NATURE OF THE PROCESS. 267 



by experiment regarding the process of combus- 

 tion at low temperatures. 



If we examine the action of oxygen upon such a 

 substance as alcohol which contains a large quantity 

 of hydrogen, we find most distinctly, that the 

 direct formation of carbonic acid is the last stage 

 of its oxidation, and that it is preceded by a series 

 of changes, the last of which is a complete com- 

 bustion of the hydrogen. Aldehyde, acetic acid, 

 formic acid, oxalic acid, and carbonic acid, form 

 a connected chain of products arising from the 

 oxidation of alcohol; and the successive changes 

 which this fluid experiences from the action of oxy- 

 gen may be readily traced in them. Aldehyde is 

 alcohol minus hydrogen ; acetic acid is formed by 

 the direct union of aldehyde with oxygen. Formic 

 acid and water are formed by the union of acetic 

 acid with oxygen. When all the hydrogen is 

 removed from this formic acid, oxalic acid is pro- 

 duced ; and the latter acid is converted into 

 carbonic acid by uniting with an additional portion 

 of oxygen. All these products appear to be formed 

 simultaneously, by the action of oxidising agents on 

 alcohol ; but it can scarcely be doubted, that the 

 formation of the last product, the carbonic acid, 

 does not take place until all the hydrogen has been 

 abstracted. 



The absorption of oxygen by drying oils certainly 

 does not depend upon the oxidation of their carbon ; 

 for in raw nut-oil, for example, which was not free 



