shine] ELEMENTARY SCIENCE 279 



to boil. Then we shut the gas off and corked the bottle quickly. 

 After a minute or two, when I could take hold of the neck of the 

 flask, I inverted the flask, holding it with a cloth, and poured some 

 of the water and ice over the flask. Immediately the water in 

 the flask began to boil. When we took the ice away the boiling 

 ceased. When the ice was placed against the flask, once more the 

 boiling commenced. 



The ice condensed the vapor inside the bottle, and causing a par- 

 tial vacuum, reduced the pressure. Since the boiling point of 

 water depends upon air pressure, a reducing of the pressure al- 

 lowed the boiling to re-commence. The teachers of geography 

 can use this experiment to explain why it is impossible for the 

 housewives of higher Colorado to boil navy beans, for instance. 

 You cannot boil potatoes or coffee in the Himalayas because the 

 boiling point of water is considerably lower than 212 Fahrenheit. 



EXPERIMENT TWELVE 



In this experiment we distilled water. The apparatus is too 

 well known to need description. Any handy person can easily fit 

 out the apparatus from the materials used in the previous exper- 

 iments. It would be well to place a little sand and salt in the boiler 

 and test the distillate for them. In this way it can be proved that 

 neither are to be found in the distillate. 



The formation of clouds and the cause of rainfall can well be 

 explained by means of this experiment. I have found that the 

 majority of elementary school children believe that a cloud is only 

 a bag of water. They explain rainfall by saying that two or more 

 bags collided, and a cloud burst by explaiming that the bag of water 

 was ripped open by a mountain peak. By this experiment they 

 can see for themselves that a cloud is only floating steam — a fog, 

 and the cooling of this vapor results in precipitation. 



By observing the steam exhausts of neighboring factories the 

 children found that it "rained" near them on cool days. By read- 

 ing reports of our aviators and by watching them we can readily 

 see that a cloud is not "a bag of water." A geography teacher 

 can explain, too, that the aviators in Belgium were shielded and 

 protected by the clouds (which prevail two days out of three) and 

 they were not afraid of "bumping" into them or sailing through 

 them. 



