Later quinidine and cinchonidine were discovered, and subsequently several other alkaloids, but in smaller quantity.
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.
A mixture of the cinchona alkaloids, consisting principally of cinchonidine sulphate, with smaller quantities of the sulphates of quinine and cinchonine, is sold under the name of "quinetum" at a cheaper rate than quinine.