a temperature term, in degrees Celsius;
fis a correction factor for units, in minutes ( f = 1 min);
vpis the rate of fall of temperature, in degrees Celsius per minute, in the preliminary period (if the temperature
is rising, vp is negative);
vais the rate of fall of temperature, in degrees Celsius per minute, in the after-period;
tpis the average temperature (without thermometer correction), in degrees Celsius, during the preliminary
period;
tais the average temperature (without thermometer correction), in degrees Celsius, during the after-period;
t0ois the firing temperature (without thermometer correction), in degrees Celsius;
t1, t2, ..., ti, ..., tnare the successive temperatures (without thermometer correction), in degrees Celsius,
recorded during the main period;
tnois the final temperature (without thermometer correction), in degrees Celsius, (see 9.6 and note 2 in 9.6);
i=i=n
it
11−
∑is the sum of the temperatures t1, t2, ..., ti, ..., tn21, in degrees Celsius.
NOTE    The calculations may also be carried out with temperatures corrected for thermometer inaccuracies, provided that the
thermometer correction is applied to each temperature.© ISO ISO 9831:1998(E)
910.4   Correction for heat of ignition
The heat release from the cotton thread and firing wire shall be subtracted from the total heat released.
Calculate the heat release ( e1) from the cotton thread from its mass (dried at 100 °C) and the calorific value of
cellulose (17 500 J/g).
Calculate the heat release ( e2) from the firing wire from the mass of a piece of wire equal in length to the distance
between the poles of the bomb, allowing 1 400 J/g for nickel/chromium wire or 420 J/g for platinum wire.
Determine the calorific value ( e1) of the polyethylene strip from the combustion of 0,5 g (approximately 10 sheets).
10.5   Correction for heat of formation of acids
The heat gain due to the formation of sulfuric acid and nitric acid shall be subtracted from the total heat released.
If V is the volume, in millilitres, of the sodium hydroxide solution (5.7) used in the titration in 9.8, the correction for
heat (e3) of formation of acids shall be 6,0 V.
10.6   Correction for incomplete combustion
Take as the value of the mass of unburned residue the loss in mass obtained after ignition of the residue contained
in the crucible. Add its heat equivalent ( e4), calculated on the basis of a calorific value of 33 500 J/g, to the heat
release determined.
10.7   Correction for polyethylene bag  (if used)
Determine the calorific value ( e5) of polyethylene from the combustion of the polyethylene bags (5.4 or 5.5). Repeat
the determination at least six times.
11   Expression of results
Calculate the gross calorific value at constant volume from the experimental values using the following equation:
()QCt t t e e e e e
mn=−+−−−−−0 12345c
where
Qis the gross calorific value, in joules per gram, at constant volume of the test portion;
Cis the effective heat capacity, in joules per degree Celsius, of the calorimeter, calculated as the mean of
five determinations (see 9.1);
t0is the firing temperature, in degrees Celsius, corrected for the thermometer error;
tnis the final temperature, in degrees Celsius, corrected for the thermometer error;
tcis the cooling correction, in degrees Celsius, according to Regnault-Pfaundler for isothermal or static
calorimeters (see 10.3);
e1is the correction for heat of combustion, in joules, of the cotton thread or the polyethylene strip (see 10.4);
e2is the correction for heat of combustion, in joules, of the firing wire (see 10.4);ISO 9831:1998(E) © ISO
10e3is the correction for heat, in joules, of formation of sulfuric acid and nitric acid (see 10.5);
e4 is the correction for incomplete combustion, in joules (see 10.6);
e5 is the correction for heat of combustion, in joules, of the polyethylene bag (see 10.7), if used;
mis the mass, in grams, of the test portion.
Report the result to the nearest multiple of 10 J/g. The result should preferably be the mean of duplicate
determinations (see clause 12).
Examples to illustrate the method of calculating the results of calorific determinations are given in annex D.
