104 Domestic Science 



quantities, noting the pressure and length of the air 

 column in the closed limb after each such addition. 



Tabulate your results as shown below and find 

 for each pressure measured the product of the 

 pressure and volume of the air in the closed limb,. 



Let us suppose that the following are the observa- 

 tions made in such an experiment as the above : 



125-0 mm. 875 mm. 17'1 cm. 14,960 

 680-0 mm. 1430 mm. 10'4 cm. 14,870 



It will be seen that, allowing for errors of experi- 

 ment, the value of the product PV remains the same 

 throughout the series of observations. Since F is a 

 measure of the volume of the air contained in the closed 

 limb, and P is the pressure, expressed in millimetres of 

 mercury, to which that air is subjected, the general 

 result of this experiment may be stated thus : 



The product of the volume and the pressure of a 

 given mass of gas is constant. 



63. The above relation between the pressure and 

 volume of a gas may be stated in another form. It 

 will be noticed that, as the pressure is increased, the 

 volume decreases, and it may readily be shown that 

 doubling the pressure decreases the volume by one-half, 

 trebling the pressure reduces the volume to one-third 

 and so on. Put into the form of a general statement, 

 this becomes : 



The volume of a given mass of gas varies inversely 

 with the pressure to which it is subjected. 



