Gas syringe

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A gas syringe showing its components separate and together

A gas syringe also known as glass collecting bottle, is a piece of laboratory glassware used to draw a volume of a gas from a beaker or other closed system, or measure the volume of gas given off in a reaction. It is often used to remove gaseous products from a reaction. The syringe will have a hermetic seal around the top and sides, and moves more freely than a normal syringe. Most gas syringes can measure up to 100 cm³ with an accuracy of 1 decimal place.

When using a gas syringe it is important to keep it dry. This is because the collected gases could disolve in water, resulting in inaccurate measurements.

The gas syringe works due to the fact that gases occupy a fixed space per mole, under equal pressure conditions. Thus the amount of a formed gas can simply be measured by measuring the space it occupies at standard pressure conditions. The inner part of the syringe and the outer tube should move freely, otherwise the friction could prevent the inner part being pushed back by the pressure of the collected gas, and thus the unequal pressure conditions would falsify the measurements.