thylamino-benzaldehyde solution.

3. Add 2 c.c. potassium persulphate solution.

The presence of indol is indicated by the appearance of a delicate
rose-pink colour throughout the mixture which deepens slightly on
standing.

Indol is tested for in many laboratories by the ordinary
nitrosoindol reaction which, however, is not so delicate a
method as that above described. The test is carried out as
follows:

1. Remove the cotton-wool plug from the tube, and run in 1
c.c. pure concentrated sulphuric acid down the side of the
tube by means of a sterile pipette. Place the tube upright
in a rack, and allow it to stand, if necessary, for ten
minutes.

A rose-pink or red colour at the junction of the two liquids
= indol (_plus a nitrite_).

2. If the colour of the medium remains unaltered, add 2 c.c.
of a 0.01 per cent. aqueous solution sodium nitrite, and
again allow the culture to stand for ten minutes.

Red colouration = indol.

NOTE.--In place of performing the test in two stages as
given above, 2 c.c. concentrated _commercial_ sulphuric,
hydrochloric, or nitric acid (all of which hold a trace of
nitrite in solution), may be run into the cultivation. The
development of a red colour within twenty minutes will
indicate the presence of indol.

~5a. Phenol Production.~--

_Medium Required_:

Nutrient bouillon.

_Reagents Required_:

Hydrochloric acid, concentrated.
Millon's reagent.
Ferric chloride, 1 per cent. aqueous solution.

METHOD.--

1. Prepare cultivation in a Bohemian flask containing at least 50 c.c.
of medium, and incubate.

Test for phenol in the following manner:

2. Add 5 c.c., 25 per cent. sulphuric acid to the cultivation and
connect up the flask with a condenser.

3. Distil over 15 to 20 c.c. Divide the distillate into three portions
a, b and c.

4. Add to (a) 0.5 c.c. Millon's reagent and boil.

Red colour = phenol.

5. Add to (b) about 0.5 c.c. ferric chloride solution. Violet colour =
phenol.

(If the distillate be acid the reaction will be negative.)

6. Add to (c) bromine water. Crystalline white ppt. of tribromo-phenol
= phenol.

NOTE.--If both indol and phenol appear to be present in
cultivations of the same organism, it is well to separate
them before testing. This may be done in the following
manner:

1. Prepare in