ISO 3405 Petroleum products - Determination of distillation characteristics at atmospheric pressure
5 Apparatus
5.1 General
Typical assemblies of the manual apparatus are shown in Figures 1 and 2.

5.2 Distillation flasks
The distillation flasks shall have a capacity of 100 ml or 125 ml and be constructed of heat-resistant glass, according to the dimensions and tolerances shown in Figures 3 and 4.

NOTE For tests specifying the dry point, especially selected flasks with bottoms and walls of uniform thickness are desirable.

5.3 Condenser tube and cooling bath
Typical types of condenser and cooling bath are illustrated in Figures 1 and 2.

NOTE Other types of apparatus may be used, provided that the test results obtained by their use are such as to correlate with the results obtained with those illustrated, and to satisfy the precision criteria given in clause 12.

5.3.1 The condenser shall be made of seamless non-corrosive metal tubing, 560 mm +/- 5 mm in length, with an outside diameter of 14 mm and a wall thickness of 0.8 mm to 0.9 mm.

NOTE Brass or stainless steel are suitable materials.

5.3.2 The condenser shall be set so that 393 mm +/- 3 mm of the tube is in contact with the cooling medium, with 50 mm +/- 3 mm outside the cooling bath at the upper end, and 114 mm +/- 3 mm outside at the lower end. The portion of tube projecting at the upper end shall be set at an angle of 75° to the vertical. The portion of the tube inside the cooling bath shall be either straight or bent in any suitable continuous smooth curve. The average gradient shall be 15° +/- 1 ° with respect to the horizontal, and no 100 mm section shall have a gradient outside a 15° +/- 3° range. The projecting lower portion of the condenser tube shall be curved downward for a length of 76 mm and the lower end cut off at an acute angle. Provisions shall be made to enable the flow of distillate to run down the side of the receiving graduated cylinder. Figure 5 gives an illustration of the lower end of the condenser tube.

NOTE The flow of distillate down the side of the graduated cylinder may be accomplished either by using a drip-deflector which is inserted in the receiver, or by having the downward length of the condenser tube curve slightly backwards so as to ensure contact with the wall of the graduated cylinder at a point 25 mm to 32 mm below the top of the graduated cylinder when it is in position to receive distillate.

5.3.3 The volume and design of the cooling bath will depend on the cooling medium employed. The cooling capacity of the bath shall be adequate to maintain the required temperature for the desired condenser performance. A single cooling bath may be used for several condenser tubes.

5.4 Metal shield or enclosure for flask (manual apparatus only)
Shields shall be provided to protect the operator from damage to the unit during operation, and to protect the distillation flask from draughts. They shall allow easy access to the distillation during operation, and be provided with at least one window to observe the dry point at the end of the distillation.

NOTE 1 A typical shield for a unit fitted with a gas burner would be 400 mm high, 280 mm long and 200 mm wide, made of sheet metal approximately 0.8 mm in thickness (see Figure 1).

NOTE 2 A typical shield for a unit fitted with an electric heater would be 440 mm high, 200 mm long and 200 mm wide, made of sheet metal approximately 0.8 mm in thickness (see Figure 2).

5.5 Heat source
5.5.1 Gas burner (see Figure 1), capable of bringing over the first drop from a cold start within the time specified, and continuing the distillation at the specified rate. A sensitive regulating valve and gas pressure governor to give complete control of heating shall be provided.

5.5.2 Electric heater (see Figure 2), of low heat retention and adjustable from 0 W to 1000 W.

5.6 Flask-support
5.6.1 Type 1 for use with gas burner (see Figure 1). Either a ring support of the ordinary laboratory type, 100 mm or larger in diameter, supported on a stand inside the shield, or a platform adjustable from the outside of the shield shall be used.

Two hard boards, made of ceramic or other heat-resistant material not containing asbestos, 3 mm to 4 mm in thickness, shall rest upon the ring or the platform, whichever is used. The board immediately above the ring or platform shall have a central opening 76 mm to 100 mm in diameter, and outside line dimensions slightly smaller than the inside boundaries of the shield.

