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D5565-95 – Standard Test Method Technical Guide
🛡️ Scope and Significance of D5565
ASTM D5565-95 (Reapproved 2011) defines the laboratory method for determining the solidification point of fatty acids. While broadly applicable to fatty acids derived from animal, marine, and vegetable fats and oils, its primary intended use is for materials employed in the softening and stuffing of leather (Section 2.1). The standard mandates that all values be regarded in SI units. Establishing the solidification point is critical for quality control and formulation in leather manufacturing.
⚠️ Regulatory Compliance: Users of this standard must establish appropriate safety and health practices. Specific safety concerns are addressed in Sections 5.2 and 5.7 of the full document. This test method does not purport to address all safety concerns, if any, associated with its use.
⚙️ Required Apparatus and Specifications
The standard specifies a highly controlled assembly designed to measure the exothermic phase change of mixed fatty acids. A 2-L Griffin low-form beaker houses an inner wide-mouth bottle (450 mL capacity, 190 mm height, 38 mm neck ID). The prepared fatty acid sample is placed in a test tube (100 mm length, 25 mm OD) filled to the 57 mm etched mark. Temperature is monitored exclusively by a Titer Test Thermometer, while a stirrer (2–3 mm wire, 19 mm loop) ensures homogeneity. Saponification is conducted in a 750 or 1000 mL flask.
| 📏 Titer Test Thermometer Specifications | 📐 Mandated Value |
|---|---|
| Liquid / Fill Gas | Mercury / Evacuated or Nitrogen |
| Temperature Range / Subdivisions | −2° to +68°C / 0.2°C |
| Overall Length / Stem Diameter | 385–390 mm / 6–7 mm |
| Bulb Length / Diameter | 15–25 mm / 5.5 mm (max. stem φ) |
| Immersion Depth / Max Error | 45 mm / 0.2°C |
| Scale Markings / Identification | A.O.C.S. Titer Test / Case Marked |
💡 Critical Apparatus Check: The stirrer must be constructed from glass, nichrome, stainless steel, or monel wire (Section 3.5). The thermometer must be standardized at the ice point and at 5°C intervals to maintain the required 0.2°C maximum scale error.
🧪 Test Procedure and Measurement Principles
The procedure begins with saponification of the fat or oil sample. After separation, the mixed fatty acids are washed, filtered, dried, and melted. The melted fatty acids are poured into the sample tube to the specified fill level. This tube is then placed into the air jacket assembly (beaker and bottle). The sample is stirred vigorously while cooling slowly around the expected solidification point. The solidification point is recorded as the maximum temperature plateau reached during the exothermic phase change, provided the temperature remains constant for at least 15 seconds. The test is invalidated and must be repeated if the sample supercools more than 2°C below the titer point before crystallization initiates.
| 🟦 Core Assembly Dimensions | 🎯 Requirement |
|---|---|
| Outer Water / Air Bath | 2-L Griffin Low-Form Beaker |
| Inner Air Jacket | 450 mL Bottle (190 mm H × 38 mm ID) |
| Sample Container | Test Tube (100 mm × 25 mm OD) |
| Stirrer Dimensions | 2–3 mm Wire, 19 mm Loop |
| Saponification Vessel | 750 or 1000 mL Flask |
❓ Frequently Asked Questions
🔍 What is the definition of the solidification point?
It is the constant temperature observed during the slow cooling of melted fatty acids, caused by the exothermic heat of crystallization, which remains stationary for at least 15 seconds under the specified test conditions.
💡 Why is a specific Titer Test Thermometer required?
The method requires a tolerance of only 0.2°C. The designated A.O.C.S. Titer Test thermometer (–2° to +68°C, graduated in 0.2°C divisions) provides the necessary precision and is specifically calibrated for this application.
⚡ What happens if the sample supercools?
If the temperature of the melted fatty acids falls more than 2°C below the expected solidification point before rising due to crystallization, the test must be discarded. The procedure should be repeated with a fresh sample to obtain a valid reading.
📌 What is the primary industry application?
This test method is standardized for evaluating fatty acids used in the softening and stuffing (tannery fatliquoring) of leather, as well as the manufacture of products for these specific purposes.