The U-shaped tube can be used to dry gas and collect low-boiling liquids.

　　The U-shaped tube is filled with desiccant to dry the passing gas. In addition, the U-shaped tube is filled with white anhydrous CuSO4 powder, and the passing gas can be checked for water. Anhydrous copper sulfate It is unstable and easy to absorb water, and forms stable copper sulfate pentahydrate CuSO4·5H2O, which is blue. The color change can prove that the gas contains water vapor, and the reaction is rapid and sensitive. Put a beaker wider than it under the U-shaped tube, and fill the beaker with ice-water mixture or ice salt, which can cool the vapor of some low-boiling liquids so that they can be liquefied and collected. So this U The tube can be used for cooling to collect some low-boiling liquids, such as SO3, NO2, C2H5OC2H5, etc.