74 REPORT—1848. 
afforded crystals of alizarin, together with white masses of fat acid. Hardly — 
any residue remained undissolved by the alcohol. 
The preceding observations have a great bearing on the manufacture and 
treatment of garancin. Garancin is the technical name for a preparation of 
madder, which is obtained by treating madder with hot sulphuric acid until 
it has acquired a dark brown colour, then adding water, straining and wash- 
ing until all the acid is removed. ‘The advantages which garancin has over 
madder are, that it dyes finer colours, that the part destined to remain white 
does not acquire any brown or yellow tinge, and that its tinctorial power is 
greater than that of the madder from which it has been prepared. These 
effects have been attributed to various causes. It has been asserted that the 
sulphuric acid destroys the gum, the mucilage, the sugar, &c., and leaves the 
colouring matter unaffected; hence the greater beauty of garancin colours. 
To account for the greater proportional effect of garancin, it has been said 
that a part of the colouring matter is enclosed in cells of the wood, so that it 
cannot be dissolved by water, and that the sulphuric acid destroys the wood 
and liberates the colouring matter. T’o these views it may be objected, that 
concentrated sulphuric acid, though it does not affect alizarin, does not de- 
stroy any of the injurious substances in the root except the xanthin, while 
the rubiacin, the resins, and the pectic acid, escape its action: and as far 
as the wood is concerned, I can affirm that the operation succeeds equally 
well if acid be taken of such dilution as not to destroy woody fibre. I think 
that the superiority of garancin can only be attributed to two causes. In the 
first place, since, as I have shown above, there is a quantity of colouring 
matter in the root combined with lime and magnesia, by which it is rendered 
insoluble and incapable of dyeing, one effect of the acid is to remove this 
lime and magnesia, and to set the alizarin at liberty, which is then capable 
of application. In the second place, the xanthin, which has an injurious 
effect in madder-dyeing, is removed by washing with cold water, since it is 
not precipitated by acids, while the whole of the alizarin remains. If hot 
acid is employed, then the xanthin, or a part of it, is converted into that dark 
green substance which I have mentioned above as the product of the action 
of muriatic and sulphuric acid on xanthin; hence the dark colour of garancin, 
which is not owing to the charring of the woody fibre, as sometimes asserted. 
It must be remembered however that the rubiacin, the resins and the pectic 
acid, as well as the alizarin, remain uncombined after treatment with acid, — 
Hence it becomes necessary to add some base with which these substances © 
may combine, so as not to interfere with the action of thealizarin. I believe — 
it is the practice of garancin manufacturers to employ soda for this purpose. — 
I think it would be better to use a small quantity of lime-water. ¥ 
I may state in conclusion that the experiments described in this and the © 
last report were made with Avignon madder. The constituents and pro-— 
perties of Dutch madder, which is of rather a different nature, remain to be 
examined. 
I have been lately engaged in examining the colouring matter of fustic, — 
which 1 have prepared in a state of purity, but the investigation is not suffi- 
ciently advanced to justify me in making known the results. on the present. 
occasion. 
