A DREAM OF FAIR HYDRONE 491 



however, is much lower than that of ammonia, whilst the boiling 

 point is much higher. But in the case of aniline, C 6 H 5 .H 2 N, 

 which is derived from ammonia and from phene or benzene, 

 C 6 H 6 , containing as it does the radicle phenyl, C H 5 , in place of 

 one of the atoms of hydrogen of ammonia, the basic tendencies 

 of the nitrogen atom are almost neutralised, aniline being a 

 very weak base in comparison with ammonia. And if the 

 phenyl in aniline be modified or weighted by introducing 

 chlorine atoms in place of several of its hydrogen atoms, the 

 basic properties are still further weakened and eventually 

 entirely neutralised, trichloraniline, C 6 H 2 C1 3 . H 2 N, having no 

 power of combining with acids. 



It is not easy, scarcely possible, indeed, to embody facts 

 such as these in models corresponding to that by which carbon 

 is represented and which gives expression so faithfully to its 

 dominant qualities. 



In the case of carbon, a tetrahedron with four rods directed 

 from its centre and fixed rigidly at its four terminal points serves 

 to indicate both the number of affinities at the disposal of the 

 carbon atom and the direction in which, apparently, these can 

 act. Hydrogen, like carbon, being also an element of steadfast 

 behaviour, its valency never exceeding unity, may be repre- 

 sented similarly by a ball provided with a single hole into 

 which the rods representing the single combining affinity may 

 be rigidly inserted. Such models serve to emphasise the fact 

 that hydrogen and carbon respectively act invariably as monadic 

 and tetradic elements. 



And these are circumstances which it is of importance to 

 emphasise, for if it be the fact that hydrogen is a consistent 

 monad, it necessarily follows that the residual affinity which 

 is manifest in so high a degree in hydrogen chloride, oxide 

 and nitride is in no way resident in the hydrogen but entirely 

 in its associate — that is to say, in chlorine or oxygen or 

 nitrogen ; the residual affinity of these elements is of such 

 nature, moreover, that it cannot be satisfied either by hydrogen 

 alone or by any equivalent radicle such as methyl. 



To express the peculiar behaviour of oxygen, a ball may be 

 taken through which pass two rods, both free to move in and 

 out. When both rods are drawn out to the maximum extent, 

 the model represents dyad oxygen as it is in a saturated com- 

 pound ; when, however, the rods project partly on both sides 



