JUNIOR GRADE SCIENCE 



Perform several experiments and record your results in the following 

 way: 



Boyle's Law.- 



the atmosphere 



A 



X 



V 



JB 



FIG. 54. Simple 

 form of apparatus 

 for verifying Boyle's 

 Law. 



To understand clearly how and why the density of 

 varies, it is necessary to become acquainted with 

 the rule expressing the relation between the volume 

 and pressure of a gas. This can be satisfactorily 

 done by one of the forms of apparatus employed 

 in Experiments 27, i. and 27 ii., which provide a 

 means of subjecting an enclosed quantity of air to 

 varying pressures, by the addition of smaller or 

 larger quantities of mercury. When in the apparatus 

 shown in Fig. 53 the mercury in both tubes stands 

 at the same level, the enclosed air is at the same 

 pressure as the air of the room, but as the tube B is 

 raised, the mercury in it stands higher than that in 

 A, and the air enclosed in A is under a total pressure 

 equal to the sum of that due to the atmosphere and 

 that due to a column of mercury equal in length to 

 the difference of levels of the mercury in A and B. 

 In these circumstances the volume of the air in A 

 decreases, and it decreases more and more as the 

 total pressure is increased. When the results of 

 experiments with any satisfactory form of apparatus 

 are tabulated, certain very important relations be- 

 tween the volume of a gas and the pressure to which 

 it is subjected become evident. It is found that 

 the volume regularly diminishes as the pressure is 

 increased, and in the same ratio. The converse is 

 also found to be true, viz., that when the volume 

 of a gas increases the pressure upon it has diminished, 

 and exactly at the same rate. 



But, in both these cases, it is understood that the 

 temperature of the gas remains the same ; that is, 

 the temperature of the gas under different pressures 

 must not alter. 



The tabulated results of the experiments reveal 



