ON SCIENCE IN SCHOOL CERTIFICATE EXAMINATIONS. 513 



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 e-ach. 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. What of solid combustibles such as 

 wood, charcoal, coal or coke ? It should not be diflficult to make observations 

 over fires miide 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 iearn as to what happens when things bjrn, 

 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 live, 

 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 air 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 substance 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 a whole but an active portion in it. 



The Kitchen. 



Books are usually divided into chapters : when the story is carried to a 

 certain point it is broken off and a new chapter is begun, in which some other 

 set of characters is considered. It will be well to leave the study of food for 

 a time and pass to the kitchen, where the etove and fender and fire irons ar« 

 to be found. All these are made of iron and, like steel knives, must be care- 

 fully looked after and kept bright. Why ? Why too is so much care taken 

 to paint ironwork out of doors ? We use many other metals and leave them 

 unpainted — at most they are tarnished, but iron rusts and spoils. What happens 

 to it — what makes it rust? Water, you say — if water be dropped on the fender 

 and be allowed to remain there or if knives are left wet, rust soon appears. 

 You must not be hasty in your conclusions — you will soon find out if you are 

 that your conclusions are often wrong. If water be the cause of rust, should 

 not iron rust if corked up with water, say, in an ordinary medicine bottle? 



1928 L L 



