ACID PRODUCTION 



283 



7. Acidify 250 c.c. with 20 c.c. concentrated phos- 

 phoric acid (this liberates the volatile acids) and distil 

 to small bulk. 



The distillate "B" may contain formic, acetic, 

 propionic, butyric and benzoic acids. 



DISTILLATE " B." 

 (Volatile Acids.) 



i. Add baryta water till alkaline, 

 and evaporate to dryness. 



2. Add 50 c.c. absolute alcohol and allow 



to stand, with frequent stirring, for 

 two to three hours. 



3. Filter and wash with alcohol. 



FILTRATE 



may contain barium propionate, 

 barium butyrate. 



1. Evaporate to dryness. 



2. Dissolve residue in 150 c.c. water. 



3. Acidify with phosphoric acid and dis- 



til. 



4. Saturate distillate with calcium chlo- 



ride and distill over a few c.c. 



5. Test distillate for butyric acid: 



Add 3 c.c. alcohol and 4 drops con- 

 centrated sulphuric acid. 

 Smell of pineapple = butyric acid. 

 Propionic acid in small quantities 

 cannot be distinguished from buty- 

 ric acid by tests within the scope 

 of the bacteriological laboratory. 



RESIDUE 



may contain barium acetate, 

 barium formate, barium benzoate. 



1. Evaporate off alcohol and dissolve 



up the residue on the filter in hot 

 water and neutralise. 



2. Divide the solution into four por- 



tions: 



(a) Add ferric chloride solution. 

 Brown colour = acetic or for- 

 mic acids. 

 Buff ppt. = benzoic acid (see 



ether soluble acids). 

 (6) Add silver nitrate solution; 

 then add one drop am- 

 monia water, and boil. 

 Black precipitate of me- 

 tallic silver = formic acid. 



(c) Evaporate to dryness; mix 



with equal quantity of 

 arsenious oxide and heat 

 on platinum foil. 

 Unpleasant smell of cacodyl 

 = acetic acid. 



(d) Add a few drops of mercuric 



chloride solution in test- 

 tube, and heat to 70 C. 

 Precipitate of mercurors 

 chloride which is slowly 

 reduced to mercury = 

 formic acid. 



