02008R0440 — EN — 16.10.2019 — 008.001
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►C1 COMMISSION REGULATION (EC) No 440/2008 of 30 May 2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (OJ L 142 31.5.2008, p. 1) |
Amended by:
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Official Journal |
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date |
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L 220 |
1 |
24.8.2009 |
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L 324 |
13 |
9.12.2010 |
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L 193 |
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20.7.2012 |
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L 81 |
1 |
19.3.2014 |
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L 247 |
1 |
21.8.2014 |
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L 54 |
1 |
1.3.2016 |
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L 112 |
1 |
28.4.2017 |
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L 247 |
1 |
26.9.2019 |
Corrected by:
COMMISSION REGULATION (EC) No 440/2008
of 30 May 2008
laying down test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH)
(Text with EEA relevance)
Article 1
The test methods to be applied for the purposes of Regulation 1907/2006/EC are set out in the Annex to this Regulation.
Article 2
The Commission shall review, where appropriate, the test methods contained in this Regulation with a view to replacing, reducing or refining testing on vertebrate animals.
Article 3
All references to Annex V to Directive 67/548/EEC shall be construed as references to this Regulation.
Article 4
This Regulation shall enter into force on the day following its publication in the Official Journal of the European Union.
It shall apply from 1 June 2008.
ANNEX
Note:
Before using any of the following test methods to test a multi-constituent substance (MCS), a substance of unknown or variable composition, complex reaction product or biological material (UVCB), or a mixture and where its applicability for the testing of MCS, UVCB, or mixtures is not indicated in the respective test method, it should be considered whether the method is adequate for the intended regulatory purpose.
If the test method is used for the testing of a MCS, UVCB or mixture, sufficient information on its composition should be made available, as far as possible, e.g. by the chemical identity of its constituents, their quantitative occurrence, and relevant properties of the constituents.
PART A: METHODS FOR THE DETERMINATION OF PHYSICO-CHEMICAL PROPERTIES
TABLE OF CONTENTS |
|
A.1. |
MELTING/FREEZING TEMPERATURE |
A.2. |
BOILING TEMPERATURE |
A.3. |
RELATIVE DENSITY |
A.4. |
VAPOUR PRESSURE |
A.5. |
SURFACE TENSION |
A.6. |
WATER SOLUBILITY |
A.8. |
PARTITION COEFFICIENT |
A.9. |
FLASH-POINT |
A.10. |
FLAMMABILITY (SOLIDS) |
A.11. |
FLAMMABILITY (GASES) |
A.12. |
FLAMMABILITY (CONTACT WITH WATER) |
A.13. |
PYROPHORIC PROPERTIES OF SOLIDS AND LIQUIDS |
A.14. |
EXPLOSIVE PROPERTIES |
A.15. |
AUTO-IGNITION TEMPERATURE (LIQUIDS AND GASES) |
A.16. |
RELATIVE SELF-IGNITION TEMPERATURE FOR SOLIDS |
A.17. |
OXIDISING PROPERTIES (SOLIDS) |
A.18. |
NUMBER — AVERAGE MOLECULAR WEIGHT AND MOLECULAR WEIGHT DISTRIBUTION OF POLYMERS |
A.19. |
LOW MOLECULAR WEIGHT CONTENT OF POLYMERS |
A.20. |
SOLUTION/EXTRACTION BEHAVIOUR OF POLYMERS IN WATER |
A.21. |
OXIDISING PROPERTIES (LIQUIDS) |
A.22. |
LENGTH WEIGHTED GEOMETRIC MEAN DIAMETER OF FIBRES |
A.23. |
PARTITION COEFFICIENT (1-OCTANOL/WATER): SLOW-STIRRING METHOD |
A.24. |
PARTITION COEFFICIENT (N-OCTANOL/WATER), HIGH PERFORMANCELIQUID CHROMATOGRAPHY (HPLC) METHOD |
A.25. |
DISSOCIATION CONSTANTS IN WATER (TITRATION METHOD — SPECTROPHOTOMETRIC METHOD — CONDUCTOMETRIC METHOD) |
A.1. MELTING/FREEZING TEMPERATURE
1. METHOD
The majority of the methods described are based on the OECD Test Guideline (1). The fundamental principles are given in references (2) and (3).
1.1. INTRODUCTION
The methods and devices described are to be applied for the determination of the melting temperature of substances, without any restriction with respect to their degree of purity.
The selection of the method is dependent on the nature of the substance to be tested. In consequence the limiting factor will be according to, whether or not the substance can be pulverised easily, with difficulty, or not at all.
For some substances, the determination of the freezing or solidification temperature is more appropriate and the standards for these determinations have also been included in this method.
Where, due to the particular properties of the substance, none of the above parameters can be conveniently measured, a pour point may be appropriate.
1.2. DEFINITIONS AND UNITS
The melting temperature is defined as the temperature at which the phase transition from solid to liquid state occurs at atmospheric pressure and this temperature ideally corresponds to the freezing temperature.
As the phase transition of many substances takes place over a temperature range, it is often described as the melting range.
Conversion of units (K to oC)
t = T - 273,15
t |
: |
Celsius temperature, degree Celsius (oC) |
T |
: |
thermodynamic temperature, kelvin (K) |
1.3. REFERENCE SUBSTANCES
Reference substances do not need to be employed in all cases when investigating a new substance. They should primarily serve to check the performance of the method from time to time and to allow comparison with results from other methods.
Some calibration substances are listed in the references (4).
1.4. PRINCIPLE OF THE TEST METHOD
The temperature (temperature range) of the phase transition from the solid to the liquid state or from the liquid to the solid state is determined. In practice while heating/cooling a sample of the test substance at atmospheric pressure the temperatures of the initial melting/freezing and the final stage of melting/freezing are determined. Five types of methods are described, namely capillary method, hot stage methods, freezing temperature determinations, methods of thermal analysis, and determination of the pour point (as developed for petroleum oils).
In certain cases, it may be convenient to measure the freezing temperature in place of the melting temperature.
1.4.1. Capillary method
1.4.1.1. Melting temperature devices with liquid bath
A small amount of the finely ground substance is placed in a capillary tube and packed tightly. The tube is heated, together with a thermometer, and the temperature rise is adjusted to less than about 1 K/min during the actual melting. The initial and final melting temperatures are determined.
1.4.1.2. Melting temperature devices with metal block
As described under 1.4.1.1, except that the capillary tube and the thermometer are situated in a heated metal block, and can be observed through holes in the block.
