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which whenever gas is used should be strenuously insisted on, would remove all possibility of danger. But the best proof of the safety of gas illumination is, that notwithstanding the many thousand lamps nightly burning in London, six* accidents only are known to have occurred, and those of a very trilling and almost unimportant nature, though the pipes and lamps are generally badly and very carelessly managed. In matters of this kind, facts, and not arguments, must be looked to for evidence.
It was my intention to have concluded this paper with some observations on the construction of burners, and with an account of several important improvements lately made in the general apparatus by Mr. Clegg: the hope of rendering my account of these subjects more correct and perfect than is at present in my power, induces me to defer it till the appearance of the next number of this Journal.
Observations on the Nature and Properties of Caoutchouc, and on the Construction of Elastic Beds, Pillows, Hammocks,&c.
[From the London Monthly Magazine, for March, 1816.] THE term Caoutchouc may be considered as the generic name for a concrete vegetable substance which possesses the properties of elasticity and extensibility, and is soluble in the essential oils, &c.; and its not being acted on by those fluids which are solvents for gums and resins, renders the term elastic gum, or elastic resin, improper for it. The specific name may be that of the vegetable producing it: as, caoutchouc of Urceola elastica, caoutchouc of Ficus indica, caoutchouc of Artocarpus integrifolia, &c.
This production is common to the East-Indies, and to all tropical climates, from whence it is imported in various artificial forms; chiefly in that of bottles and solid blocks; sometimes in the shape of balls, or in the rude figures of birds, horses,
* Two of these arose from holes having been mischievously bored in the pipes of supply.
and other animals. It grows very abundantly in South America, particularly on the banks of the Amazon river, eastward of Quito; also in the colonies of Surinam and Cayennc, in Guiana; and has been found plentifully in Brazil, and in small quantities near Buenos Ayres, and beyond the river Plata at near 40 degrees South latitude, or 16 degrees beyond the tropics: so that it may possibly be propagated in Spain, or in the South of France, as these are both situated under the corresponding degree of North latitude: and there are some English trees and plants affording a white juice, which, if collected in sufficient quantities, may possibly produce by coagulation a similar elastic substance.
Caoutchouc, as an article of commerce, is of comparatively modern introduction; its uses have been locally confined, and but little known; whilst its great abundance, and the easy mode of its being obtained and applied, renders it an advantageous subject of general investigation: and the principal object herein is to collect and arrange a series of well authenticated facts relating to it; and, from the inferences deducible therefrom, to elucidate and confirm the advantages of its application to numerous and more extensive purposes. I have therefore subjoined abstracts from the accounts of M. de la Borde, physician at Cayenne, in Guiana, &c. and also from the fol. lowing works: Linnæus. Spec. Plant. SIPHONIA CAHUCHU.
Suppl. JATROPA ELASTICA.
-- Londinensis. CAOUTCHOUC, URCEOLA ELASTICA.
The French naturalists mostly call this substance Caochouch:
M. Bomare describes it under the name of Resin elastique. The memoires de l'Academie des Sciences, 1751, contain a description of it by M. de la Condamine, and two papers on the manner of softening and dissolving it, by M. Macquer, and Herissant, 1763; also some observations by M. Macquer, 1768, on the caochouch discovered in Cayenne; and in the same publication for 1769, there are remarks by the Chevalier Turgot on the elastic resin found in the Isle of France. The trees, vines, and plants, of different climates, producing it, are numerous, and of various sorts.
The vegetable substance of caoutchouc or elastic gum, as produced from the tree or vine in its native climate, cannot be imported in its original fluid state, on account of a spontaneous fermentation which would take place, and ultimately render it useless. It is technically called Indian rubber, lead eater, &c. from its being an Indian production, and chiefly used for the purpose of erasing the strokes of black-lead pencils, an inherent property for which it appears exclusively to possess. It is the indurated juice or sap of a tree; and is extracted from incisions made in the bark or otherwise by cutting off whole branches. The fluid, when first exuded, is of a white colour, and of a glutinous consistency, soon acquiring a firm texture by exposure to the air; after which its colour gradually changes to a dark brown or black, which penetrates more or less deep beneath the surface, according to its age and thick. ness. It is pliable, extensible, and elastic to a remarkable degree; being capable of great extension in any direction, and afterwards of regaining nearly its former size and shape, on the extending force being withdrawn. A great degree of cold renders it stiff and rigid. A moderate warmth restores its original elasticity, renders it more pliable, and increases its capability of extension. A violent heat destroys it by melting; producing at the same time a dense smoke. If the heat be increased beyond this, ignition takes place, when it burns slowly with a bright flame; and on this account it has been used for torches.
