152 



Domestic Science 



the tube causes the further end of the mercury column 

 to push the index in front of it till the temperature 

 ceases to rise. The index stays in its new position by 

 virtue of the spring. Thus the temperatures registered 

 by the scale on the limb further from the 

 bulb are maxima. Similarly, the other 

 index is pushed back toward the bulb 

 during a drop in temperature, and the 

 point on the scale at which its lower end 

 comes to rest is the minimum tempera- 

 ture experienced since the last setting of 

 the index. The indexes are once more 

 brought into contact with the ends of the 

 column of mercury, after observations 

 have been made, by means of a magnet. 

 96. In Chapter vm it was demon- 

 strated that gases undergo large changes 

 of volume as the result of rise or fall of 

 temperature. The measurement of the 

 change of volume consequent upon a 

 given change of temperature may be 

 approximately estimated by performing 



Fig. 50. 



EXPERIMENT 51. Draw out a piece of capillary 

 tubing as described in Experiment 46. Cut off the 

 drawn-out portion so as to obtain a tube about 20" 

 long, similar to that shown in Fig. 40. Pass dry air" 

 through this tube for some minutes and then seal the 

 pointed end, by heating it in a Bunsen or a blowpipe 

 flame. Heat the tube thus prepared by passing a 

 flame backwards and forwards along its length several 

 times. While it is still warm, put the open end under 

 the surface of some mercury in a dish and let the tube 

 cool a little. When a thread of mercury of about 

 half an inch in length has entered the tube as a result 



