PROBLEMS OF MODERN SCIENCE 



up the desired structures with suitable fragments 

 obtained from various sources. The organic 

 chemist has not confined his work to the imitation 

 of natural products in this way ; but, taking por- 

 tions from various types of molecules, he has 

 synthesised a very large number of entirely new 

 substances. Many of these find use in industry. 

 Some, for example, are highly coloured ; among 

 these, some are suitable for use as dyes ; others 

 emit a fragrant odour and are employed in the 

 scent industry ; others have unstable molecules 

 and are used as explosives ; whilst others have 

 specific physiological action and are employed as 

 drugs. At the same time many other substances 

 of purely theoretical interest have been obtained, 

 and the study of these has in many ways led to 

 valuable advances in the theory of the science. In 

 the course of all this work an enormous number 

 of synthetical carbon compounds have been pre- 

 pared at the present time about 200,000 are 

 known and it cannot be denied that the great 

 majority of these have been of very little service 

 to the science or to industry. However, it can 

 hardly be expected that such important results could 

 be attained without the accumulation of a great deal 

 of waste material. No machine ever is completely 

 efficient, and human effort applied to the investi- 

 gation of nature meets with very many failures. 



Attention may now be turned to a more recent 

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