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D6017-97 – Standard Test Method Technical Guide
ASTM D6017-97 (Reapproved 2020) defines a standardized gravimetric test method for the quantitative determination of magnesium sulfate, commonly known as Epsom salt, in leather. This method is specifically designed to distinguish magnesium sulfate from other water-soluble non-tanning salts present in the leather, providing essential data for quality control and material specification compliance. The standard was developed from Federal Test Standard No. 311, Method 6541.
🔬 Purpose and Scope
The scope of this test method is strictly limited to the quantitative determination of magnesium sulfate in leather. All values are expressed exclusively in SI units. As a chemical analysis procedure, it is the responsibility of the user to establish all appropriate safety, health, and environmental practices prior to conducting the test, as the method involves several strong reagents.
⚙️ Apparatus, Reagents, and Procedure
The successful execution of this test method requires specific laboratory apparatus and reagents to ensure accurate gravimetric separation and quantification.
| 🟦 Apparatus Component | 📏 Specification / Function |
|---|---|
| Platinum Crucible | For high-temperature ignition of the magnesium ammonium phosphate precipitate |
| Filtering Crucible | Used for initial filtration and collection of the precipitates |
| Suction Flask | Facilitates vacuum-assisted filtration |
| Muffle Furnace | Required to ignite the precipitate to constant weight as Mg₂P₂O₇ |
| 🧪 Critical Reagent | 🎯 Specification / Concentration |
|---|---|
| Hydrochloric Acid (HCl) | Specific gravity 1.19 (concentrated) |
| Nitric Acid (HNO₃) | Specific gravity 1.42 (concentrated) |
| Ammonium Hydroxide (NH₄OH) | Dilutions of 1:1 and 1:9 with distilled water |
| Sodium Ammonium Hydrogen Phosphate | Saturated solution (precipitating agent for magnesium) |
| Ammonium Oxalate | Saturated solution (removal of calcium interferences) |
| Ferric Chloride (FeCl₃) | 10 g/L solution (coagulant aid) |
| Methyl Orange Indicator | 0.05 % solution (pH indicator) |
The procedure requires that the moisture content of the composite sample be determined in accordance with Test Method D3790. A test specimen of 5 grams, weighed to the nearest 0.001 gram, is placed in a tared porcelain crucible. It is critical that the specimens for moisture and chemical analysis are taken simultaneously under identical ambient conditions. The chemical analysis involves dissolving the leather, precipitating magnesium as magnesium ammonium phosphate (MgNH₄PO₄) using sodium ammonium hydrogen phosphate, and filtering the solution.
⚠️ Safety Alert: The procedure requires handling concentrated mineral acids (HCl and HNO₃) and ammonium hydroxide. A properly functioning fume hood and appropriate personal protective equipment, including acid-resistant gloves and safety goggles, are mandatory per standard Section 1.3.
📊 Calculation and Expression of Results
The final determination relies on a gravimetric finish. The filtered magnesium ammonium phosphate precipitate (MgNH₄PO₄) is carefully washed to remove soluble salts. The precipitate is then ignited in a muffle furnace, converting it to magnesium pyrophosphate (Mg₂P₂O₇). The residue is cooled in a desiccator and weighed. The percentage of magnesium sulfate (MgSO₄) in the leather is subsequently calculated using the stoichiometric ratio between the mass of the ignited Mg₂P₂O₇ and the original magnesium content expressed as MgSO₄.
💡 Technical Note: The accuracy of this gravimetric method is highly dependent on the correct ignition temperature and duration in the muffle furnace to ensure complete conversion to the pyrophosphate without decomposition or reaction with the crucible material. Using a platinum crucible minimizes this risk.
❓ Frequently Asked Questions
🔍 What does ASTM D6017 specifically measure?
It quantitatively determines the amount of magnesium sulfate (Epsom salt) present in a leather sample, distinguishing it from other water-soluble non-tanning salts.
💡 What is the fundamental analytical principle behind the method?
The method is based on classical gravimetric analysis. Magnesium is selectively precipitated as magnesium ammonium phosphate, which is then ignited to magnesium pyrophosphate (Mg₂P₂O₇) and weighed.
⚡ What is the specified mass and weighing tolerance for the test specimen?
The standard dictates a test specimen mass of 5 grams, which must be weighed to a precision of 0.001 gram.
📌 Which ASTM standard is referenced for moisture determination in this method?
ASTM D3790, the Standard Test Method for Volatile Matter (Moisture) of Leather by Oven Drying, is explicitly referenced and must be conducted simultaneously with the chemical test specimens.