1.4.1.3. Photocell detection
The sample in the capillary tube is heated automatically in a metal cylinder. A beam of light is directed through the substance, by way of a hole in the cylinder, to a precisely calibrated photocell. The optical properties of most substances change from opaque to transparent when they are melting. The intensity of light reaching the photocell increases and sends a stop signal to the digital indicator reading out the temperature of a platinum resistance thermometer located in the heating chamber. This method is not suitable for some highly coloured substances.
1.4.2. Hot stages
1.4.2.1. Kofler hot bar
The Kofler hot bar uses two pieces of metal of different thermal conductivity, heated electrically, with the bar designed so that the temperature gradient is almost linear along its length. The temperature of the hot bar can range from 283 to 573 K with a special temperature-reading device including a runner with a pointer and tab designed for the specific bar. In order to determine a melting temperature, the substance is laid, in a thin layer, directly on the surface of the hot bar. In a few seconds a sharp dividing line between the fluid and solid phase develops. The temperature at the dividing line is read by adjusting the pointer to rest at the line.
1.4.2.2. Melt microscope
Several microscope hot stages are in use for the determination of melting temperatures with very small quantities of material. In most of the hot stages the temperature is measured with a sensitive thermocouple but sometimes mercury thermometers are used. A typical microscope hot stage melting temperature apparatus has a heating chamber which contains a metal plate upon which the sample is placed on a slide. The centre of the metal plate contains a hole permitting the entrance of light from the illuminating mirror of the microscope. When in use, the chamber is closed by a glass plate to exclude air from the sample area.
The heating of the sample is regulated by a rheostat. For very precise measurements on optically anisotropic substances, polarised light may be used.
1.4.2.3. Meniscus method
This method is specifically used for polyamides.
The temperature at which the displacement of a meniscus of silicone oil, enclosed between a hot stage and a cover-glass supported by the polyamide test specimen, is determined visually.
1.4.3. Method to determine the freezing temperature
The sample is placed in a special test tube and placed in an apparatus for the determination of the freezing temperature. The sample is stirred gently and continuously during cooling and the temperature is measured at suitable intervals. As soon as the temperature remains constant for a few readings this temperature (corrected for thermometer error) is recorded as the freezing temperature.
Supercooling must be avoided by maintaining equilibrium between the solid and the liquid phases.
1.4.4. Thermal analysis
1.4.4.1 Differential thermal analysis (DTA)
This technique records the difference in temperatures between the substance and a reference material as a function of temperature, while the substance and reference material are subjected to the same controlled temperature programme. When the sample undergoes a transition involving a change of enthalpy, that change is indicated by an endothermic (melting) or exothermic (freezing) departure from the base line of the temperature record.
1.4.4.2 Differential scanning calorimetry (DSC)
This technique records the difference in energy inputs into a substance and a reference material, as a function of temperature, while the substance and reference material are subjected to the same controlled temperature programme. This energy is the energy necessary to establish zero temperature difference between the substance and the reference material. When the sample undergoes a transition involving a change of enthalpy, that change is indicated by an endothermic (melting) or exothermic (freezing) departure from the base line of the heat flow record.
1.4.5. Pour point
This method was developed for use with petroleum oils and is suitable for use with oily substances with low melting temperatures.
After preliminary heating, the sample is cooled at a specific rate and examined at intervals of 3 K for flow characteristics. The lowest temperature at which movement of the substance is observed is recorded as the pour point.
1.5. QUALITY CRITERIA
The applicability and accuracy of the different methods used for the determination of the melting temperature/melting range are listed in the following table:
TABLE: APPLICABILITY OF THE METHODS
A. Capillary methods
Method of measurement |
Substances which can be pulverised |
Substances which are not readily pulverised |
Temperature range |
Estimated accuracy (1) |
Existing standards |
Melting temperature devices with liquid bath |
yes |
only to a few |
273 to 573 K |
± 0,3 K |
JIS K 0064 |
Melting temperature with metal block |
yes |
only to a few |
293 to > 573 K |
± 0,5 K |
ISO 1218 (E) |
Photocell detection |
yes |
several with appliance devices |
253 to 573 K |
± 0,5 K |
|
(1)
Dependent on type of instrument and on degree of purity of the substance. |
B. Hot stages and freezing methods
Method of measurement |
Substances which can be pulverised |
Substances which are not readily pulverised |
Temperature range |
Estimated accuracy (1) |
Existing standards |
Kofler hot bar |
yes |
no |
283 to > 573 K |
± 1K |
ANSI/ASTM D 3451-76 |
Melt microscope |
yes |
only to a few |
273 to > 573 K |
± 0,5 K |
DIN 53736 |
Meniscus method |
no |
specifically for polyamides |
293 to > 573 K |
± 0,5 K |
ISO 1218 (E) |
Freezing temperature |
yes |
yes |
223 to 573 K |
± 0,5 K |
e.g. BS 4695 |
(1)
Dependent on type of instrument and on degree of purity of the substance |
C. Thermal analysis
Method of measurement |
Substances which can be pulverised |
Substances which are not readily pulverised |
Temperature range |
Estimated accuracy (1) |
Existing standards |
Differential thermal analysis |
yes |
yes |
173 to 1 273 K |
up to 600 K ± 0,5 K up to 1 273 K ± 2,0 K |
ASTM E 537-76 |
Differential scanning calorimetry |
yes |
yes |
173 to 1 273 K |
up to 600 K ± 0,5 K up to 1 273 K ± 2,0 K |
ASTM E 537-76 |
(1)
Dependent on type of instrument and on degree of purity of the substance |
D. Pour point
Method of measurement |
Substances which can be pulverised |
Substances which are not readily pulverised |
Temperature range |
Estimated accuracy (1) |
Existing standards |
Pour point |
for petroleum oils and oily substances |
for petroleum oils and oily substances |
223 to 323 K |
± 0,3 K |
ASTM D 97-66 |
(1)
Dependent on type of instrument and on degree of purity of the substance |
1.6. DESCRIPTION OF THE METHODS
The procedures of nearly all the test methods have been described in international and national standards (see Appendix 1).
1.6.1. Methods with capillary tube
When subjected to a slow temperature rise, finely pulverised substances usually show the stages of melting shown in figure 1.
Figure 1
During the determination of the melting temperature, the temperatures are recorded at the beginning of the melting and at the final stage.
1.6.1.1. Melting temperature devices with liquid bath apparatus
Figure 2 shows a type of standardised melting temperature apparatus made of glass (JIS K 0064); all specifications are in millimeters.
Figure 2
Bath liquid:
A suitable liquid should be chosen. The choice of the liquid depends upon the melting temperature to be determined, e.g. liquid paraffin for melting temperatures no higher than 473 K, silicone oil for melting temperatures no higher than 573 K.
