Water Detection and Estimation

The presence of water in a gas is easily recognised by the increase in weight suffered by desiccating agents, such as phosphoric oxide, sulphuric acid, anhydrous calcium chloride, and anhydrous copper sulphate when exposed in the gas. In neutral organic liquids, e.g. ether, chloroform, acetone, etc., calcium carbide supplies an easily applicable reagent, which can also be extended to the estimation of water of crystallisation, the volume of acetylene liberated being proportional to the water present. On account of its change in colour on hydration, anhydrous copper sulphate can be used to detect the presence of moisture in organic liquids; potassium lead iodide has also been recommended as an especially sensitive indicator in such cases, the colour of strips of paper coated with this changing from white to yellow when immersed in a liquid containing even minute traces of water.

The estimation of water in a substance is almost invariably effected by drying; gases are passed through the desiccating agent, and the increase in the weight of the latter is recorded. Solids are placed in a confined space also enclosing the desiccating agent, or may even be merely heated in the open atmosphere, the amount of moisture being measured in either case by the loss in weight.