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D1966-69 – Standard Test Method Technical Guide
📜 Scope and Definition of Foots
ASTM D1966-69 (Reapproved 1998) specifies the standard gravimetric method for determining the foots content in raw linseed oil. This procedure is commonly known in Europe as the PAT foots method. The term “foots” refers broadly to solid impurities that precipitate from raw linseed oil during storage and settle at the bottom of storage tanks. Specifically, for the purpose of this test method, foots are defined as the solid material that is precipitated from the oil by 85% phosphoric acid and remains insoluble in acetone under the controlled conditions of the test.
This standard does not claim to address all safety concerns associated with its use. It is the responsibility of the user to establish appropriate safety and health practices prior to handling the reagents and materials involved.
⚙️ Critical Apparatus and Reagent Specifications
Precision in this method depends on strict adherence to the specified equipment tolerances and reagent purities. The following table summarizes the critical components and their required parameters as mandated by the standard.
| 🟦 Component | 📐 Required Specification | 🎯 Tolerance / Details |
|---|---|---|
| Filter Crucible | Fritted Glass, Medium Porosity | 10 to 15 µm pore size, 30 mL capacity |
| Agitator (Slow Speed) | 16 rpm | ± 2 rpm, end-over-end rotation |
| Agitator (Fast Speed) | 32 rpm | ± 2 rpm, end-over-end rotation |
| Centrifuge Force (RCF) | 500 to 800 g | Measured at the tip of the rotating tubes |
| Pipet | 1 mL | Graduated in 0.01 mL subdivisions |
| Phosphoric Acid | 85 % | Reagent Grade ACS |
| Water | Type II Reagent Water | Per ASTM Specification D 1193 |
| Desiccant | Anhydrous Calcium Sulfate | Or other efficient desiccant |
⚠️ Safety Alert
Acetone is highly flammable. 85% Phosphoric Acid is corrosive. Raw linseed oil can undergo exothermic oxidation. Perform all steps in a well-ventilated fume hood and wear appropriate PPE (chemical splash goggles, gloves, lab coat).
Acetone is highly flammable. 85% Phosphoric Acid is corrosive. Raw linseed oil can undergo exothermic oxidation. Perform all steps in a well-ventilated fume hood and wear appropriate PPE (chemical splash goggles, gloves, lab coat).
📊 Test Procedure and Centrifuge Speed Calculation
The gravimetric determination begins with the acid refining of a precise oil sample. The sample is treated with 85% phosphoric acid and mixed thoroughly using the specified agitator speeds. The tube is then centrifuged at a carefully calculated speed to settle the precipitated foots. The supernatant oil is decanted, and the foots are washed repeatedly with acetone until the washings are free of oil. Finally, the foots are transferred to a pre-weighed fritted glass crucible, dried, and weighed gravimetrically.
A critical parameter is the centrifuge speed, which must generate a relative centrifugal force of 500 to 800 g. The required revolutions per minute (RPM) depends on the swing diameter of the centrifuge head. Use the formulas below for precise calculation.
| ⚡ Parameter | 📏 Formula / Value |
|---|---|
| Required Relative Centrifugal Force (RCF) | 500 to 800 g |
| RPM Formula (Swing Diameter d in inches) | rpm = 265 √(rcf / d) |
| RPM Formula (Swing Diameter d in millimeters) | rpm = 1346 √(rcf / d) |
💡 Technical Tip
Strictly maintain the RCF between 500 and 800 g. An RCF lower than 500 g may result in incomplete
Strictly maintain the RCF between 500 and 800 g. An RCF lower than 500 g may result in incomplete