102

Adopted:

27.07.95

OECD GUID ELIN E FOR THE TESTIN G OF CHEMICALS

Adopted by the Council on 27th July 1995

Melting Point / Melting Range

IN TRODUCTION

1. This guideline is a revised version of the original Guideline 102 which was adopted in 1981.

Mainly the format has been changed. The differences of substance between this version and that from

1981 are few. The meniscus method, which is applicable to polyamides, has not been retained and

the pour point is included. The revision was based on the EC method "Melting/Freezing Temperature"

published in 1992 (1).

IN ITIAL CONSID ERATIONS

2. Frequently the transition from solid to liquid phase takes place over a temperature range.

Therefore, the term "melting range" is often used and, in practice, the temperatures of the initial and

final stages of melting are determined. The melting point ideally is identical with the solidification

or freezing point. For some substances (rather products and mixtures) however, the determination of

the freezing or solidification temperature is easier. Where, due to the particular properties of the

substance (or product), none of the above parameters can be conveniently measured, a pour point may

be appropriate.

3. The fundamental principles are given in references 2 and 3. Several methods and devices

are described in this guideline. They can be applied irrespective of the degree of purity of the

substance. The melting point of a substance is considerably affected by impurities. For this reason

it serves as a measure of a substance's purity. The selection of a particular method depends mainly

on the state of physical aggregation of the sample and on whether or not the substance can be

pulverized easily, with difficulty, or not at all. Standards describing the various devices and

procedures are listed in the Appendix.

D EFIN ITIONS AN D UNITS

4. The melting point is defined as the temperature at which the phase transition from the solid

to the liquid state at atmospheric pressure takes place.

5. The conversion of kelvins to degrees Celsius is according to the formula

T = t + 273.15 , where 

T is the Kelvin or thermodynamic temperature and t the Celsius temperature. 

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102 OCD E/OECD

REFEREN CE SUBSTAN CES

6. Reference substances do not need to be employed when investigating a substance. Some

calibration substances are listed in reference 4.

PRIN CIPLE OF THE TES T

7. The temperature or temperature range of the phase transition from the solid to the liquid state

or from the liquid to the solid state is determined. 

COMPARISON OF THE METHODS

8. The temperature range and accuracy of the different methods are listed in Table 1.

Table 1

Method Temperature range (in K) Estimated accuracy (in K)

Capillary/liquid bath 273 to 573 ± 0.3

Capillary/metal block 293 to >573 ± 0.5

Kofler hot bar 293 to >573 ± 1.0 

Melt microscope 293 to >573 ± 0.5

Differential thermal analysis and

differential scanning calorimetry

173 to 1273 ± 0.5 up to 600 K

± 2.0 up to 1273 K

Freezing temperature 223 to 573 ± 0.5

Pour point 223 to 323 ± 3.0

D ESCRIPTION OF THE METHODS

Capillary tube in a liquid bath

Apparatus 

9. The apparatus made of glass is shown in Figure 1. The choice of the bath liquid depends

upon the melting temperature to be determined, e.g. liquid paraffin for temperatures not higher than

473 K and silicone oil for temperatures not higher than 573 K. For temperatures above 523 K, a

mixture of three parts sulfuric acid and two parts of potassium sulphate (weight ratio) can be used.

Precautions should be taken if a mixture such as this is used. Only thermometers, fulfilling the

requirements of the standards ASTM E 1-71, DIN 12770, and JIS K 8001, or equivalent, should be

used. The middle part of the mercury bulb of the thermometer should touch the capillary at the

position where the sample is located.

