r changes, if any, which ensue. This is
a very useful test and should not be omitted, and it is often employed
in the testing of indigo dyed goods with nitric acid, those of logwood
with hydrochloric acid, alizarine with caustic soda, and many others. It
is simple and easy to carry out, and only takes a few minutes.

To make a complete series of tests of dyed fabrics there should be
provided the following reagents:--

1. Strong sulphuric acid, as bought.
2. Dilute sulphuric acid, being the strong acid diluted with twenty
times its volume of water.
3. Concentrated hydrochloric acid.
4. Dilute hydrochloric acid, 1 acid to 20 water.
5. Concentrated nitric acid.
6. Dilute nitric acid, 1 acid to 20 water.
7. Acetic acid.
8. Caustic soda solution, 5 grams in 100 c.c. water.
9. Ammonia (strong).
10. Dilute ammonia, 1 strong ammonia to 10 water.
11. Carbonate of soda solution, 6 grams in 100 c.c. water.
12. Bleaching powder solution, 2 deg. Tw.
13. Bisulphite of soda, 72 deg. Tw.
14. Stannous chloride, 10 grams crystals in 100 c.c. water, with a
little hydrochloric acid.
15. Methylated spirit.

Small swatches of the dyed goods are put in clean porcelain basins, and
some of these solutions poured over them. Any change of colour of the
cloth is noted, as well as whether any colour is imparted to the
solutions. After making observations of the effects in the cold the
liquids may be warmed and the results again noted. After being treated
with the acids the swatches should be well washed with water, when the
original colour may be wholly or partially restored.

To give tables showing the effects of these reagents on the numerous
dyes now known would take up too much room and not serve a very useful
purpose, as such tables, if too much relied on, leave the operator
somewhat uncertain as to what he has before him. The reader will find in
Hurst's _Dictionary of Coal-tar Colours_ some useful notes as to the
action of acids and alkalies on the various colours that may be of
service to him.

Alizarine and the series of dye-stuffs to which it has given its name,
fustic, cochineal, logwood and other dyes of a similar class require the
fabric to be mordanted, and the presence of such mordant is occasionally
an indirect proof of the presence of these dyes.

To detect these mordants, a piece of the swatch should be burnt in a
porcelain or platinum crucible over a Bunsen burner, care being taken
that all carbonaceous matter