All its qualities are permanent excepting its white colour, and its original vegetable odour, which much resembles that of Chinese or Indian ink. Its specific gravity is rather less than that of water. It is, in its original fuid state, capable of being moulded or formed into any requisite shape, impervious to air and water; and it appears to be indestructible excepting by fire, and by its known solvents of nitric ether, essential oil of turpentine, &c. Water, or the generality of oils, will not dissolve it unless at a very high temperature.
When reduced to a fluid, either by melting or by solution, it is not easily restored to a solid form, and most of its original properties are lost; excepting when nitric ether is em. ployed, which completely dissolves it at the common temperature of the atmosphere: and if the solution be afterwards spread on the surface of paper or clay, &c. and exposed to the air, the ether soon evaporates, leaving the caoutchouc unaltered in its properties. This solution is transparent, of an amber colour; and, on being thrown into water, rises to the surface, forming a solid membrane, possessing the great elasticity and the other qualities of original caoutchouc: but, as the ether requires much expensive preparation, with longer time than the other solvents, this method for most purposes is not eligible. Essential oil of turpentine is a solvent for it, with the application of a small degree of heat. If the caoutchouc bottles are cut into small pieces, and those pieces are examined a few hours after their immersion into this solvent, they will be found to be considerably augmented in their size by absorbing the turpentine; and rendered so transparent, that all the different layers, strata, or coatings of which the bottles, and other artificial figures of elastic gum are constructed, may easily be seen through the edges of the flat pieces: this solution may be completed in about four days, by repeatedly straining it by force through cloth or hair bags. If pieces of paper or of silk or cotton-cloth, previously saturated with linseed oil and dried, be immersed in this solution, and afterwards exposed to the air, the turpentine evaporates, leaving the oil-case completely covered with the caoutchouc, possessing a remarkable degree of adhesiveness and tenacity; so that if two or more such pieces be laid over each other, and pressed together to expel the air between them, they will unite with great firmness; and, if afterwards torn asunder, they will appear to have been held in contact by numerous strings or fibres of the elastic gum on
their surfaces. Several pieces of silk, cotton, or paper oil-case, may thus be joined together to any size and shape; forming a resemblance to paste-board, flexible, and impervious to air. Compositions, for careening the balloons of aerostation, are made of elastic gum, digested in essential oil of turpentine, and afterwards dissolved by boiling it in drying linseed oil, in various proportions. A piece of indurated caoutchouc possesses an inherent toughness, resisting the edge of any sharp instrument; but if required to be cut, it may be done in any direction by making it rather warm, to increase its flexibility sufficiently to bend it over the edge of a table, and applying the sharp point of a knife to its strained surface.
The trees or vides producing caoutchouc, are numerous, and not confined to one species; but they are chiefly of the genus EUPHORBIA, 3d section, 11th class, Linnæus. Those which are found in Bengal, particularly near the mouths of the Ganges, mostly resemble the English ivy, bearing leaves at the extremities of the small branches only. The largest stems are from four to six inches in diameter, proceeding in numerous ramifications on the ground, until they meet with other support; when they ascend, and frequently bind several trees together in the numerous folds of their branches: these growing over them descend, and again take root in the ground, from whence other ramifications of stems proceed in the same manner as before. This property of taking root in numerous places is common to many English trees and plants, when suffered to grow naturally and without mutilation.
The common method of extracting the gum from the caoutchouc trees, is either by incision or by cutting off whole branches. The first method is usually preferred, and is the most easily performed; being nothing more than cutting several deep gashes through the bark, and placing shells round the tree in any convenient manner to receive the gum. The second method is injurious to the trees, but produces the greatest quantity; being sometimes more than one third of the whole weight of the amputated branches or stems: these are cut into convenient lengths, and set standing on their ends in the receiving vessels, until a sufficient quantity is collected from them. To form the caoutchouc bottles which are com