COLOURING MATTER IN COTTON.

39

Colouring Matter B.

This substance is deposited from its solution in boiling alcohol as a brownpowder, which, after being filtered off and dried, forms coherent masses ofa colour varying from light to dark brown, which may be easily broken, thefradture being dull and earthy. In boiling water it softens and yields a darkbrown cake. It is almost insoluble in cold alcohol, and when it has oncebeen dried it dissolves with great difficulty even in boiling alcohol. By thisproperty it may easily be distinguished from the other colouring matter, whichit closely resembles in most other respedts. When heated on platinum, itburns without previously melting; and the carbonaceous residue burns awaywith difficulty, leaving at last a bulky white or yellowish ash. This ash is notalkaline, and consists principally of alumina and sulphate of lime. The ashwas in most cases so considerable that Dr. Schunck was led to suspedt thatthis colouring matter might possibly be a compound of the other with someearthy base, in which case the striking similarity in the properties andreactions of the two substances would have admitted of an easy explanation.In order to submit this supposition to the test of experiment, he took someof the colouring matter B, pounded it very fine, added a little concentratedsulphuric acid and then absolute alcohol, after which the whole was well stirredin a mortar and left to stand for some time. The liquid, which had a browncolour, was filtered and mixed with water, which gave a brown precipitate.This was filtered off, washed with water, and dissolved in boiling alcohol. Thesolution left, on evaporation, a brown resinous residue, which was almostinsoluble in cold alcohol, and contained, therefore, none of the colouringmatter A.

In determining the composition of this substance, results were obtainedwhich, after deducing the ash, correspond in 100 parts to—

I.

II.

III.

IV.

V.

Mean.

c ..

•• 57'28

57'53

57-32

58-47

58-26

5777

H ..

.. .. 6 25

6*26

6-32

577

5-65

6-05

N . .

• • • • 9'39

9‘59

9*53

777

7‘43

8-74

0 ..

.. 27-08

26‘62

26-83

2 7'99

28-66

2 7'44

IOO'OO

IOO'OO

IOO'OO

IOO'OO IOO'OO

It will be

seen that in this

case, as

in that of colouring

matter

A, there

a wider discrepancy in the numbers yielded by analysis than ever takes placewith a perfectly pure substance. Nevertheless the composition of colouringmatter B, as represented by the mean of the numbers just given, approachesso closely that of colouring matter A from East-Indian cotton as to make itprobable that, when pure, the two bodies do not differ in composition from oneanother.*

From what has just been stated it may be inferred that, as regards theirchemical properties, these colouring matters possess very little interest. It issimply the fadt of their being the cause of the yellow or brownish tingenatural to raw cotton which gives them any importance, and makes a

* It is quite possible that these colouring matters may be products of decomposition derivedfrom some other substance existing in the fibre, and that they may consequently vary incomposition according to the strength of the solvent used for extraction, the time duringwhich it aCts, and other circumstances.