308 Mr. J. F. Heyes on Valency, 



and removes the difficulties which have been raised as to the 

 doubtful trivalent character of aluminium. It certainly turns 

 the scale in favour of the questioned A1(CH 3 ) 3 , and leaves Al 

 trivalent, as its place in the periodic system emphatically 

 requires. So striking a chemical substance as the Greenland 

 mineral cryolite, Na 3 AlP 6 ,has hitherto been between the Scylla 

 of the old dot formula, A1F 3 . 3NaF, and the Charybdis of 

 nonad or enneavalent aluminium. But it is difficult to resist 

 the conclusion that fluorine is here trivalent, 

 F=FNa 

 Al-F=FNa. 

 X F=FNa 

 In the case of other double fluorides it may be that certain of 

 the atoms are in these circumstances trivalent, e.g. in 



\ F TTTT 



NbF 5 .2KF as F-Nb^ 



.F=FK 

 U0 2 F 2 .2KF as 2 U( 



It scarcely seems to follow that two out of the five F atoms 

 in NbF 5 are not "chemically equal." The questions of 

 "validity," "residual affinity/' &c. concern the FK or FNa 

 connexion. These ideas at least seem worth taking as a 

 working hypothesis. 



(7) Although it is premature to generalize, it is well worthy 

 of attention that temperature is a function of validity, very 

 often, to say the least, in the direction of change, whether of 

 degree only or not, from validity to valency, i, e. to the 

 smaller number. The analogy between polymerism and 

 allotropy then seems to be as close as possible. A discussion 

 of the following parallels would exemplify this idea: — 



o 2 



o 3 



s 2 



s 6 



HF 



H 2 F 2 



C 2 N 2 



C 6 N 6 



C 2 H 2 



C 6 H 6 



P 4 



P, 



CO 



co 2 



N0 2 



N 2 4 



K 2 



K 2 4 



Aul 



A11I3 



