Page:Experimental researches in chemistry and.djvu/196

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1826.]
181
On pure Caoutchouc.

Thinking it probable that whilst in its natural state of division the caoutchouc would combine more intimately or readily with fixed and volatile oils than when aggregated, as it generally is in commerce, an experiment or two were made in consequence. A portion of well-washed milky caoutchouc being added to olive oil, and the two beaten well together, a singularly adhesive stringy substance was produced, which holding the water diffused through it, assumed a very pearly aspect, stiffened, and was almost solid; upon being heated so as to drive off the water, it became oily, fluid and clear, and was then a solution of caoutchouc in the fixed oil. On adding water and stirring considerably, it again became adhesive as before. Thus introduced, caoutchouc would probably be a useful element in varnishes. `

Oil of turpentine being added to a mixture of one volume of sap and one volume of water, and well agitated with it, was found to be only imperfectly miscible; after standing twenty four hours, three portions were formed: the lower, the usual aqueous solution; the upper, oil of turpentine, holding a little caoutchouc in solution; the intervening part a clot or tenacious mass, soft and adhesive, like bird-lime, consisting of caoutchouc, with some oil of turpentine. It was very difficult to dry, and always remained adhesive at the surface; but experiments of this kind were not pursued, for want, at that time, of further quantities of the original sap.

Such is a general view of the nature of the sap from which the substance is obtained, and of the substance itselfl I have not endeavoured to give an accurate account of the properties or quantities of the other substances present, because there is reason to believe that both vary in different specimens, probably according to the age of the tree, the time of the year, or the manner in which the sap is drawn; nor have I dwelt upon the inaccuracies of former accounts, inasmuch as they are evidently referable to the impurity of the substance examined. Those who wish to look to former accounts of the chemical or physical qualities of this remarkable substance, will perhaps find the following references useful:


1751. De la Condamine on an Elastic Resin, newly discovered at Cayenne, by M. Fresneau; and on the Use of various Milky Sap: from Trees of Guiane or France Equinoctiale.—Man. do l'Acad. Royale, 1751. pp. 17, 319