SIST EN ISO 4787:2022

SLOVENSKI STANDARD
01-februar-2022
Nadomešča:
SIST EN ISO 4787:2011
Laboratorijska oprema iz stekla in plastike - Instrumenti za volumetrična merjenja -
Metode za preskušanje zmogljivosti in uporaba (ISO 4787:2021)
Laboratory glass and plastic ware - Volumetric instruments - Methods for testing of
capacity and for use (ISO 4787:2021)
Laborgeräte aus Glas und Kunststoff - Volumenmessgeräte - Prüfverfahren und
Anwendung (ISO 4787:2021)
Verrerie et matériel en plastique de laboratoire - Instruments volumétriques - Méthodes
d'essai de la capacité et d'utilisation (ISO 4787:2021)
Ta slovenski standard je istoveten z: EN ISO 4787:2021
ICS:
17.060 Merjenje prostornine, mase, Measurement of volume,
gostote, viskoznosti mass, density, viscosity
71.040.20 Laboratorijska posoda in Laboratory ware and related
aparati apparatus
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 4787
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2021
EUROPÄISCHE NORM
ICS 17.060 Supersedes EN ISO 4787:2011
English Version
Laboratory glass and plastic ware - Volumetric
instruments - Methods for testing of capacity and for use
(ISO 4787:2021)
Verrerie et matériel en plastique de laboratoire - Laborgeräte aus Glas und Kunststoff -
Instruments volumétriques - Méthodes d'essai de la Volumenmessgeräte - Prüfverfahren und Anwendung
capacité et d'utilisation (ISO 4787:2021) (ISO 4787:2021)
This European Standard was approved by CEN on 20 November 2021.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4787:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 4787:2021) has been prepared by Technical Committee ISO/TC 48 "Laboratory
equipment" in collaboration with Technical Committee CEN/TC 332 “Laboratory equipment” the
secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2022, and conflicting national standards shall be
withdrawn at the latest by June 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 4787:2011.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 4787:2021 has been approved by CEN as EN ISO 4787:2021 without any modification.

INTERNATIONAL ISO
STANDARD 4787
Third edition
2021-11
Laboratory glass and plastic ware —
Volumetric instruments — Methods
for testing of capacity and for use
Verrerie et matériel en plastique de laboratoire — Instruments
volumétriques — Méthodes d'essai de la capacité et d'utilisation
Reference number
ISO 4787:2021(E)
ISO 4787:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 4787:2021(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Principle . 2
5 Volume and reference temperature . 2
5.1 Unit of volume . 2
5.2 Reference temperature . 2
6 Apparatus and calibration liquid . 2
6.1 Balance . 2
6.2 Measurement devices . 2
6.3 Calibration liquid . 3
6.4 Receiving vessel . 3
7 Factors affecting the accuracy of volumetric instruments . 3
7.1 General . 3
7.2 Temperature . 3
7.2.1 Temperature of the volumetric instrument . 3
7.2.2 Temperature of calibration liquid . 3
7.3 Cleanliness of surface . 4
7.4 Conditions of used volumetric instruments . 4
7.5 Delivery time and waiting time . 4
8 Setting the meniscus . 5
8.1 General . 5
8.2 Setting the meniscus . 5
8.2.1 Meniscus of transparent liquids . 5
8.2.2 Meniscus of opaque liquids . 7
9 Calibration procedure . 7
9.1 General . 7
9.2 Test room . 7
9.3 Filling and delivery . 7
9.3.1 Volumetric flasks and measuring cylinders . 7
9.3.2 Pipettes adjusted to deliver . 7
9.3.3 Pipettes adjusted to contain . 8
9.3.4 Burettes adjusted to deliver . 8
9.3.5 Pycnometers . . 9
9.4 Weighing . 9
9.5 Volume and uncertainty calculation . 9
10 Procedure for use .10
10.1 General . 10
10.2 Volumetric flasks (in accordance with ISO 1042 or ISO 5215) . 11
10.3 Measuring cylinders (in accordance with ISO 4788 or ISO 6706) . 11
10.4 Burettes (in accordance with ISO 385) . 11
10.5 Pipettes .12
10.5.1 Pipettes adjusted to deliver (see ISO 648 and ISO 835, or other pipettes,
e.g. plastic ones) .12
10.5.2 Pipettes adjusted to contain .12
10.6 Pycnometers .12
Annex A (informative) Cleaning of volumetric glassware .13
iii
ISO 4787:2021(E)
Annex B (informative) Cleaning of volumetric plasticware .14
Annex C (normative) Calculation formulae and tables .15
Annex D (informative) Coefficient of cubic thermal expansion .19
Annex E (informative) Uncertainty estimation and repeatability calculation .20
Bibliography .21
iv
ISO 4787:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 48, Laboratory equipment, in collaboration
with the European Committee for Standardization (CEN) Technical Committee CEN/TC 332, Laboratory
equipment, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This third edition cancels and replaces the second edition (ISO 4787:2010), which has been technically
revised.
