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D2177-99 – Standard Test Method Technical Guide
📐 Scope and Significance
This test method, designated D2177-99, provides a standardized approach to measure the ink absorption rate of blotting papers. It specifies the use of a standard writing ink at 23°C (73.4°F) and the time required for 1 mL of this ink to be completely absorbed. The results are essential for predicting and assessing the absorptive quality of blotting papers in practical applications.
⚙️ Apparatus and Test Liquid
The following apparatus is required:
| 🔧 Equipment | 📐 Specification |
|---|---|
| Pipet | 1-mL, graduated to 0.01 mL |
| Support | 75-mm ID metal ring or 400-mL beaker |
| Stop Watch | Timer for accurate measurement |
The test ink is prepared from the formula below:
| 🟦 Ingredient | 📏 Quantity |
|---|---|
| Gallic acid (National Formulary VII) | 5.0 g |
| Ferrous sulfate (FeSO4·7H2O, USP) | 7.5 g |
| Tartaric acid (USP) | 1.0 g |
| Sodium benzoate (USP) | 1.0 g |
| Soluble blue dye (Color Index 42755, acid blue 22) | 3.5 g |
| Distilled water | To 1000 mL at 20°C |
Careful preparation is essential. Ferrous sulfate must be unweathered to maintain correct iron concentration of 1.5068 g per 7.5 g of FeSO4·7H2O.
📊 Test Procedure and Key Measured Properties
Condition blotting paper specimens according to Practice D685 and sample per Practice D585. Place the paper on a suitable support, dispense exactly 1 mL of the standard ink from the pipet onto the paper, and start the stop watch. Measure the time taken for the ink to be completely absorbed at 23°C. This absorption time is the key result, directly indicating the ink absorption rate of the blotting paper.
⚠️ Critical Note: Ferrous sulfate (FeSO4·7H2O) can lose water of crystallization when exposed to air. Use only fresh, unweathered crystals. If weathered, adjust the weight to maintain the correct iron content of 1.5068 g per 7.5 g of unweathered crystals to avoid sediment formation in the ink.
💡 Good Practice: Always condition paper specimens according to ASTM D685 to standardize moisture content before testing. This ensures consistent and reproducible results across different samples.
❓ Frequently Asked Questions
🔍 Why is the iron content in ferrous sulfate important?
The iron content is critical because it affects the ink’s stability. Unweathered FeSO4·7H2O contains exactly 1.5068 g of iron per 7.5 g