1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 239 



beads to prevent bumping. Attach the flask to the apparatus, 

 make all the connections air-tight, and aerate briskly for 5 minutes 

 to free the apparatus from C0 2 . Close the pinch-cock at "a", 

 loosen the rubber stopper at "d", and raise the tower enough to 

 permit pipetting in 50 cc. of NaOH (25 cc. if only a small amount 

 of carbon is present). Connect again and start aerating steadily. 

 The solution automatically rises in the tower and covers the beads. 

 Start the water running through the condensers. Add 10 cc. 

 of the oxidizing solution through the separatory funnel A and 

 follow it with 25 cc. of H 2 P0 4 and 25 cc. of H 2 SO«. Heat cauti- 

 ously with a low flame until the reaction mixture boils, to avoid 

 forcing the solution back into the aeration tube. Continue 

 boiling and aeration for 30 minutes, cut off the heat, aerate briskly 

 for 5 minutes, then cut off the suction and raise the tower and 

 fix it in a clamp so that it drains into the flask E. Wash the tower 

 with small quantities of distilled water, using a total of 250 cc. 

 and allowing a few seconds for draining after each addition. 

 This method of washing removes practically all the NaOH to 

 the flask E, it being less difficult to free the tower of alkali when 

 NaOH is used than when Ba(OH) 2 , as in the original method, 

 since there is no precipitate of BaCOi to hold back the solution. 

 Add 20 cc. of the BaCl 2 solution and 1 cc. phenolphthalein 

 and titrate. The difference between the titration of the determi- 

 nation and that of a blank gives the amount of HC1 equivalent 

 to carbon. 



Efficiency of the method. — Both Friedeman ('21) and Schollen- 

 berger ( ? 16) gave data to indicate that this method of oxidation 

 as applied to soils gave results approximating very closely those 

 given by the usual dry combustion methods. Friedeman ? s ('21) 

 figures on the combustion of cane sugar by his method indicated 

 about 98 per cent oxidation as compared with figures by the dry 

 combustion method. The writer was not equipped to carry out 

 dry combustions but combustions by the Friedeman method were 

 carried out on a number of solutions made up by weight as accu- 

 rately as possible and then checked by other methods. The figures 

 for the percentage of oxidation on duplicate determinations were 

 as follows: 



