Overview
ISO 2479:1972 - "Sodium chloride for industrial use - Determination of matter insoluble in water or in acid and preparation of principal solutions for other determinations" defines a laboratory method to quantify insoluble matter in industrial sodium chloride. The standard specifies test conditions (aqueous or acidic media) that deliberately define which impurities are considered "insoluble" for industrial use - it does not aim to dissolve every impurity, only those relevant to users. The procedure combines solution, filtration, gravimetric drying/weighing of the residue and preparation of main filtrate solutions for subsequent determinations.
Key topics and requirements
- Scope and principle
- Determines insoluble matter after dissolving a measured test portion in water or in acid, filtering, drying and weighing the residue.
- Produces a primary solution (Solution A for water-based tests; Solution B for acid-based tests) from the filtrate for other analyses (e.g., chloride, alkalinity).
- Apparatus
- Filter crucible (glass or porcelain) with P10–P16 porosity (pore size ~4–16 µm).
- Laboratory oven adjustable to 110 ± 2 °C, desiccator with drying agent, and common glassware.
- Reagents and controls
- Distilled or equivalent purity water.
- Silver nitrate solution (approx. 5 g/L AgNO3 in nitric acid) for chloride checks during washing.
- In acid procedure: titrated hydrochloric acid and sodium hydroxide, methyl orange indicator.
- Procedure highlights
- Typical test portion ~100 g (weighed to 0.01 g); filtrate volumes and wash series specified.
- Repeated washing of residue and verification of absence of chloride in final wash (checked with AgNO3).
- Dry crucible and residue at 110 °C, cool in desiccator and weigh (precision down to 0.1 mg for crucible/residue).
- Use of filtration aid (kieselguhr) recommended if very fine insolubles clog the filter.
- Results
- Insoluble matter reported as mass percentage. The standard prescribes how to prepare and store primary solutions for downstream assays.
Applications and users
ISO 2479 is practical for:
- Quality control laboratories at salt producers and processors.
- Industrial users of technical-grade sodium chloride (chemical plants, water treatment, de-icing material suppliers) who require defined limits on insolubles.
- Testing laboratories performing routine compositional analysis, specification compliance, or incoming material inspection.
- Regulatory or standards bodies defining industrial salt specifications.
Keywords: ISO 2479, sodium chloride for industrial use, insoluble matter determination, gravimetric analysis, sample preparation, filtration, filtration crucible, sodium chloride quality control.
Related standards
Refer to other ISO and national standards on sampling procedures, chloride determination methods and industrial salt specifications for complementary requirements and sampling/lot-sizing guidance. ISO Technical Committee: ISO/TC 47 (Chemistry).