PURPURIN.

251

than alizarin, and yielding, on elementary analysis, carbon 57-42, hydrogen5-39, the rest being oxgen. These figures may be formulated—

C20H20 O10 — (-'20H12O6or C20H22 O10 — C 2 oHi 2 0 6 +H 2 + 4 H 2 0 .There is little doubt but that rubianin may exist pre-formed in madder;(3) rubiretin, or a resin, a brown-coloured fusible substance ; formula—C 2 oHj 606 = C 2 oH I2 C>6 4 - H4.

6. By the adtion of boiling solutions of caustic alkalies rubian yields—(1) alizarin; (2) the resins a and described above ; (3) a yellow matterobtained in crystals from an alcoholic solution, and capable of subliming. Itis soluble in water, and has been named rubiadin. It contains—

Carbon .71-22

Hydrogen. 4-83

Oxygen .23-95

ioo-oo

By splitting up rubian with a peculiar ferment (erythrozym) contained inmadder it yields—(1) alizarin; (2) resins o and jS; (3) rubiafin, a yellow,crystalline sublimable matter, composed of—

Carbon .6g'30

Hydrogen. 4-56

Oxygen .26-14

ioo-oo

(4) rubiagin, a yellow matter, crystallising in small needles, and yielding—

Carbon .68-10

Hydrogen. 5-14

Oxygen .26-76

lOO'OO

Rubiadin and rubiafin appear to be one and the same substance, representableas C 20 Hi 6 0 6 . Rubiacin, or madder-orange, first discovered by Runge, may beobtained in brilliant flakes and masses, or in the shape of needles of a yellowcolour, resembling in shade iodide of lead. This substance is sublimableunchanged, and is sparingly soluble in boiling water, but readily soluble inboiling alcohol. It contains—

Carbon .67-01

Hydrogen. 3-28

Oxygen .29-71

ioo-oo

Rubiacin dissolves in sulphuric acid, yielding a yellow solution, unaffedled byheat. It is decomposed by boiling sulphuric acid. If rubiacin is dissolved inperchloride or pernitrate of iron, a brownish-red solution is formed, whichturns yellow on the addition of acids, and deposits rubiacic acid as a flocculentmass. This dissolves in alkalies, giving purple solutions, from which acidsre-precipitate the rubiacic acid unchanged. The ammoniacal solution gives adirty red precipitate with chlorides of barium and calcium. If hydrate ofalumina is added to an alcoholic solution of rubiacin it takes an orangecolour, whilst the liquid is rendered colourless. This aluminous lake »issoluble in caustic potassa, yielding a purple solution, a particular in which