What is the most accurate method to determine how much nitrous oxide is left in an E-cylinder?

Weighing the tank is the most accurate method to determine how much nitrous oxide is left in an E-cylinder because it directly measures the weight of the tank and its contents. By knowing the empty weight of the cylinder and subtracting it from the current weight, you can accurately assess the amount of gas remaining. This method accounts for both the liquid and gas phases of nitrous oxide, which can be important since nitrous oxide remains in liquid form until a certain pressure is reached.

While calculating pressure changes using Boyle’s law is useful for understanding gas behavior under varying pressures, it does not provide a direct measurement of the actual remaining volume in the cylinder, especially since nitrous oxide can exist in both liquid and gas states depending on the conditions. Subtracting the pressure from a fixed value, though it may provide an estimation, is also not a reliable indicator of the volume remaining, especially given that the relationship between pressure and quantity of gas can vary significantly. Dalton's law relates to partial pressures in mixtures of gases and isn't applicable for determining the volume of gas left in a single gas cylinder.

Therefore, weighing the tank stands out as the most accurate and preferred method for measuring the remaining quantity of nitrous oxide in an E-cylinder.