376 I. K. Phelps — Combustion of Organic 



It seems possible to draw the general conclusion from the 

 results recorded that organic substances which are oxidized 

 completely by the permanganate may be determined by the 

 process outlined above. It will also be seen that the use of 

 the rubber stopper in the boiling flask, with due care to prevent 

 its contact with the solution, does not introduce an appreciable 

 error. 



Wanklyn and Cooper* and others have noted the fact that 

 potassium permanganate, whether in acid or alkaline solution, 

 will not oxidize all organic substances (acetates, for example), 

 even at the boiling temperature. It is well known that a mix- 

 ture of concentrated sulphuric and chromic acids has a much 

 wider field of action in oxidizing organic compounds than the 

 permanganate. With hopes of applying this reagent more 

 widely to the determination of organic carbon, the experiments 

 about to be recorded were tried. 



Method of Oxidation with Chromic Acid. 



A concentrated mixture of chromic and sulphuric acids, 

 although a much more powerful oxidizer than potassium per- 

 manganate in aqueous solutions, fails to oxidize completely 

 many organic compounds. Thus Cross and Higginf have 

 shown that carbohydrates are among the number of organic 

 substances ; later Cross and Bevan find that carbohydrates and 

 many other substances are oxidized completely to a mixture of 

 carbon dioxide and monoxide. Messinger^: has proven that 

 carbon may be determined in organic compounds by passing 

 the mixed products, resulting from the oxidation with chromic 

 and sulphuric acids, through a short combustion tube, filled 

 with granular copper oxide and heated in a furnace — all of 

 which facts have been confirmed in my own experience. 



Ludwig§ has observed that the contact of carbon monoxide 

 with a mixture of chromic and sulphuric acids, especially 

 when hot, results in the oxidation of that gas to carbon dioxide. 

 This fact suggested the idea of substituting for the apparatus 

 described above a new form, adapted to retain the first products 

 of oxidation in prolonged contact with the oxidizing mixture. 

 This apparatus, shown in the accompanying figure, by means 

 of which, as the sequel shows, it has been found possible to 

 extend the availability of the oxidizing mixture, is put together 



*Phil. Mag. (5), vii, 138. 



f Jour. Chem. Soc, 1882, 113. 



% Ber., xxiii, 2756. 



§ Am. Chem. Pharm., clxii, 47. 