For melting temperatures above 523 K, a mixture consisting of three parts sulphuric acid and two parts potassium sulphate (in mass ratio) can be used. Suitable precautions should be taken if a mixture such as this is used.
Thermometer:
Only those thermometers should be used which fulfil the requirements of the following or equivalent standards:
ASTM E 1-71, DIN 12770, JIS K 8001.
Procedure:
The dry substance is finely pulverised in a mortar and is put into the capillary tube, fused at one end, so that the filling level is approximately 3 mm after being tightly packed. To obtain a uniform packed sample, the capillary tube should be dropped from a height of approximately 700 mm through a glass tube vertically onto a watch glass.
The filled capillary tube is placed in the bath so that the middle part of the mercury bulb of the thermometer touches the capillary tube at the part where the sample is located. Usually the capillary tube is introduced into the apparatus about 10 K below the melting temperature.
The bath liquid is heated so that the temperature rise is approximately 3 K/min. The liquid should be stirred. At about 10 K below the expected melting temperature the rate of temperature rise is adjusted to a maximum of 1 K/min.
Calculation:
The calculation of the melting temperature is as follows:
T = TD + 0,00016 (TD - TE) n
where:
T |
= |
corrected melting temperature in K |
TD |
= |
temperature reading of thermometer D in K |
TE |
= |
temperature reading of thermometer E in K |
n |
= |
number of graduations of mercury thread on thermometer D at emergent stem. |
1.6.1.2. Melting temperature devices with metal block
Apparatus:
This consists of:
Thermometer:
See standards mentioned in 1.6.1.1. Thermoelectrical measuring devices with comparable accuracy are also applicable.
Figure 3
1.6.1.3. Photocell detection
Apparatus and procedure:
The apparatus consists of a metal chamber with automated heating system. Three capillary are filled accordingly to 1.6.1.1 and placed in the oven.
Several linear increases of temperature are available for calibrating the apparatus and the suitable temperature rise is electrically adjusted at a pre-selected constant and linear rate. recorders show the actual oven temperature and the temperature of the substance in the capillary tubes.
1.6.2. Hot stages
1.6.2.1. Kofler hot bar
See Appendix.
1.6.2.2. Melt microscope
See Appendix.
1.6.2.3. Meniscus method (polyamides)
See Appendix.
The heating rate through the melting temperature should be less than 1 K/min.
1.6.3. Methods for the determination of the freezing temperature
See Appendix.
1.6.4. Thermal analysis
1.6.4.1. Differential thermal analysis
See Appendix.
1.6.4.2. Differential scanning calorimetry
See Appendix.
1.6.5. Determination of the pour point
See Appendix.
2. DATA
A thermometer correction is necessary in some cases.
3. REPORTING
The test report shall, if possible, include the following information:
The mean of at least two measurements which are in the range of the estimated accuracy (see tables) is reported as the melting temperature.
If the difference between the temperature at the beginning and at the final stage of melting is within the limits of the accuracy of the method, the temperature at the final stage of melting is taken as the melting temperature; otherwise the two temperatures are reported.
If the substance decomposes or sublimes before the melting temperature is reached, the temperature at which the effect is observed shall be reported.
All information and remarks relevant for the interpretation of results have to be reported, especially with regard to impurities and physical state of the substance.
4. REFERENCES
(1) OECD, Paris, 1981, Test Guideline 102, Decision of the Council C(81) 30 final.
(2) IUPAC, B. Le Neindre, B. Vodar, eds. Experimental thermodynamics, Butterworths, London 1975, vol. II, p. 803-834.
(3) R. Weissberger ed.: Technique of organic Chemistry, Physical Methods of Organic Chemistry, 3rd ed., Interscience Publ., New York, 1959, vol. I, Part I, Chapter VII.
(4) IUPAC, Physicochemical measurements: Catalogue of reference materials from national laboratories, Pure and applied chemistry, 1976, vol. 48, p. 505-515.
Appendix
For additional technical details, the following standards may be consulted for example.
1. Capillary methods
1.1. Melting temperature devices with liquid bath
ASTM E 324-69 |
Standard test method for relative initial and final melting points and the melting range of organic chemicals |
BS 4634 |
Method for the determination of melting point and/or melting range |
DIN 53181 |
Bestimmung des Schmelzintervalles von Harzen nach Kapillarverfarehn |
JIS K 00-64 |
Testing methods for melting point of chemical products |
1.2. Melting temperature devices with metal block
DIN 53736 |
Visuelle Bestimmung der Schmelztemperatur von teilkristallinen Kunststoffen |
ISO 1218 (E) |
Plastics — polyamides — determination of ‘melting point’ |
2. Hot stages
2.1. Kofler hot bar
ANSI/ASTM D 3451-76 |
Standard recommended practices for testing polymeric powder coatings |
2.2. Melt microscope
DIN 53736 |
Visuelle Bestimmung der Schmelztemperatur von teilkristallinen Kunststoffen |
2.3. Meniscus method (polyamides)
ISO 1218 (E) |
Plastics — polyamides — determination of ‘melting point’ |
ANSI/ASTM D 2133-66 |
Standard specification for acetal resin injection moulding and extrusion materials |
NF T 51-050 |
Résines de polyamides. Détermination du ‘point de fusion’ méthode du ménisque |
3. Methods for the determination of the freezing temperature
BS 4633 |
Method for the determination of crystallising point |
BS 4695 |
Method for Determination of Melting Point of petroleum wax (Cooling Curve) |
DIN 51421 |
Bestimmung des Gefrierpunktes von Flugkraftstoffen, Ottokraftstoffen und Motorenbenzolen |
ISO 2207 |
Cires de pétrole: détermination de la température de figeage |
DIN 53175 |
Bestimmung des Erstarrungspunktes von Fettsäuren |
NF T 60-114 |
Point de fusion des paraffines |
NF T 20-051 |
Méthode de détermination du point de cristallisation (point de congélation) |
ISO 1392 |
Method for the determination of the freezing point |
4. Thermal analysis
4.1. Differential thermal analysis
ASTM E 537-76 |
Standard method for assessing the thermal stability of chemicals by methods of differential thermal analysis |
ASTM E 473-85 |
Standard definitions of terms relating to thermal analysis |
ASTM E 472-86 |
Standard practice for reporting thermoanalytical data |
DIN 51005 |
Thermische Analyse, Begriffe |
4.2. Differential scanning calorimetry
ASTM E 537-76 |
Standard method for assessing the thermal stability of chemicals by methods of differential thermal analysis |
ASTM E 473-85 |
Standard definitions of terms relating to thermal analysis |
ASTM E 472-86 |
Standard practice for reporting thermoanalytical data |
DIN 51005 |
Thermische Analyse, Begriffe |
5. Determination of the pour point
NBN 52014 |
Echantillonnage et analyse des produits du pétrole: Point de trouble et point d'écoulement limite — Monsterneming en ontleding van aardolieproducten: Troebelingspunt en vloeipunt |
ASTM D 97-66 |
Standard test method for pour point of petroleum oils |
ISO 3016 |
Petroleum oils — Determination of pour point |
A.2. BOILING TEMPERATURE
1. METHOD
The majority of the methods described are based on the OECD Test Guideline (1). The fundamental principles are given in references (2) and (3).
