India-rubber of commerce, is of a soft, gummy nature, not very tenacious, and astonishingly elastic. Gutta-percha of commerce is a fibrous material, much resembling the inner coating of white oak bark, is extremely tenacious, and without elasticity, or much flexibility. India-rubber, when once reduced to a liquid state by heat, appears like tar, and is unfit for further manufacture. Gutta-percha may be melted and cooled any number of times, without injury for future manufacture. India-rubber, by coming in contact with oil or other fatty substances, is soon decomposed and ruined for future use. Gutta-percha is not injured by coming in contact with oil or other fatty substances—in fact one good use of it is for oil cans. India-rubber is soon ruined for future use, if brought in contact with sulphuric, muriatic, and other acids. Gutta-percha resists the action of sulphuric, muriatic, and nearly all other acids—in fact one great use of it is for acid vats, &c., and other vessels for holding acids. India-rubber is a conductor of heat, cold and electricity. Gutta-percha is a non-conductor of electricity, as well as of heat and cold. India-rubber, in its crude state, when exposed to the action of boiling water, increases in bulk, does not lose its elastic properties, and cannot be moulded. Gutta-percha, in its crude state, when exposed to the action of boiling water, contracts and becomes soft like dough or paste, and may then be moulded to any shape—which shape it will retain when cool. India-rubber is vulcanized to reduce its elasticity and give it more firmness than is natural to the crude material. India-rubber, vulcanized, is not so perfectly a repellent of water, as before being vulcanized. India-rubber is _not_ a perfect repellent of water, but is more or less absorbent, according to quality. Gutta-percha has an exceedingly fine grain, and its oily property makes it a _perfect repellent_ of liquids, oils, acids, and all oleaginous substances, so that when united to tanned leather, the _oil_ in the leather _will not affect the adhesive properties of the gutta-percha_. Whereas oil in leather _will decompose any India-rubber_ cement that may be applied to it. Pure gutta-percha is _without_ smell or disagreeable odor, and whenever it is found to produce any but a perfectly sweet odor, it arises from its _impurities_, and may be regarded as a test of its quality. India-rubber when vulcanized has an odor about it very disagreeable. It _will decompose_, become sticky like tar, and much of it becomes entirely useless. It is vulcanized to reduce its elasticity and give it more firmness than is natural to the crude material, and when exposed to friction, even after vulcanization, it rolls up a dirty, sticky mass.