12   Precision
12.1   Interlaboratory tests
Details of interlaboratory tests on the precision of the method are given in annex E. The values derived from these
tests may not be applicable to concentration ranges and matrices other than those given.
12.2   Repeatability
The absolute difference between two independent single test results, obtained using the same method on identicaltest material in the same laboratory by the same operator using the same equipment within a short interval of time,will in not more than 5 % of the cases exceed the value of r shown in table 1.
12.3   Reproducibility
The absolute difference between two single test results, obtained using the same method on identical test material
in different laboratories by different operators using different equipment, will in not more than 5 % of the casesexceed the value of R shown in table 1.
Table 1 — Repeatability limit ( r) and reproducibility limit ( R)
SampleGross calorific value at
constant volumerR
J/g1) J/g J/g
Hay 17 421 108 322
Wilted silage 17 467 115 292
Mixed feed 17 106 81 347
Pig faeces 18 311 49 316
Urine 2) 7 184 426 957
Milk powder 2) 17 770 333 697
1)   Based on air-dry matter.
2)   Outliers were not removed. The indicated values are for the sum of the test portion and the polyethylene bag.© ISO ISO 9831:1998(E)
1113   Test report
The test report shall specify:
— all information necessary for the complete identification of the sample;
— the sampling method used, if known;— the test method used, with reference to this International Standard;— all operating details not specified in this International Standard, or regarded as optional, together with details of
any incidents which may have influenced the test result(s);
— the test result(s) obtained; or— if the repeatability has been checked, the final quoted result obtained.ISO 9831:1998(E) © ISO
12Annex A
(normative)
Determination of the effective heat capacity of the calorimeter
A.1   Principle
Combustion of a known mass of benzoic acid of certified calorific value in oxygen in a bomb calorimeter. Calculation
of the sum of the heat of combustion of the benzoic acid, the heats of combustion of the cotton thread and the firingwire and the heat of formation of nitric acid.
Carry out at least five complete determinations of effective heat capacity. Provided that their range does not exceed
55 J/°C, take the mean of the five test results for calculation of the calorific value of the test sample (see clause 11).
A.2   Procedure
Proceed as specified in 9.3 to 9.8 for the determination of calorific value. If necessary, use the small metal cruciblespecified in 6.6.
When determining the effective heat capacity of an adiabatic calorimeter, read the temperature at 1-min intervals
over a period of 10 min, commencing 5 min after firing the charge (see A.4).
Dilute the bomb washings to approximately 50 ml with water. Titrate the nitric acid directly with the sodium
hydroxide solution (5.7) using the screened methyl orange solution (5.8) as indicator.
A.3   Calculation of a single complete determination
Calculate the effective heat capacity of the calorimeter by the equation:
CmQ e e e
tttn=+++
−+bb
c123
0
where
Cis the effective heat capacity, in joules per degree Celsius, of the calorimeter;
mbis the mass, in grams, of benzoic acid (5.9);
Qbis the certified gross calorific value, in joules per gram, at constant volume of benzoic acid (5.9);
e1is the correction for heat of combustion, in joules, of the cotton thread or the polyethylene strip (see 10.4);
e2is the correction for heat of combustion, in joules, of the firing wire (see 10.4);
e3is the correction for heat, in joules, of formation of sulfuric acid and nitric acid (see 10.5);
t0is the firing temperature, in degrees Celsius, corrected for the thermometer error;
tnis the final temperature, in degrees Celsius, corrected for the thermometer error;
tcis the cooling correction, in degrees Celsius, according to Regnault-Pfaundler for isothermal or static
calorimeters (see 10.3).© ISO ISO 9831:1998(E)
13A.4   Predetermined interval (adiabatic calorimeter)
The period between the firing of the charge and the reading of the final temperature, is the predetermined interval. It
is calculated from the temperature readings taken at intervals of 1 min in each determination of effective heatcapacity.
For each of the five determinations, note the shortest time, in minutes, from the firing of the charge to reaching the
second of three consecutive readings which do not differ by more than 0,001 °C.
