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.)
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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.

3. Filter and wash with alcohol.
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FILTRATE RESIDUE
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may contain b