The main changes compared to the previous edition are as follows:
a) volumetric plastic ware has been included;
b) new information on meniscus adjustment of convex meniscus has been added; namely, altered
procedure “Upper edge of the graduation line is horizontally tangential to the highest point of
meniscus” as compared to older procedure “Upper edge of the graduation line is horizontally
tangential to the lowest point of the meniscus”;
c) improved figures for meniscus adjustment have been provided;
d) Table 1 has been improved;
e) new Table 2 for minimum requirements for the measurement devices has been added;
f) new test room ambient conditions have been added;
g) new information regarding repeatability and uncertainty has been added in Annex E;
h) Formula (C.1) has been changed to Formula (1).
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
ISO 4787:2021(E)
Introduction
The International Standards for the individual volumetric instruments include clauses on the
specification of capacity (volume); these clauses describe the method of manipulation in sufficient detail
to determine the capacity without ambiguity. This document contains supplementary information.
vi
INTERNATIONAL STANDARD ISO 4787:2021(E)
Laboratory glass and plastic ware — Volumetric
instruments — Methods for testing of capacity and for use
1 Scope
This document provides methods for the testing, calibration and use of volumetric instruments made
from glass and plastic in order to obtain the best accuracy in use.
NOTE Testing is the process by which the conformity of the individual volumetric instrument with the
appropriate standard is determined, resulting in the determination of its error of measurement at one or more
points.
This document is applicable to volumetric instruments with nominal capacities in the range of 100 µl
to 10 000 ml. These include single-volume pipettes (see ISO 648), graduated pipettes (see ISO 835),
burettes (see ISO 385), volumetric flasks (see ISO 1042 and ISO 5215), and graduated measuring
cylinders (see ISO 4788 and ISO 6706).
The methods are not intended for testing of volumetric instruments with capacities below 100 µl such
as micro-glassware.
This document does not deal specifically with pycnometers as specified in ISO 3507. However, the
procedures specified for the determination of volume of glassware can, for the most part, also be
followed for the determination of a pycnometer volume. For some types of pycnometers, special
handling can be necessary.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 385, Laboratory glassware — Burettes
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 835, Laboratory glassware — Graduated pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 1773, Laboratory glassware — Narrow-necked boiling flasks
ISO 3507, Laboratory glassware — Pyknometers
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4788, Laboratory glassware — Graduated measuring cylinders
ISO 4797, Laboratory glassware — Boiling flasks with conical ground joints
1)
ISO 5215 , Laboratory plastic ware — Volumetric flasks
ISO 6706, Plastics laboratory ware — Graduated measuring cylinders
ISO 24450, Laboratory glassware — Wide-necked boiling flasks
1) Under preparation. Stage at the time of publication: ISO/DIS 5215:2021.
ISO 4787:2021(E)
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC Guide 99 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
The general procedure for testing the capacity (volume) and for use is based upon a determination of
volume of water, either contained in or delivered by the volumetric instrument. This volume of water
is based upon knowledge of its mass under consideration of buoyancy and its density (gravimetric
method).
5 Volume and reference temperature
5.1 Unit of volume
The unit of volume shall be the millilitre (ml), which is equivalent to one cubic centimetre (cm ).
5.2 Reference temperature
The standard reference temperature, i.e. the temperature at which the volumetric instrument is
intended to contain or deliver its volume (capacity), shall be 20 °C.
When the volumetric instrument is required for use in a country which has adopted a standard
reference temperature of 27 °C (according to ISO 384), this figure shall replace 20 °C in Formula (1).
