474 



Dr, A. W, Hofmann 



[April 11, 



You observe the molecules of hydrochloric acid, of sulphuretted and 

 of phosphoretted hydrogen respectively contain the same number of 

 atoms which are present in the molecules of hydrogen, of water, and of 

 ammonia. We have thus indicated that hydrochloric acid is con- 

 structed upon the hydrogen-type, sulphuretted hydrogen upon the 

 water- type, phosphoretted hydrogen, lastly, upon the type of ammonia. 

 The three bodies just considered were formed by the insertion of ele- 

 mentary atoms ; but our type-moulds receive compound atoms with 

 the same facility. Let me take as an illustration the compound atom 

 ethyl^ consisting of two atoms of carbon and five of hydrogen, 

 (Ca H5 = E), which is familiar to the members of the Royal Insti- 

 tution. By inserting one or two ethyl-atoms into the hydrogen- 

 mould I generate the molecules of ethylated hydrogen, or ethylated 

 ethyl (free ethyl). 



In a similar manner, by introducing either one or two ethyl-atoms 

 into water, I convert the molecule of water into the molecules of the 

 two ethylated waters, alcohol and ether. 



Displace, lastly, one, two, or three hydrogen-atoms in ammonia, by 

 one, two, or three ethyl-atoms, and you give rise to the formation of 

 the molecules of the three ethylated ammonias. 



better known as ethylamine, diethylamine, and triethylamine. 



At the risk of exhausting your patience, I repeat some of these 

 changes with another compound atom of a composition differing from 

 that of ethyl. These mauve-coloured cubes may represent a com- 

 pound atom, containing six atoms of carbon and five of hydrogen 

 [0] H5 = Ph), to which chemists have given the name of phenyl. 



