Chapter 13.1, Problem 1RQ

Interpretation Introduction

Interpretation:

The reason behind the use of mercury in barometers and manometers instead of water have to be described.

Concept Introduction:

Barometer: It is a scientific instrument used to measure atmospheric pressure.

Manometer: It is also a scientific device used to measure gas pressure in a closed vessel.

These two instruments are constructed by filling a glass tube with liquid mercury.

Answer to Problem 1RQ

Mercury has more density approximately 13.6 times than water. Rise of water level inside the tube is about 34 feet high by the upward force exerted by the atmospheric gas while the rise of mercury level inside the tube is only 30 inches to exert pressure equal to that of the atmosphere. So long glass tube or a large instrument have to be used for the experiment using water. This is why mercury is used in barometers and manometers instead of water although mercury is a toxic substance.

Explanation of Solution

In both barometers and manometers a glass tube is used for the experiment. The height of the fluid in the tube increases by the upward force exerted by the atmospheric gas. The pressure can be measured from the rise of the fluid level in the tube. The extent rise of fluid level depends on the density of the fluid used. Mercury has more density approximately 13.6 times than water. Rise of water level inside the tube is about 34 feet high by the upward force exerted by the atmospheric gas while the rise of mercury level inside the tube is only 30 inches to exert pressure equal to that of the atmosphere. So long glass tube or a large instrument have to be used for the experiment using water. This is why mercury is used in barometers and manometers instead of water although mercury is a toxic substance.