The gas is then passed into the caustic potash burette, left to stand for about two minutes and then withdrawn, isolating the remaining gas via the stopcock arrangements.
After making a minor adjustment to the device, he opened a stopcock leading into one of the cylinders and the witnesses heard a hiss as of escaping air.
The stopcock has holes bored through it which allow the tubes attached to the female joint to be connected or separated with partial turns of the stopcock.