204 Mr. M. M. Pattison Muir 07i Chemical Classification. 



to these compounds any other formulae than those given above. 

 The differences in the properties of these substances cannot, 

 therefore, be accounted for by differences in structure ; they 

 must be dependent upon the nature of the constituent atoms 

 other than oxygen and hydrogen. But we know of bodies 

 possessed of the same empirical formula and of the same mo- 

 lecular weight as acetic acid, yet differing altogether in pro- 

 perties from this compound ; these differences in properties 

 are most probably due to differences in structure. If this 

 view be accepted, it follows that just as diff'erences in the 

 nature of the atoms in a series of molecules, each containing 

 the group OH, may cause this group to assume different func- 

 tions, so differences in the structure of such molecules may 

 produce a similar effect. Now the constitutional formuljB 

 already assigned to alcohol and acetic acid exhibit differences 

 in the structures of the two molecules*. In alcohol we have 

 the OH group joined to the group CH2 (CH3 — CHg — OH); 

 in acetic acid the OH group is joined to the group CO 

 (CH3 — CO — OH). I have already detailed some of the rea- 

 sons for adopting these constitutional formulae. These two 

 compound groups — CHg — OH and — CO — OH are believed 

 to exist in certain classes of alcohols and in acids respectively. 

 Granting that carbon acids contain the group — CO — OH, it 

 becomes possible very readily to determine the constitutional 

 formulae of many acids. Thus formic acid, Hg CO2, can have (on 

 our theory) but one constitutional formula, viz. H — CO — OH. 

 There are many reactions by which we may recognize the 

 compound groups — CHg — OH and — CO — OH : the action 

 of PCI5, with the subsequent action of water upon the body 

 produced, is one of the best ; the action of the haloid acids is 

 another ; the action of the alkali-metals, contrasted with that 

 of the alkalies, is a third ; the action of methyl or ethyl 

 iodide upon the metallic derivatives of the body under consi- 

 deration, combined with the action of potash or ammonia upon 

 the product so obtained, is a fourth. There are many other 

 reactions. 



We find that compounds containing the group — CH2 — OH 

 yield, on oxidation, acids containing the group — CO — OH ; 

 but we have reasons for regarding the first group as charac- 

 teristic of alcohols : some bodies which, for other reasons, must 

 be classed among the alcohols, do not yield such oxidation- 

 products as we should expect to be produced from substances 

 containing the group — CH2 — OH. Such a result naturally 

 leads to a further study of the apparently anomalous alcohols ; 



* Although these bodies are not isomeric, they may nevertheless be 

 used as illustrations. 



