§ 153. A great many essential oils deposit, after exposure to air, camphors produced by oxidation of their terpenes. Ordinary camphor is imported in the rough state from China and Japan, and is prepared by distilling with water the wood of Camphora officinarum; it is resublimed in England. The formula of camphor is C10H10O; it has a density of ·986 to ·996; melts at 175°, and boils at 205°. It is readily sublimed, especially in a vacuum, and is indeed so volatile at all temperatures, that a lump of camphor exposed to the air wastes away. It is somewhat insoluble in water (about 1 part in 1000), but this is enough to impart a distinct taste to the water; it is insoluble in chloroform, ether, acetone, acetic acid, carbon disulphide, and oils. It has a fragrant odour and a burning taste. A 10 per cent. solution in alcohol turns a ray of polarised light to the right +42·8°. By distillation with zinc chloride, cymene and other products are produced. By prolonged treatment with nitric acid, camphor is oxidised to camphoric acid (C10H16O4). Camphor unites with bromine to form a crystalline, unstable dibromide, which splits up on distillation into hydrobromic acid and monobrom-camphor (C10H15BrO). The latter is used in medicine; it crystallises in prisms fusible at 76°, and is readily soluble in alcohol.
§ 154. Pharmaceutical Preparations.—The preparations officinal in the British Pharmacopœia are camphor water—water saturated with camphor, containing about one part per thousand.
Camphor Liniment.—A solution of camphor in olive oil, strength 25 per cent.
Compound Camphor Liniment.—Composed of camphor, oil of lavender, strong solution of ammonia and alcohol; strength in camphor about 11 per cent.
Spirit of Camphor.—A solution of camphor in spirit; strength, 10 per cent.
Camphor is also a constituent of the compound tincture of camphor; but in this case it may be considered only a flavouring agent. There is a homœopathic solution of camphor in spirit (Rubini’s Essence of Camphor). The solution is made by saturating alcohol with camphor; it is, therefore, very strong—about half the bulk consisting of camphor. Camphor is used in veterinary medicine, both externally and internally.
§ 155. Symptoms.—Camphor acts energetically on the brain and nervous system, especially if it is given in strong alcoholic solution, and thus placed under conditions favouring absorption. Some years ago, Dr. G. Johnson[145] published a series of cases arising from the injudicious use of “homœopathic solution of camphor,” from 7 to 40 drops of Rubini’s homœopathic camphor taken for colds, sore throat, &c., having produced coma, foaming at the mouth, convulsions, and partial paralysis. All the patients recovered, but their condition was for a little time alarming.
[145] Brit. Med. Journ., Feb. 27, 1878, p. 272; see also ibid., Feb. 1875.