xvn MOLECULAR ARCHITECTURE 385 



only less difficult to study than the alchemistic period 

 itself. 



The supreme feature of the period was the gradual 

 development of structural chemistry, leading at last to a 

 clear knowledge of the way in which the atoms are linked 

 together, even in the more complex products of vegetable 

 and animal life. But apart altogether from all progress 

 in the region of theory, there was a marvellous growth in 

 the experimental knowledge of organic compounds. In 

 this period we find recorded the discovery, or the first 

 analysis, of methyl alcohol and its higher homologues, of a 

 series of fats and fatty acids, of acetone and the ethers, of 

 chloral and chloroform, glycerol and glycol, aniline and the 

 amines, camphor and camphoric acid, benzene and naphtha- 

 lene, and the many products obtained by chlorinating, 

 brominating, nitrating and sulphonating these different 

 materials. The organic chemist of to-day will recognise in 

 this imperfect list evidences of advance along most of the 

 principal routes by which the growth of knowledge is pro- 

 ceeding in his science at the present time ; and the structural 

 formulae assigned by Kekule to ethyl acetate and to benzene 

 are but typical of those which are now being assigned, fifty 

 years later, to the more complex terpenes and alkaloids. 



Lavoisier (1784) shows that organic substances are 

 compounds of carbon and hydrogen. The formation of 

 fixed air and of water as products of the combustion of 

 organic materials had been recognised vaguely from the 

 time of Van Helmont (p. 64). In the case of fixed air the 

 information first became definite in the hands of Black, 1 



1 In his Lectures on the Elements of Chemistry, published in 1803, 

 after his death, Black says that in the year 1757 he had discovered or 

 proved : 



(1) That fixed air "is deadly to all animals that breathe it by the 

 mouth and nostrils together." 



(2) That " the change produced on wholesome air by breathing it 

 consisted chiefly, if not solely, in the conversion of part of it into fixed 



C C 



