ADDRESS. 19 



of chlorine, goods which meet with much favour, especially for hospital 



use I 



But the debt which chemistry, both inorganic and organic, thus owes 

 to Dumas' law of substitution is serious enough, for it proved to be 

 the germ of Williamson's classical researches on etherefication, as well as 

 of those of Wurtz and Hofmann on the compound ammonias, investi- 

 gations which lie at the base of the structure of modern chemistry. 

 Its influence has been, however, still more far-reaching, inasmuch as 

 upon it depends in great measure the astounding progress made in the 

 wide field of organic synthesis. 



It may here be permitted to me to sketch in rough outline the prin- 

 ciples upon which all organic syntheses have been effected. We have 

 already seen that as soon as the chemical structure of a body has been 

 ascertained its artificial preparation may be certainly anticipated, so 

 that the first step to be taken is the study of the structure of the 

 naturally occurring substance which it is desired to prepare artificially 

 by resolving it into simpler constituents, the constitution of which is 

 already known. In this way, for example, Hofmann discovered that the 

 alkaloid coneine, the poisonous principle of hemlock, may be decomposed 

 into a simpler substance well known to chemists under the name of 

 pyridine. This fact having been established by Hofmann, and the 

 grouping of the atoms approximately determined, it was then necessary 

 to reverse the process, and, starting with pyridine, to build up a com- 

 pound of the required constitution and properties, a result recently 

 achieved by Ladenburg in a series of brilliant researches. The well- 

 known synthesis of the colouring matter of madder by Graebe and 

 Liebermann, preceded by the important researches of Schunck, and that 

 of indigo by Baeyer, are other striking examples in which this method has 

 been successfully followed. 



Not only has this intimate acquaintance with the changes which 

 occur within the molecules of organic compounds been utilised, as we 

 have seen, in the synthesis of naturally occurring substances, but it has 

 also led to the discovery of many new ones. Of these perhaps the 

 most remarkable instance is the production of an artificial sweetening 

 agent termed saccharin, 250 times sweeter than sugar, prepared by a 

 complicated series of reactions from coal-tar. Nor must we imagine 

 that these discoveries are of scientific interest only, for they have given 

 rise to the industry of the coal-tar colours, the value of which is measured 

 by millions sterling annually, an industry which Englishmen may be 

 proud to remember was founded by our countryman Perkin. 



Another interesting application of synthetic chemistry to the needs 

 of everyday life is the discovery of a series of valuable febrifuges, 

 amongst which I may mention antipyrin as the most useful. An im- 

 portant aspect in connection with the study of these bodies is the 

 physiological value which has been found to attach to the introduction 

 of certain organic radicals, so that an indication is given of the possibility 