1.1. INTRODUCTION
The methods and devices described here can be applied to liquid and low melting substances, provided that these do not undergo chemical reaction below the boiling temperature (for example: auto-oxidation, rearrangement, degradation, etc.). The methods can be applied to pure and to impure liquid substances.
Emphasis is put on the methods using photocell detection and thermal analysis, because these methods allow the determination of melting as well as boiling temperatures. Moreover, measurements can be performed automatically.
The ‘dynamic method’ has the advantage that it can also be applied to the determination of the vapour pressure and it is not necessary to correct the boiling temperature to the normal pressure (101,325 kPa) because the normal pressure can be adjusted during the measurement by a manostat.
Remarks:
The influence of impurities on the determination of the boiling temperature depends greatly upon the nature of the impurity. When there are volatile impurities in the sample, which could affect the results, the substance may be purified.
1.2. DEFINITIONS AND UNITS
The normal boiling temperature is defined as the temperature at which the vapour pressure of a liquid is 101,325 kPa.
If the boiling temperature is not measured at normal atmospheric pressure, the temperature dependence of the vapour pressure can be described by the Clausius-Clapeyron equation:
where:
p |
= |
the vapour pressure of the substance in pascals |
Δ Hv |
= |
its heat of vaporisation in J mol-1 |
R |
= |
the universal molar gas constant = 8,314 J mol-1 K-1 |
T |
= |
thermodynamic temperature in K |
The boiling temperature is stated with regard to the ambient pressure during the measurement.
Conversions
Pressure (units: kPa)
100 kPa |
= |
1 bar = 0,1 MPa (‘bar’ is still permissible but not recommended) |
133 Pa |
= |
1 mm Hg = 1 Torr (the units ‘mm Hg’ and ‘Torr’ are not permitted) |
1 atm |
= |
standard atmosphere = 101 325 Pa (the unit ‘atm’ is not permitted) |
Temperature (units: K)
t = T - 273,15
t |
: |
Celsius temperature, degree Celsius (oC) |
T |
: |
thermodynamic temperature, kelvin (K) |
1.3. REFERENCE SUBSTANCES
Reference substances do not need to be employed in all cases when investigating a new substance. They should primarily serve to check the performance of the method from time to time and to allow comparison with results from other methods.
Some calibration substances can be found in the methods listed in the Appendix.
1.4. PRINCIPLE OF THE TEST METHOD
Five methods for the determination of the boiling temperature (boiling range) are based on the measurement of the boiling temperature, two others are based on thermal analysis.
1.4.1. Determination by use of the ebulliometer
Ebulliometers were originally developed for the determination of the molecular weight by boiling temperature elevation, but they are also suited for exact boiling temperature measurements. A very simple apparatus is described in ASTM D 1120-72 (see Appendix). The liquid is heated in this apparatus under equilibrium conditions at atmospheric pressure until it is boiling.
1.4.2. Dynamic method
This method involves the measurement of the vapour recondensation temperature by means of an appropriate thermometer in the reflux while boiling. The pressure can be varied in this method.
1.4.3. Distillation method for boiling temperature
This method involves distillation of the liquid and measurement of the vapour recondensation temperature and determination of the amount of distillate.
1.4.4. Method according to Siwoloboff
A sample is heated in a sample tube, which is immersed in a liquid in a heat-bath. A fused capillary, containing an air bubble in the lower part, is dipped in the sample tube.
1.4.5. Photocell detection
Following the principle according to Siwoloboff, automatic photo-electrical measurement is made using rising bubbles.
1.4.6. Differential thermal analysis
This technique records the difference in temperatures between the substance and a reference material as a function of temperature, while the substance and reference material are subjected to the same controlled temperature programme. When the sample undergoes a transition involving a change of enthalpy, that change is indicated by an endothermic departure (boiling) from the base line of the temperature record.
1.4.7. Differential scanning calorimetry
This technique records the difference in energy inputs into a substance and a reference material as a function of temperature, while the substance and reference material are subjected to the same controlled temperature programme. This energy is the energy necessary to establish zero temperature difference between the substance and the reference material. When the sample undergoes a transition involving a change of enthalpy, that change is indicated by an endothermic departure (boiling) from the base line of the heat flow record.
1.5. QUALITY CRITERIA
The applicability and accuracy of the different methods used for the determination of the boiling temperature/boiling range are listed in table 1.
Table 1:
Comparison of the methods
Method of measurement |
Estimated accuracy |
Existing standard |
Ebulliometer |
ASTM D 1120-72 (1) |
|
Dynamic method |
± 0,5 K (up to 600 K) (2) |
|
Distillation process (boiling range) |
± 0,5 K (up to 600 K) |
ISO/R 918, DIN 53171, BS 4591/71 |
According to Siwoloboff |
± 2 K (up to 600 K) (2) |
|
Photocell detection |
± 0,3 K (up to 373 K) (2) |
|
Differential thermal calorimetry |
± 0,5 K (up to 600 K) ± 2,0 K (up to 1 273 K) |
ASTM E 537-76 |
Differential scanning calorimetry |
± 0,5 K (up to 600 K) ± 2,0 K (up to 1 273 K) |
ASTM E 537-76 |
(1)
This accuracy is only valid for the simple device as for example described in ASTM D 1120-72; it can be improved with more sophisticated ebulliometer devices.
(2)
Only valid for pure substances. The use in other circumstances should be justified. |
1.6. DESCRIPTION OF THE METHODS
The procedures of some test methods have been described in international and national standards (see Appendix).
1.6.1. Ebulliometer
See Appendix.
1.6.2. Dynamic method
See test method A.4 for the determination of the vapour pressure.
The boiling temperature observed with an applied pressure of 101,325 kPa is recorded.
1.6.3. Distillation process (boiling range)
See Appendix.
1.6.4. Method according to Siwoloboff
The sample is heated in a melting temperature apparatus in a sample tube, with a diameter of approximately 5 mm (figure 1).
