128 CHEMICAL PROPERTIES AND COMPOSITION 



as to the breaking up of carbon chains, of which some 

 may be mentioned here. 



In the simplest case, with only two carbon atoms the 

 facility of decomposition increases with the quantity of 

 oxygen contained, as may be seen by comparing the 

 following grades of oxidation: 



CH 3 CH 2 OH CH 2 OH CHO COOH 



II ! II 



CH 3 CH 3 CH 2 OH CH 3 CH 3 

 CHO COOH CHO COOH COOH 



4 



H 2 OH CH 2 OH CHO CHO COOH 



The last member, oxalic acid, is comparatively easy to 

 decompose, and breaks up on oxidation, and also on heating, 

 either alone or with sulphuric acid, into carbonic and formic 

 acid or carbonic oxide ; the seventh member, gly colic acid, 

 also breaks up on heating with sulphuric acid, forming 

 formaldehydes and carbonic oxide. Acetic acid, earlier in 

 the series, needs strong heating with excess of alkali to 

 break it up with formation of methane. The compounds 

 preceding that show the greatest tenacity in the carbon 

 linkage. 



In more complex derivatives the consequences of this 

 behaviour are again seen, e. g. in PopofFs rule, according to 

 which ketones, 



C.H.COCpH, 



on oxidation break up at the oxidized carbon atom, so that 

 for example dipropylketone, 



C 3 H 7 COC 3 H 7 , 



goes to propionic and butyric acid, and not to acetic and 

 valerianic. A still more complete break up occurs when 

 two oxidized carbon atoms are attached to another carbon 

 atom, as in aceto-acetic acid, 



CH 3 COCH 2 COOH, 



which forms, with absorption of water, two molecules of 



