Later quinidine and cinchonidine were discovered, and subsequently several other alkaloids, but in smaller quantity.
The other alkaloids are distinguished from quinine thus: quinidine resembles quinine, but is dextro-rotatory, and the iodide is very insoluble in water; the solution of cinchonidine, which is laevo-rotatory, does not give the thalleoquin test, nor fluorescence; cinchonine resembles cinchonidine in these respects, but is dextrorotatory.
Commercial sulphate of quinine frequently contains from I tc 10% of cinchonidine sulphate, owing to the use of barks containing it.
The sulphate of cinchonidine is more soluble than that of quinine; and, when 1 part of quinine sulphate suspected to contain it is nearly dissolved in 24 parts of boiling water, the sulphate of quinine crystallizes out on' cooling, and the cinchonidine is found in the clear mother liquor, from which it can be precipitated by a solution of potassium and sodium tartrate.
Samples of quinine in which cinchonidine is present usually contain a smaller percentage of water than the pure sulphate.