Tests. By the microscope very minute particles may be discovered in the stomach and intestines, on a post-mortem examination. Orfila thus found particles of cantharides in a body that had been interred nine months.
Uses, &c. Spanish flies are used externally to raise blisters, and internally as a stimulant and diuretic, generally in the form of tincture. In excess they produce strangury, bloody urine, satyriasis, delirium, convulsions, and death. See Tinctures, Vesicants, &c.
CANTHARI′DIN. C5H12O2. Isomeric with picrotoxin. This substance is found in, and is the vesicating principle of, the Spanish fly, Chinese blistering fly, and other coleopterous insects. Prep. Pulverised cantharides are allowed to remain in contact for 24 hours with twice their weight of chloroform, in a displacement apparatus. The chloroform is then drained off, and finally displaced by alcohol, and the solution is left to evaporate. The cantharidin crystallises out, saturated with green oil. In order to purify the cantharidin it is laid on bibulous paper, which absorbs the greater part of the oil, and then crystallised out of a mixture of alcohol and chloroform. (Procter.)
Prop. Prismatic crystals, melts at 200° C., volatilises in white fumes, which strongly irritate the eyes, nose, and throat, and condenses in rectangular prisms. Cantharidin is insoluble in water, but soluble in alcohol, ether, chloroform, acetic acid, and in the fixed and volatile oils. Its solution in any of the liquids above mentioned possesses vesicating properties, which, however, is not exhibited by solid cantharidin.
CAOUT′CHOUC. Syn. India rubber, Elastic gum. India rubber is the concrete juice of the Ficus elastica, Siphonia elastica, the Urceola elastica, and many other tropical plants. The fresh milky juice is spread over moulds of unbaked clay, and is then exposed to the heat and smoke of a fire, or torches, to dry it, whence it derives its dark colour. Successive coats of juice are laid on, and the operation of drying repeated until the bottles acquire sufficient thickness. When it has become thoroughly hard and dry, the clay is beaten out. In this form it is commonly imported.
Prop., &c. The general properties of india rubber, as well as its numerous applications, are well known. The fresh juice has a cream-like appearance and consistence, is coagulated by heat, and is miscible with water, alcohol, and wood naphtha; sp. gr. 1·012 to 1·041; it yields from 18% to 45% of solid caoutchouc, either by heat or evaporation. By excluding it from the air it may be preserved unchanged for a considerable period.
Solid caoutchouc has a sp. gr. ranging between ·919 and ·941; it melts at 248° Fahr. into a viscid mass, which does not again harden on cooling; it is unaltered by chlorine, hydrochloric acid, sulphurous acid, fluosilicic acid, ammonia, caustic alkaline lyes (even when boiling), and most similar substances; nitric acid and sulphuric acid act on it only by long contact when concentrated. Some specimens of caoutchouc are harder than gutta percha itself, and equally inelastic, whilst others never perfectly solidify, but remain in a condition resembling that of birdlime or printers’ varnish.
The best solvents of caoutchouc are rectified sulphuric ether (which has been washed with water to remove alcohol and acidity), chloroform, bisulphide of carbon, a mixture of bisulphide of carbon and absolute alcohol (94 of the first to 6 or 7 of the last), and caoutchoucin. All these liquids dissolve india rubber rapidly in the cold, and leave it unaltered on evaporation. The first two are, however, too expensive to be generally employed. The others have a disagreeable odour, but are much cheaper than the rest, and possess the advantage of leaving the film of caoutchouc in a firmer and stronger condition than other solvents. Pyrogenous oil of turpentine is another cheap and good solvent. Benzol, rectified mineral or coal-tar naphtha, crude petroleum, and oil of turpentine dissolve india rubber by long digestion and trituration (with heat), otherwise they merely form with it a glutinous jelly that dries very slowly and imperfectly, leaving it much reduced in hardness and elasticity. The fats and fixed oils also readily dissolve caoutchouc (with heat), forming permanently glutinous solutions or pastes; so also do most of the volatile oils, but the solutions with the majority of them dry with difficulty.
One of the most remarkable properties of india rubber is the great amount of heat which is disengaged during its condensation by pressure or in the exercise of its elasticity. During the process of kneading the raw caoutchouc in the “masticators,” the cold water thrown in to reduce the temperature soon becomes boiling hot. When no water is added, a temperature so high is often reached as to occasion the melting of the rubber. This is particularly the case during the process of “dry kneading” with quick-lime. A tube 21⁄4 inches in diameter, impactly secured, was subjected to a force of 200 tons. The result was a compression amounting to 1-10th; great heat was evolved, and the excessive elasticity of the substance caused a fly-wheel weighing five tons to recoil with alarming violence. Mr Brockedon states that he succeeded in raising the temperature of an ounce of water 2° in about fifteen minutes by collecting the heat evolved by the extension of a small thread of caoutchouc. He refers this effect to the
change in specific gravity, and contends that the heat thus produced is not due to friction, because the same amount of friction is occasioned in the contraction as in the extension of the substance, and the result of this contraction is to reduce the caoutchouc thus acted upon to its original temperature.