192 REPORTS ON THE STATE OF SCIENCE.—1917. 
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. 
But why does some of the air disappear—is it because it is in some way 
changed into water vapour which condenses on the jar and on contact with the 
water used in shutting up the air in the bell jar? Do all combustible substances 
give water when burnt? Can water be condensed from the candle flame and 
other flames? Try the effect of exposing a cold surface (a flask full of cold 
water) to each. At once it is bedewed but except in the case of the spirit 
flame it is soon smoked or coated with soot, which looks like charcoal or carbon 
in a fine state of division—so there seems to be carbon in combustibles, as there 
is in starch. Although the liquid which bedews the flask looks like water, 
you have no proof that it is water: as nothing is to be taken for granted, you 
must burn the several combustibles in such a way that you can collect enough 
of the liquid from each to contrast it with water. 
Having done this, you feel sure that water comes from each of the liquid 
combustibles when they are burnt in air. But what of solid combustibles such 
as wood, charcoal, coal, coke? It should not be difficult to make observations 
over fires made with these and to convince yourself that charcoal and coke give 
practically no water although indications are obtained that it is formed on 
burning wood and coal. 
What becomes of carbon when it is burnt, therefore, remains a mystery to 
be solved only by further inquiry. 
Although there is yet much to jearn as to what happens when things burn, 
it is now at least clear that starch may be burnt with the aid of air and that 
much heat is given out : knowing as we all do that we must have air to liye, 
may it not be that the air we inhale serves to burn part, at least, of our food, 
quietly and in such a way that we are kept warm by the process? If so, the 
fact that it is an indispensable article of food meets with an explanation. 
Before taking up fresh subjects, it is worth while to take stock of the 
knowledge gained by studying flour and starch experimentally : Flour has been 
resolved into starch and gluten; the latter, however, has been set aside tem- 
porarily while starch was being examined It has been ascertained that although 
wheaten flour has certain advantages, owing to the peculiar properties of its 
gluten, other cereal grains give flours which are also mixtures of starch and 
gluten-like substances; potatoes, however, have been found to consist almost 
wholly of starch. Starch, it has been discovered, contains both carbon and 
water, associated apparently in some strange way which altogether masks their 
ordinary properties. Itself insoluble but convertible into a peculiar jelly-like 
material (starch paste) by heating with water, starch is changed by diastase 
(a constituent of barley and of human saliva) into a soluble diffusible sugar. 
A little reflection will show that these properties give starch its peculiar value. 
It occurs in the seed of cereals and in the potato tuber—the resting parts of 
the plants : if it were soluble, it could not well be stored up; and unless it 
could be rendered soluble by digestion, it could not pass into circulation and 
serve as food—in fact it has just the attributes which are required of a sub- 
stance occupying the position it holds in the plant world. Starch is a substance 
which is easily burnt: in studying it from this point of view, it has been 
discovered that burning is a process in which air is concerned—not air as 2 
whole but an active portion in it. 
