Brucine melts at 151° into a pale yellow liquid, at higher temperatures becoming deep-brown. If the lower disc, after melting, be examined, no crystals are observed, the residue being quite transparent, with branching lines like the twigs of a leafless tree; light mists, produced rather by decomposition than by true sublimation, condense on the upper disc at 185°, and above.
Saponin neither melts nor sublimes; it begins to brown about 145°, is almost black at 185°, and quite so at 190°.
Delphinine begins to brown about 102°; it becomes amber at 119°, and melts, and bubbles appear. There is no crystalline sublimate; residue not characteristic.
Pilocarpine gives a distinct crystalline sublimate at 153°; but thin mists, consisting of fine dots, may be observed as low as 140°. Pilocarpine melts at 159°; the sublimates at 160° to 170° are in light yellow drops. If these drops are treated with water, and the water evaporated, feathery crystals are obtained; the residue is resinous.
Theine wholly sublimes; the first sublimate is minute dots, at 79°; at half a degree above that very small crystals may be obtained; and at such a temperature as 120°, the crystals are often long and silky.
Theobromine likewise wholly sublimes; nebulæ at 134°, crystals at 170°, and above.
Salicin melts at 170°; it gives no crystalline sublimate. The melted mass remains up to 180° almost perfectly colourless; above that temperature browning is evident. The residue is not characteristic.
Picrotoxin gives no crystalline sublimate. The lowest temperature at which it sublimes is 128°; the usual nebulæ then make their appearance; between 165° and 170° there is slight browning; at 170° it melts. The residue, slowly cooled, is not characteristic.
Cantharidin sublimes very scantily between 82° and 83°; at 85° the sublimate is copious.
The active principles of plants may, in regard to their behaviour to heat, be classed for practical purposes into—