ASTM D1015 Standard Test Method for Freezing Points of High-Purity Hydrocarbons
5. Apparatus
5.1 Freezing-Point Apparatus, as shown in Figs. 1-3 comprising a freezing tube, a metal sheath for the freezing tube, a Dewar flask for the cooling bath, a Dewar flask for the warming bath, a stirring mechanism, suitable clamps and holders for the parts, and the absorption tubes. The outer walls of all Dewar flasks can be covered with adhesive tape to minimize danger from glass in case of breakage. (Warning - When using liquid nitrogen as a refrigerant, provide a means to prevent condensation of oxygen in the space between the freezing tube and the metal sheath and subsequent sealing of the space by ice forming on the asbestos collar. Provide the metal sheath with suitable openings in the sides and bottom. Failure to do this may result in breakage of the freezing tube when the liquefied oxygen evaporates within the sealed space.)
5.2 Resistance Bridge, Mueller type, reading from 0.0001 to 50 Ω, in steps of 0.001 Ω.
5.3 Platinum Resistance Thermometer, precision grade, with a resistance near 25.5 Ω at 0°C, calibrated by the National Institute of Standards and Technology for the range from −190 to 500°C.
5.4 Null Point Indicator, may be either a galvanometer or a microvolt ammeter.
5.4.1 Galvanometer, having a sensitivity of 0.1 mV/m at 1 m for highest precision or a sensitivity of 0.5 mV/m at 1 m for routine precision.
5.4.2 Microvolt Ammeter.5,7
5.5 Lamp and Scale, any suitable type.
5.6 Stopwatch or Clock, preferably having graduations in minutes and hundredths of minutes.
5.7 High-Vacuum Oil Pump, capable of evacuating the jacket of the freezing tube to a pressure of 0.133 Pa in 10 min or less.
5.8 Seeding Apparatus, as shown in Fig. 4, for inducing crystallization.
5.9 Silica Gel Funnel, as shown in Fig. 5, for filtering compounds through silica gel to remove water. To be used only when specified in Test Method D1016.
6. Materials
6.1 Carbon Dioxide Refrigerant - Solid carbon dioxide in a suitable liquid. (Warning - Extremely cold (-78.5°C). Liberates heavy gas which can cause suffocation. Contact with skin causes burns or freezing, or both. Vapors can react violently with hot magnesium or aluminum alloys.) Acetone is recommended. (Warning - Extremely flammable. Harmful if inhaled. High concentrations can cause unconsciousness or death. Contact can cause skin irritation and dermatitis. Use refrigerant bath only with adequate ventilation.)
6.2 Liquid Nitrogen or Liquid Air - (Warning - Extremely cold. Liberates gas which can cause suffocation. Contact with skin causes burns or freezing, or both. Vapors can react violently with hot magnesium or aluminum alloys.) For use as a refrigerant. If obtainable, liquid nitrogen is preferable because of its safety.
6.2.1 Use liquid nitrogen refrigerant only with adequate ventilation. If liquid air is used as a refrigerant, it is imperative that any glass vessel containing hydrocarbon or other combustible compound and immersed in liquid air be protected with a suitable metal shield. The mixing of a hydrocarbon or other combustible compound with liquid air due to the breaking of a glass container would almost certainly result in a violent explosion. If liquid nitrogen is used as a refrigerant, no hydrocarbon sample should ever be permitted to cool below the condensation temperature of oxygen (-183°C at 1 atm). This would not be likely to occur in normal operation, but might occur if the apparatus were left unattended for some time.
6.3 Silica Gel, for use in silica gel funnel. If the gel has been exposed to the atmosphere because of punctured or loosely sealed containers, before use, dry the gel in a shallow vessel at 150 to 205°C for 3 h, then transfer while hot to an air-tight container.
