JUNIOR GRADE SCIENCE 



B 



into the shape shown at A in Fig. 62, or a small funnel may be connected 

 with it, as at B, and the liquid with which the thermometer is to be 

 filled poured in. Let us suppose mercury is 

 being used. Warming the tube makes the air 

 inside it expand, and of course some is driven 

 out. As the tube cools the mercury is forced 

 in, by the weight of the atmosphere, to fill the 

 place of the expelled air. By repeating this 

 alternate process of warming and cooling, in 

 the circumstances described, enough mercury 

 is soon introduced into the tube. The next 

 step is to seal up the tube, leaving no air 

 above the mercury ; to do this the bulb is 

 heated to a temperature slightly higher than 

 the thermometer is expected to register. The 

 mercury expands, and when it has reached 

 the drawn-out part, C, of the tube, a blow- 

 pipe flame is directed against the glass, and 

 the tube is thus closed up. This method of 

 closing a tube and keeping the air out is 

 called hermetically sealing it. The thermo- 

 meter at this stage should be put on one side 

 for some days at least, in order that it may 

 assume its final size, which it does very 

 slowly. 



FIG. 62. Thermometers 

 in course of construction : 

 (i) tube enlarged at top ; 

 (ii) tube with small funnel 

 attached. 



30. GEADUATION AND USE OF THEEMOMETEES. 



i. The temperature of melting ice. (a) Place some pieces of clean ice 

 in a beaker or test-tube and push a thermometer amongst them. Notice 

 the reading of the thermometer ; it will be either no degrees (0) or very 

 near it. 1 Warm the beaker or test-tube, and observe that as long as there 

 is a.ny ice unmelted the reading of the thermometer remains the same. 



(b) Repeat the experiment with pieces of some other blocks of ice, and 

 observe the important fact that the temperature of clean melting ice is the 

 same in all your tests. 



ii. Effect of adding salt to the ice. (a) Add salt to the melting ice, 

 and notice that the thermometer indicates a lower degree tff , temperature. 



iii. The temperature of boiling water. (a) Boil some distilled water 

 in a flask, test-tube (Fig. 63), or beaker, and hold a thermometer in the 

 boiling water. Notice the temperature. Raise the thermometer until 



1 A Centigrade thermometer is supposed to be used. If a Fahrenheit thermometer is 

 used the reading will be 32*. 



