Temperature. Thermometers 



141 



the fine jet, may be used. A flame about 1" high will 

 be found most convenient for the purpose.) As soon 

 as a satisfactory seal has been obtained remove the 

 warm water and allow the thermometer to cool. By 

 cautiously heating the glass at the sealed end in a small 

 flame, with constant rotation, a small ball of glass may 

 be formed, which will give a better finish to the 

 thermometer. It will then have an appearance similar 

 to that shown in Fig. 42. 



To graduate our instrument, it should be placed with 

 its bulb in a quantity of finely pounded ice, as illustrated 

 in Fig. 43. Allow it to remain in the ice for some minutes, 

 noting at intervals of one minute the position of the 

 upper surface of the liquid. When no further fall 

 has occurred between two such observa- 

 tions, mark the level of the alcohol by 

 making a light scratch on the glass with 

 a sharp file. This point will mark for 

 future work with the thermometer the 

 melting-point of ice, and may be called 

 the zero of our scale. To obtain some 

 further points on the scale, place the 

 thermometer side by side with a Centi- 

 grade thermometer in the same vessel 

 of water, and, by adding small pieces of 

 ice (if necessary) adjust the temperature 

 of the water to 10 C. The water must 

 be stirred continuously, so as to be of the 

 same temperature throughout. When a steady tem- 

 perature of 10 has been attained, mark the level of 

 the alcohol as before. By gently heating the water 

 to 20 C. and 30 C. in turn, further points on our 

 scale may be marked. The intermediate divisions 

 may be marked off by dividing each part of the 



Fig. 43. 



