or KAOUTCHUCK, a resin found in different parts of Asia and South America, and possessed of the most singular properties. No substance is yet known which is so pliable, and at the same time so elastic; and it is farther a matter of curiosity as being capable of resisting the action of very powerful menstrua. From the account of M. de la Condamine, we learn, that this substance oozes out, under the form of a vegetable milk, from incisions made in a certain species of tree in the country in which it is found. This liquor gradually dries, and is formed into a substance of the appearance of leather, which is in a very high degree pliable and elastic, while at the same time it possesses a considerable degree of solidity. On account of these properties, the Omaguas, a numerous nation on the banks of the river of the Amazons, employ this resin, while yet in the state of milk, for making several utensils, as goblets, bottles, and the like. As the same properties would render it of singular utility for many other purposes in arts, philosophers have long endeavoured to discover some method of dissolving it in such a manner, that it would assume different figures with equal ease as when in its original state of milk. In the memoirs of the academy of sciences for 1768 we have an account of several attempts for this purpose, and how it may be effected.—The state of vegetable milk in which the caoutchouc resin is found when it comes from the tree, led Mr Macquer to imagine that it was composed of an oil and a watery matter. From its wanting aromatic flavour, from its little volatility, and from its being incapable of solution in spirit of wine, he concluded that the oil which entered its composition was not an essential, but a fatty, one. Hence he thought it probable that it passed from a fluid to a solid form by the evaporation of the watery part, and that the oily solvents would reduce it to a soft state. The first trials he made for dissolving it were with linseed oil, essence of turpentine, and several others. But all he could obtain by means of these menstrua was a viscid substance incapable of being hardened, and totally void of elasticity. The rectified essential oil of turpentine was employed seemingly with greater success. To separate from this menstruum the caoutchouc which it had dissolved, Mr Macquer added spirit of wine: but the consequence was, that part only of the oil united with the spirit; the rest remaining obstinately attached to the resin which it had dissolved, and thus preventing it from assuming a solid consistency. The author next endeavoured to dissolve it by means of heat in Papin's digester. But neither water, nor spirit of wine, although in this way capable of dissolving the hardest bones, could produce any other effect upon it than to render it more firm than before. After this, he tried what effect the milky juice of other vegetables would have upon it. He used several kinds, particularly that of the fig. But, in this way, he could obtain no solution. From the great volatility of ether, he was next induced to try it as a menstruum; and, for this purpose, he prepared some with great attention. The caoutchouc, cut into little bits, and put into a proper vessel with as much ether as was sufficient to cover it, was perfectly dissolved without any other heat than that of the atmosphere. This solution was transparent, and of an amber colour. It still preserved the smell of ether, but mixed with the disagreeable odour of the caoutchouc, and it was a little less fluid than pure ether. Upon its being thrown into water, no milky liquor was produced; but there arose to the surface a solid membrane which possessed the great elasticity and other peculiar properties of the caoutchouc.

The Indian method of forming bottles, goblets, &c. of the caoutchouc is, by making moulds of clay, which they cover with thin layers of the caoutchouc, taking care never to lay on a fresh one till the former is dry. After it has acquired the proper thickness, by an instrument fitted for that purpose, they take out the clay. The same process may be followed in forming vessels of the caoutchouc dissolved in ether. But in forming small vessels, Mr Macquer did not employ moulds made of clay, but of wax, which were easily removed, by throwing the vessel after it was formed into boiling water.

Of this gum, it is said, the Chinese make elastic rings for lascivious purposes.—Among us, it is used by surgeons for injecting liquids, and by painters for rubbing out black-lead pencil marks.