50 



FIE8T YEAR SCIENCE 



out of the tube back into the beaker. Cool the bulb with a piece of 

 ice or a damp cloth. The water will come farther up in the tube 

 than it did when simply exposed to the air. We have here an ap- 

 paratus for telling the relative temperatures of bodies. 



Instruments arranged to show the amount of the expan- 

 sion or contraction of certain materials due to changes in 

 their temperature are called thermometers. These may be 

 gas, liquid or metal thermometers. There must be some 

 uniform temperatures between which the expansion shall 

 be measured if we are to have a basis of comparison. 

 These definite points have been taken as the freezing and 

 boiling points of water at sea level. 



Experiment 22. Fill a four-inch ignition tube with mercury and 

 insert a one-hole rubber stopper having a straight glass tube extend- 

 ing through it and about 20 cm. above it. It may 

 be necessary to cover the stopper with vaseline to 

 keep out air bubbles. When the stopper was in- 

 serted the mercury should have risen a few centi- 

 meters in the tube. Mark with a rubber band 

 the end of the mercury column. Gently warm the 

 ignition tube. The mercury column rises. Cool 

 the tube and the column falls. We have here 

 a crude thermometer. 



The substance whose expansion is most 

 commonly used to measure the degree of 

 temperature is mercury. This expands 

 Fig. 25. noticeably for an increase in temperature 

 and the amount of its expansion can be 

 very readily determined. The ordinary thermometer 

 consists of a glass tube of uniform bore- which has a bulb 

 at one end. The bulb and part of the tube are filled 

 with mercury. The remaining part of the tube is empty, 

 so that the mercury can freely rise or fall. When the 

 temperature rises, the mercury expands and rises, when 

 the temperature falls, the mercury contracts and sinks. 



