1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 217 



recommended. For the analysis of citric acid by precipitation 

 as calcium citrate, L. and J. Gadais ('09) collected the nitrate 

 and washings from the first precipitation, concentrated to a small 

 volume, and reprecipitated, adding the second residue to the 

 first. This is probably the best modification of the use of the 

 calcium precipitation and increases the scope of the general 

 method considerably. 



Spindler ('03) pointed out that the calcium precipitation was 

 not quantitative but dependent upon the volume of the solution, 

 also that tri-calcium citrate, which is supposed to crystallize 

 with 4 H s O, loses water when dried at 100° C. Yoder ('11) 

 gave the limits of concentration of citric acid for producing a 

 precipitate with calcium acetate, without stirring or scratching 

 the sides of the beaker, as more than 0.32 gm. of acid in 100 cc. 

 of solution in the cold, and less than 0.32 gm. in 100 cc. of boiling 

 solution. The writer obtained by this method an appreciable 

 crystalline precipitate from 0.025 gm. of citric acid in 100 cc. 

 of solution by autoclaving at 15 pounds for 20 minutes. The 

 precipitates obtained at higher concentrations of citric acid were 

 well crystallized by this method and easily filtered. By preci- 

 pitating always from the same volume of solution it might be 

 possible to make use of the precipitation in the autoclave satis- 

 factorily. Calcium citrate is quantitatively insoluble in 50 per 

 cent alcohol, but apparently no work has been done on the water 

 content of the salt when precipitated by this method. 



Creuse (72) noted that the barium salt of citric acid was 

 almost totally insoluble in alcohol of 0.908 sp. gr., and he offered 

 a tentative formula for the precipitated compound of the general 

 structure: Ba0 3 .C 12 H 6 0n.2 H 2 0. He precipitated from a neutral 

 solution in 63 per cent alcohol. The precipitate by this method 

 is gelatinous but fairly heavy, and after standing over night can 

 be filtered, washing mostly by decantation. Jorgensen ('07) 

 offered a method for separating the barium salt of citric acid 

 from that of malic acid, based upon the comparative insolubility 

 of the citrate in 26 per cent alcohol and the greater solubility of 

 the malate in that solvent. The separation is not sharp and re- 

 quires considerable manipulation, depending on the relative 

 concentrations of the 2 acids. Moreover, the precipitate is very 



