There are several different varieties of this plant, there being no indications, however, tending to point out any one of these preferable to another with regard to the question of its yield. The latex is of a bluish tint, its richness in rubber varying greatly. Each mangabeira supplies on an average one kilogram of rubber. Besides the plants mentioned, there are still many others in Brazil which furnish rubber, but which continue to grow without being taken advantage of, on account of the little profit they give. To speak only of those which exploited on a small scale have yet supplied the Brazilian markets with an appreciable product, we may yet mention the =Massaranduba=, =Mimosups elata=, and =Frei-Allem=, gigantic trees found from the Amazon and Pará to Rio de Janeiro and Minas, abundant in the milky latex, which being coagulated produces a rubber very similar to gutta-percha, to which it serves as a substitute in all the latter’s most important applications; and the =Sorva=, =Couma utilis=, =Muell. Arg.=, which grow in Pará and in the Amazon valley, the latex of which, the =leite de sorva=, enters, with a small coefficient into the production of rubber in these two States. EXTRACTION OF RUBBER, METHODS AND PROCESSES The great organic and biologic differences which exist between rubber-trees, exact divers processes of preparation in order to obtain a complete utilization of the productive capacity of each. It is, however, interesting before entering into a description of the different processes adopted in Brazil, to here state what the chemists think as to what rubber really is. Rubber is a carburate of hydrogen which in the shape of white globules more or less elongated, are found suspended in the milky latex. The composition of those globules, although even yet, badly defined, is represented by the formula (C¹⁰ H¹⁶)ⁿ. Rubber is generally considered as a derivative of the Isoprina, into which it transforms itself when submitted to the action of dry heat, as Bouchardat demonstrated by his experiments in 1879. Treating the isoprina in a strong solution of chloridic acid, an interesting body is obtained, which reminds one of rubber on account of its elastic properties. Wallach, Tilden, Weber, Harries and others gave themselves up to accurate studies upon the composition of rubber; nevertheless, up till to-day, however, no definite result has as yet been arrived at. The latex, a thick liquid which has the appearance of animal milk, circulates in special vessels, distributed diversely in the organism of certain plants. The following are the results of the analysis obtained from the latex of the =hevea braziliensis= by Seelingmann, Scott and Bamber: