ON SCIENCE IN SCHOOL CERTIFICATE EXAMINATIONS. 515 



a match. What is a match? — nothing ie more commonly used and yet few know 

 anything about it. 



The easily inflammable substance — that which is fired by the heat developed 

 by friction in drawing the match over the rough surface of the box — i.i 

 fhosfhorus. What does the word mean — what language is it derived from? 

 Phosphorus is made largely from animal bones. From bones, you say : can"t 

 we get away from ourselves and our food even in studying the matches used 

 in lighting the fire with the aid of which our food is cooked ? Do all things 

 move in a circle? 



Phosphorus, you will see, when it is put before you, is a yellow wax-like 

 solid ; it is always kept under water and must be handled with extreme care 

 and only kept in the fingers during a short time, as it takes fire very easily 

 and the burns it produces heal with difficulty. Why should it inflame sooner 

 or later when taken out of water and not in water ? Does this behaviour 

 suggest anything to you? If so, make an experiment to verify your idea. 

 What has this experiment taught you — does it not serve also to bring the match 

 more closely into relationship with the iron stove than you before thought to 

 be likely ' 



Very little phosphorus is used in matches — how does ic burn alone ? Care- 

 fully dry a small piece, first on a duster and then on porous paper, place it on 

 a brick or tile and touch it with a warm wire : at once it takes fire and burns 

 brightly; as it burns, dense white smoke is given off. Try to stop the smoke 

 from escaping by covering the burning phosphorus with a glass shade. Note 

 what happens — describe the product. 



In burning other substances, you have found that the air is concerned — 

 that, in part, it is ' burnt ' as well as the inflammable substance : is the air 

 concerned in the burning of phosphorus ? Try. 



As the phosphorus takes fire so very easily, will it not be well to try to burn 

 it alone to make sure that the air is concerned ? It is possible to remove the 

 air from a vessel by means of an air pump. Let us put a piece of carefully 

 dried phosphorus into a strong globular flask, provided with a tightly fitting 

 rubber stopper to which a glass tap is fitted : having exhausted the air by means 

 of the pump and closed the tap, let us now cautiously heat the flask, where the 

 phosphorus lies, over a small flame, sufficiently to melt the phosphorus : nothing 

 happens. Now let us repeat the experiment with a strong flask full of air closed 

 by a simple rubber stopper : the phosphorus takes fire but soon ceases to burn 

 and apparently some remains unburnt. There was not much air in the flask — 

 was any or all of it burnt along with the phosphorus ? Think what happened 

 when the phosphorus was exposed in air over water. What then will happen 

 if the stopper be withdrawn from the flask while the neck of the flask is under 

 water ? See ! 



It is clear therefore that whether it be merely exposed in air or burnt in 

 air, the phosphorus kills, as it were, very nearly one-fifth of the air — its 

 behaviour is much like that of all other burning substances, except that, to be 

 precise, it is more like that of iron — which also gives a solid product, unlike the 

 other substances which were burnt. But the air behaves alike to iron and 

 phosphorus, seeing that one-fifth disappears under the influence of each. This 

 fact would seem to indicate that the same constituent of the air is concerned 

 in both cases — try to place this beyond doubt by experiment. 



How does the phosphorus act — does it associate with the active gns in air — 

 is the white snow-like product a rust? How will you ascertain? You must 

 prevent the smoke from escaping, must you not, if you wish to contrast its 

 weight with that of the phosphorus — how will you do this — how is smoke to 

 be held back or screened off — what is a respirator used for? Very well, then: 

 fit up a suitable respirator to prevent the smoke f'.om escaping from a tube in 

 which phosphorus is burnt. 



From the result, it is clear, you see. that the phosphorus and iron behave 

 alike towards air, withdrawing and combining with the same proportion — very 

 nearly one-fifth ; and it seems probable, does it not, that this one-fifth about 

 (the Fire air, as we have called it) is a special constituent present to this extent 

 in air ? You have thus discovered what of air — that air is a mixture of at 

 least two kinds of air, have you not? 



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