298 Introduction to the Study of Science 



above the water. Does it register a lower or a higher temperature 

 than boiling water? Continue the boiling long enough to determine 

 accurately the temperature of steam. 



Observe the bubbles formed in the water at practically all places 

 in contact with the vessel soon after heat is applied. How can you 

 prove that they are not steam bubbles? How can you prove that 

 they are air bubbles? What happens when water is allowed to stand 

 in a glass for a while ? If you cannot answer these questions fully at 

 once, keep them in mind for later consideration. 



Does continued application of heat to the water cause a rise in the 

 temperature of the water or the steam above 212 F. ? Apply heat in 

 larger or more intense amount to bring out the result unmistakably. 

 It may appear that more intense heat causes more violent boiling and 

 an increased rate of evaporation, but no change in temperature of 

 water or steam. 



Is the steam visible when it is imprisoned in the bubbles? Is it 

 visible as it escapes from the water? Or does it remain invisible 

 until it has left the surface of the water, as when it enters or leaves 

 the neck of the flask? Have you observed steam rushing from the 

 spout of a teakettle or the "blow-out" of a safety valve on a boiler? 

 Is it visible directly when it makes its escape? 



Insert a thermometer into the space above the water surface and 

 try to determine whether steam remains invisible as long as it retains 

 the temperature of boiling water. Do the observed facts support the 

 view that steam remains invisible as long as it retains the temperature 

 of the boiling water; and that it becomes visible when its tempera- 

 ture is reduced below that point? 



The behavior of the water where the heat is directly applied 

 may be made easily visible by putting some solid coloring 

 matter, as aniline dye, in the flask. The water in contact with 

 the heated surface is warmed and loses density. Steam bubbles 

 are produced there, and they too are less dense than the water 

 from which they are generated. Both the heated water and 

 the steam bubbles are forced upward by the cooler, denser water 

 descending from the upper layers. As the steam bubbles 

 strike the layers of colder water, they are cooled and collapse. 

 The slight noise associated with their collapse may help in 

 understanding the " singing " of water in the teakettle or 

 boiler. As the temperature of the upper layers of water be- 



