Sodium metaphosphate, molecular formula NaPO3, molecular weight 101.96. It is often found in the form of (NaPO3)6 sodium hexametaphosphate (also known as "Graeme salt") polymers. Density (20℃)2.484g/cm3. Melting point 640℃. Heat of formation -1206.3kJ/mol. After the phosphoric anhydride and soda ash are mixed in the mixer at the ratio of 1:0.8, they enter the graphite crucible and melt and polymerize at the temperature of 750℃ -850 ℃, and quickly remove them in the cooling dish to obtain sodium hmetaphosphate. Or the anhydrous sodium dihydrogen phosphate after drying is heated in the graphite crucible, the temperature is 700-800 ℃, the treatment time is about 1h-1.5h, and the sodium hmetaphosphate is quickly removed in the cooling dish to be cooled. Transparent glass flakes or white granular crystals. The solubility in water is large, but the dissolution rate is slow, and the aqueous solution is acidic. It is readily hydrolyzed to orthophosphate in warm water, acid or alkali solutions. Sodium hexametaphosphate has strong hygroscopic properties and becomes sticky after hygroscopic. For some metal ions (such as calcium, magnesium, etc.) have the ability to form soluble complexes, so it can be used to soften water. With lead, silver plasma will also form precipitates, these precipitates redissolve in excess sodium hexametaphosphate solution to form a complex, barium salt can also form a complex with sodium hexametaphosphate. It is used as an efficient water softener for power stations, boiler water for locomotives and vehicles, an auxiliary agent for detergents, an agent for controlling or preventing corrosion, a cement hardening promoter, a purification agent for streptomycin, a cleaning agent for fiber industry and bleaching industry. It is used as a sedative in medicine, and as a preservative, stabilizer and juice precipitator in the food industry. In the petroleum industry, it is used to prevent rust in drilling pipes and to control the viscosity of mud during oil drilling. It is also used in textile dyeing, leather tanning, paper making, color film, soil analysis, radiochemistry and analytical chemistry.