196 Dr. Play fair on Transformations 



additional atoms of oxygen, being less firmly attached, are 

 capable of gratifying the disposition of a less oxygenized atom 

 (the base) to attach itself to a higher oxide, or, to use the 

 convenient phraseology of Graham, the base becomes zincous 

 to the acid, which is now chlorous. 



On heating the nitrates, nitric acid is not given off, but 

 NO4 + O. The decomposition readily results from the dis- 

 position of the base to appropriate more oxygen and pass 

 into the higher oxides. If the base be oxide of nickel, the 

 oxygen becomes attached to the oxide and remains ; if, how- 

 ever, an oxide which has but a feeble affinity for oxygen 

 at an elevated temperature, the elasticity of that element 

 is able to overcome the affinity, which succeeded in break- 

 ing up the nitric acid. The final action is so obviously de- 

 pendent upon the oxygenous part of the acid, as to make 

 Schonbein believe that salts contain peroxides ready-formed ; 

 thus that NO5, IIO=N04 + H02, or PbO, N05 = N04-f 

 PbOg. This however is an unnecessary supposition, the pre- 

 vious view accounting sufficiently for the decomposition of a 

 nitrate, so as to produce NO4 and O. Admitting this view 

 to be correct in the expression that the preponderating quan- 

 tity of a chlorous element in an acid renders the latter chlo- 

 rous to a base, the mechanical attachment being to the chlo- 

 rous element, we can understand why the number of atoms 

 of oxygen in a base should regulate the number of atoms of 

 acid attached to it. Thus RO presents only one chlorous 

 element of attachment to the acid, and therefore the latter 

 adheres to it in one proportion ; whereas Rg O3, which pos- 

 • sesses three atoms of a chlorous element equally distributed 

 round a zincous nucleus, presents three points of attach- 

 ment, and therefore produces a salt Rg O3, 3A. This view 

 in result gives all the simplicity of the acid radical theory, 

 both views entertaining the idea that the oxygenous atoms of 

 the base and acid are attached to each other. We have cer- 

 tain instances, as for example KO, CIO5 ; PbO, NO5, where 

 the elastic atoms of oxygen combine as closely together as 

 non-elastic atoms, such as lead or silver. 



Although to aid conception we may suppose the atoms of 

 oxygen of the base and of the acid to be in mechanical con- 

 nexion, the true arrangement is probably not so, seeing that 

 in a base there is always a part more zincous than the oxy- 

 genous atom, although the base as unity is zincous to the 

 acid. We see many instances in chemistry of union of atoms 

 in pairs, or what may be called dual affinity. This Graham* 



* Trans. Royal Soc. Edin. vol. xiii. ; Phil. Trans. 1837, p. 47 etseq,-, 

 Phil. Mag. Third Series, vol. xxiv. p. 401 et seq. 



