Residual Valence of Various Molecules 477 



Granting that this number really represents the residual 

 valence, the accuracy with which it can be determined will 

 depend on the accuracy with which M 2 K, C, the molecular 

 weight and the number of valences reaching between the 

 atoms can be determined. The molecular weight may be 

 assumed to be normal for non-associating substances at the 

 critical temperature; and we have to assume that the number 

 of valences between the atoms are those which chemists 

 usually assign to these elements. The determination of the 

 constant C, however, is more difficult. It could be deter- 

 mined empirically if M 2 K was known accurately for any 

 substance of which the valence is fixed and certain. Hydrogen 

 is the only element with an unchanging valence, but un- 

 fortunately the critical pressure of hydrogen is uncertain. 

 Moreover, it cannot be assumed that the valence of hydrogen 

 is exactly unity. There are several indications that a mole- 

 cule of hydrogen has some residual valence although it is 

 certainly small in amount. One such indication is the solu- 

 bility of hydrogen in water. At the same pressure and tem- 

 perature more molecules of hydrogen dissolve in water than of 

 helium, and hydrogen is half as soluble as nitrogen which al- 

 most certainly has residual valence. If solubility involves 

 residual valence, as it may, this means that hydrogen would 

 have some residual valence. Its solubility in platinum may 

 be interpreted in the same sense. The catalytic reducing 

 action of platinum, nickel or other metals or metallic oxides 

 in a hydrogen atmosphere is interpreted by Sabatier 1 to mean 

 that a chemical union of the reacting substances occurs. 

 Armstrong, 2 too, has expressed the opinion that hydrogen 

 has a small amount of residual valence. For these reasons 

 we cannot accurately determine C from hydrogen. Never- 

 theless I have calculated M 2 K and C for hydrogen to show 

 what the value of C would be if hydrogen were univalent. 



1 Sabatier: Nobel Prize Address, p. 9, et seq.; Les Prix Nobel en 1912; 

 La Methode d'Hydrogenation directe par Catalyse. 



2 Armstrong: "Valency," Encyclopaedia Britannica, nth Ed., 27, 848 

 (1911). 



