262 COAL-TAR DYES 



Since then various methods have been tried, and at present 

 Indigo is produced by a very complicated process in which 

 naphthalene, 1 another coal-tar product, is the initial com- 

 ponent. 



It is now produced cheaply and in large quantities, and 

 is a serious rival to natural or vegetable indigo. 



ANALYSIS AND SYNTHESIS. Water is composed of hydrogen 

 and oxygen. It can be separated into its component parts by 

 passing steam over heated magnesium, when the oxygen of 

 the steam joins with the magnesium to form magnesium oxide, 

 and hydrogen is given off as a gas. In this case an Analysis 

 of water has been made (Greek analusis, from analuein, to 

 unloose, from ana, again, and luein, to loose). 



On the other hand, when hydrogen is passed over copper 

 oxide (i.e. copper and oxygen), the hydrogen joins with the 

 oxygen to form water, and the copper is left. In this way 

 water has been formed synthetically, by putting together its 

 elements (Greek sunthesis, from suntithenai, to put together). 



The whole history of the discovery of artificial dyes consists 

 of these two processes ; first, an analysis of the natural 

 product, in order to find out of what elements it is composed, 

 and then a synthesis of these elements, obtained from other 

 sources. 



There are at present about 700 Synthetic Dyes, obtained 

 from Coal-tar Products. 



Although the foundation of the coal-tar colour industry 

 was laid by an Englishman, and although many subsequent 

 discoveries were made by us, the bulk of the trade passed 

 into German hands, so that in 1910 out of 20,000,000 worth 

 of coal-tar dyes, three-quarters were produced in Germany. 



During the war we have tried to remove this national 

 disgrace, and to some extent have succeeded, although five 

 years' strenuous effort has not been sufficient to make up for 

 forty years of slackness. 



1 C 10 H 8 ; it is a white solid, one of the products of the carbolic oils 



