MADDER.

259

and the washing repeated three to five times. The last washings assume acolour not unlike red Hermitage wine.* When the liquid has run off as far aspossible the garancin is farther dried, first by being pressed—in powerfulhydraulic presses—into cakes, which, after having been stove-dried, are brokenup and reduced to powder by a mill.

The washings from garancin—especially the first, which contains most ofthe acid—are applied in various ways, either for washing illuminating gas, andremoving ammonia therefrom, or for dissolving phosphatic minerals for themanufacture of artificial manures and the like; the subsequent washingscontain, according to recent reports,! a peculiar pigment, and also oxalic acid.

One hundred kilos, of madder produce from 34 to 37 kilos, of garancin,according to the quality of the madder employed. The superior qualitiesyield a smaller quantity of garancin than the inferior. When madder whichhas not been previously washed is aCted upon by acid, as just described, theresult is a very dark—almost carbonised—material. This colouration is dueto the decomposition of the chlorogenin, which is converted into chlorrubin.

There are several points connected with the manufacture of garancin whichare scarcely or not at all explained by Science, and, moreover, its preparationfrom Zealand madders especially requires far more careful study and attentionthan is the case with Avignon or other madders grown in Southern Europe.What is the real and essential action of the acids in producing garancin is notknown. It has been thought that they aCted by breaking up the woody fibre,tearing it asunder, and letting the water get access to the colouring particlespreviously enclosed, and so transferring them to the dye-bath; but theweakness of the acids which can be employed, consistent with successfulissue, is fatal to this explanation. The supposition that the colouring matteris in a state of combination with some earthy base, as lime and magnesia, andthat it cannot dye while so combined, and that the acids liberate the colouringmatter by combining with the bases, is an explanation not supported by anyreal fadts or experiments. It appears probable that some chemical affinitiesof a more refined and subtle nature are brought into play. It is likely thatthe acid employed forms a combination with the colouring matter, which isitself easily decomposed even by water. It is not in accordance with analogy tosuppose any formation or creation of colouring matter, but simply that aportion of the colouring matter is present in some form or other upon whichwater cannot a< 5 t, whilst acids in some unknown manner make it susceptibleto the influence of water. There are some ascertained fadts bearing upon theaction of acids upon the colouring matter of madder, which, though they haveno dirett practical significance, are full of suggestions. It is very well knownthat garancin is not the same as a dyeing material as madder. Its coloursare not so fast, either as against soaping, clearing, or exposure to air ; the acidhaving evidently, if not injured, at least somewhat altered, the colouringmatter in setting it free. It is no longer what it was in the untouched root.Chemistry has hitherto failed to explain this, which, as a fa&, stands in oppo-sition or exception to other known cases of the attion of acids upon thecolouring matter of this root. For example, a piece of Turkey red cloth ordark purple dyed with madder can be treated with strong sulphuric acid, which

* Genuine Hermitage rouge has a delicate yellowish rose-red shade.

t See “ Chemical News,” vol. xxi., p. 58, February 4, 1870.