BINARY MORDANTS.

305

applied as a discharge at all. The eye of an inexperienced observer inthese matters cannot fail to dete& that, after the cloth has been thoroughlycleared, the shades given by the alumino-stannic mordant are far deeper andfar faster than those yielded by each of them separately. As a further proofof the effed of the two mordants together, the clearing operation (avivage)may be so far pushed as to lead to the partial destruction of the colours ofeach of the mordants singly, whilst those of the compound mordant will befound to have resisted this energetic adion. The following results of ex-periments confirmatory of M. Schlumberger’s opinion may be useful here:—A piece of white calico was taken and mordanted with acetate of alumina,the mordant was fixed and dunged, a portion was dyed with Avignon andanother portion with Alsace madder, and cleared. After this the pieces werecut up into swatches of 50 square centimetres, and these were incineratedwith proper precautions. In the ash the amounts of lime and alumina werequantitatively estimated, leading to the undermentioned results :—

Quantities by weightin grammes.

1.

2 .

3 -

4 '

5 -

6 .

7 -

8 .

9 -

10.

White cotton without any preparation but bleaching..White cotton as above, but passed through chalk-\milk of the same strength as that used in the dye-beck, and next washed in water very slightly [

acidulated with acetic acid.J

Mordanted and cleansed cloth.

The same dyed with Alsace madder .

The same as No. 4, but cleared .

Mordanted and cleansed cloth dyed with Avignon)

madder.I

The same as No. 6, but cleared .

Cloth properly mordanted and cleansed, dyed with\Alsace madder, with the addition of one-sixth off

its weight of chalk in the beck. )

The same as No. 8, but cleared .

The same as No. 2 above, but experiment repeated ..

Lime. Alumina.

0*01 —

0*01

0*005

1-25

0*06

1*27

0*05

0*42

0*23

1*28

0*17

0*21

0*23

1*29

0*20

0*25

0*005

_

We learn, from the above-quoted results, that white unmordanted calico aswell as the mordanted material does not retain chalk by being passed throughchalk-milk, or at least does not contain any of that material after being washedin water slightly acidulated with acetic acid; but it is different during thedyeing process, and after the clearing process the relation of the alumina tothe lime is 2 atoms of alumina for 3 atoms of lime.* During the dyeingprocess there is dissolved ahzarate of lime, which combines with the mor-danted portions of the tissue. The clearing process takes away the lime, andstill more of the alumina, but leaves a definite compound of alizarin, lime,and alumina. The analysis of the dyes obtained with oxide of iron as base

* In the opinion of many competent authorities there is little foundation for the view thatchalk adds to the fastness of madder colours, by forming a triple compound of colour, alumina,and lime. In using pure alizarin the smallest quantity of lime adts injuriously, by diminishingthe strength of the colour. In crude madder there are not merely acids, but other colouringmatters, which combine with the lime and allow the alizarin to produce its full effedt.

X