5. Quinamine.—The crystals are anhydrous, fuse at 172° C., and form at a temp. of 20°, with 32 parts of ether or 100 parts of spirit of wine, a dextrogyre solution. Quinamine is even to some extent soluble in boiling water, and abundantly in boiling ether, benzol, or petroleum ether. The solutions of quinamine do not stand the thalleioquin test, nor do they display fluorescence; in acid solution, the alkaloid is liable to be transformed into an amorphous state. Quinamine moistened with concentrated nitric acid, assumes like paytine a yellow coloration. Its hydriodate is readily soluble in boiling water, but very sparingly in cold water, especially in presence of iodide of potassium, in which respect it is allied to quinidine as well as to paytine.
The more important properties of the Cinchona alkaloids may be summarized as follows:—
| a. | Hydrated crystals are formed by | Quinine, Quinidine, (or Conquinine). |
| No hydrated crystals by | Cinchonine, Cinchonidine, Quinamine. | |
| b. | Abundantly_ soluble in ether | Quinine, Quinidine, Quinamine, and the amorphous alkaloids. |
| Sparingly soluble in ether | Cinchonidine. | |
| Almost insoluble in ether | ||
| c. | Levogyre solutions afforded by | Quinine, Cinchonidine. |
| Dextrogyre solutions by | Cinchonine, Quinidine, Quinamine, Conquinamine, and the amorphous alkaloids. | |
| d. | Thalleioquin is formed by | Quinine, Quinidine, and also by Quinicine. |
| Thalleioquin cannot be obtained from | Cinchonine, Cinchonidine, Quinamine, nor from Cinchonicine. | |
| e. | Fluorescence is displayed by solutions of Quinine, Quinidine. | |
| No fluorescence in solutions of pure Cinchonine, Cinchonidine, Quinamine. | ||
Proportion of Alkaloids in Cinchona Barks—This is liable to very great variation. We know from the experiments of Hesse (1871), that the bark of C. pubescens Vahl is sometimes devoid of alkaloid.[1359] Similar observations made near Bogota upon C. pitayensis Wedd., C. corymbosa Karst., and C. lancifolia Mutis, are due to Karsten. He ascertained[1360] that barks of one district were sometimes devoid of quinine, while those of the same species from a neighbouring locality yielded 3½ to 4½ per cent. of sulphate of quinine.
Another striking example is furnished by De Vry[1361] in his examination of quills of C. officinalis grown at Ootacamund, which he found to vary in percentage of alkaloids, from 11·96 (of which 9·1 per cent. was quinine) down to less than 1 per cent. An extremely remarkable variation has also been displayed, as already alluded to at [p. 351], by Ledger’s Calisaya.
Among the innumerable published analyses of cinchona bark, there are a great number showing but a very small percentage of the useful principles, of which quinine, the most valuable of all, is not seldom altogether wanting. The highest yield on the other hand hitherto observed, was obtained by Broughton[1362] from a bark grown at Ootacamund. This bark afforded not less than 13½ per cent. of alkaloids, among which quinine was predominant. In Java too, Cinchona Ledgeriana (see pp. [341], [351]) has proved since to afford much more alkaloid than any American barks; as much as 13·25 per cent. of quinine have been observed in its bark.
The few facts just mentioned show that it is impossible to state even approximately any constant percentage of alkaloids in any given bark. We may however say that good Flat Calisaya Bark, as offered in the drug trade for pharmaceutical preparations, contains at least 5 to 6 per cent. of quinine.
As to Crown or Loxa Bark, the Cortex Cinchonæ pallidæ of pharmacy, its merits are, to say the least, very uncertain. On its first introduction in the 17th century, when it was taken from the trunks and large branches of full-grown trees, it was doubtless an excellent medicinal bark; but the same cannot be said of much of that now found in commerce, which is to a large extent collected from very young wood.[1363] Some of the Crown Bark produced in India is however of extraordinary excellence, as shown by the recent experiments of De Vry.[1364]
As to Red Bark, the thick flat sort contains only 3 to 4 per cent. of alkaloids, but a large amount of coloring matter. The quill Red Bark of the Indian plantations is a much better drug, some of it yielding 5 to 10 per cent. of alkaloids, less than a third of which is quinine and a fourth cinchonidine, the remainder being cinchonine and sometimes also traces of quinidine (conquinine).
The variations in the amount of alkaloids relates not merely to their total percentage, but also to the proportion which one bears to another. Quinine and cinchonine are of the most frequent occurrence; cinchonidine is less usual, while quinidine is still less frequently met with and never in large amount. The experiments performed in India[1365] have already shown that external influences contribute in an important manner to the formation of this or that alkaloid; and it may even be hoped that the cultivators of cinchona will discover methods of promoting the formation of quinine and of reducing, if not of excluding, that of the less valuable alkaloids.