Thursday, December 4, 2008

Regnault method to determine the Volume co-efficient of a gas


A large bulb A of about 700 cc capacity is kept in a glass chamber and a capillary tube K with side tube E is attached to it. Other end of the capillary tube is connected to a manometer. The manometer is calibrated to find the pressure and it is kept in a glass container filled with water to maintain constant temperature.


The glass bulb is evacuated with a vacuum pump and several times hot air is sent into it to clean the moisture. The glass chamber is filled with ice cubes, after some time, the glass bulb attains 00c. The mercury level in the manometer adjusted such that the mercury level in the two limbs remains same. Now find the volume of gas in the bulb with the manometer calibration. Note it as V0.

Now the ice cubes in the manometer are replaced with water vapors. After some time the bulb attains 1000C., gas in the bulb attains the same temperature and expands, Due to this the mercury level in the left limb falls down and the mercury level in the right limb increases. At this stage, the mercury level is adjusted by the bottom tap. such that the levels in the two limbs are same. Now find the volume of the gas Vt.

Substitute the values in the formula

Result of the Experiment:

Regnault found the; volume coefficient of air as 0.003671/0C . or 1/ 273.16/0C.


1. The temperature in the container at the monometer must be maintained constant.

2. The two levels of the mercury must kept at the same level

Before the experiment the apparatus must be cleaned with dry air properly


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