148 OUR PHYSICAL WORLD 



friction match was invented. It rapidly replaced the flint and 

 steel. The bit of dry wood is tipped with a paste containing 

 some substance that ignites at low temperatures, such as phos- 

 phorus, one that burns readily like sulphur, and a substance that 

 parts with its oxygen easily as do potassium chlorate or man- 

 ganese dioxide. The friction of striking the match generates 

 heat enough to ignite the phosphorus, which lights the sulphur, 

 which makes heat enough to start the wood burning. The white 

 phosphorus used in these early matches was poisonous, and 

 sometimes a child was killed by eating the heads of matches 

 carelessly left where it could get them ; and the workers who made 

 matches were affected by a very painful disease, a result of inhal- 

 ing the fumes. The sulphur used produced choking fumes when 

 the match burned. So the phosphorus is now replaced by sub- 

 stances like antimony sulphide or phosphorus sulphide, which 

 also ignite at a low temperature but are safe; and paraffin is 

 used in place of sulphur. In the safety match the potassium 

 chlorate and antimony sulphide or similar substance is used in 

 the head, and the red phosphorus is present in small quantity 

 in the prepared surface on which the match must be scratched 

 to light it readily. 



Break a lump of sugar into smaller lumps and these into 

 still smaller bits. You might think you could keep on doing 

 this indefinitely if eyes were sharp enough to see the finer particles 

 and fingers were skilful enough to use fine-pointed instruments 

 to do such a delicate job. But the chemist and physicist tell us 

 that this is wrong and that sugar (and, in fact, every substance) 

 is made up of very minute particles called molecules that cannot 

 be broken up without destroying the sugar as such. True, the 

 molecule is made up of still smaller particles, the atoms, but when 

 the sugar molecule is broken up into its atoms we have carbon, 

 hydrogen, and oxygen, simple substances having properties quite 

 unlike sugar. 



Now atoms of substances like carbon, hydrogen, and oxygen 

 have a very strong attraction for one another and tend to rush 