Figure 1 shows a type of standardised melting and boiling temperature apparatus (JIS K 0064) (made of glass, all specifications in millimetres).
Figure 1
A capillary tube (boiling capillary) which is fused about 1 cm above the lower end is placed in the sample tube. The level to which the test substance is added is such that the fused section of the capillary is below the surface of the liquid. The sample tube containing the boiling capillary is fastened either to the thermometer with a rubber band or is fixed with a support from the side (see figure 2).
Figure 2 Principle according to Siwoloboff |
Figure 3 Modified principle |
|
|
The bath liquid is chosen according to boiling temperature. At temperatures up to 573 K, silicone oil can be used. Liquid paraffin may only be used up to 473 K. The heating of the bath liquid should be adjusted to a temperature rise of 3 K/min at first. The bath liquid must be stirred. At about 10 K below the expected boiling temperature, the heating is reduced so that the rate of temperature rise is less than 1 K/min. Upon approach of the boiling temperature, bubbles begin to emerge rapidly from the boiling capillary.
The boiling temperature is that temperature when, on momentary cooling, the string of bubbles stops and fluid suddenly starts rising in the capillary. The corresponding thermometer reading is the boiling temperature of the substance.
In the modified principle (figure 3) the boiling temperature is determined in a melting temperature capillary. It is stretched to a fine point about 2 cm in length (a) and a small amount of the sample is sucked up. The open end of the fine capillary is closed by melting, so that a small air bubble is located at the end. While heating in the melting temperature apparatus (b), the air bubble expands. The boiling temperature corresponds to the temperature at which the substance plug reaches the level of the surface of the bath liquid (c).
1.6.5. Photocell detection
The sample is heated in a capillary tube inside a heated metal block.
A light beam is directed, via suitable holes in the block, through the substance onto a precisely calibrated photocell.
During the increase of the sample temperature, single air bubbles emerge from the boiling capillary. When the boiling temperature is reached the number of bubbles increases greatly. This causes a change in the intensity of light, recorded by a photocell, and gives a stop signal to the indicator reading out the temperature of a platinum resistance thermometer located in the block.
This method is especially useful because it allows determinations below room temperature down to 253,15 K (– 20 oC) without any changes in the apparatus. The instrument merely has to be placed in a cooling bath.
1.6.6. Thermal analysis
1.6.6.1. Differential thermal analysis
See Appendix.
1.6.6.2. Differential scanning calorimetry
See Appendix.
2. DATA
At small deviations from the normal pressure (max. ± 5 kPa) the boiling temperatures are normalised to Tn by means of the following number-value equation by Sidney Young:
Tn = T + (fT × Δp)
where:
Δp |
= |
(101,325 - p) [note sign] |
P |
= |
pressure measurement in kPa |
fT |
= |
rate of change of boiling temperature with pressure in K/kPa |
T |
= |
measured boiling temperature in K |
Tn |
= |
boiling temperature corrected to normal pressure in K |
The temperature-correction factors, fT, and equations for their approximation are included in the international and national standards mentioned above for many substances.
For example, the DIN 53171 method mentions the following rough corrections for solvents included in paints:
Table 2:
Temperature — corrections factors fT
Temperature T (K) |
Correction factor fT (K/kPa) |
323,15 |
0,26 |
348,15 |
0,28 |
373,15 |
0,31 |
398,15 |
0,33 |
423,15 |
0,35 |
448,15 |
0,37 |
473,15 |
0,39 |
498,15 |
0,41 |
523,15 |
0,4 |
548,15 |
0,45 |
573,15 |
0,47 |
3. REPORTING
The test report shall, if possible, include the following information:
The mean of at least two measurements which are in the range of the estimated accuracy (see table 1) is reported as the boiling temperature.
The measured boiling temperatures and their mean shall be stated and the pressure(s) at which the measurements were made shall be reported in kPa. The pressure should preferably be close to normal atmospheric pressure.
All information and remarks relevant for the interpretation of results have to be reported, especially with regard to impurities and physical state of the substance.
4. REFERENCES
(1) OECD, Paris, 1981, Test Guideline 103, Decision of the Council C (81) 30 final.
(2) IUPAC, B. Le Neindre, B. Vodar, editions. Experimental thermodynamics, Butterworths, London, 1975, vol. II.
(3) R. Weissberger edition: Technique of organic chemistry, Physical methods of organic chemistry, Third Edition, Interscience Publications, New York, 1959, vol. I, Part I, Chapter VIII.
Appendix
For additional technical details, the following standards may be consulted for example.
1. Ebulliometer
1.1. Melting temperature devices with liquid bath
ASTM D 1120-72 |
Standard test method for boiling point of engine anti-freezes |
2. Distillation process (boiling range)
ISO/R 918 |
Test Method for Distillation (Distillation Yield and Distillation Range) |
BS 4349/68 |
Method for determination of distillation of petroleum products |
BS 4591/71 |
Method for the determination of distillation characteristics |
DIN 53171 |
Losungsmittel für Anstrichstoffe, Bestimmung des Siedeverlaufes |
NF T 20-608 |
Distillation: détermination du rendement et de l'intervalle de distillation |
3. Differential thermal analysis and differential scanning calorimetry
ASTM E 537-76 |
Standard method for assessing the thermal stability of chemicals by methods of differential thermal analysis |
ASTM E 473-85 |
Standard definitions of terms relating to thermal analysis |
ASTM E 472-86 |
Standard practice for reporting thermoanalytical data |
DIN 51005 |
Thermische Analyse, Begriffe |
A.3. RELATIVE DENSITY
1. METHOD
The methods described are based on the OECD Test Guideline (1). The fundamental principles are given in reference (2).
1.1. INTRODUCTION
The methods for determining relative density described are applicable to solid and to liquid substances, without any restriction in respect to their degree of purity. The various methods to be used are listed in table 1.
1.2. DEFINITIONS AND UNITS
The relative density D20 4 of solids or liquids is the ratio between the mass of a volume of substance to be examined, determined at 20 oC, and the mass of the same volume of water, determined at 4 oC. The relative density has no dimension.
The density, ρ, of a substance is the quotient of the mass, m, and its volume, v.
The density, ρ, is given, in SI units, in kg/m3.
1.3. REFERENCE SUBSTANCES (1) (3)
Reference substances do not need to be employed in all cases when investigating a new substance. They should primarily serve to check the performance of the method from time to time and to allow comparison with results from other methods.
1.4. PRINCIPLE OF THE METHODS
Four classes of methods are used.
1.4.1. Buoyancy methods
1.4.1.1. Hydrometer (for liquid substances)
Sufficiently accurate and quick determinations of density may be obtained by the floating hydrometers, which allow the density of a liquid to be deduced from the depth of immersion by reading a graduated scale.
