EXERCISE 48 

 HOW RAPIDLY DOES WATER EVAPORATE IN THE CLASSROOM? 



Materials. A cup or beaker ; a pair of balances with metric weights. 



Directions. Fill a cup or beaker with water to within half an inch of the top. Weigh it and set 

 it aside in an exposed place. Note the time when it was weighed. 



On the next day or some succeeding day at the same time weigh again. How much evaporated 

 during each 24-hour period? Secure the diameter of the cup in centimeters or millimeters, and 

 calculate what depth of water evaporated from the cup. (One cubic centimeter, or 1000 cubic 

 millimeters, weigh one gram.) 



Additional problems. Assuming that evaporation would continue at the rate shown in the above 

 experiment, what depth of water would evaporate in one year ? 



Perform the experiment of this exercise in the outdoor air, make calculations for the yearly evapo- 

 ration as above, and compare the results with those secured from the schoolroom. Does this help to 

 explain why one's nasal membranes become extremely dry during schooltime ? 



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