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OCD E/OECD 102

Figure 1

Dimensions in mm

A. Vessel

B. Stopper

C. Vent

D. Thermometer

E. Auxiliary thermometer

F. Bath liquid

G. Sample tube; max 5 mm outer

diameter; capillary tube, approx

100 mm long and approx 1 mm

inner diameter, and approx 0.2

to 0.3 mm wall-thickness

H. Side tube

Figure 2

Stage A, beginning of melting, fine droplets adhere uniformly to the wall of the tube

Stage B, a clearance between the sample and the wall due to shrinkage of the melt

Stage C, the shrunken sample collapses and liquefies

Stage D, a complete meniscus is formed but part of the sample remains solid

Stage E, final stage of melting, no solid particles are left

Procedure 

10. The dry substance is finely pulverized and put into a capillary tube, fused at one end, so that

the filling level is approximately 3 mm after the sample has been tightly packed. To obtain a

uniformly packed sample, the capillary tube should be dropped from a height of approximately 700

mm through a glass tube onto a watch glass. The bath is heated so that the temperature rise is

approximately 3 K/min. The bath should be stirred. Usually the capillary tube is put into the

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102 OCD E/OECD

apparatus when the temperature has risen to about 10 K below the melting temperature. From then

on, and throughout the actual melting, the temperature rise is adjusted to maximum 1K/min. When

subjected to a slow temperature rise, finely pulverized substances usually show the stages of melting

shown in Figure 2. During the determination of the melting temperature, the temperatures are recorded

at the beginning of the melting (stage A in the figure) and at the final stage (stage E in the figure).

Calculations

11. A corrected melting temperature is calculated using the formula

T = TD + 0.00016 (TD - TE ) n , where

T = corrected melting temperature,

TD = reading of thermometer D,

TE = reading of thermometer E,

n = number of graduations of the mercury column on the emergent stem of

thermometer D.

Capillary tube in a metal block

Apparatus for visual observation 

Figure 3

A. Thermometer

B. Capillary tube

C. Eye-piece

D. Electrical

resistance

E. Metal heating

block

F. Lamp

G. Metal plug

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OCD E/OECD 102

12. The apparatus shown in Figure 3 consists of:

- a cylindrical metal block, the upper part of which is hollow and forms a chamber;

- a metal plug, with two or more holes, allowing capillary tubes to be mounted in the block;

- an electrical heating system with regulated power input;

- four windows of heat-resistant glass on the lateral walls of the chamber, diametrically disposed

at right angles;

- an eyepiece for observing the capillary tube, mounted in front of one of these windows (the

other three windows are used for illuminating the inside of the enclosure);

- a thermometer according to standards mentioned in paragraph 9 or thermoelectrical measuring

devices of comparable accuracy.

Apparatus with photocell detection 

13. A capillary tube, filled as described in paragraph 10, is placed in a heated metal block. The

temperature rise is adjusted at a suitable pre-selected linear rate. A beam of light is directed through

the sample to a photocell. On melting of the sample, the intensity of the light reaching the photocell

increases and a stop signal is sent to the digital indicator reading out the temperature of the heating

chamber.

Kofler hot bar

Apparatus

14. The Kofler hot bar uses two pieces of metal of different thermal conductivity. The bar is

heated electrically and is designed so that the temperature gradient is almost linear along its length.

The temperature of the hot bar can range approximately from room temperature to 573 K. The bar

is fitted with a graduated temperature scala and a movable pointer.

Procedure

15. The substance is laid in a thin layer on the hot bar. A sharp dividing line develops between

the solid and fluid phase within a few seconds. The temperature at the dividing line is read by

adjusting the pointer to the dividing line.

Melt microscope

16. The specimen holder of a melt microscope is a metal plate which is part of a heating chamber.

A hole in the metal plate permits the entrance of light from an illuminating device. The sample is

placed on a slide over the hole and may be covered by another slide to minimise exposure to air. The

plate is heated gradually until melting is observed and the temperature is recorded. The accuracy of

the measurement can be increased for crystalline substances through the use of polarised light.

Differential thermal analysis (DTA)

17. Samples of the test substance and of a reference material are subjected to the same controlled

temperature programme. When the test substance undergoes a phase transition, the corresponding

change of enthalpy gives an endothermic (melting) or exothermic (freezing) departure from the base

line of the temperature record.