1.4.1.2. Hydrostatic balance (for liquid and solid substances)
The difference between the weight of a test sample measured in air and in a suitable liquid (e.g. water) can be employed to determine its density.
For solids, the measured density is only representative of the particular sample employed. For the determination of density of liquids, a body of known volume, v, is weighed first in air and then in the liquid.
1.4.1.3. Immersed body method (for liquid substances) (4)
In this method, the density of a liquid is determined from the difference between the results of weighing the liquid before and after immersing a body of known volume in the test liquid.
1.4.2. Pycnometer methods
For solids or liquids, pycnometers of various shapes and with known volumes may be employed. The density is calculated from the difference in weight between the full and empty pycnometer and its known volume.
1.4.3. Air comparison pycnometer (for solids)
The density of a solid in any form can be measured at room temperature with the gas comparison pycnometer. The volume of a substance is measured in air or in an inert gas in a cylinder of variable calibrated volume. For the calculation of density one mass measurement is taken after concluding the volume measurement.
1.4.4. Oscillating densitimeter (5) (6) (7)
The density of a liquid can be measured by an oscillating densitimeter. A mechanical oscillator constructed in the form of a U-tube is vibrated at the resonance frequency of the oscillator which depends on its mass. Introducing a sample changes the resonance frequency of the oscillator. The apparatus has to be calibrated by two liquid substances of known densities. These substances should preferably be chosen such that their densities span the range to be measured.
1.5. QUALITY CRITERIA
The applicability of the different methods used for the determination of the relative density is listed in the table.
1.6. DESCRIPTION OF THE METHODS
The standards given as examples, which are to be consulted for additional technical details, are attached in the Appendix.
The tests have to be run at 20 oC, and at least two measurements performed.
2. DATA
See standards.
3. REPORTING
The test report shall, if possible, include the following information:
The relative density,
, shall be reported as defined in 1.2, along with the physical state of the measured substance.
All information and remarks relevant for the interpretation of results have to be reported, especially with regard to impurities and physical state of the substance.
Table:
Applicability of methods
Method of measurement |
Density |
Maximum possible dynamic viscosity |
Existing Standards |
|
solid |
liquid |
|||
1.4.1.1. Hydrometer |
|
yes |
5 Pa s |
ISO 387, ISO 649-2, NF T 20-050 |
1.4.1.2. Hydrostatic balance |
|
|
|
|
(a) solids |
yes |
|
|
ISO 1183 (A) |
(b) liquids |
|
yes |
5 Pa s |
ISO 901 and 758 |
1.4.1.3. Immersed body method |
|
yes |
20 Pa s |
DIN 53217 |
1.4.2. Pycnometer |
|
|
|
ISO 3507 |
(a) solids |
yes |
|
|
ISO 1183(B), NF T 20-053 |
(b) liquids |
|
yes |
500 Pa s |
ISO 758 |
1.4.3. Air comparison pycnometer |
yes |
|
|
DIN 55990 Teil 3, DIN 53243 |
1.4.4. Oscillating densitimer |
|
yes |
5 Pa s |
|
4. REFERENCES
(1) OECD, Paris, 1981, Test Guideline 109, Decision of the Council C(81) 30 final.
(2) R. Weissberger ed., Technique of Organic Chemistry, Physical Methods of Organic Chemistry, 3rd ed., Chapter IV, Interscience Publ., New York, 1959, vol. I, Part 1.
(3) IUPAC, Recommended reference materials for realization of physico-chemical properties, Pure and applied chemistry, 1976, vol. 48, p. 508.
(4) Wagenbreth, H., Die Tauchkugel zur Bestimmung der Dichte von Flüssigkeiten, Technisches Messen tm, 1979, vol. II, p. 427-430.
(5) Leopold, H., Die digitale Messung von Flüssigkeiten, Elektronik, 1970, vol. 19, p. 297-302.
(6) Baumgarten, D., Füllmengenkontrolle bei vorgepackten Erzeugnissen -Verfahren zur Dichtebestimmung bei flüssigen Produkten und ihre praktische Anwendung, Die Pharmazeutische Industrie, 1975, vol. 37, p. 717-726.
(7) Riemann, J., Der Einsatz der digitalen Dichtemessung im Brauereilaboratorium, Brauwissenschaft, 1976, vol. 9, p. 253-255.
Appendix
For additional technical details, the following standards may be consulted for example.
1. Buoyancy methods
1.1. Hydrometer
DIN 12790, ISO 387 |
Hydrometer; general instructions |
DIN 12791 |
Part I: Density hydrometers; construction, adjustment and use Part II: Density hydrometers; standardised sizes, designation Part III: Use and test |
ISO 649-2 |
Laboratory glassware: Density hydrometers for general purpose |
NF T 20-050 |
Chemical products for industrial use — Determination of density of liquids — Areometric method |
DIN 12793 |
Laboratory glassware: range find hydrometers |
1.2. Hydrostatic balance
For solid substances
ISO 1183 |
Method A: Methods for determining the density and relative density of plastics excluding cellular plastics |
NF T 20-049 |
Chemical products for industrial use — Determination of the density of solids other than powders and cellular products — Hydrostatic balance method |
ASTM-D-792 |
Specific gravity and density of plastics by displacement |
DIN 53479 |
Testing of plastics and elastomers; determination of density |
For liquid substances
ISO 901 |
ISO 758 |
DIN 51757 |
Testing of mineral oils and related materials; determination of density |
ASTM D 941-55, ASTM D 1296-67 and ASTM D 1481-62 |
|
ASTM D 1298 |
Density, specific gravity or API gravity of crude petroleum and liquid petroleum products by hydrometer method |
BS 4714 |
Density, specific gravity or API gravity of crude petroleum and liquid petroleum products by hydrometer method |
1.3. Immersed body method
DIN 53217 |
Testing of paints, varnishes and similar coating materials; determination of density; immersed body method |
2. Pycnometer methods
2.1. For liquid substances
ISO 3507 |
Pycnometers |
ISO 758 |
Liquid chemical products; determination of density at 20 oC |
DIN 12797 |
Gay-Lussac pycnometer (for non-volatile liquids which are not too viscous) |
DIN 12798 |
Lipkin pycnometer (for liquids with a kinematic viscosity of less than 100 10-6 m2 s-1 at 15 oC) |
DIN 12800 |
Sprengel pycnometer (for liquids as DIN 12798) |
DIN 12801 |
Reischauer pycnometer (for liquids with a kinematic viscosity of less than 100. 10-6 m2 s-1 at 20 oC, applicable in particular also to hydrocarbons and aqueous solutions as well as to liquids with higher vapour pressure, approximately 1 bar at 90 oC) |
DIN 12806 |
Hubbard pycnometer (for viscous liquids of all types which do not have too high a vapour pressure, in particular also for paints, varnishes and bitumen) |
DIN 12807 |
Bingham pycnometer (for liquids, as in DIN 12801) |
DIN 12808 |
Jaulmes pycnometer (in particular for ethanol — water mixture) |
DIN 12809 |
Pycnometer with ground-in thermometer and capillary side tube (for liquids which are not too viscous) |
DIN 53217 |
Testing of paints, varnishes and similar products; determination of density by pycnometer |
DIN 51757 |
Point 7: Testing of mineral oils and related materials; determination of density |
ASTM D 297 |
Section 15: Rubber products — chemical analysis |
ASTM D 2111 |
Method C: Halogenated organic compounds |
BS 4699 |
Method for determination of specific gravity and density of petroleum products (graduated bicapillary pycnometer method) |
BS 5903 |
Method for determination of relative density and density of petroleum products by the capillary — stoppered pycnometer method |
NF T 20-053 |
Chemical products for industrial use — Determination of density of solids in powder and liquids — Pyknometric method |
2.2. For solid substances
ISO 1183 |
Method B: Methods for determining the density and relative density of plastics excluding cellular plastics |
NF T 20-053 |
Chemical products for industrial use — Determination of density of solids in powder and liquids — Pyknometric method |
DIN 19683 |
Determination of the density of soils |
3. Air comparison pycnometer
DIN 55990 |
Part 3: Prüfung von Anstrichstoffen und ähnlichen Beschichtungsstoffen; Pulverlack; Bestimmung der Dichte |
DIN 53243 |
Anstrichstoffe; chlorhaltige Polymere; Prüfung |
A.4. VAPOUR PRESSURE
1. METHOD
This method is equivalent to OECD TG 104 (2004).
