1923] 



CAMP — CITRIC ACID AS A SOURCE OP CARBON 237 



there with NaOH. In the original method Ba(OH), was used to 

 absorb the CO* but NaOH was found more satisfactory, being 

 less difficult to handle in the air and forming no precipitate in 

 the tower. BaCI, is added just before titration and the excess 

 NaOH titrated in the presence of the precipitated carbonate 

 according to the method of Bear and Salter ('16). The end 

 point of the titration is very sharp but a little slow due to adsorp- 

 tion of the indicator by the particles of the precipitate. The 

 difference between the titration of a blank on the chemicals and 

 the titration of the determination represents CO,, 1 cc. of 0.5 

 N HC1 being equivalent to 3 mgms. of carbon. Concerning the 

 technical chemistry of the method the reader is referred to Friede- 

 man's work. 



Apparatus. — A single unit of the apparatus is shown in fig. 1, 

 and in pi. 14 is shown the equipment used, which included 4 such 

 units. The figure and plate are largely self-explanatory. The 

 tower (F) is made of glass tubing 25 mm. in internal diameter 

 blown on to tubing of 5-6 mm. internal diameter. The length 

 from "a" to "b" is 45-50 cm. and from "b" to "c" 30 cm. A 

 perforated porcelain filter plate is placed at "b" and the tower 

 filled about two-thirds full of glass beads ( one 4-mm. perforated 

 bead to two 3-mm. solid beads). When the joints are closed and 

 suction applied liquid in E is drawn up over the beads in F. 

 Carbon dioxide-free air is supplied by a soda-lime tower and the 

 aeration tube for B should be of very small diameter, drawn 

 down at the tip and bent as in fig. 1 to prevent the solution bac Ic- 

 ing up into the tube during heating. The suction must be steady 

 and a Richards pump was found very desirable; the bubbler G 

 aids in keeping the suction steady, and, the addition of a drop of 

 alkali and a drop of phenolphthalein indicates whether any CO, 

 is being carried over from the absorption tower. 



Reagents. — The following reagents are necessary : an oxidizing 

 mixture, consisting of 340 gms. of chromic acid crystals (chromic 

 trioxide) dissolved in 600 cc. of hot distilled water and diluted 

 to 1 liter with syrupy H,P0 4 ; syrupy H,PO«, 85 per cent, a good 

 commercial grade; cone. H,S0 4 , 1.84 sp. gr., a good commercial 

 grade; 0.5 N NaOH; 0.5 N HC1, standardized to be used for 

 titration; BaCl,.2H,0, 75 gms. per 500 cc. of solution (rough 



