128 Mr. W. A. Dixon on the Constitution of Acids. 



nearly allied to alcohols and phenols than to the true acids. 

 Hydrogen also enters directly into combination; but when it 

 does so the compound generally exhibits acid properties of 

 the feeblest description except when in combination with the 

 extremely chlorous analogues, and when in combination in 

 complex acids it is not replaceable by metals. 



I give a few examples from the common acids to explain 

 my meaning ; and it will be observed that as a rule the lower, 

 and what is generally to be regarded as the most stable, ato- 

 micity of the elements only is required. The exception to 

 this is the halogen group, which must be regarded as entering 

 into oxacid combination as triads. This is scarcely extraordi- 

 nary, as we know that iodine forms a trichloride, and that 

 therefore it at least must be a triad, or develops triadic func- 

 tions by reason of its juxtaposition to chlorine. If iodine 

 does so, why may not the other members of this closely allied 

 group of halogens ? It appears to me that the metals are 

 more elemental in character, so to speak, and therefore less 

 liable to atomic changes than the non-metals, and that most 

 of the supposed variation in metallic atomicities would dis- 

 appear if the halogens were triads in certain combinations. If 

 iodine only of the group could assume triatomicity, there is 

 no reason why the monatomic chlorine in iodine trichloride 

 should not be replaceable by monatomic hydrogen ; but there is 

 little reason to expect such a substitution if by the combina- 

 tion of these elements triatomic functions were developed in 

 both, so that the compound was not 



/CI /01\ 



if CI, but / { \ • 



\C1 Cl^Cl 



To come to examples, let us first take tlie phosphorous acids. 



/)OH 

 The orthoacid has probably the composition P— OH , because 



the acid itself has strong acid properties ; but these are imme- 

 diately lost or neutralized by the replacement of the hydrogen 

 of the oxyhydroxyl group by sodium, whilst the replacement 

 of the hydrogen of one hydroxyl group gives a salt having an 

 alkaline reaction. 



/)OH 

 Phosphorous acid has probably the constitution P-OH , 



H 

 and is therefore dibasic, the hydrogen atom being only re- 

 placeable by compound radicals resembling itself; but this acid 

 does not form a true acid salt with the alkali metals. 



