16 



THE PRODUCTION AND USE OF LIGHT 



few small nails or some common glass beads in the flask. T he pres- 

 ence of something of this kind in the flask will cause water to boil 

 more steadily and prevent "bumping." (Fig. 10.) 



Clamp the iron ring to the stand at a point about 2 in. above the 

 flame. Place a wire gauze upon the ring and set the flask on the 

 gauze. Steady its top by clamping it loosely with the burette clamp. 



Adjust the flame so that it will not be 

 too high. Slip it under the flask and 

 watch for results. 



The first small bubbles which you see 

 rising through the water are bubbles of 

 air, not of steam. Keep watch of the 

 reading of the thermometer. Do you see 

 any evidence of steam, or water vapor, 

 before the water actually boils? Does 

 the steam rise from a pan of hot water 

 on the stove before the water really be- 

 gins to boil? At what temperature by 

 your thermometer does the water finally 

 boil? Continue to heat the water to see 

 if it is possible to raise the temperature 

 higher. Can you see steam in the upper 

 portion of the flask? Can you see it im- 

 mediately after it escapes from the side 

 tube? (Caution. Do not permit the flame 



to reach higher than the surface of the water in the flask, else the flask 

 will probably crack.) 



If you are not careful you may be led to give incorrect 

 answers to the last two questions. Steam, or water vapor, is 

 invisible. But something escaped from the side tube. What do 

 you now think that it was? What happens to steam when it is 

 again cooled after escaping from the flask? We sometimes say 

 that we see steam escaping from an engine or locomotive. 

 This is not strictly true. We see only the small particles of 

 water which have been formed again from the steam and 

 which are floating in the air. 



Unless you are living at or very near the sea level you have 

 probably found that the temperature of the boiling water 

 according to your thermometer is somewhat below 212F., or 

 100C. 



FIG. 10. Boiling point of 

 water. 



