Salts are crystallised, either by allowing their hot and saturated solutions to cool slowly, or by simply evaporating the menstrua as long as crystals form. In the first case the liquid is commonly evaporated until a pellicle appears on the surface, when the vessel is set aside in some sheltered situation until cold, at which time the crystals are collected, and the process repeated for fresh crystals. In the second case the crystals are usually removed from the liquid as soon as they are deposited. The first method is adopted for those salts that are considerably
more soluble in hot than in cold water, as carbonate of soda, Epsom salts, &c.; the last method, for those that possess nearly equal solubility in both cases, and also for many salts which are not required in handsome crystals; thus common salt and chromate of potash are crystallised in this way. Many of the alkaloids, and their salts, are obtained in crystals, by allowing their solutions (generally alcoholic or ethereal) to evaporate spontaneously. By repeating the processes of solution and crystallisation two or three times with the same body, the crystals obtained by the last operation will usually be found to be quite pure.
Many solids may be readily obtained in a crystalline state by melting them and allowing them to cool very slowly. Thus, iodide of sulphur is crystallised by melting it in a flask placed in a salt-water bath, and allowing it to remain in the water until the whole becomes cold. Sulphur and many metals are crystallised by pouring them, in a state of fusion, into a hot vessel having a plug in the bottom, which is withdrawn as soon as the surface becomes cool, when the liquid portion runs out, and leaves the under surface in the form of a mass of agglomerated crystals. Perfectly pure wax, stearine, and spermaceti have a very pleasing appearance when treated in this way.
CRYS′TALLOID. See Dialysis.
CU′BEBIN. A peculiar substance obtained from cubebs.
Prep. From cubebs (from which the oil has been expelled by distillation), by digestion in alcohol, evaporating the resulting tincture to one fourth, filtering, and then evaporating the remaining fluid almost to dryness. The residuum is left in a cold place until it assumes a semi-crystalline appearance, when it is thrown on a filter, and the fluid portion (the ‘cubebine’ of M. Cassola) allowed to drain off. In 24 hours the substance left on the filter is dissolved in 4 times its weight of boiling alcohol (sp. gr. ·90), the solution allowed to deposit its undissolved resin (still maintaining it near the boiling temperature), after which the clear portion is decanted. The crystals deposited as the liquid cools are cubebin. It is purified by redissolving it in boiling concentrated alcohol, and the addition of a little boiling water and animal charcoal, when long, white needles will be deposited if the solution is allowed to cool very slowly.
Prop., &c. It is insoluble in water, and nearly so in cold alcohol, but very soluble in boiling alcohol. It strikes a fine crimson colour with sulphuric acid, which remains unaltered for some hours; a property which distinguishes it from piperin. Its physiological action has been but little studied. According to Dr Görres, this for the most part resembles that of cubebs.
CU′BEBS. Syn. Cubeb pepper; Cubeba (B. P. & U. S.), Cubebæ (B. P.), L. The immature and stalked fruit of Piper cubeba or Cubeba officinalis. Cubebs are stimulant, stomachic, and aromatic, like the other peppers; they are also diuretic, and appear to possess a specific influence over the urino-genital organs.—Dose, 10 to 20 gr., in affections of the bladder and prostate gland, and in gleet and leucorrhœa; 1 to 3 dr., in the early and inflammatory stages of gonorrhœa, in piles, &c. They may be taken in water, milk, or bitter ale.
CU′CUMBER. The fruit of the Cucumis sativus (Linn.). Used as a salad vegetable. It is somewhat indigestible, but when properly dressed, with plenty of oil, it may be eaten without the slightest fear of evil consequences. The practice of pouring off the natural juice extracted from the cucumber by salt cannot be too strongly condemned. See Elaterium.
CUD′BEAR. Syn. Persio. A dye-stuff obtained from Lecanora tartarea and other lichens, by a process nearly similar to that used in making ARCHIL. The lichen is watered with stale urine or other ammoniacal liquor, and suffered to ferment for 3 or 4 weeks, after which the whole is poured into a flat vessel, and exposed to the air until the urinous smell has disappeared, and it has assumed a violet colour. It is then ground to powder. Its use is confined to a few cases of silk dyeing, where it is employed to yield shades of ruby and maroon; upon wool it gives deep-red shades. The colours produced by it are very fugitive. Like archil, there are two varieties of this dye-stuff—BLUE CUDBEAR and RED CUDBEAR. See Archil.