vin ATMOSPHERIC PRESSURE AND BOYLE'S LAW 113 



small brass clamps. Upon the lower end a piece of thick india- 

 rubber tubing is firmly tied. The tubing is also tied upon one 

 end of a three-way piece, B. A long glass tube, C, connected 

 with another end of the three-way junction is supported upon 

 the stand side by side with the burette. To the third end of 

 the junction a long piece of rubber tubing, D, is fixed, and at 

 the top of this a large funnel or bottle, E, with the bottom cut 



FIG. 50. Apparatus to show the Relation between the volume and Pressure 

 of a Gas. (Boyle's Law). 



off, is tied. The use of this apparatus will be seen by the follow- 

 ing experiments : 



EXPT. 110. Open the stop-cock of the burette. Pour mer- 

 cury into the bottle until its level is about half-way up 

 the burette. This mercury is evidently at the same level 

 in the burette, long glass tube, and rubber tube, and the 

 air in the burette is at the pressure of the atmosphere. Now 

 close the stop-cock. We have enclosed a given volume of air, 

 which is indicated by the length of tube it occupies. Pour 

 mercury into the bottle until the bottle is nearly half full. 

 By lifting or lowering the bottle the level of the mercury is, 

 of course, varied. Move the bottle until the difference be- 

 tween the level of the mercury in the burette and in the 

 straight glass tube is 30 inches, or whatever is the reading of 

 the barometer at the time of the experiment. 



