Temperature. Thermometers 



143 



contain is lessened, with the result that some is driven 

 into the capillary tube. 



91. A second fixed point is obtained on a mercury 

 thermometer by noting the level to which the liquid 

 rises when the instrument is immersed in the steam 

 from boiling water. This point could not be marked 

 on our experimental thermometer, since alcohol boils 

 at a lower temperature than water. To check the 

 boiling-points of the laboratory thermometers, we will 

 do 



EXPERIMENT 48. Arrange the apparatus shown in 

 Fig. 44. The best check is obtained when the boiling- 

 point of the instrument 100 C. or 212 F. just 

 appears above the cork. Heat the 

 water until it boils freely, and 

 allow boiling to continue till the 

 top of the mercury column in the 

 thermometer has remained steady 

 for two minutes. The readings 

 should be very close to those quoted 

 above, but slight variations may 

 be noted, which may possibly be 

 due to the decrease in the capacit}^ 

 of the bulb already mentioned, or 

 to the pressure of the laboratory 

 being above or below the standard 

 pressure, 760 mm. 



If the behaviour of the liquid 

 be carefully watched during this 

 experiment, it will be noted that 

 small bubbles are formed at an 

 early stage of the heating, chiefly 

 upon the bottom of the flask. These 

 gradually increase in size and at 



Fig. 44. 



