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D458-85 – Standard Test Method Technical Guide
🔬 Chemical Composition and Purity
This specification, designated D458-85 (Reapproved 1998), covers high-grade anhydrous sodium carbonate (Na₂CO₃) suitable for washing, cleaning, and scouring processes with or without soap. The material provides a moderately strong alkaline agent and must meet the following chemical requirements after drying for 1 hour at 155°C:
| 🔬 Component | 📏 Requirement | 📐 Test Method |
|---|---|---|
| Total alkalinity (as Na₂CO₃), min % | 99.26 | ASTM D501 |
| Sodium bicarbonate (NaHCO₃), max % | 0.5 | ASTM D501 |
| Matter insoluble in water, max % | 0.25 | ASTM D501 |
This corresponds to the 58% Na₂O grade, ensuring consistent performance in industrial and household applications where a strong but manageable alkali is required.
⚙️ Physical Properties and Heating Loss
Soda ash is supplied as a free-flowing powder with density-based classifications detailed in Table 1 of the standard. The loss on heating at the place of manufacture must not exceed 1% when a 2 g sample is dried at 150–155°C for 1 hour. Because soda ash is hygroscopic, samples taken away from the manufacturing site require a correction: the percentage gain in net package weight over the shipping weight must be deducted from the apparent loss on heating to determine the true value at manufacture.
Sampling and chemical analysis shall follow ASTM D501 to ensure compliance.
📦 Ordering and Safe Handling
Unless otherwise specified, soda ash shall be purchased by net weight as packed at the place of manufacture. Packaging and labeling must conform to local, state, and federal requirements. The material is intended for use in powdered form as specified by the purchaser.
⚠️ Hazard Warning: This material may be hazardous if not properly managed. Obtain precautionary information from suppliers, apply appropriate first aid in case of accident, telephone the nearest Poison Control Center, and seek medical attention immediately.
💡 Sampling Consideration: Due to its hygroscopic nature, moisture pickup in transit or storage must be accounted for when testing loss on heating away from the manufacturing site to avoid inaccurate results.
❓ Frequently Asked Questions
🔍 What is the intended use of soda ash under this standard?
It is specified for washing, cleaning, and scouring processes where a moderately strong alkaline material is desired, with or without soap.
💡 What are the purity limits for soda ash?
After drying, total alkalinity as Na₂CO₃ must be at least 99.26%, with sodium bicarbonate limited to 0.5% and water-insoluble matter to 0.25%.
⚡ How is loss on heating determined?
A 2 g sample is heated at 150–155°C for 1 hour. The weight loss must not exceed 1% at the point of manufacture.
📌 What safety measures are recommended?
Suppliers should be consulted for safety, storage, and disposal information. In case of personal accident, apply first aid, contact poison control, and get medical attention immediately.