These materials are in different proportions according to the barks. Grey bark chiefly contains chinchonine and tannin; Calisaya, or yellow bark, much quinine, and a little chinchonine; red bark holds quinine and chinchonine in nearly equal proportions; while the barks of New Granada chiefly contain chinchonidine and quinidine. The two latter alkaloids were definitively discovered in 1852 by M. Pasteur; although the Dutch chemist Heijningen had, in 1848, found what he called β quinine or quinidine. Chinchonidine is only second to quinine itself in importance as a febrifugal principle. _Quinine_ is a white substance, without smell, bitter, fusible, crystallized, with the property of left-handed rotatory polarization. The salts of quinine are soluble in water, alcohol, and ether. Of all the salts the bisulphate of quinine is preferred, because it constitutes a stable salt, easy to prepare, and containing a strong proportion of the alkaloid. It is very bitter and soluble, and crystallizes in long silky needles. It is prepared by adding sulphuric acid to the sulphate.[31] _Chinchonine_ differs from quinine in being less soluble in water, and being altogether insoluble in ether. It has the property of right-handed rotatory polarization. _Quinidine_ also has the property of right-handed rotatory polarization, and forms salts like those of quinine. It becomes green by successive additions of chlorine and ammonia. _Chinchonidine_ has not the property of turning green, and forms a sulphate almost exactly like sulphate of quinine.[32]