explosion. This provesthatthe gas washydrogen.Thereshouldalso be some
moistureinside the test tube. This isadditionalproofthatthe gas washydrogen,
because whenhydrogenexplodes, it unites with oxygen in air to form water.
So now you haveestablishedthatthe two gases you collected werehydrogen
and oxygen,andthere was twice as muchhydrogenas oxygen. Theelectrical
currentbrokedownordecomposedthe molecules of water into theirconstituent
parts-2atomsofhydrogenand 1atomof oxygen. The electricalmethodof
decomposinga substanceis known aselectrolysis.Theequationfor thereaction
in thisexperimentis: 2H 20 ~2H 2 +02'
HOW WATER IS MADE FIT TO DRINK
In the different phases of the water cycle, discussed on page 33,waterfalls
to different places. As it falls on different kinds of rock or runsunderground
throughdifferent types of soil, differentchemicals-mainlyminerals-dissolve
in it.
The chemicalsthatare dissolved inourdrinkingwater give it its very special
taste. Did you ever have the experience of visitinganothercity orspendingthe
summerin thecountry,and noticingthatthe watertasteddifferent?This was
because minerals which you werenotaccustomedto were dissolved inthat
water.
Manythings can makewaterunfit to drink. Some mineralsthatdissolve in it,
like sulfur, give it anunpleasanttaste. Some give it a sickeningodor.Some-
times industrial plants producechemical wastesthatfind their way into the
drinkingwater. Manyharmfulbacteria(microscopic plants,sometimes called
germs) live in water. Each communityis responsible forprovidingpure water
for its citizens. How do they doit?And how can they do iteconomically?
Thereare six basic ways of removing all theunpleasantand unsafematerials
thatfind their way intodrinkingwater.Mosttowns and cities use acombination
of thesemethodsthatis best suited to theirparticularsituation.
Boiling.The mostdangeroustypes ofcontaminantsin water arebacteria.All
bacteriado not cause disease,butmany of them do. Since they are too small to
be seen with thenakedeye, you can'ttelljustbylookingat waterwhetherit
containsbacteria,harmfulor otherwise. Boiling killsalmostall germs, but it
is an impractical methodofpurifyingwater, except in small amounts.You
don'thave to worryaboutbacteriain water from the tap, because it hasalready
been purified byothermethods. When you camp out, though,and take water
from a lake orstream,youshouldalways boil it beforedrinkingit.
Filtering. Some of thecontaminantsin water are solid,inanimateparticles.
Thesedon'tnecessarily make people sick, but they areunpleasant.If you live