668 BOTANY AND PHAR]\IACOGNOSY. 



coats of latex formed during the drying process ; odor slight, 

 empyreumatic ; nearly tasteless. 



Caoutchouc is insoluble in water, dilute acids, or dilute solu- 

 tions of the alkalies ; more or less soluble in chloroform, carbon 

 disulphide, oil of turpentine, benzin and benzol. It melts at about 

 125" C, remaining soft and adhesive after cooHng. 



Constituents. — Caoutchouc consists chiefly of two hydro- 

 carbons, one of which is ductile and readily soluble in chloroform, 

 and the other elastic and less soluble in chloroform ; it also con- 

 tains I to 2 per cent, of resin, volatile oil, etc. 



Allied Plants. — African rubber is obtained from several 

 species of Landolphia and Kichsia africana (Fam. Apocynaceae). 

 Bahia rubber is derived from Hancornia speciosa (Fam. Apocy- 

 naceae). Central American or Panama rubber is obtained 

 from Castilloa elastica (Fam. Mor-acese). Ceara rubber is the 

 product of Manihot Glaziovii (Fam. Euphorbiacese). East India 

 rubber is the prodvict of the commonly cultivated rubber plant, 

 Ficus elastica (Fam. Moracese). Penang or Borneo rubber is 

 the product of several species of Urceola (Fam. Apocynacex). 



Vulcanization of Rubber. — Caoutchouc retains its elastic 

 and other properties and is not alifected by heat if it is first purified 

 and then mixed with sulphur or sulphides. Ordinary rubber 

 articles are prepared in this manner. Hard rubber articles are 

 manufactured from Borneo rubber, to which colophony, gUm 

 balata and caoutchouc are added ; a number of mineral substances 

 being added to cheapen as well as to color the final product. 



GUAIACUM.— GUAIAC RESIN.— A resin obtained from 

 the stem and branches of Guaiacum officinale, a small tree grow- 

 ing in Florida, the Antilles and Northern South America, and 

 Guaiacum sanctum (Fam. Zygophyllacese), indigenous to the 

 West Indies and the northern part of South America. The resin 

 exudes spontaneously or is obtained from incisions in the bark or 

 by heating the fallen trunks. The commercial article comes chiefly 

 from Cuba and Hayti. The resin obtained from trees growing 

 in the Bahama Islands is most highly esteemed (p. 303 ; Fig. 156). 



Description. — Usually in irregular masses ; externally green- 

 ish-brown, frequently covered with a greenish powder; brittle, 

 the fracture having a glassy luster and being yellowish-green or 



