78 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



chemical science in its power of classifying known and predicting un- 

 known facts, includes all that was valuable in the generalisations 

 which preceded it. The study of the behaviour of organo-metallic 

 compounds in chemical reactions led to the conclusion that various 

 metallic elements possess a definite capacity of saturation with regard 

 to the number of atoms of other elements with which they can com- 

 bine, and demonstrated this regularity of atom-fixing power in the 

 case of zinc, tin, arsenic and antimony. A serious obstacle, however, 

 in the way of determining the true atomicities of the elements was 

 the general employment of the old so-called equivalent weights, which 

 were by most chemists confounded with the atomic weights. This 

 difficulty was removed by the rectification of the atomic weights, 

 which, though begun by Gerhardt as early as 1842, met for a long 

 time with but little recognition, and was not completed till the sub- 

 ject was taken up by Cannizarro in 1858. The law of atomicity has 

 given to chemistry an exactness which it did not previously possess, and 

 since its discovery and recognition chemical research has moved very 

 much on the lines laid down by this law. 



Chemists have been engaged in determining by means of decompo- 

 sitions, the molecular architecture, or constitution as it is called, of 

 various compounds, natural and artificial, and in verifying by synthesis 

 the correctness of the views tlms arrived at. 



It was long supposed that an impassable barrier existed between 

 inorganic and organic substances : that the chemist could make the 

 former in his laboratory, while the latter could only be produced in 

 the living bodies of animals or plants requiring for their construc- 

 tion not only chemical attractions, but a supposed ' vital force.' It 

 was not until 1828 that Wohler broke down this barrier by the 

 synthetic production of urea, and since his time this branch of science 

 in the hands of Hofmann, Wurtz, Berthelot, Butlerow, and others, 

 has made great strides. Innumerable natural compounds have thus 

 been produced in the laboratory ranging from bodies of relatively 

 simple constitution, such as the alcohols and acids of the fatty series, 

 to bodies of such complex molecular structure as alizarin (the prin- 

 cipal coloring matter of madder), coumarin (the odoriferous principle of 

 the tonqua bean), vanillin, and indigo. The problem of the natural 

 alkaloids has also been attacked, in some cases with more than partial 

 sviccess. Methylconine, which occurs along with conine in the hem- 

 lock, has been recently prepared artificially by Michael and Gundelach, 

 this being the first instance of the synthesis of a natural alkaloid. A 

 proximate synthesis of atropine, the alkaloid of the deadly nightshade. 



