Question

An inert gas has a weight density of 0.066 lb/ft^3 and its pressure is to be measured with a manometer. Liquids available for the manometer are water (62.4 lb/ft^3), oil (specific gravity 0.82) and mercury (specific gravity 13.57) . If the pressure range is from 0-10 psi, which liquid would you use, Explain Why?

Answer 1

For inert gas has a weight density of 0.066 lb/ft^3 ,the liquid to be used should have higher density than this .

Liquids available =water (62.4 lb/ft^3),

oil (specific gravity 0.82) ,density =0.82 g/ml *62.428 =51.19 lb/ft3

and mercury (specific gravity 13.57) ,density=13.57 g/ml*62.428=847.15 lb/ft3

[1g/ml=62.428 lb/ft3]

As all three liquids, has higher density so other properties need to be considered=the liquid should have low Viscosity,Low surface tension, it should stick on the walls,and should not get vaporized.

Hence , mercury is preferred for its high density and low vapour pressure.