512 KEPORTS ON THE STATE OF SCIENCE, ETC. 



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 expensiv^e ; in France and Japan, however, it 

 is still much used in cooking and also for warming rooms. 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 supplied 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 

 bun brightlv 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 start. 

 When the jar is again cool, the point to which the water rises should be marked in 

 some suitable way and the capacity of the jar ascertained above this mark and also 

 between it and the lower mark : the amount of air which disappears is then 

 ascertained. 



Similar experiments should then be made with other combustibles — spirit, 

 different oils and gas. In every case, the flame soon gives out and some air 

 disappears : less than a fifth. Clearly the air is concerned in the burning — but 

 very partially : does it not seem that it contains something which is active rather 

 than that it is active as a whole? 



Solid combustibles are not so easily dealt with : if an electric current be 

 available, you may fire such substances in air, in a bell jar standing over water, 

 by means of a spiral of platinum heated to redness by the current — in every 

 case air disappears but never quite a fifth. Why does some disappear— is it because 

 it is in some way changed into water vapour which condenses on the jar and on contact 



