_Reagents Required_: Hydrochloric acid, concentrated. Hydrochloric acid, 25 per cent. Sulphuric acid, concentrated (pure). Phosphoric acid, concentrated solution. Ammonia. Ammonium sulphate. Baryta water. Sodium carbonate, saturated aqueous solution. Absolute alcohol. Ether. Calcium chloride. Calcium chloride solution. Zinc carbonate. Copper sulphate saturated aqueous solution. Alcoholic thiophene solution (0.15 c.c. in 100 c.c.). Animal charcoal. Five per cent. sodium nitroprusside solution. Potassium bichromate. Schiff's reagent. Arsenious oxide. Ferric chloride, 4 per cent. aqueous solution. Silver nitrate, 1 per cent. aqueous solution. Lugol's iodine. Ten per cent. caustic soda solution. Hard paraffin wax (melting-point about 52° C.). METHOD.-- 1. Prepare cultivation in bulk (500 c.c.) in a litre flask and add sterilised precipitated chalk, 10 grammes. Incubate at the optimum temperature. 2. After incubation throw a piece of paraffin wax (about a centimetre cube) into the cultivation and connect up the flask with a condenser. The paraffin, which liquefies and forms a thin layer on the surface of the fluid, is necessary to prevent the cultivation frothing up and running unaltered through the condenser during the subsequent process of distillation. 3. Distill over 200 to 300 c.c. Use a rose-top burner to minimise the danger of cracking the flask; and to the same end, well agitate the contents of the flask to prevent the chalk settling. The distillate "A" will contain alcohol, etc. (_vide_ page 285); the residue "a" will contain the volatile and fixed acids. 4. Disconnect the flask and filter. The residue "a" then = filtrate B and residue b. [Illustration: FIG. 152.--Arrangement of distillation apparatus for acids, etc.] 5. Residue b. Wash the residue from the filter paper, dissolve by heating with dilute hydrochloric acid, and add calcium chloride solution and ammonia until alkaline. White precipitate insoluble in acetic acid = oxalic acid. 6. Make up filtrate B to 500 c.c. with distilled water and divide into two parts. 7. Acidify 250 c.c. with 20 c.c. concentrated phosphoric 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.) ¦ ¦ 1. 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.