Differential scanning calorimetry (DSC)

18. Samples of the test substance and of a reference material are subjected to the same controlled

temperature programme. The difference in energy input necessary to maintain identical temperatures

between the substance and the reference material is recorded. When the sample undergoes a phase

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102 OCD E/OECD

transition, the corresponding change of enthalpy gives a departure form the base line of the heat flow

record.

Freezing temperature

19. A sample of the substance is placed in a test tube and stirred continuously. As the sample is

cooled, its temperature is measured at regular intervals. As soon as the temperature remains constant

for a few readings (corrected for thermometer error), this temperature is recorded as the freezing

temperature. Supercooling must be avoided by maintaining equilibrium between the solid and the

liquid phases.

Pour point

20. This method was developed for petroleum oils and is suitable for oily substances with low

melting temperatures. After preliminary heating, the sample is cooled and its flow characteristics are

examined at intervals of 3 K. The lowest temperature at which movement of the substance is observed

is recorded as the pour point.

TES T REPORT

21. The test report shall include the following information:

- method used;

- chemical identity and impurities (preliminary purification step, if any);

- estimated accuracy;

- melting temperature (the mean of at least two measurements which are in the range of the

estimated accuracy; if the difference between the temperature at the beginning and at the final

stage of melting is within the limits of the accuracy, 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 melting occurs, the temperature at which the effect

is observed is reported);

- all information and remarks relevant for the interpretation of the results, especially with regards

to impurities and physical state of the substance.

LITERATURE

(1) Official Journal of the European Communities L 383 A, 5-14 (1992) 

(2) Le Neindre, B. and Vodar B., eds. (1975). IUPAC, Experimental Thermodynamics, Vol.II,

Butterworths, London, pp. 803 to 834

(3) Weissberger, R., ed. (1959). Technique of Organic Chemistry, Vol. I, Part I, Chapter VII,

Physical Methods of Organic Chemistry, 3rd ed., Interscience Publ., New York. 

(4) IUPAC (1976). Physicochemical measurements: Catalogue of reference materials from national

laboratories, Pure and Applied Chemistry, 48, 505 to 515

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APPENDIX

LIS T OF S TANDARDS

Capillary tube in a 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 Bindemittel für Lacke und ähnliche Beschichtungsstoffe;

Bestimmung des Schmelzbereiches von Harzen nach KapillarVerfahren 

JIS K 00-64 Testing methods for melting point of chemical products

Capillary tube in a metal block

DIN 53736 Visuelle Bestimmung der Schmelztemperatur von 

teilkristallinen Kunststoffen 

Kofler hot bar

ANSI / ASTM D 3451-76 Standard recommended practices for testing polymeric

powders and powder coatings

Melt microscope

DIN 53736 Visuelle Bestimmung der Schmelztemperatur von 

teilkristallinen Kunststoffen

Differential thermal analysis and differential scanning calorimetry

ASTM E 472-86 Standard practice for reporting thermoanalytical data 

ASTM E 473-85 Standard definitions of terms relating to thermal analysis

ASTM E 537-76 Standard method for assessing the thermal stability of

chemicals by methods of differential thermal analysis 

DIN 51005 Thermische Analyse (TA)

Freezing temperature

BS 4633 Method for the determination of crystallizing point

BS 4695 Method for the determination of melting point of petroleum

wax (cooling curve)

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102 OCD E/OECD

DIN 51421 Bestimmung des Gefrierpunktes von Flugkraftstoffen,

Ottokraftstoffen und Motorenbenzolen

DIN 53175 Bestimmung des Erstarrungspunktes von Fettsäuren

ISO 1392 Method for the determination of the crystallizing point

ISO 2207 Petroleum waxes - Determination of congealing point

JIS K 00 - 65 Test methods for freezing point of chemical products

NF T 60-114 Point de fusion des paraffines

NF T 20-051 Méthode de détermination du point de cristallisation 

Pour point

ASTM D 97-66 Standard test method for pour point of petroleum oils

ISO 3016 Petroleum oils - Determination of pour point

NBN 52014 Echantillonnage et analyse des produits de pétrole: Point de

trouble et point d'écoulement limite

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OECD 102, July 27,1995

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