PLANTS PRODUCING GUMS AND RESINS 32I 



Bauhinia purpurea — The trunk exudes a gum of small value 

 {Lanessan). 



Bauhinia variegata — In India this plant prv^duces a gum known as 

 Semkigond. It is brownish in colour, insoluble, and forms a product 

 of but mediocre importance. 



Caesalpinia seplaria — The fruit contains a gum with strong 

 adhesive qualities. 



Copalfera copallina — According to Baillon, Bentham and Hooker, 

 the species has the following synonyms : Co-paifera Ouibourtiana; 

 Gmboitrtia co-pallifera. 



The natives call this large tree, which produces the West African 

 copal, kobo. It occurs in the Congo, Gaboon, Sierra Leone, &c. 



In nature copal appears in two forms : green copal and fossil or 

 semi-fossil copal. 



Green copal is the product of the actual copal trees. This resin 

 flows spontaneously from every fissure in the tree in the form of whitish 

 tears. These latter subsequently acquire a greenish or lemon yellow 

 hue, the colour increasing in intensity with exposure to air and light, 

 and become covered with a whitish efflorescence. The negroes 

 make incisions in the trunk and lower branches, they then attach 

 small clay pots, coming to change them three days later. The contents 

 are kneaded into balls and dried in the sun. 



Fossil copal is much more valuable. It is found at a depth of 

 50 cm. to I metre, and deposits are found in places where the copal 

 tree has practically disappeared. In the Belgian Congo these deposits 

 have been exploited for several years. Welwitsch mentions chiefly the 

 countries which extend from the south of the Coanza, near Novo 

 Redondo, Egito, and Benguela. 



Fossil copal is sometimes found in the superficial layers, especially 

 at the bottom of ravines excavated by rainwater. 



From the commercial standpoint African copals are divided into 

 fossil copal, W'hich is hard, and green or tree copal, which is semi-hard. 

 Semi-fossil copal is usually classed in one or other of these two groups, 

 according to its state of petrifaction, but it may form an intermediate 

 class. 



Copals must be washed and sorted. Fossil copal in the natural 

 state contains extraneous matter which is removed with a knife ; it is 

 thsn placed in a i per cent, bath of caustic soda in order to get rid 

 of the whitish crust formed by damp or by oxidation. The same soda 

 solution should be used for green copal if the washing in boiling water 

 is not sufficient to remove this whitish layer. 



De Cordemoy lays stress on the fact that for commercial purposes 

 it is not sufficient to class copals according to their colour; in view of 

 their use in the manufacture of varnishes they should be classified 

 according to the melting point. 



Distinction is made between the following principal shades : silver 

 white, lemon yellow, amber yellow, rhubarb yellow, pale red, dark 

 red, brown, and finally green. 



According to de Cordemoy, hard copal has a density of 1*139 

 21 