Calculate, to the nearest 1 min, the mean of the five values to obtain the length of time of the predetermined
interval. This should not exceed 10 min.
Use the predetermined interval for all determinations of calorific value, until a new value is established (e.g. when
commissioning a new calorimeter). The predetermined interval shall be checked after changing any component.
A.5   Re-determination of the mean effective heat capacity
When any part of the system is changed, the mean effective heat capacity shall be re-determined. It shall also bere-determined at intervals of not longer than 6 months.
Where a change to the system is not involved, the re-determined mean effective heat capacity shall be within
20 J/°C of that previously determined. If the difference is greater than 20 J/°C, the experimental procedures shall beexamined and carefully checked.ISO 9831:1998(E) © ISO
14Annex B
(normative)
Special procedures for preparation of the test sample
B.1   Air-dry samples
B.1.1   Air-dry samples with a fat content exceeding 100 g/kg
Samples with a high fat content are preferably pre-extracted (see ISO 6498) and the calorific value determined for
both the sample and the collected fat.
Dissolve the collected fat in hexane. Take a sample, put it into a polyethylene bag (5.4) and then treat it like a liquid
(see B.2).
Alternatively, mix 10 g to 20 g of the test sample thoroughly with sufficient fine silica gel powder (5.6), so that it is
possible to prepare a pellet with the briquette press (6.8.3) without separation of fat or oil. Determine the mixing ratioto the nearest 0,001.
B.1.2   Air-dry samples which cannot easily be pelleted
Weigh, to the nearest 0,1 mg, the necessary number of polyethylene bags (5.4) of known calorific value.
Weigh the required mass of the test sample in a weighed polyethylene bag and wrap up the bag. The test portion
and the bag shall undergo combustion together.
B.2   Liquid samples
Weigh, to the nearest 0,1 mg, the necessary number of polyethylene bags (5.5) of known calorific value.
Place a weighed bag in a small beaker with the aid of a rod fitting in the bag. Weigh the beaker with the bag. Fill the
bag with the desired quantity of liquid. Weigh the beaker with the bag and its contents again.
Evaporate the liquid to dryness in a vacuum oven at room temperature, or freeze-dry the liquid.After complete drying, fold the bag containing the liquid residue and fit it into the bomb in which the firing wire is
attached so, that a curve of wire lies in the crucible.
If combustible compounds disappear during the drying process, analyse these compounds in the wet material as
well as in the material after drying, so that appropriate corrections for loss of calorific value can be made.
B.2.1   Milk samples
Before taking a sample, heat to 40 °C milk samples which have been stored, and mix them thoroughly. The samplevolume shall be approximately 5 ml.
B.2.2   Urine samples
Mix the urine thoroughly. Fill the polyethylene bag (5.5) in the beaker with about 25 ml of urine. Weigh the beakerwith the bag and its contents again. On drying, carefully obtain a vacuum, since acidified urine may contain muchdissolved carbon dioxide.
NOTE    Urine is acidified with sulfuric acid, since it is necessary to preserve the daily urine sample. Before use, the urine is
neutralized.© ISO ISO 9831:1998(E)
15B.3   Samples of fresh materials
B.3.1   Samples of faeces
Mix fresh faeces thoroughly. Mince them in a disc cutter mixer or similar device.
Sample the faeces at random. Constitute fresh samples for analysis from at least 10 sub-samples.Store the samples in closed glass containers in a refrigerator.Weigh 2 g into a polyethylene bag (5.5) in a beaker for immediate analysis.
B.3.2   Samples of other fresh materials
In general, samples of fresh faeces and other fresh materials may be analysed as such, when their moisture
content is less than 70 % ( m/m).
Although samples of other fresh materials, like silages, may be analysed in this way, subsequent sample
preparation may cause an observed loss of moisture.
