378 /. K. Phelps — Combustion of Organic 



tion flask, together with an amount of pure potassium dichro- 

 mate, which is known to be in excess of that required to oxi- 

 dize the organic substance. The flasks are connected, as 

 already described, with an appropriate amount of barium 

 hydroxide solution in the absorption flask and 10 cm3 of pure 

 water in the evolution flask and the vacuum obtained (as 

 described above) by boiling both flasks, the boiling being 

 stopped when the water in the evolution flask has decreased to 

 2 or 3 cm3 . Naturally, this boiling must be so regulated as not 

 to allow loss of the solid material in either flask. The vacuum 

 obtained, the tube containing the organic substance is broken 

 by shaking the flask, and 20 cm3 of concentrated sulphuric acid, 

 previously purified from organic material by heating to the 

 fuming point with a few crystals of potassium dichromate, are 

 run in through the funnel tube, when reduction of the chromic 

 acid soon becomes evident. While still hot, the acid is shaken 

 in the flask violently, the platinum foil hung in the neck serv- 

 ing to protect the rubber stopper. The flask is warmed to 

 approximately 105° C, the highest temperature to which, as 

 shown by Cross and Bevan,* a mixture of chromic and sul- 

 phuric acids may be safely heated without the disengagement 

 of oxygen gas. Water is then run in until the crystals of 

 chromic anhydride have disappeared and the danger of the 

 evolution of oxygen is past. The solution is heated to its boil- 

 ing point, care being taken that it shall not get under pressure, 

 which can easily be observed by opening momentarily the 

 stop-cock of the funnel tube and noting the direction of the 

 flow of water, contained in the funnel. The flask is shaken 

 and heated alternately for live minutes — a period of time 

 which appears to be sufficient to bring about the oxidation of 

 the small amount of carbon monoxide, originally produced. 

 Then more water (60-70 cm3 ) is introduced through the funnel 

 and the stop-cock between the boiling and absorption flasks 

 opened, when the carbon dioxide enters the absorption flask, 

 which is kept cool and shaken as before. The contents of the 

 evolution flask are then heated to boiling and a slow current of 

 air, freed from carbon dioxide by passage through potash bulbs, 

 allowed to enter through the funnel tube to keep the liquid 

 from undue bumping. The boiling is continued for fifteen 

 minutes, after which the excess of barium hydroxide is deter- 

 mined iodometrically and thus the carbon dioxide present esti- 

 mated as before. Table IV shows results obtained by the 

 treatment of ciystallized ammonium oxalate and cane sugar, 

 recrystallized from dilute alcoholic solution, in this manner. 



* Jour. Chem. Soc, liii, 889. 



