A DREAM OF FAIR HYDRONE 489 



the other : the two no longer fit in the sense that the coloured 

 angles match. In fact, two non-superposable models are 

 obtained ; but it is only when all four angles are differently 

 occupied that two non-superposable forms are possible. 



Applying this argument to the atom itself, the conclusion 

 is arrived at that a compound such as tartaric acid in which 

 the four affinities of a single carbon atom are satisfied by four 

 different units or radicles may exist in two forms : the fact 

 that these are optically active to equal extents but in different 

 directions being accounted for by the spiral arrangement in 

 space in reverse order of the four radicles in the two cases. 



A carbon atom in the condition pictured is termed an asym- 

 metric atom, as such a system as that described has no plane 

 of symmetry — in other words, it cannot be cut into halves. 

 Asymmetric carbon plays a dominant part in Nature ; it may, 

 indeed, be said that it is the Rosetta stone with the aid of 

 which it is becoming possible to arrive at an interpretation of 

 the fundamental phenomena of life in so far as these can in 

 any way be made clear by the chemist. 



Argument 



The hydrides of chlorine, oxygen and nitrogen — hydrogen 

 chloride, hydrogen oxide and hydrogen nitride (ammonia) — 

 are compounds the behaviour of which is in striking contrast 

 with that of the simplest hydride of carbon. Three of these 

 four hydrides are gaseous far below ordinary temperatures : 



hydrogen oxide alone liquefying without compulsion. The 

 degree of readiness with which they pass into the liquid state 

 obviously, however, bears no relation to their molecular 

 weights, which differ but slightly in three cases, the fourth 

 compound (hydrogen chloride) being intermediate in volatility 

 between the two which are less than half as dense. 



The mere fact that hydrogen oxide becomes water so readily 

 must be held to be proof in itself that the molecules of the 

 oxide are gifted in a high degree with attractive forces which 

 lead them to combine inter se. No such evidence of mutual 



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