6 Apparatus and calibration liquid
6.1 Balance
The balance used for testing shall be chosen in accordance with the minimum requirements specified
in Table 1, depending on the nominal volume of the volumetric instrument under test.
Table 1 — Minimum requirements for the balance
Nominal capacity Expanded uncertainty in
Resolution Repeatability
a
(volume) use U (k = 2)
V mg mg mg
100 µl ≤ V ≤ 10 ml 0,1 0,2 0,4
10 ml < V ≤ 1 000 ml 1 2 4
V > 1 000 ml 10 10 40
a
Expanded uncertainty in use estimated according to Reference [1] (which includes applicable definitions) at the value
of the nominal volume. If uncertainty in use is not available, then the uncertainty at calibration should be taken.
6.2 Measurement devices
The minimum requirements for each relevant measurement device are specified in Table 2.
ISO 4787:2021(E)
Table 2 — Minimum requirements for the measurement devices
Expanded uncertainty of meas-
urement
Device Resolution
U (k = 2)
Thermometer for liquids 0,1 °C 0,2 °C
Thermometer for room air 0,1 °C 0,2 °C
Hygrometer 1 % relative humidity 5 % relative humidity
Barometer 0,1 kPa 1 kPa
Timing device 1 s Not applicable
6.3 Calibration liquid
As calibration liquid during testing, distilled or de-ionized water complying with ISO 3696, Grade 3 or
better should be used. The water temperature shall be within ± 0,5 °C of room air temperature.
6.4 Receiving vessel
The receiving vessel shall be a conical flask, manufactured from glass, e.g. in accordance with ISO 1773,
ISO 4797, or ISO 24450, if possible, with ground joint. The receiving vessel shall have a capacity adequate
to the amount of water delivered by the volumetric instrument.
7 Factors affecting the accuracy of volumetric instruments
7.1 General
The same sources of error are, naturally, inherent to calibration, testing and use. In calibration, every
attempt is made to reduce these errors to a minimum; in use, the care needed is dependent upon the
degree of accuracy required. When the greatest possible accuracy is desired, the volumetric instrument
should be used as closely as possible to the way it has been calibrated.
7.2 Temperature
7.2.1 Temperature of the volumetric instrument
The capacity of the volumetric instruments varies with change of temperature. The particular
temperature at which a volumetric instrument is intended to contain or deliver its nominal capacity is
the “reference temperature” of the instrument (see 5.2).
When performing calibrations, it is important to refer to the reference temperature in the report. For
example, if a volumetric instrument made of borosilicate glass having a coefficient of cubic thermal
−6 −1
expansion of 9,9 × 10 °C is calibrated at 20 °C but used at a temperature of 27 °C it would show an
extra error of 0,007 %. A volumetric instrument made of soda-lime glass having a coefficient of cubic
−6 −1
thermal expansion of 27 × 10 °C would show an extra error of 0,02 %, for a 7 °C temperature change.
7.2.2 Temperature of calibration liquid
The temperature of the water used for the calibration shall be measured to ± 0,1 °C, with a maximum
variation of ± 1 °C during the test. Corrections for differences in temperature, prevailing during testing
or use, from the reference temperature shall be applied in accordance with Formula (1) (see 9.5) and
Annex C. The liquid temperature should be measured in the vessel where the instruments are filled
from or directly inside the instruments, if technically possible.
ISO 4787:2021(E)
7.3 Cleanliness of surface
The volume contained in, or delivered by, a volumetric instrument depends on the cleanliness of the
internal surface. Lack of cleanliness of glass surface results in errors through a poorly shaped meniscus
involving two defects:
— incomplete wetting of the glass surface, i.e. the liquid surface meets the glass at an arbitrary angle
instead of forming a curve such that it meets the glass tangentially;
— a generally increased radius of curvature, due to contamination of the liquid surface reducing the
surface tension.
Volumetric instruments made of polyolefins, such as polypropylene (PP) and polymethylpentene (PMP),
or fluoroplastics, such as perfluoroalkoxy-copolymer (PFA), have water-repellent surfaces which
results in a poorly shaped convex or even flat meniscus (see 8.2).
The ascending or descending liquid meniscus shall not change shape (i.e. it shall not crinkle at its edges).
