ies of
elaborate tables showing the action of various chemical reagents on
fabrics dyed with various colours, and such indeed serve very little
purpose, for it is most difficult to describe the minor differences
which often serve to distinguish one colour from another. Instead of
doing so we will point out in some detail the methods of carrying out
the various tests, and advise all dyers to carry these out for
themselves on samples dyed with known colours, and when they have an
unknown colour to test to make tests comparatively with known (p. 219)
colours that they think are likely to have been used in the production
of the dyed fabric they are testing.

One very common method is to spot the fabric, that is to put a drop of
the reagent on it, usually with the aid of the stopper of the reagent
bottle, and to observe the colour 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 20
times its volume of water.

3. Concentrated hydrochloric acid as bought.

4. Dilute hydrochloric acid, 1 acid to 20 water.

5. Concentrated nitric acid as bought.

6. Dilute nitric acid, 1 acid to 20 water.

7. Acetic acid.

8. Caustic soda solution, 5 grammes in 100 c.c. water.

9. Ammonia (strong).

10. Dilute ammonia, 1 strong ammonia to 10 water.

11. Carbonate of soda solution, 5 grammes in 100 c.c. water.

12. Bleaching powder solution, 2 deg. Tw.

13. Bisulphite of soda, 72 deg. Tw.

14. Stannous chloride, 10 grammes 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 (p. 220)
of the fabric 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