1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 221 



oxidation was carried out in the usual manner. One distillate 

 was titrated directly by the Messenger method. On adding the 

 alkali a white precipitate formed, the titration being only 4.0 cc. 

 of thiosulphate on a blank of 23.15 cc. The second distillate was 

 redistilled with 10 cc. of 10 per cent NaOH and 30 cc. of 3 per 

 cent Hj0 2 and the distillate from this titrated. The titration 

 was 23.15 with a blank of 23.25 cc. The procedure was repeated 

 with small amounts of dextrose with the following results: 



Thiosulphate 

 (cc.) 



Single distillation 22 . 35 



Redistilled 23.25 



Redistilled 23.2 



Blank 23.25 



Shaffer and Marriott ('13) stated that a small amount of inter- 

 fering substance, which was not eliminated by the redistillation, 

 was formed when dextrose was oxidized by K 2 Cr 2 7 in the presence 

 of HjSO<. Such a substance is not in evidence here, though it 

 might be formed under certain conditions. 



Using the apparatus and general procedure described under 

 " Methods" a number of determinations were made on known 

 solutions of citric acid, varying the time of oxidation, amount 

 of mineral acid, volume of solution, and the amount of citric 

 acid. Some of these results are given in table i. The results 

 varied more than if an efficient condenser had been used. Part 

 of the results shown were obtained from a single distillation, 



part were redistilled. 



It may be seen that the yield with H s PO< as the mineral acid 

 was around 80 per cent and very variable. Where H 2 SO< was 

 used the yield varied from 87 per cent to 95 per cent, depending 

 on the volume of the solution, the amount of mineral acid, and 

 the period of oxidation. No one of these factors, however, is 

 as important as maintaining the same conditions for all determina- 

 tions. The amount of solution, especially, seemed to affect the 

 yield very slightly, even when raised to 200 cc, but this made 

 distilling more difficult. On the whole, about the best conditions 

 indicated by the results of a large number of experiments were 

 (1) a volume of 50 to 125 cc, (2) about 1 per cent H 2 S0 4 , (3) 



A 



