Abstract: Sample of water glass sand (10-20 g) was placed into the reaction flask of the analytical apparatus, and 25.00 mL of standard solution of Ba(OH)2 were added to the absorption flask and diluted to 60 mL with water. The apparatus should examined for air-tightness at this moment. An excess amount of H2SO4(1+9) was added to the reaction flask to react with the carbonate for ca. 0.5 min to liberate equivalent amount of CO2 which was led to the absorption flask and absorbed by Ba(OH)2 to form precipitated BaCO3. The un-reacted Ba(OH)2 was then titrated with standard HCl solution, and content of Na2CO3 was calculated indirectly from the titrant consumed. To attain full absorption of CO2 by Ba(OH)2, compulsory recycling absorption in the absorption medium was adopted, with the time of absorption set at 15 min and prolonged to 20 min or 30 min if necessary. It was shown that on the determination of a known quantity of Na2CO3 of 0.104 7 g, an average of 0.106 5 g (n=3) were found by the proposed method, giving relative average deviation of 1.8%.