CAOUTCHOUC 427 



substances present in the Para rubber. It usually occurs in large thin 

 sheets of a pale yellow or brownish black colour or in translucent 

 dark brown or golden brown blocks about 4 cm. thick. 



The keeping properties of rubber are much increased by combining 

 it with sulphur (vulcanisation) . This may be effected by heating 

 the rubber with sulphur, or by means of a solution of sulphur chloride 

 in carbon disulphide. Ordinary soft rubber usually contains from 

 2 to 4 per cent, of sulphur, hard rubber (ebonite) from 20 to 30 per 

 cent. 



The description of the numerous other commercial varieties of 

 rubber would be far beyond the scope of this work, but the follow- 

 ing may be briefly noticed as illustrating the various methods of 

 preparation and the varying appearance of this important and 

 interesting substance : 



Assam Rubber from Ficus elastica, Roxburgh (N.O. Urticacece) ; 

 the latex is coagulated by boiling and formed into dark red lumps 

 which are compacted into larger masses. 



Mangabeira Robber from Hancornia speciosa, Muller Argoviensis 

 (N.O. Apocynacece) ; collected in Eastern Brazil, the latex being 

 coagulated with alum or salt water. It occurs in large, flat, pinkish 

 white pieces often very wet from presence of salt water. 



Central American Rubber from Castilloa elastica, Cervantes (N.O. 

 Urticacece) ; the latex is coagulated with salt or sodium bicarbonate 

 or with an infusion of various plants ; the masses of coagulum are 

 pressed together into slabs composed of black, wavy sheets. 



West African Rubber. The latex of Funtumia (Kickxia) elastica, 

 Stapf (N.O. Apocynacece), is coagulated by boiling or by pouring it 

 into cavities in the trunk of the tree. That of Landolphia florida, 

 Bentham (N.O. Apocynacece), is smeared by the natives over their 

 bodies, and after drying rolled into balls. 



Mozambique Rubber from Landolphia Kirkii, Dyer (N.O. Apocy- 

 nacece), occurs in balls or in sausage-shaped masses consisting of strings 

 of rubber wound round a little wooden spindle. 



Ceara Rubber from Manihot Glaziovii, Muller Argoviensis (N.O. 

 Euphorbiacece) . The bark is shaved off until the latex trickles down 

 the trunk ; it is allowed to dry, peeled off in strings and rolled into 

 balls. 



EUPHORBIUM 



(Euphorbium) 



Source, &C. Euphorbium is the dried latex of Euphorbia resini- 

 fera, Berg (N.O. Euphorbiacece), a plant about a metre in height, 

 resembling in appearance and habit a cactus, and common in the 

 mountainous districts of Morocco, especially on the spurs of .the 



