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D5557-95 – Standard Test Method Technical Guide
📐 Scope and Significance of ASTM D5557
ASTM D5557−95 (Reapproved 2023) outlines a standard test method for determining the quantity of impurities that are insoluble in kerosine and petroleum ether within fats and oils. These materials are specifically intended for use in the production of fatliquors and stuffing compounds for leather processing. The method quantifies filterable solids such as sand, dirt, and other non-fatty residues that can negatively impact the quality and performance of the final leather product.
The values stated in SI units are to be regarded as the standard. This test method serves as a critical quality control tool for manufacturers, ensuring the purity of base oils before they are formulated into fatliquoring emulsions. The method is directly tied to Test Method D5556 for moisture and volatile matter determination.
⚠️ Flammable Solvent Safety: This procedure requires heating and filtering kerosine (flash point ≥ 23°C) and using petroleum ether. Conduct all steps in a fume hood away from ignition sources. Flash point must be verified per Test Method D56.
⚙️ Test Procedure and Key Equipment
The test uses a precise gravimetric procedure involving solvent extraction, vacuum filtration, and drying. The sample matrix is typically the dry residue obtained from the moisture and volatile determination described in Test Method D5556.
| 🟦 Apparatus / Reagent | 📏 Specification | 🎯 Primary Function |
|---|---|---|
| Gooch Crucible | Fine/very fine filtering disc (0.7 µm retention) | Retaining insoluble solids during vacuum filtration |
| Kerosine | Refined distillate; Flash point ≥ 23°C (D56) | Hot solvent to fully dissolve the fat/oil matrix |
| Petroleum Ether | Standard reagent grade | Removing residual kerosine from the retained residue |
💡 Crucible Conditioning: Before weighing, the Gooch crucible must be washed with water, alcohol, and ether, then dried to constant weight at 101°C ± 1°C and cooled in a desiccator. This eliminates moisture or residual solvents that could affect the tare weight.
The key procedural steps are strictly defined to ensure repeatability:
- Add 50 mL of kerosine to the sample residue and heat on a water bath to dissolve the fat.
- Filter the hot solution through the prepared Gooch crucible using vacuum.
- Wash the crucible contents with five 10 mL portions of hot kerosine, allowing each to drain completely.
- Wash the residue thoroughly with petroleum ether to remove all kerosine.
- Dry the crucible and contents to constant weight at 101°C ± 1°C, cool in a desiccator, and weigh.
📊 Calculation and Reporting of Results
Results are calculated as a percentage of the original sample weight taken for the moisture determination. The report must reference the specific test method used.
| 📐 Parameter | ⚡ Specification / Formula |
|---|---|
| Sample Source | Residue from moisture determination (Test Method D5556) or equivalent |
| Drying Temperature | 101°C ± 1°C to constant weight |
| Calculation | % Insoluble Impurities = (Gain in weight of crucible × 100) / Weight of sample taken for moisture |
| Reporting | Explicitly reference ASTM D5557 in the test report |
The calculation directly provides the percentage of non-soluble contaminants, which is a critical indicator of the purity and quality of the fats and oils used in leather fatliquoring processes.
❓ Frequently Asked Questions
🔍 What is the fundamental purpose of ASTM D5557?
To determine the percentage of insoluble impurities (e.g., sand, dirt, and filterable solids) contained in fats and oils used in fatliquors and stuffing compounds. High levels of insolubles indicate poor quality or contamination of the base materials.
💡 How should the test sample be prepared?
The preferred method is to use the dry residue obtained from the moisture and volatile matter determination outlined in Test Method D5556. This connects the two analyses and ensures the sample has been properly conditioned.
⚡ Why is the kerosine flash point specification critical?
The kerosine must have a flash point not below 23°C (75°F) as determined by Test Method D56. This safety requirement ensures the solvent does not ignite during the water bath heating step while still maintaining adequate solvency for the fats.
📌 How do I ensure accurate crucible weight measurements?
The Gooch crucible (with a 0.7 µm filtering disc) must be washed with water, alcohol, and ether, then dried to a constant weight at 101°C ± 1°C. After drying, it must be cooled to room temperature in a desiccator before weighing to prevent absorption of atmospheric moisture.