SCIENCE IN SECONDARY SCHOOLS. 191 
starch when it is heated alone ? Study the effect of heat on starch very care- 
fully, at gradually increasing temperatures. 
At an early stage, vapour is given off—what does this look like ? Steam— 
that is to say, water vapour. Perhaps the starch was not dry—dry it carefully 
at a temperature at which wet things are easily dried and repeat the experiment. 
Vapour is still given off when the dried starch is heated—is it water vapour ? 
How can you find out ? What happens when water vapour meets a cold 
surface ? Try! The vapour becomes liquid—it condenses. See if the 
vapour from starch can be condensed. You find it can and that the liquid is 
like water—is it water? Would not the discovery that it is water be of in- 
terest and importance as an indication that water is in some way contained 
in starch? Try therefore to prove that the liquid is water. Heat... grams 
of starch in a vessel from which the vapour can only escape through a cooled 
tube (a condenser), and when you have sufficient of the liquid, contrast it 
carefully with water. 
But water is not the only product on heating starch: as the heating is 
continued, the starch becomes more and more burnt or charred; at last, it is 
converted into a mass of very light charcoal, which easily takes fire and burns 
away to nothing! Are not these strange changes—who would suppose that in 
white starch there are hidden away in some mysterious manner both black 
charcoal or carbon (to give it its Latin name) and water? 
How comes it that starch is useful to us as food—has the presence of carbon 
and water in it anything to do with its value as a foodstuff? We certainly 
cannot eat charcoal as such but what can we do with it? What is it used 
for? In England, we no longer use it as fuel, as it is too expensive; in France 
and Japan, however, it is still much used in cooking and also for warming 
rooms. And have you not heard through the newspapers of people being killed 
by the fumes of burning charcoal? Does not this show that it must not be 
assumed, because nothing is seen to escape, that charcoal gives nothing when 
burnt ? 
What does food do for us? It makes us grow, you will say! But does it 
not also keep us warm—may not perhaps the warmth be produced at least in 
part by the burning of the carbon which is in the starch we eat? Is not the 
suggestion one which it is well worth following up—will it not be well to 
study burning? What are the things we burn or which we know will burn? 
Make out a list. 
CoMBUSTIBLEs. 
From the domestic point of view, our most important fuel or combustible is 
coal—what do you know of the way in which coal burns—does it just burn when 
set fire to? You know it does not. To keep a fire burning, air must be sup- 
plied to it; if a fire be low, it is often restored by holding a newspaper in front 
of the stove or grate in such a way that a draught of air is forced through 
the feebly glowing embers—very soon these begin to burn brightly; and at 
any time a fire may be caused to burn brightly by increasing the draught 
through it : by using bellows, we often make a fire burn up quickly. 
Must we not conclude, therefore, that air has something to do with the 
burning of coal? Is this true of other combustibles? Consider what you know 
and if you cannot produce evidence one way or the other—but such questions 
should be settled by trial or by experiment, not by guessing. 
Under ordinary conditions, we cannot see what happens to the air during 
burning—suppose you shut up a burning candle with air so that you can watch 
the air as well as the candle flame. You will probably think of several ways 
of making such an experiment; the easiest perhaps is to place a small piece 
of candle on a block of wood floating on water in a basin and cautiously to 
invert over the flame a bell jar provided with a stopper which you insert the 
moment the bell jar is in position; or you may use a small statuette cover. 
Noting everything that happens, you see that almost at once the sides of the 
jar become bedewed; the flame grows dim and after a time goes out; at the 
same time the water rises in the jar, showing that some of the air is used up. 
It is desirable to paint a line a short way up the jar with Brunswick black, 
such as is used in blacking stoves, to mark the position of the water at the 
