In the Red bark, Fourcroy detected also a portion of citric acid, some muriate of ammonia, and muriate of lime. Upon which of these principles the tonic and febrifuge virtues of bark depends, has ever proved a fruitful source of controversy. Deschamps attributed them to Cinchonate of Lime, and asserted that two doses of thirty-six grains each, would cure any intermittent. Westering considered Tannin as the active constituent; while M. Seguin assigned all the virtues to the principle which precipitates gallic acid, and which, as it has been before stated, he mistook for gelatine. Fabroni concluded from his experiments, that the febrifuge power of the bark did not belong exclusively and essentially to the astringent, bitter, or to any other individual principle, since the quantity of these would necessarily be increased by long boiling, whereas the virtues of the bark are notoriously diminished by protracted ebullition. This argument however will not go far, when we consider the chemical changes which the liquid is known to suffer during that operation, and by which a considerable portion of its matter is rendered insoluble. Such was the state of our knowledge respecting the composition of the Cinchona, when Pelletier and Caventou, guided by analogy, were led to infer the presence of an alkaline element of activity in its composition. The merit, belonging to the researches of these eminent chemists, does not so much consist in the discovery of new elements, as in the proofs which they have furnished of the well known principle, Cinchonine, being a salifiable base,[[461]] and in demonstrating the peculiar states of combination in which it exists in the different species of Cinchona.
1. Cinchona Lancifolia.
Their analysis of the Pale Bark, furnished the following principles.
1. Acidulous Kinate of Cinchonia.[[462]] 2. A green fatty matter. 3. Red Colouring matter, slightly soluble. 4. Ditto soluble. (Tannin.) 5. Yellow colouring matter. 6. Kinate of Lime. 7. Gum. 8. Starch. 9. Lignin.
Cinchonia, when obtained in an isolated form,[[463]] is distinguished by the following characters and habitudes.
It is white, transparent, and crystallizes in the form of needles; it has but little taste, circumstance depending upon its comparative insolubility, as it requires no less than 7000 parts of cold water for its solution; in boiling water it is soluble in 2500 times its weight, but a considerable part separates, on cooling. In alcohol and the acids it is much more soluble, and imparts to such menstrua the characteristic bitter of the bark; it dissolves only in small quantities in the fixed and volatile oils, or in sulphuric ether. Cinchonia restores the colour of litmus which has been reddened by an acid. With acids it combines and forms neutral salts, of which the solubility and crystalline form vary with the acid employed.
Sulphate of Cinchonia, easily crystallizable and moderately soluble, has been found to consist of Cinchonia 100, Sulphuric acid 13·02.
Nitrate of Cinchonia, uncrystallizable, and sparingly soluble.
Muriate of Cinchonia, crystallizes in very beautiful needles, and is more soluble than the preceding salts.
Oxalate of Cinchonia, nearly insoluble; hence by pouring oxalic acid, or oxalate of ammonia into solutions of any of the soluble salts of cinchonia, we obtain a very white and abundant precipitate, which might be mistaken for oxalate of lime; it is however soluble in an excess of acid, and in alcohol.