Sodium Hexametaphosphate (SHMP for short) is an inorganic polyphosphate compound, commonly represented by the chemical formula (NaPO₃)₆ and with a CAS number of 10124-56-8. It is widely used as a food moisture-retaining agent, industrial water softener, and dispersing chelating agent. ‌‌

Core physicochemical properties and appearance: It is a colorless or white glassy amorphous solid, presenting in flaky, fibrous, or powdered form, with strong hygroscopicity.

Molecular weight: approximately 611.17–611.77 g/mol.

Solubility: It is easily soluble in water (with extremely high solubility at 20℃), but insoluble in organic solvents such as ethanol and ether.

Acidity and alkalinity: The aqueous solution is weakly alkaline (pH of 1% solution is about 6.0–7.0, with some sources indicating a range of 5.8–9.0).

Thermal stability: The melting point is approximately 616℃ (decomposition). It is prone to hydrolysis into orthophosphate in warm water, acids, or alkalis.

Main functions and application scenarios: Food industry: As a legal food additive (GB 2760), it is used as a moisture retention agent, chelating agent, and stabilizer; commonly used in meat products (to enhance water retention and tenderness), dairy products, beverages, and canned foods (to prevent sedimentation and oxidative browning).

Water treatment: High-efficiency water softener, which prevents boiler and pipeline scaling by chelating calcium and magnesium ions.

Industrial auxiliary agent: Used as a detergent builder, ceramic/coating dispersant, flotation agent, and cement hardening accelerator.

Safety and precautions: Toxicity: Low toxicity, with an ADI value of 0–70 mg/kg (FAO/WHO); excessive intake may cause diarrhea or electrolyte imbalance.

Grade differentiation: Strictly differentiate between food grade (low heavy metal content, high purity) and industrial grade, with the latter strictly prohibited for use in food processing.

Storage: It needs to be sealed and placed in a dry and ventilated place to avoid moisture absorption, caking, and hydrolysis failure.

Note: This substance is often referred to as "Graham's salt", but the actual product is mostly a mixture of sodium polyphosphate with different degrees of polymerization, rather than a single pure six-membered ring structure.