What is the best method to determine if a chlorine cylinder is empty?

The most accurate method to determine if a chlorine cylinder is empty is by weighing the chlorine cylinders. This approach provides a reliable measurement of the actual contents of the cylinder. By comparing the weight of the cylinder to the known weight of a full cylinder, operators can determine how much chlorine remains inside. This method minimizes the risk of relying on potentially misleading indicators, such as pressure gauges, which may still show pressure even when the cylinder is nearing empty due to gas being present without liquid chlorine.

While checking the pressure gauge can provide an indication of the vapor pressure of the chlorine gas, it does not give a definitive answer about the amount of liquid chlorine remaining. A cylinder that appears full by visual inspection may also contain gas, which can lead to an inaccurate assessment of its status. Checking the expiration date is not a reliable method for determining the cylinder's contents, as it relates to the cylinder's usability and safety rather than the actual volume of the chemical inside. Weighing the cylinder provides a straightforward and effective means for determining its contents, making it the best choice for this question.