218 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



JVol. 10 



gelatinous and difficult to filter as compared with that from 

 63 per cent alcohol. 



Several attempts have been made to base a quantitative method 

 on the fact that KMnO< oxidizes citric acid to acetonedicarbonic 

 acid which in turn decomposes at temperatures above 80° C. to 

 form acetone. Jorgensen ( '07) oxidized citric acid with KMn0 4 

 under various conditions but his yields of acetone were uniformly 

 low. Fleischer ("72) obtained acetone only in the presence of 

 mineral acid, but Jorgensen obtained it in the presence of NaOH. 



Kunz ('14) modified Stahre's qualitative test and weighed 

 the precipitate of pentabromacetone. This method has been 

 used considerably by biochemists for determining small quantities 

 of citric acid and has been tentatively adopted by the Association 

 of Official Agricultural Chemists ('09). Following the lead of 

 others Salant and Wise ('16) added DenigeY reagent to the solu- 

 tion to be tested, oxidized with KMnO<, and weighed the mercury 

 complex. McClure and Sauer ('22) studied both of the above 

 methods and decided that on the whole the pentabromacetone 

 method of Kunz was best. Both methods require tedious mani- 

 pulation, are easily interfered with by substances other than 

 citric acid, and neither gives a very good yield of the compound 

 to be weighed. 



Pratt ('12) distilled off the acetone as fast as it was formed 

 the interaction of citric acid and KMnO«, the latter being 

 added slowly through a separatory funnel as the reaction pro- 

 ceeded. The receiver flask contained DcnigeV reagent. When 

 the reaction was complete the distillate was relluxed and the 

 precipitate weighed. Willaman ('16) modified the distillation 

 arrangement and substituted a titration for the gravimetric 

 determination of the acetone in the complex precipitate. This 



was a material improvement, since gravimetric methods are to 



be avoided wherever possible in the routine of physiological 

 work where many analyses must be made. 



Any method based upon the determination of the mercury- 

 acetone complex of Denig6s is necessarily empirical and is more 

 difficult still in that the mercury-acetone complex is probably 

 of varying as well as uncertain composition. Denig6s ( '98) gave 

 for this complex the formula: 





