1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 219 



Hg - - Hg - (X /R' 



so/ \ / 



>Hg >C 



SO, 



^Hg - - Hg - o/ \ 



R' 



In a later publication ('98a) he stated that this formula was 

 correct if the compound was dried at 110° C, but if dried at a 

 lower temperature it probably had a composition represented by 

 [(SO,Hg) 2 .3HgO) 3 .4CO.R,. Oppenheimer ('99) arrived at a 

 different formula and factor for conversion to acetone and stated 

 that there was no difference in the compound whether it was 

 dried at 110° C. or at a lower temperature. The uncertain 

 composition of this compound prevented a critical study of this 

 method, since it was impossible to determine accurately the 

 actual yield of acetone from citric acid. Theoretically 1 molecule 

 of citric acid should yield 1 molecule of acetone, but since the 

 rate of oxidation in some degree controlled the yield it was evident 

 that the yield did not, in all probability, reach 100 per cent in 

 any case. On account of this fact it was the feeling of the writer 

 that some better method for determining the acetone might lead 

 to a much improved method. 



Pratt ( '12) stated that the Messenger titration was not adapted 

 to this method; however, Shaffer ('08) offered a method for the 

 determination of /3-oxybutyric acid based upon the oxidation of 

 that compound to acetone by chromic acid in the presence of 

 HjSO*, and the determination of acetone by the Messenger 

 method. The interference due to the formation of volatile pro- 

 ducts from the oxidation of sugar, which were probably of an 

 aldehyde nature, was overcome by redistillation of the first 

 distillate, after rendering it alkaline with NaOH and adding 

 30 cc. of 3 per cent H 2 2 . It was at first thought that the yield 

 was 100 per cent, but in a later paper Shaffer and Marriott ('13) 

 showed that the yield was about 90 per cent of the theoretical and 

 that some of the products of the oxidation of sugar were not elimi- 

 nated by the redistillation, although the error from this source was 

 negligible. Marriott ( ' 13) , studying the distillation of acetone and 

 its determination by the Messenger method, showed that by 

 boiling 10 minutes the acetone was completely removed to the 



