Commercial strychnine is met with either in colourless crystals or as a white powder, the most usual form being that of the alkaloid itself; but the nitrate, sulphate, and acetate are also sold to a small extent.
The microscopical appearance of strychnine, as thrown down by the solution of vapour of ammonia, may be referred to three leading forms—the long rectangular prism, the short hexagonal prism, or the regular octahedron. If obtained from the slow evaporation of an alcoholic solution, it is usually in the form of four-sided pyramids or long prisms; but if obtained by speedy evaporation or rapid cooling, it appears as a white granular powder. If obtained from a benzene solution, the deposit is usually crystalline, but without a constant form, though at times the crystals are extremely distinct, the short six-sided prism prevailing; but triangular plates, dodecahedral, rhomboidal, and pentagonal, may also be met with. An ethereal solution on evaporation assumes dendritic forms, but may contain octahedra and four-sided prisms. A chloroform solution deposits rosettes, veined leaves, stellate dotted needles, circles with broken radii, and branched and reticulated forms of great delicacy and beauty.—Guy.
Strychnine is very insoluble in water, although readily dissolved by acidulated water. According to Wormley’s repeated experiments, one part of strychnine dissolves in 8333 parts of cold water; and, according to Pelletier and Cahours, it dissolves in 6667 parts of cold, and 2500 parts of boiling water. It may be convenient, then, to remember that a gallon of cold water would hardly dissolve more than 10 grains (·142 grm. per litre); the same amount, if boiling, about 30 grains (·426 grm. per litre) of strychnine. The solubility of one part of strychnine in other menstrua is as follows:—Cold alcohol, 0·833 specific gravity, 120, boiling, 10 parts (Wittstein); cold alcohol, 0·936 specific gravity, 240 parts (Merck); cold alcohol, 0·815 specific gravity, 107 parts (Dragendorff); amyl alcohol, 181 parts; benzene, 164; chloroform, 6·9 (Schlimpert), 5 (Pettenkofer); ether, 1250 parts; carbon disulphide, 485 parts; glycerin, 300 parts. Creosote and essential and fixed oils also dissolve strychnine.
Of all the above solvents, it is evident that chloroform is the best for purposes of separation, and next to chloroform, benzene.
If a speck of strychnine be placed in the subliming cell, it will be found to sublime usually in a crystalline form at 169°. A common form at this temperature, according to the writer’s own observations, is minute needles, disposed in lines; but, as Dr. Guy has remarked, the sublimate may consist of drops, of waving patterns, and various other forms; and, further, while the sublimates of morphia are made up of curved lines, those of strychnine consist of lines either straight or slightly curved, with parallel feathery lines at right angles. On continuing the heat, strychnine melts at about 221°, and the lower disc, if removed and examined, is found to have a resinous residue; but it still continues to yield sublimates until reduced to a spot of carbon. The melting-point taken in a tube is 268°.
Strychnine is so powerfully bitter, that one part dissolved in 70,000 of water is distinctly perceptible; it is a strong base, with a marked alkaline reaction, neutralising the strongest acids fully, and precipitating many metallic oxides from their combinations, often with the formation of double salts. Most of the salts of strychnine are crystalline, and all extremely bitter. Strychnine, in the presence of oxygen, combines with SH2 to form a beautiful crystalline compound:—
2C21H22N2O2 + 6H2S + O3 = 2C21H22N2O23H2S2 + 3H2O.
On treatment with an acid this compound yields H2S2.—Schmidt, Ber. Deutsch. Chem. Ges., 8, 1267.
An alcoholic solution of strychnine turns the plane of polarisation to the left, [α]r = -132·08° to 136·78° (Bouchardat); but acid solutions show a much smaller rotatory power.
The salts used in medicine are—the sulphate, officinal only in the French pharmacopœia; the nitrate, officinal in the German, Austrian, Swiss, Norse, and Dutch pharmacopœias; and the acetate, well known in commerce, but not officinal.