It may be expected that the substances mentioned under the heads 1, 2, and 3 will be, in general, fully obtained by degrees. This is not the case, however, as regards piperin and picric acid.
IV. The watery fluid is now similarly shaken up with benzene, and the benzene removed and evaporated. Should the evaporated residue show signs of an alkaloid (and especially of theine), the watery fluid is treated several times with a fresh mixture of benzene, till a little of the last-obtained benzene extraction leaves on evaporation no residue. The benzene extracts are now united, and washed by shaking with distilled water; again separated and filtered, the greater part of the benzene distilled from the filtrate, and the remainder of the fluid divided and evaporated on several watch-glasses.
The evaporated residue may contain theine, colchicine, cubebin, digitalin, cantharidin, colocynthin, elaterin, caryophylline, absinthin, cascarillin, populin, santonin, &c., and traces of veratrine, delphinine, physostigmine, and berberine.
A remnant of piperin and picric acid may remain from the previous treatment with petroleum ether.
THE BENZENE RESIDUE FROM THE ACID SOLUTION.
| 1. It is Crystalline. | 2. It is Amorphous. |
| A. Well-formed, Colourless Crystals. | A. Colourless or Pale Yellow Residue. |
| α. Sulphuric acid dissolves the hair-like crystals without change of colour; evaporation with chlorine water, and subsequent treatment with ammonia, gives a murexide reaction. | α. Sulphuric acid dissolves it at first yellow; the solution becoming later red. Fröhde’s reagent does not colour it violet. |
| Theine. | Elaterin. |
| β. Sulphuric acid leaves the rhombic crystals uncoloured. The substance, taken up by oil, and applied to the skin, produces a blister. | β. Sulphuric acid dissolves red; Fröhde’s reagent violet-red;[333] tannic acid does not precipitate. |
| Cantharidin. | Populin. |
| γ. Sulphuric acid leaves the scaly crystals at first uncoloured, then slowly develops a reddening. It does not blister. Warm alcoholic potash-lye colours it a transitory red. | γ. Sulphuric acid dissolves it with a red colour; Fröhde’s reagent[334] a beautiful cherry-red; tannic acid precipitates a yellowish-white. |
| Santonin. | Colocynthin. |
| δ. Sulphuric acid colours the crystals almost black, whilst it takes itself a beautiful red colour. | δ. Sulphuric acid colours it gradually a beautiful red, whilst tannin does not precipitate. |
| Cubebin. | Constituents of the Pimento. |
| B. Crystals Pale to Clear Yellow. | B. Pure Yellow Residue. |
| α. Piperin. | α. Sulphuric acid dissolves it yellow; on the addition of nitric acid, this solution is green, quickly changing to blue and violet. |
| Colchicine. | |
| β. Picric Acid. | β. Sulphuric acid dissolves with separation of a violet powder; caustic potash colours it red; sulphide of ammonia violet, and, by heating, indigo-blue. |
| Chrysammic acid. | |
| γ. Caustic potash dissolves it purple. | |
| Aloetin. | |
| C. Mostly Undefined Colourless Crystals. | C. A Greenish Bitter Residue, which dissolves brown in concentrated sulphuric acid; in Fröhde’s reagent, likewise, at first brown, then at the edge green, changing into blue-violet, and lastly violet. |
| Constituents of wormwood, with absynthin, besides quassiin, menyanthin, ericolin, daphnin, cnicin, and others. | |
| α. Sulphuric acid dissolves it green-brown; bromine colours this solution red; dilution with water again green. The substance renders the heart-action of a frog slower. | |
| Digitalin. | |
| β. Sulphuric acid dissolves it orange, then brown, lastly red-violet. Nitric acid dissolves it yellow, and water separates as a jelly out of the latter solution. Sulphuric acid and bromine do not colour it red. | |
| Gratiolin. | |
| γ. Sulphuric acid dissolves it red-brown. Bromine produces in this solution red-violet stripes. It does not act on frogs. | |
| Cascarillin. | |
| D. Generally Undefined Yellow Crystallisation.—Sulphuric acid dissolves it olive-green. The alcoholic solution gives with potassic iodide a colourless and green crystalline precipitate. | |
| Berberin. | |
[[333], [334]] Fröhde’s reagent is described at [page 239].
V. As a complete exhaustion of the watery solution is not yet attained by the benzene agency, another solvent is tried.