ANNIVERSARY ADDRESS. 17 



generalities, but we may, I think, try and picture in space and 

 follow in imagination, the track of a molecule of ammonia, con- 

 fining ourselves to common terrestial temperatures, disregarding 

 on the one hand dissociation temperatures, as well as that 

 wonderful approach to the absolute zero, made during the last 

 year or so, by Dewar in solidifying hydrogen. 



The mental picture I have of the ammonia molecule is that of 

 a central nucleus and attendant atoms, which we may call the 

 central sun and planets of an imaginary planetary system. This 

 sun we call nitrogen, and, without doing violence to our newer 

 conceptions of matter being a vortex motion, is a conceivable 

 mass, holding three planets at fixed but, to us, unknown distances. 

 These three planets are none other than the hydrogen atoms. 

 Place these planets in their proper orbits, and we picture the 

 ammonia system in space. But facts show us that there must be 

 five possible orbits ; witness the compound sal-ammoniac. But, 

 with the magic clash of atoms and the redistribution of vantage 

 positions in the molecule, let both a carbon atom, two oxygen 

 atoms and a water molecule, come into position in opposition to 

 two molecules of ammonia, and we have ammonia carbonate. 1 



Once again, rearrange the positions inside the molecule and we 

 have the molecule of urea, being in fact, the famous synthesis by 

 Wohler of the first compound of animal origin made artificially in 

 the laboratory. Nitrogen being the central figure of the ancient 

 alkaline air we call ammonia, is moreover the pivot-atom of a class 

 of bodies of much later discovery, which, having the power of 

 combining with an acid to form a salt, resemble an alkali and 

 were therefore called alkaloids, [like alkali]. The relations and 

 constitution of some of these alkaloids will be seen from what 

 follows : — After the synthesis of urea by Friedrich Wohler in 

 1828, it was felt that the structure of the more complex uric acid 

 would yield to the atom-building-instinct of the modern chemist ; 

 this was effected by Behrend and Roosen, also by Horbaczewski, 



1 The Spiritus urinse of the ancients. 

 B— May 2, 1900. 