Some samples cannot be cut finely enough, even after freezing in liquid nitrogen.ISO 9831:1998(E) © ISO
16Annex C
(informative)
Method of checking that the average deviation of the rate of change of
temperature is within the specified limit
When an isothermal or a static calorimeter is applied, the following method may conveniently be used to check that
the average deviation of the rate of change of temperature during the preliminary period and the after-period iswithin the specified limit.
List the five differences obtained during the 5-min period as units without the decimal place. Code them by
subtracting the smallest and arrange the resulting coded differences in descending sequence.
If the sequence is listed in table C.1, the average deviation is within the specified limit. Table C.2 gives an example.
The sequence 33220 is acceptable.
Table C.1 — Acceptable difference sequences
Coded differenceAverage deviation
× 103Coded differenceAverage deviation
× 103
10000 0,32 30000 0,96
11000 0,48 31000 0,96
11100 0,48 31100 0,80
11110 0,32 31110 0,72
20000 0,64 32110 0,88
21000 0,72 32210 0,88
21100 0,64 32220 0,72
21110 0,40
33220 0,80
22000 0,96 33320 0,96
22100 0,80 33330 0,96
22110 0,64
22200 0,96
22210 0,72
22220 0,64© ISO ISO 9831:1998(E)
17Table C.2 — Example
Time
minTemperature
°CDifference
unitsCoded difference
0 24,157
72
1 24,164
50
2 24,169
83
3 24,177
83
4 24,185
72
5 24,192ISO 9831:1998(E) © ISO
18Annex D
(informative)
Examples of calculating the results of calorific determinations
D.1   Determination of effective heat capacity
D.1.1   Measurement data
Gross calorific value of benzoic acid (5.9) at 25,5 °C Qb = 26 467 J/g
Mass of benzoic acid (5.9) mb = 1,183 3 g
Volume of sodium hydroxide solution (5.7) used V = 7,0 ml
Temperature rise tn 2 t0 1 tc = 3,036 °C
Final calorimeter temperature  = 25,5 °CCorrection for cotton thread ( e
1) and firing wire ( e2)( e1 1 e2) = 84 J
NOTE    For adiabatic calorimeters: tc = 0 °C
D.1.2   Calculations
Correction for acids ( e3): e3 = (6,0 J/ml) × 7,0 ml = 42 J.
Applying the equation of clause A.3, the effective heat capacity ( C) of the calorimeter is calculated as follows.
()CmQ e e e
tttn=+++
−+bb
c12 3
0
C=¥+ +
∞=+
∞11833 26467 84 42
303631 318 126
3036,g J / gJJ
,CJJ
,C
C=∞=∞31 444
303610357J
,CJ/ C
This is the result of a single determination. As specified in annex A, the determination shall be carried out at least
five times.
Provided that the range of the test results does not exceed 55 J/°C, their mean is used as the effective heat
capacity of the calorimeter.
D.2   Determination with an adiabatic calorimeter
D.2.1   Measurement data
Effective heat capacity of the calorimeter C = 10 370 J/°C
Mass of the test portion m = 0,999 2 g
Volume of sodium hydroxide solution (5.7) used V = 17,0 ml© ISO ISO 9831:1998(E)
19Firing temperature observed t0o = 22,793 °C
Thermometer correction for firing temperature t0c = 1 0,017 °C
Final temperature observed tno = 25,416 °C
Thermometer correction for final temperature tnc = 1 0,011 °C
Cooling correction: not applicable tc = 0 °C
Correction for cotton thread ( e1) and firing wire ( e2)( e1 1 e2) = 83 J
Correction for incomplete combustion e4 = 0 J
Correction for polyethylene bag: not applicable e5 = 0 J
D.2.2   Calculations
Firing temperature ( t0) corrected for the thermometer error:
t0 = t0o 1 t0c = 22,793 °C 1 0,017 °C = 22,810 °C
Final temperature ( tn) corrected for the thermometer error:
tn = tno 1 tnc = 25,416 °C 1 0,011 °C = 25,427 °C
Correction for acids ( e3): e3 = (6,0 J/ml) × 17,0 ml = 102 J.
