6o SCIENCE REMAKING THE WORLD 



themselves, do not properly belong to any one of the 

 traditional three kingdoms for they may be made from 

 material found in any of them and the product is the 

 same whatever the source. So with the substances that 

 we are considering. They are commonly called coal- 

 tar products because that is the ordinary source of the 

 raw material, for tar is a by-product of the gas and coke 

 industry, formerly thrown away and even yet often 

 wasted. But it is necessary to understand that there is 

 nothing exclusive or peculiar about coal-tar. It does 

 not contain the various valuable things that are made 

 from it. These are mostly composed of four elements, 

 the commonest in the world : carbon, hydrogen, oxygen, 

 and nitrogen. These four make up air and water, and 

 out of air and water these compounds could be made, 

 although it would be a difficult and expensive process. ; 



In the chemistry books they are known either as the 

 "aromatic compounds," because a good many of them 

 have an aromatic odour, or the " benzene series " from 

 the light colourless oil known as benzene which distils off 

 when tar is heated, and which serves as the basic sub- 

 stance of those compounds. This benzene is composed 

 of molecules consisting of six carbon atoms hooked up 

 into a ring. But the benzene ring and similar structures 

 are commonly found in vegetable and animal sub- 

 stances. 



The reason why I call your attention to this is that 

 there is a prevalent impression that the coal-tar prod- 

 ucts are some new invention of the chemists, perhaps 

 instigated by the devil with whom chemists have always 

 been accused of being too familiar. Many of the things 



