DETECTION OF DYES. 665

a. The colour of the cloth changes to a brown, and is restored to a yellow

by a very dilute acid .. .. Turmeric.

b. The cloth is nearly decolourised.Fustic.

c. The soap has little or no adtion. In this latter case we may haveweld, berries, or bark.

To distinguish these three colours, we take a fresh swatch and submit it toa bath of very dilute boiling sulphuric acid. If the colour fades it is weld ;if it does not change it is berries or bark. We then take another swatch andsoak it in a solution of tin crystals. If the colour changes to orange it isberry-yellow. If scarcely affedted it is bark or flavin.

If we suspedt a bottom of annatto we soak a swatch in concentrated sul-phuric acid. The colour changes suddenly to greenish blue. Annatto is theonly tindtorial body presenting this readtion. Bark, berries, fustic, turmeric,and weld are all bleached by chlorine. Annatto resists this reagent. Fustet(young fustic) is rarely met with, except in wool-dyeing.

Chrome Yellows and Oranges.—Sulphuretted hydrogen or alkalinesulphides blacken them. They are destroyed by caustic soda.

Annatto.—Chlorine and bleaching-liquor have little adtion. Concen-trated sulphuric acid turns it a bluish-green. Nitric acid discharges.

D. REDS.

The red dyes that may present themselves are the following:—

1. Cochineal.

2. Brazil wood, &c.

3. Madder and garancin.

4. Safflower and carthamin.

5. Aniline-red.

6. Murexide.

7. Corallin.

8. Weed-colours, orchil, cudbear, &c.

We begin by ascertaining the presence or absence of madder-red. Weplace in four glasses or capsules the following reagents :—Boiling soap-lyes,caustic ammonia, citric acid (or lemon juice), a mixture of equal parts of tincrystals, hydrochloric acid, and water. In each of these a swatch is plunged.If all four remain unattacked we have madder-red. If there is a change weinfer its absence and-the presence of one of the other reds.

Complete decolouration by soap-lyes indicates safflower. In this case thecolour reappears with its original shade on washing in pure water andbrightening with citric acid. If on washing with water and brightening thecolour reappears fainter, we have aniline red. If the washing and brighteningchange the red to an orange or yellow, we have cochineal or Brazil-wood.We may distinguish between these two colours as follows :—A swatch of theoriginal fabric, steeped in sulphuric acid, is turned a cherry-red if it beBrazil-wood, and a yellowish orange if cochineal.

Murexide.—It is discharged by citric acid and by boiling soap-lye.

Corallin.—If a swatch is digested in hot alcohol the colour is extra&ed.The addition of ammonia then brightens the liquid.

Weed-Colours, Orchil, Cudbear, &c.—Destroyed by solution of tincrystals.