To ascertain whether a piece of apparatus is satisfactorily clean, it shall be observed during filling
and dispensing. Additionally, an experienced operator can recognize the shape of an uncontaminated
meniscus, in relation to its diameter.
Lack of cleanliness causes additional errors with volumetric instruments used for delivery due to
the film of liquid on the walls being irregularly distributed or incomplete, e.g. forming drops on the
glass surface. Furthermore, chemical residues can introduce an error in the analytical result by
contamination. Where volumetric instruments are fitted with ground stoppers, special attention shall
be paid to cleaning the ground zone.
NOTE Small residues of acid, for example, can impair the concentration of the alkaline solution with which
the volumetric instrument is filled.
Recommended cleaning procedures are included in Annex A (for glass) and Annex B (for plastic). Other
cleaning procedures can be used as well.
Fluoride containing cleaning agents should be strictly avoided in the case of glassware.
7.4 Conditions of used volumetric instruments
The surface of volumetric instruments shall be free from obvious damage, the graduations and
inscriptions shall be clearly readable and especially with instruments adjusted to deliver the jet shall
be free from damage and allow an unrestricted outflow of liquid.
Volumetric glassware should not be heated to a temperature considerably above 180 °C. Although the
strain point of glasses used for volumetric purposes is in the range of 500 °C, alterations of volume may
occur at temperatures considerably below the strain point.
7.5 Delivery time and waiting time
For volumetric instruments used for delivery of a liquid, the volume delivered is always less than the
volume contained, due to the film of liquid left on the inner walls of the volumetric instrument. The
volume of this film depends on the time taken to deliver the liquid, and the volume delivered decreases
with decreasing delivery time. For example, the delivered volume of a pipette or burette decreases if
the jet is broken (shorter delivery time) or increases if the jet is not clean and the outflow of liquid is
restricted.
In view of the above, delivery times and waiting times have been specified in the International Standards
on volumetric instruments; these times shall be used.
ISO 4787:2021(E)
8 Setting the meniscus
8.1 General
Most volumetric instruments employ the principle of setting or reading a meniscus (the interface
between air and the liquid) against a graduation line or ring mark. Wherever practicable, the meniscus
should descend to the position of setting.
The tubing of the volumetric instrument shall be in a vertical position. The eye of the operator shall be
in the same horizontal plane as the meniscus or the graduation line (graduation mark).
8.2 Setting the meniscus
8.2.1 Meniscus of transparent liquids
In case of a concave meniscus, the meniscus shall be set so that the plane of the upper edge of the
graduation line is horizontally tangential to the lowest point of the meniscus, the line of sight being in
the same plane (see Figure 1).
Key
1 meniscus
2 graduation line
3 dark coloured paper
Figure 1 — Setting of concave meniscus
In case of a convex or even flat meniscus, known for water-repellent, non-wetting surfaces of polyolefins,
such as PP and PMP, or fluoroplastics, such as PFA, the meniscus shall be set so that the plane of the
upper edge of the graduation line is horizontally tangential to the highest point of the meniscus, the line
of sight being in the same plane (see Figure 2).
ISO 4787:2021(E)
Key
1 meniscus
2 graduation line
3 dark coloured paper
Figure 2 — Setting of convex meniscus (left) or even flat (right)
On volumetric instruments fitted with a Schellbach ribbon, the meniscus shall be set using the
constriction produced by the interaction between the meniscus and the Schellbach ribbon. Setting is
done when the tip of the constriction points to the graduation line (see Figure 3).
Key
1 meniscus
2 graduation line
3 Schellbach ribbon
Figure 3 — Setting of meniscus with Schellbach ribbon
The lighting should be arranged so that the meniscus appears dark and distinct in outline. For this
purpose, it should be viewed against a white background and shaded from undesirable illumination.
This can be achieved, for example, by securing a strip of black or blue paper directly below the level of
the graduation line or ring mark or by using a short section of thick black rubber tubing cut open at one
side and of such size as to clasp the tube firmly. Parallax is avoided when the graduation lines are of
sufficient length to be seen at the front and back of the volumetric instrument simultaneously.
