was present unless you took the
combination apart. Take the black element carbon, for instance. Sugar
is made entirely of carbon and water. You can tell this by making
sugar very hot. When it is hot enough, it turns black; the water part
is driven off and the carbon is left behind. Yet to look at dry, white
sugar, or to taste its sweetness, one would never suspect that it was
made of pure black, tasteless carbon and colorless, tasteless water.
Mixing carbon and water would never give you sugar. But combining them
in the right proportions into a chemical compound does produce sugar.

Not only is carbon concealed in sugar, but it is present in all plant
and animal matter. That is why burning almost any kind of food makes
it black. You drive off most of the other elements and separate the
food into its parts by getting it too hot; the water evaporates and so
does the nitrogen; what is left is mainly black carbon.

MAKING HYDROGEN COME OUT OF HIDING. The light gas, hydrogen, conceals
itself as perfectly as carbon does by combining with other elements.
It is hiding in everything that is sour and in many things that are
not sour. And you can get it out of sour things with metals. In
some cases it is harder to separate than in others; and some metals
separate it better than others do. But one sour compound that you can
easily get the hydrogen out of is hydrochloric acid (HCl), which
is hydrogen combined with the poison gas, chlorine. One of the best
metals to get the hydrogen out with is zinc. Here are the directions
for doing it and incidentally for making a toy balloon:

EXPERIMENT 91. _Do this experiment on the side of the
laboratory farthest from any flames or fire. Do not let any
flame come near the flask in which you are making hydrogen._

In the bottom of a flask put two or three wads of zinc
shavings, each about the size of your thumb. Fit a one-hole
rubber stopper to the flask. Take the stopper out and put a
piece of glass tubing about 5 inches long through the hole of
the stopper, letting half an inch or so stick down into the
flask when the stopper is in place (Fig. 162). With a rubber
band fasten the mouth of a rubber balloon over the end of the
glass tube that will be uppermost. Fill the balloon by blowing
through the glass tube to see if all connections are tight,
and to see how far it may be expanded without danger of
breaking. You can tell when the ba