Specifies a method for the determination of the volatile water, that which volatilizes at the same time as the liquid chlorine. It is intended for products with a moisture content of 0,001 % (m/m). The principle consists in contious absorption of the water in the gasified chlorine, flowing at a rate of 100 ml/min over phosphorus pentoxide applied in a thin layer on a glass rod. The glass rod forms an electrolytic cell be means of two electrodes (for example, platinum) wound over its entire length. Decomposition of the water, on absorption. by electrolysis. Measurement of the electrolytic current, which is a function of the water content.