294 Common Science 



gas which is often used to fill balloons that are to go very 

 high ; it is the lightest in the world and is called hydro- 

 gen. Hydrogen is an element. 



For a long time people thought that water was an 

 element. Water certainly looks and seems as if it were 

 made only of itself. Yet during the thousands of years 

 that people believed water was an element, they were 

 daily putting two elements together and making water 

 out of them. When you put a kettle, or anything cold, 

 over a fire, tiny drops of water always form on it. These 

 are not drops of water that were dissolved in the air, 

 and that condense on the sides of the cold kettle ; if they 

 were, they would gather on the kettle better in the open 

 air than over the hot fire. Really there is some of that 

 very light gas, hydrogen, in the wood or coal or gas that 

 you use, and this hydrogen joins the oxygen in the air 

 to make water whenever we burn ordinary fuel. 



But the best way to prove that water is made of two 

 gases is to take the water apart and get the gases from 

 it. Here are the directions for doing this : 



Experiment 90. A regular bought electrolysis apparatus 

 may be used, or you can make a simple one as follows : 



Use a tumbler and two test tubes. If the test tubes are 

 rather small (f " X 3") they will fill more quickly. Dissolve 

 a little lye (about f teaspoonful) in half a pint of water to 

 make the water conduct electricity easily, or you may use 

 sulfuric acid in place of lye. Pour half of this solution into 

 the tumbler. Pour as much more as possible into the test 

 tubes, filling both tubes brim full. Cover the mouth of each 

 test tube with a small square of dry paper or cardboard, and 

 turn it upside down, lowering it into the tumbler. 



The "electrodes" are two J" pieces of platinum wire (#30), 



