Class 1 Class 2 Class 3
Test items Superior grade A first-rate product Acceptable product A first-rate product Acceptable product
Sodium Sulphide （Na2S） % ≥ 60 60 60 60 60 65
Sodium sulfite （Na2SO3） % ≤ 2 － － － － －
Thiosulfuric acid （Na2S2O3）% ≤ 2 － － － － －
Iron (Fe) % ≤ 0.03 0.12 0.2 0.003 0.005 0.08
Sodium carbonate （Na2CO3） % ≤ 3.5 5 － 2 3 4
Water insoluble matter % ≤ 0.2 0.4 0.8 0.05 0.1 0.3
Industrial sodium sulfide into three categories: one for ordinary sodium sulfide (commonly known as red alkali); Class 2 low iron sodium sulfide (commonly known as the yellow base); three types of high levels of sodium sulfide.