On volumetric instruments that have graduation lines on the front only, parallax can be made negligible
when making a setting on the top edge of the line by using the black shading strip, taking care that the
top edge of this is in a horizontal plane. In this case, the eye shall be placed so that the front and back
portions of the top edge appear to be coincident.
ISO 4787:2021(E)
8.2.2 Meniscus of opaque liquids
When the volumetric instrument is used with opaque wetting liquids forming a concave meniscus, the
horizontal line of sight shall be taken through the upper edge of the meniscus and, where necessary, an
appropriate correction shall be applied.
In case of a convex or even flat meniscus, the meniscus shall be set so that the plane of the upper edge of
the graduation line is horizontally tangential to the highest point of the meniscus, the line of sight being
in the same plane, and, where necessary, an appropriate correction shall be applied.
9 Calibration procedure
9.1 General
Volumetric instruments other than disposable pipettes shall be thoroughly cleaned shortly before
calibration (see 7.3). Volumetric instruments adjusted to contain shall be dried after cleaning.
For volumetric instruments adjusted to deliver, it is important that receiving vessels manufactured
from glass are used. Capillary effects influencing the delivery time and the delivered volume depend
considerably on the material on which the liquid runs down. In addition, the electrostatic charges of
glass are minimal; this is important for the weighing procedure.
9.2 Test room
The test shall be carried out in a draught-free room with a stable environment. The test room shall have
a relative humidity (RH) between 30 % and 80 % and a temperature of (20 ± 3) °C or (27 ± 3) °C with a
maximum variation of ± 1 °C during the test.
NOTE 1 Humidity below 40 % can facilitate the occurrence of static charges that render the weighing process
[1]
very difficult. At humidity above 60 %, corrosion of some balances can occur .
Prior to the test, the apparatus to be tested, all test equipment, and water shall have stood in the test
room for a sufficient time to reach equilibrium with the test room conditions, the temperature variation
of the room during this time should not be more than 1 °C per hour. Test water should be covered to
avoid evaporation cooling. Temperatures (room and calibration liquid), atmospheric pressure and
humidity shall be recorded.
NOTE 2 The equilibration time is usually about 2 h and can be considerably longer.
9.3 Filling and delivery
9.3.1 Volumetric flasks and measuring cylinders
Volumetric flasks made of glass in accordance with ISO 1042, volumetric flasks made of plastic in
accordance with ISO 5215 and measuring cylinders in accordance with ISO 4788 or ISO 6706 shall
be dried after cleaning. They shall be filled by means of a plastic tube with tip to a distance of a few
millimetres above the ring mark or the graduation line to be tested, so that the walls of the volumetric
instrument above the ring mark are not wetted. The final setting of the meniscus to the ring mark or
graduation line shall be made by withdrawing the surplus water by means of a plastic tube drawn out
to a jet. The movement of the meniscus when setting shall be downwards. If a little refilling is necessary
or if the reading is delayed to the adjustment of the meniscus, careful swaying is necessary to refresh
the meniscus shape.
9.3.2 Pipettes adjusted to deliver
Pipettes adjusted to deliver in accordance with the specifications given in ISO 648 and ISO 835, or other
pipettes, e.g. plastic ones, shall be clamped in a vertical position and filled through the jet to a few
millimetres above the graduation line to be tested; any liquid remaining on the outside of the jet shall
ISO 4787:2021(E)
be removed. The final setting of the meniscus shall then be made by running out the surplus water
through the jet. Any drop of liquid adhering to the jet shall be removed, for example by bringing a
ground glass surface into contact with the tip of the jet at an angle of about 30°. Draw this ground glass
surface downwards through a distance of about 10 mm to remove residual water. Delivery into the
tared receiving vessel shall then be made with the flow unrestricted while the tip of the jet is in contact
with the inner ground surface of the receiving vessel, finally drawing it over a distance of about 10 mm,
with the receiving vessel held inclined at an angle of about 30°.
Other precautions that are necessary to obtain the correct delivered volume vary with different types
of instruments and are described in the clause defining capacity in the appropriate International
Standards, ISO 648 and ISO 835.
Determine the delivery time while the tip of the jet is in contact with the inner surface of the receiving
vessel, above the level of any collected liquid, but without movement of one against the other throughout
the delivery period. The delivery time thus determined should be within the limits specified in the
corresponding International Standard (ISO 648 or ISO 835) for the particular pipette.