1.1. INTRODUCTION
This revised version of method A.4(1) includes one additional method; Effusion method: isothermal thermogravimetry, designed for substances with very low pressures (down to 10–10 Pa). In the light of needs for procedures, especially in relation to obtaining vapour pressure for substances with low vapour pressure, other procedures of this method are re-evaluated with respect to other applicability ranges.
At the thermodynamic equilibrium the vapour pressure of a pure substance is a function of temperature only. The fundamental principles are described elsewhere (2)(3).
No single measurement procedure is applicable to the entire range of vapour pressures from less than 10–10 to 105 Pa. Eight methods for measuring vapour pressure are included in this method which can be applied in different vapour pressure ranges. The various methods are compared as to application and measuring range in Table 1. The methods can only be applied for compounds that do not decompose under the conditions of the test. In cases where the experimental methods cannot be applied due to technical reasons, the vapour pressure can also be estimated, and a recommended estimation method is set out in the Appendix.
1.2. DEFINITIONS AND UNITS
The vapour pressure of a substance is defined as the saturation pressure above a solid or liquid substance.
The SI unit of pressure, which is the pascal (Pa), should be used. Other units which have been employed historically are given hereafter, together with their conversion factors:
1 Torr |
= |
1 mm Hg |
= |
1,333 × 102 Pa |
1 atmosphere |
= |
1,013 × 105 Pa |
|
|
1 bar |
= |
105 Pa |
|
|
The SI unit of temperature is the kelvin (K). The conversion of degrees Celsius to kelvin is according to the formula:
T = t + 273,15
where, T is the kelvin or thermodynamic temperature and t is the Celsius temperature.
Table 1
Measuring method |
Substances |
Estimated repeatability |
Estimated reproducibility |
Recommended range |
|
Solid |
Liquid |
||||
Dynamic method |
Low melting |
Yes |
up to 25 % 1 to 5 % |
up to 25 % 1 to 5 % |
103 Pa to 2 × 103 Pa 2 × 103 Pa to 105 Pa |
Static method |
Yes |
Yes |
5 to 10 % |
5 to 10 % |
10 Pa to 105 Pa 10–2 Pa to 105 Pa (1) |
Isoteniscope method |
Yes |
Yes |
5 to 10 % |
5 to 10 % |
102 Pa to 105 Pa |
Effusion method: vapour pressure balance |
Yes |
Yes |
5 to 20 % |
up to 50 % |
10–3 to 1 Pa |
Effusion method: Knudsen cell |
Yes |
Yes |
10 to 30 % |
— |
10–10 to 1 P |
Effusion method: isothermal thermogravimetry |
Yes |
Yes |
5 to 30 % |
up to 50 % |
10–10 to 1 Pa |
Gas saturation method |
Yes |
Yes |
10 to 30 % |
up to 50 % |
10–10 to 103 Pa |
Spinning rotor method |
Yes |
Yes |
10 to 20 % |
— |
10–4 to 0,5 Pa |
(1)
When using a capacitance manometer |
1.3. PRINCIPLE OF THE TEST
In general, the vapour pressure is determined at various temperatures. In a limited temperature range, the logarithm of the vapour pressure of a pure substance is a linear function of the inverse of the thermodynamic temperature according to the simplified Clapeyron-Clausius equation:
where:
p |
= |
the vapour pressure in pascals |
ΔHv |
= |
the heat of vaporisation in J mol–1 |
R |
= |
the universal gas constant, 8,314 J mol–1 K–1 |
T |
= |
the temperature in K |
1.4. REFERENCE SUBSTANCES
Reference substances do not need to be employed. They serve primarily to check the performance of a method from time to time as well as to allow comparison between results of different methods.
1.5. DESCRIPTION OF THE METHOD
1.5.1. Dynamic method (Cottrell’s method)
1.5.1.1. Principle
The vapour pressure is determined by measuring the boiling temperature of the substance at various specified pressures between roughly 103 and 105 Pa. This method is also recommended for the determination of the boiling temperature. For that purpose it is useful up to 600 K. The boiling temperatures of liquids are approximately 0,1 °C higher at a depth of 3 to 4 cm than at the surface because of the hydrostatic pressure of the column of liquid. In Cottrell’s method (4) the thermometer is placed in the vapour above the surface of the liquid and the boiling liquid is made to pump itself continuously over the bulb of the thermometer. A thin layer of liquid which is in equilibrium with vapour at atmospheric pressure covers the bulb. The thermometer thus reads the true boiling point, without errors due to superheating or hydrostatic pressure. The pump originally employed by Cottrell is shown in figure 1. Tube A contains the boiling liquid. A platinum wire B sealed into the bottom facilitates uniform boiling. The side tube C leads to a condenser, and the sheath D prevents the cold condensate from reaching the thermometer E. When the liquid in A is boiling, bubbles and liquid trapped by the funnel are poured via the two arms of the pump F over the bulb of the thermometer.