The second, or flask-support board, shall be slightly smaller in outside dimensions than the first board and shall have a central opening conforming to the dimensions given in Table 2. It shall be 3 mm to 4 mm in thickness at the central hole rim. The flask-support board may be moved slightly in accordance with the directions for positioning the distillation flask so that direct heat is applied to the flask only through the opening in this board. The position of the flask is set by adjusting the length of the side-arm inserted into the condenser.

5.6.2 Type 2 for use with an electric heater (see Figure 2). The flask-support is a platform on top of the electric heater and adjustable from the outside of the shield. The two hard boards described in 5.6.1 are mounted on this support. Provision shall be made for moving the upper (flask-support) board slightly in the horizontal plane to ensure that direct heat is applied only through the specified opening in this board. The flask-support assembly shall be able to move vertically to ensure contact of the flask-support board with the bottom of the distillation flask during the distillation, and to allow for easy mounting and removal of the distillation flask from the unit.

5.7 Graduated cylinders
5.7.1 Receiving cylinder, of 100 ml capacity, generally in accordance with ISO 4788. It shall be graduated at intervals of 1 ml and have a graduation at the 100 ml mark. The shape of the base shall be such that the receiver does not topple when placed empty on a surface inclined at an angle of 13° to the horizontal. Construction details and tolerances for the graduated cylinder are shown in Figure 6.

For automated apparatus, the cylinder shall conform to the physical specifications described in this subclause, with the exception of all graduations but that at 100 ml. Graduated cylinders for use in automated units may also have a metal base.

5.7.1.1 If required, the graduated cylinder shall be immersed up to above the 100 ml graduation line in a cooling liquid contained in a cooling bath, such as a tall-form beaker of clear glass or transparent plastic, or placed in a thermostatically controlled air-circulation chamber.

5.7.2 Residue cylinder, of 5 ml capacity, generally in accordance with ISO 4788.

5.8 Temperature measurement system
5.8.1 Thermometers, if used, shall be of the mercury-in-glass type, nitrogen filled, graduated on the stem and enamel backed, and shall conform to the specifications given in annex A.

CAUTIONARY NOTE - Under certain test conditions, the bulb of the thermometer can be 28 °C above the temperature indicated, and at an indicated temperature of 371 °C, the temperature of the bulb is approaching a critical range in the glass. It is thus strongly recommended that distillation temperature readings above 371 °C are avoided, but in those cases where thermometers have been exposed to observed temperature readings above 371 °C, they shall not be re-used without checking their ice point to verify calibration.

5.8.2 Electronic temperature-measurement devices, if used, shall exhibit the same temperature lag, emergent stem effect and accuracy as the equivalent mercury-in-glass thermometer.
5.8.2.1 To simulate the temperature lag of a mercury-in-glass thermometer, the circuitry and/or the algorithms used for the electronic system shall take this fact into account.

5.8.2.2 Alternatively, place the sensor in a casing with the tip covered, so that the assembly, because of its adjusted thermal mass and conductivity, has a temperature lag time similar to that of mercury-in-glass thermometers.

5.8.2.3 In case of dispute, unless otherwise agreed, the referee test shall be carried out using the specified mercury-in-glass thermometers.

5.8.2.4 A means of determining the difference in lag time between an electronic measurement system and mercury-in-glass thermometers is given in annex B.

5.9 Centring device
The temperature sensor shall be fitted through a snug-fitting device designed for mechanically centring the sensor in the neck of the distillation flask without vapour leakage. The use of a cork or silicone rubber stopper with a hole drilled through the centre is not acceptable for this purpose. Examples of acceptable centring devices are shown in Figures 7 and 8.

NOTE 1 When running tests by the manual method, products with a low initial boiling point may have one or more temperature readings obscured by the centring device.

NOTE 2 Other centring devices not shown in Figures 7 and 8 are also acceptable provided that they position and hold the temperature sensor in the middle of the neck of the distillation flask.

5.10 Barometer
The barometer shall be capable of measuring atmospheric pressure with an accuracy of 0.1 kPa or better, at the same elevation relative to sea level as the apparatus in the laboratory. Do not take readings from aneroid barometers that are precorrected to give sea level pressures.

NOTE The barometer should ideally be located in the room in which the distillation is carried out.