Transportation on Land 305 



a short piece of glass tubing, with the water on the balances. See 

 that the tubing reaches nearly to the bottom of the water in the 

 beaker, but does not touch the beaker. Balance exactly. Bring 

 the water to boiling and continue heating until a ten gram weight on 

 the scale pan is balanced by the condensed steam in the beaker on the 

 opposite pan. This means that ten grams of water have been trans- 

 ferred by steam from the boiling flask. What is the resulting tem- 

 perature of the water in the beaker? Your result is satisfactory if it is 

 about 58 C. or 136 F. 



Determine the heating effect of boiling water upon water at freez- 

 ing temperature. Balance a beaker containing 100 grams of cold 

 water on the scales. Put on the weight pan a ten gram weight, then 

 pour into the beaker exactly ten grams of boiling water. Take the 

 resulting temperature. You may find a rise in temperature to about 

 9.1C., or 37 F. If your result is anywhere near these figures, you 

 may consider the experiment successful. Some of the heat is lost in 

 different ways, as in transferring steam through the tubing, in the air, 

 the glass, and otherwise. But you find that approximately six times 

 as much heat is transferred by the steam as by boiling water. 



Latent heat of steam. Steam in pipes, radiators, engine 

 cylinders, and so on, condenses, and in so doing, gives up the 

 same quantity of heat that is required to convert water into 

 steam. This fact has been proved experimentally. After water 

 is heated to boiling temperature, the heat required to change 

 it into steam is utilized in driving asunder the molecules of 

 water from each other and setting them free in space as 

 steam. It is also needed in making the pressure of steam 

 equal to the pressure exerted upon the surface of the water. 

 As there is no change in the temperature of steam, as long as 

 it is in contact with water, from the temperature of the boiling 

 liquid, this extra amount of heat is called the hidden or latent 

 heat of steam. 



133. Evaporation and condensation. Water is vaporized 

 by heat under men's control for definite purposes. In nature 

 water is always and everywhere being evaporated or vaporized 

 when exposed to the air and as long as the air's capacity for 

 moisture at a given temperature has not reached its limit 



