In this reaction, nitrogen gas is introduced through a tube into the flask which contains the solution. As it passes through, it gently bubbles. The gas then exits, first passing a drying agent (here CaSO4, the common desiccant "Drierite"). It then passes a mixture of the drying agent "and" sodium hydroxide which lays on asbestos or "Ascarite II", a non-fibrous silicate containing sodium hydroxide The mass of the carbon dioxide is obtained by measuring the increase in mass of this absorbent. This is performed by measuring the difference in weight of the tube in which the ascarite contained before and after the procedure.