The major uses of heavy sodium carbonate are as a solid, particularly in making glass, where it is used as a flux in the melting of silica (sand).

The uses for light sodium carbonate are traditionally where the chemical is required in solution.

Tests   Specifications
Appearance      white, granular crystals       
Identification         
Sodium  Positive       
Carbonate       Positive       
Assay   99.5 - 100.5%   
Heavy Metals (as Pb)    0.001% maximum
Lead    4 ppm maximum   
LOD (NF)        0.5% maximum   
LOD (EP)        1.0% maximum   
Chloride        125 ppm maximum
Sulfate 250 ppm maximum
Iron    50 ppm maximum
Arsenic 3.1 ppm maximum
Alkali Hydroxides and Bicarbonates
pass   
Residual Solvents       Conforms to NF