274 



Misses M. Stephenson and M. D. Whei^iam. 



reached 60° for at least five minutes. The apparatus was then disconnected, 

 the baryta carefully washed into the filtering flask, and the excess titrated 

 with standard hydrochloric acid. A small and variable amount of barium 

 carbonate was always present and was separately estimated. The neutralised 

 liquid was filtered, the solid (barium carbonate) washed twice and then trans- 

 ferred into a flask fitted with a small reflux condenser (preferably ground 

 in) ; 10 c.c. of OTN HCi was then added to the contents of the flask and 

 the whole boiled for five minutes under the reflux condenser. The excess 

 HCI was back-titrated with baryta. 

 The method was tested as follows : — 



10 c.c. of a solution of acetic acid were titrated direct against O'lN 

 baryta, using phenol phthalein ; 10 c.c. of the same solution of acetic acid 

 were distilled into baryta as described above, and the results compared. The 

 following are the figures for the distillation : — 



A. 



C.c. 

 acetic acid 

 taken. 



B. 



C.c. 

 0-lN 

 Ba(OH) 2 

 taken. 



C. 



C.c. 

 0-lN 

 HCI used 

 for back 

 titration. 



D. 



C.c. 

 O-IN 



Ba(OH) 2 

 neutralised 

 by acetic 

 acid and 

 C0 2 [B-C]. 



E. 



C.c. 

 0-lN 

 Ba(OH) 2 

 neutralised 

 by C0 2 

 only. 



F. 



C.c. 



Ba(OH), 

 neutralised 



by acetic 

 acid [D-E]. 



Per cent, 

 of acetic 

 acid in 

 solution. 



10 

 10 



25 -8 

 25 -4 



2-6 

 1 -6 



23 -2 

 23 -8 



0-7 

 1 '4 



22 -5 

 22 -4 



1-35 

 1 34 



10 c.c. of acetic acid titrated direct = 22 - 1 c.c. "IN Ba(OH) 2 . 



. " . 10 c.c. acetic acid contain - 133 grm. = 1 33 per cent, compared with 1 '35 and 1 '34 by 

 the distillation method. 



The disappearance of acetic acid from the medium is summarized below, 

 and shown graphically on Curve 3. 



Day of 



Acetic acid present ; 



Acetic acid utilised ; 



experiment. 



grm. in 100 c.c. of medium. 



grm. in 100 c.c. of medium. 







-53 



-oo 



4 



0-49 



-04 



28 



-46 



0-07 



The growth of the organism was too small to admit of accurate estimation. 

 From this it appears that, in the conditions holding in this experiment, the 

 organism suffers from almost complete inability to use acetic acid as a source 

 ■of organic : food material. The slight disappearance of acetic acid is pro- 