Applying the equation of clause 11, the gross calorific value ( Q) at constant volume of the test portion is calculated
as follows.
() ()QCt t t e e e e e
mn=−+ − + −−−01 2 3 4 5c
() ( )Q=∞¥ ∞ - ∞ ∞- - - -10370 25427 22810 83 102 0 0
09992J / C C C + 0 C J JJJ
g,,
,
() ( )Q=∞¥ ∞-==10370 2617 185
0999226953
0999226975J/ C C J
gJ
gJ/g,
,,
D.3   Determination with an isothermal calorimeter
D.3.1   Measurement data
Effective heat capacity of the calorimeter C = 10 370 J/°C
Mass of the test portion m = 0,999 2 g
Volume of sodium hydroxide solution (5.7) used V = 17,0 ml
Correction for cotton thread ( e1) and firing wire ( e2)( e1 1 e2) = 83 J
Correction for incomplete combustion e4 = 0 J
Correction for polyethylene bag: not applicable e5 = 0 J
Temperature of the water jacket = 25 °CObserved temperature readings: see table D.1 °CISO 9831:1998(E) © ISO
20Table D.1 — Observed temperature readings
Time
minTemperature
°CPeriod
0 22,771 ---
↑
1 22,775
2 22,780 preliminary period
3 22,785
4 22,789 ↓
5 22,793 ( t0o) ---
↑
6 23,990
7 25,000
8 25,295
9 25,373 main period
10 25,400
11 25,407
12 25,408 ↓
13 25,407 ( tno) ---
14 25,405 ↑
15 25,403
after-period
16 25,400
17 25,398
18 25,396 ↓
D.3.2   Data derived from the temperature readings
Number of minutes in the main period n = 8
Firing temperature observed t0o = 22,793 °C
Thermometer correction for firing temperature t0c = 1 0,017 °C
Final temperature observed tno = 25,407 °C
Thermometer correction for final temperature tnc = 1 0,011 °C
Average temperature in the preliminary period tp = 22,782 °C
Average temperature in the after-period ta = 25,402 °C
Rate of fall of temperature in the preliminary period vp = 20,004 4 °C/min
Rate of fall of temperature in the after-period va = 0,002 2 °C/min
Sum of temperatures in the main period ti
iin
==-
Â
11
 = 175,873 °C© ISO ISO 9831:1998(E)
21D.3.3   Calculation of the cooling correction
Applying the equation in 10.3, the cooling correction ( tc) is calculated as follows.
dvv
tt=-
-ap
ap
()d=∞- - ∞
∞- ∞=∞
∞=- 00022 00044
25402 2278200066
26200002521 ,,
,,,
,,C/min C/min
CCC/min
Cmin
() Zt t t n ti
iin
n =++ −



==−
∑
11
005,oop
Z = [175,873 °C 1 0,5 (22,793 °C 1 25,407 °C) 2 8 × 22,782 °C]
Z = 175,873 °C 1 24,100 °C 2 182,256 °C = 17,717 °C
tc = (nvp 1 dZ)f
tc = [8 × ( 20,004 4 °C/min) 1 (0,002 52 min 21) × 17,717 °C] × 1 min
tc = [20,035 2 °C/min 1 0,044 6 °C/min] × 1 min = 0,009 4 °C
D.3.4   Calculation of the gross calorific value
Firing temperature ( t0) corrected for the thermometer error:
t0 = t0o 1 t0c = 22,793 °C 1 0,017 °C = 22,810 °C
Final temperature ( tn) corrected for the thermometer error:
tn = tno 1 tnc = 25,407 °C 1 0,011 °C = 25,418 °C
Correction for acids ( e3): e3 = (6,0 J/ml) × 17,0 ml = 102 J.
Applying the equation in clause 11, the gross calorific value ( Q) at constant volume of the test portion is calculated
as follows.
