This vulcanized India-rubber is in fact a compound of sulphur with the vegetable gum. When a sheet of India-rubber is immersed in liquid sulphur, a marked change takes place in its qualities; the sulphur acts upon the gum and combines with it; and indeed the two may almost be said to form a new substance. The methods by which the combination is brought about are varied, but the effect is in all cases very remarkable. The strength of the India-rubber is increased to an extraordinary degree. The elasticity is rendered more permanent, analogous in some respects to that of gutta-percha. The new substance will absorb essential oils without injury, whereas such oils would dissolve India-rubber. It retains its properties at a temperature so low that India-rubber would be too much hardened for use; and at a temperature so high that India-rubber would be destroyed. Later experimenters have found that antimony, and many other substances, may similarly be combined with India-rubber; and it is reasonable to expect that many useful novelties are in use for us in this “vulcanized” rubber. INDIA-RUBBER OR (CAOUTCHOUC) AND GUTTA-PERCHA—COMPARISON OF THE CRUDE MATERIALS. Much ignorance exists in relation to the intrinsic merits of gutta-percha and India-rubber. It is generally supposed that there is so little difference that it is hardly perceptible, and that the one or the other may be used for the same purposes, with the same results. In order to correct this impression and convey an intelligent idea of their relative properties, we here give an analysis of the two gums: Gutta-percha when immersed in boiling water contracts considerably in bulk, whilst India rubber, when immersed in boiling water, expands and very materially increases in bulk. Gutta-percha juice also is of a dark brown color, and consolidates in a few moments after exuding from the tree, when it becomes about as hard as wood. India-rubber sap, on the contrary, is perfectly white, and of about the consistency of thick cream; when it coagulates it gives from four to six parts water out of ten. Gutta-percha first treated with water, alcohol, and ether, and then dissolved with spirits of turpentine and precipitated, yields a substance consistent with the common properties of gutta-percha; but India-rubber similarly treated, results in a substance resembling in appearance the gum arabic. Gutta-percha by distillation yields 57⅔ per cent. of volatile matter; India-rubber by the same process, yields 85¾ per cent. India-rubber, or caoutchouc, is produced from a milk-white sap taken chiefly from the Sephonca Cahuca tree, afterwards coagulated, and the whey pressed out or dried off by heat—the residue is the India-rubber of commerce. Gutta-percha is produced from the Isonandra, or Gutta tree; is of a brownish color, and when exposed to air, soon solidifies, and forms the gutta-percha of commerce.