Mr. M. M. Pattison Muir on Chemical Classification. 199 



type, viz. Cg H3 (OH). But in many reactions acetic acid 

 splits up more completely than in those already enumerated. 

 When an acetate is heated with an alkali-hydrate, methane is 

 produced along with carhonate of the alkali ; that is, one half 

 of the carbon in the acetate passes away as gas in combination 

 with the whole of the hydrogen, while the other half enters 

 into combination with the whole of the oxygen, and with the 

 whole of the metal both of the acetate and of the hydrate. 

 The possibility of such a reaction is rendered apparent by 

 adopting the constitutional formula CH3 — CO — — H for 

 acetic acid. Other reactions of acetic acid also find their ex- 

 planation in this formula, thus : — 



JH3-J-CO— 0— Na + NaO-i-H = CH4 + NaO - CO - NaO, 

 JH,— CO 



:jh,— CO- 



.Q-Na+KaO— C0-i-H = CH3— CO— H + NaO— CO— NaO, 

 Sodium formate. Aldehyde. 



-0— Na + NaO— CO-I-CH3 = CH3— CO— CH3 + NaO— CO— NaO. 



; Acetone. 



In certain cases we are able to trace a connexion between 

 the results deduced from such purely chemical considerations 

 as those enumerated above, and the results of experiments 

 upon the physical properties of a group of related compounds *. 

 In my paper on Isomerism f I have endeavoured (par. 5) 

 to show that a regular alteration in the boiling-points of the 

 four butylic alcohols is correlated with a regular alteration in 

 molecular structure. The constitutional formulae there given 

 to the four alcohols are obtained by a process of reasoning on 

 chemical data similar to that illustrated in the cases of alcohol 

 and acetic acid. 



In endeavouring, therefore, to construct a constitutional 

 formula attention should be paid to the physical properties as 

 well as to the chemical reactions of formation and decomposi- 

 tion of the body to be formulated. Until, however, much 

 more extended observations on the physical properties of 

 groups of compounds have been carried out, the chemical 

 method of arriving at constitutional formulae must be regarded 

 as the more important. 



24. What I have called the chemical method of ascertaining 



* For a fuller discussion of these and of other examples, see Die mo- 

 dernen Theorien, 2nd edit. pp. 176-192. 

 t This Magazine, September 1876. 



