If it waits another fraction of a second, the force of gravity will overtake inertia, causing the column to break, the liquid to fall back into the bowl, and the cat's tongue to come up empty.

The precision of liquid column manometer was described. The correct use method and error correction of U tube manometer and double tube differential pressure gauge were analysed.

Synchronized movements of the six-way valve and DIV made it possible to establish a simple flow path of the sample and a continuous liquid flow through the column.