Figure 1 |
Figure 2 |
Cottrell pump (4)
A: Thermocouple
B: Vacuum buffer volume
C: Pressure gauge
D: Vacuum
E: Measuring point
F: Heating element c.a. 150 W
1.5.1.2. Apparatus
A very accurate apparatus, employing the Cottrell principle, is shown in figure 2. It consists of a tube with a boiling section in the lower part, a cooler in the middle part, and an outlet and flange in the upper part. The Cottrell pump is placed in the boiling section which is heated by means of an electrical cartridge. The temperature is measured by a jacketed thermocouple, or resistance thermometer inserting through the flange at the top. The outlet is connected to the pressure regulation system. The latter consists of a vacuum pump, a buffer volume, a manostat for admitting nitrogen for pressure regulation and manometer.
1.5.1.3. Procedure
The substance is placed in the boiling section. Problems may be encountered with non-powder solids but these can sometimes be solved by heating the cooling jacket. The apparatus is sealed at the flange and the substance degassed. Frothing substances cannot be measured using this method.
The lowest desired pressure is then set and the heating is switched on. At the same time, the temperature sensor is connected to a recorder.
Equilibrium is reached when a constant boiling temperature is recorded at constant pressure. Particular care must be taken to avoid bumping during boiling. In addition, complete condensation must occur on the cooler. When determining the vapour pressure of low melting solids, care should be taken to prevent the condenser from blocking.
After recording this equilibrium point, a higher pressure is set. The process is continued in this manner until 105 Pa has been reached (approximately 5 to 10 measuring points in all). As a check, equilibrium points must be repeated at decreasing pressures.
1.5.2. Static method
1.5.2.1. Principle
In the static method (5), the vapour pressure at thermodynamic equilibrium is determined at a specified temperature. This method is suitable for substances and multicomponent liquids and solids in the range from 10–1 to 105 Pa and, provided care is taken, also in the range 1 to 10 Pa.
1.5.2.2. Apparatus
The equipment consists of a constant-temperature bath (precision of ± 0,2 K), a container for the sample connected to a vacuum line, a manometer and a system to regulate the pressure. The sample chamber (figure 3a) is connected to the vacuum line via a valve and a differential manometer (U-tube containing a suitable manometer fluid) which serves as zero indicator. Mercury, silicones and phthalates are suitable for use in the differential manometer, depending on the pressure range and the chemical behaviour of the test substance. However, based on environmental concerns, the use of mercury should be avoided, if possible. The test substance must not dissolve noticeably in, or react with, the U-tube fluid. A pressure gauge can be used instead of a U-tube (figure 3b). For the manometer, mercury can be used in the range from normal pressure down to 102 Pa, while silicone fluids and phthalates are suitable for use below 102 Pa down to 10 Pa. There are other pressure gauges which can be used below 102 Pa and heatable membrane capacity manometers can even be used at below 10–1 Pa. The temperature is measured on the outside wall of the vessel containing the sample or in the vessel itself.
1.5.2.3. Procedure
Using the apparatus as described in figure 3a, fill the U-tube with the chosen liquid, which must be degassed at an elevated temperature before readings are taken. The test substance is placed in the apparatus and degassed at reduced temperature. In the case of a multiple-component sample, the temperature should be low enough to ensure that the composition of the material is not altered. Equilibrium can be established more quickly by stirring. The sample can be cooled with liquid nitrogen or dry ice, but care should be taken to avoid condensation of air or pump-fluid. With the valve over the sample vessel open, suction is applied for several minutes to remove the air. If necessary, the degassing operation is repeated several times.
Figure 3a |
Figure 3b |
When the sample is heated with the valve closed, the vapour pressure increases. This alters the equilibrium of the fluid in the U-tube. To compensate for this, nitrogen or air is admitted to the apparatus until the differential pressure indicator is at zero again. The pressure required for this can be read off the manometer or off an instrument of higher precision. This pressure corresponds to the vapour pressure of the substance at the temperature of the measurement. Using the apparatus described in figure 3b, the vapour pressure is read off directly.
The vapour pressure is determined at suitably small temperature intervals (approximately 5 to 10 measuring points in all) up to the desired temperature maximum.
Low-temperature readings must be repeated as a check. If the values obtained from the repeated readings do not coincide with the curve obtained for increasing temperature, this may be due to one of the following situations:
the sample still contains air (e.g. in the case of highly viscous materials) or low-boiling substances which is or are released during heating;
the substance undergoes a chemical reaction in the temperature range investigated (e.g. decomposition, polymerisation).
1.5.3. Isoteniscope Method
1.5.3.1. Principle
The isoteniscope (6) is based on the principle of the static method. The method involves placing a sample in a bulb maintained at constant temperature and connected to a manometer and a vacuum pump. Impurities more volatile than the substance are removed by degassing at reduced pressure. The vapour pressure of the sample at selected temperatures is balanced by a known pressure of inert gas. The isoteniscope was developed to measure the vapour pressure of certain liquid hydrocarbons but it is appropriate for the investigation of solids as well. The method is usually not suitable for multicomponent systems. Results are subject to only slight errors for samples containing non-volatile impurities. The recommended range is 102 to 105 Pa.
1.5.3.2. Apparatus
An example of a measuring device is shown in figure 4. A complete description can be found in ASTM D 2879-86 (6).
1.5.3.3. Procedure
In the case of liquids, the substance itself serves as the fluid in the differential manometer. A quantity of the liquid, sufficient to fill the bulb and the short leg of the manometer, is put in the isoteniscope. The isoteniscope is attached to a vacuum system and evacuated, then filled by nitrogen. The evacuation and purge of the system is repeated twice to remove residual oxygen. The filled isoteniscope is placed in a horizontal position so that the sample spreads out into a thin layer in the sample bulb and manometer. The pressure of the system is reduced to 133 Pa and the sample is gently warmed until it just boils (removal of dissolved gases). The isoteniscope is then placed so that the sample returns to the bulb and fills the short leg of the manometer. The pressure is maintained at 133 Pa. The drawn-out tip of the sample bulb is heated with a small flame until the sample vapour released expands sufficiently to displace part of the sample from the upper part of the bulb and manometer arm into the manometer, creating a vapour-filled, nitrogen-free space. The isoteniscope is then placed in a constant temperature bath, and the pressure of the nitrogen is adjusted until it equals that of the sample. At the equilibrium, the pressure of the nitrogen equals the vapour pressure of the substance.
Figure 4