() ()QCt t t e e e e e
mn=−+ − + −−−0c12 345
() ( )Q=∞¥ ∞ - ∞ ∞- - - -10370 25418 22810 83 102 0 0
09992J/ C C C+0,009 C J J J J
g,,
,
() ( )Q=∞¥ ∞-==10370 2617 185
0999226953
0999226975J/ C C J
gJ
gJ/g,
,,ISO 9831:1998(E) © ISO
22Annex E
(informative)
Results of interlaboratory tests
The precision of the method was established by two interlaboratory tests carried out in accordance with
ISO 5725 3) [3].
In the first test (in 1982) 21 laboratories from 10 countries participated. Samples investigated were of hay, wilted
silage, a mixed feed, pig faeces, urine, and milk powder.
NOTE 1    The results of the test were submitted to Technical Committee ISO/TC 34/SC 10. In view of the results, the
committee decided to investigate the influence of the quality testing of the equipment and, in particular, the calibration of t he
effective heat capacity of the calorimeter. For that purpose, an additional interlaboratory test was organized.
In the second test (in 1986) 17 laboratories participated. Samples of pelleted benzoic acid with a stated gross
calorific value were investigated.
NOTE 2    The results of the test were submitted to ISO/TC 34/SC 10. Based on the results, further progressing of the method
to draft International Standard was approved.
The statistical results of the two interlaboratory tests are summarized in table E.1.
Table E.1 — Statistical results of the interlaboratory tests
ParameterSample1)
1234 5 2) 62) 7
Number of participating laboratories 21 21 21 21 21 21 17
Number of laboratories retained after eliminating
outliers 13 13 13 13 21 21 12
Mean gross calorific value at constant volume,J/g
3) 17 421 17 467 17 106 18 311 7 184 17 770 26 415
Repeatability standard deviation ( sr), J/g 38,3 40,7 28,7 17,3 150,6 117,7 34,9
Coefficient of variation of repeatability, % 0,22 0,23 0,17 0,09 2,10 0,66 0,13
Repeatability limit,  r (r = 2,8 sr), J/g 108,5 115,2 81,3 49,1 426,1 333,1 98,8
Reproducibility standard deviation ( sR), J/g 113,9 103,2 119,3 110,3 338,3 246,4 48,4
Coefficient of variation of reproducibility, % 0,65 0,59 0,70 0,60 4,71 1,39 0,18
Reproducibility limit, R (R = 2,8 sR), J/g 322,5 292,1 347,4 315,5 957,3 697,2 136,9
1)   Sample:
1   hay, air-dry matter (at 70 °C) content of fresh sample wad = 900,5 g/kg
2   wilted silage, air-dry matter (at 70 °C) content of fresh sample wad = 384,9 g/kg
3   mixed feed, air-dry matter (at 70 °C) content of fresh sample wad = 891,7 g/kg
4   pigs faeces, air-dry matter (at 70 °C) content of fresh sample wad = 252,8 g/kg
5   urine, freeze-dried; provided as weighed and dried in polyethylene bags6   milk powder; provided as weighed in polyethylene bags7   benzoic acid, stated gross calorific value Q
b = 26 420 J/g
2)   Outliers were not removed. The indicated values are for the sum of the test portion and the polyethylene bag.3)   Based on air-dry matter.
                            
 
3)   ISO 5725:1986 (now withdrawn) was used to obtain the precision data.© ISO ISO 9831:1998(E)
23Annex F
(informative)
Bibliography
[1] ISO 609:1996, Solid mineral fuels — Determination of carbon and hydrogen — High temperature combustion
method.
[2] ISO 625:1996, Solid mineral fuels — Determination of carbon and hydrogen — Liebig method .
[3] ISO 5725:1986, Precision of test methods — Determination of repeatability and reproducibility for a standard
test method by inter-laboratory tests .
[4] ISO 6497:— 4), Animal feeding stuffs — Sampling .
                             
4)   To be published .ISO 9831:1998(E) © ISO
ICS   65.120
Descriptors:   agricultural products,  animal feeding products,  tests,  determination,  calorific value,  calorimetric analysis.
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