A waiting time, if specified, shall be observed before making the final setting of the meniscus for
delivery of a given volume. If the setting after delivery is done at a lower graduation line, the liquid flow
shall be nearly stopped a few millimetres above the graduation line. After observation of the waiting
time, the final setting shall be completed quickly.
9.3.3 Pipettes adjusted to contain
Fill the pipette by suction slowly and carefully, stopping when the meniscus reaches the graduation
line. Carefully wipe off any residual water from the end of the pipette.
The filled pipette shall be weighted in the balance using the appropriated means in order to measure its
contained volume.
9.3.4 Burettes adjusted to deliver
Burettes adjusted to deliver in accordance with the specifications given in ISO 385 shall be clamped in a
vertical position and filled to a few millimetres above the graduation line to be tested. The stopcock and
jet shall be free from air bubbles. Any liquid remaining on the outside of the jet shall be removed. The
final setting of the meniscus shall then be made by running out the surplus water through the jet. Any
drop of liquid adhering to the jet shall be removed by bringing a ground glass surface into contact with
the tip of the jet at an angle of about 30°. Draw this ground glass surface downwards through a distance
of about 10 mm.
Delivery into the tared receiving vessel shall then be made with the flow unrestricted until the meniscus
has come to a few millimetres above the graduation line to be tested, while the stopcock is fully open
and the jet is not in contact with the receiving vessel. After the final setting of the meniscus, any drop
of liquid adhering to the jet is removed by bringing an inclined glass surface into contact with the tip of
the jet at an angle of about 30°, finally drawing it over a distance of about 10 mm.
Class A and AS burettes manufactured from standard drawn tubing should be tested at five points on
the scale. Burettes manufactured from “precision bore” tubing can be tested only at three points on the
scale. For more details see ISO 385.
Other precautions which are necessary to obtain the correct delivered volume vary with different
types of burettes and are described in the appropriate International Standards in the clause defining
capacity.
Determine the delivery time by the unrestricted outflow of the liquid from the zero mark to the lowest
graduation mark with the stopcock fully open and the jet not being in contact with the surface of
the receiving vessel. The delivery time thus determined should be within the limits specified for the
particular burette.
ISO 4787:2021(E)
A waiting time, if specified, shall be observed before making the final setting of the meniscus for
delivery of a given volume. If the setting after delivery is done at a lower graduation line, the liquid flow
shall be nearly stopped a few millimetres above the graduation line. After observation of the waiting
time, the final setting shall be completed quickly.
9.3.5 Pycnometers
The filling of a pycnometer shall be performed in accordance with the specifications given in ISO 3507
and the manufacturer's instructions.
9.4 Weighing
The volumetric instrument or the receiving vessel (see 6.4) shall be tared and weighed using a balance
in accordance with 6.1 and the temperature of the water shall be measured to ± 0,1 °C.
Alternatively, two weighings can be performed (empty and loaded vessel). The corresponding balance
indications are I , referring to the loaded vessel, and I , referring to the empty vessel. Usually, I and I
L E E L
are observed under the same conditions, hence a precise zero adjustment of the balance is not necessary.
Both of the required weighings shall be carried out in a short time interval as convenient to ensure that
they have been made at the same temperature. This air temperature, the humidity and the barometric
pressure shall be recorded for use in the subsequent calculations.
The manufacturer’s instructions shall be followed in making the required measurements. Weighings
shall be made with care and made expeditiously to minimize evaporation losses which would constitute
a source of error.
To perform repeated tests in flasks and cylinders two options may be used:
a) Option 1 — The flask or cylinder is dried after each run. Obtaining an initial dry weight will allow
the operator to determine when the flask or cylinder is sufficiently dry.
b) Option 2 — After the first run, for the subsequent runs, a sufficient amount of liquid is removed, the
temperature of the water inside the flask or cylinder is measured, the inner walls of the volumetric
instrument above the graduation line to be calibrated are dried and finally the meniscus is set
again. The initial value of the dried flask or cylinder (tare) is used in all repetitions.
9.5 Volume and uncertainty calculation
In order to obtain the volume contained in, or delivered by, the volumetric instrument under test at the
reference temperature from the mass of water, the following factors shall be taken into ac
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