264 ECONOMIC BOTANY. 



and the juice collected in vessels ; but a more rational 

 method of obtaining it is followed now, namely, the same 

 ■which is employed in getting Caoutchouc. From the same 

 tree Gutta-Percha may be obtained for several years. The 

 juice hardens to a porous, spongy mass, to which water is 

 added, and then i^ is kneaded. The Gutta-Percha when 

 pure is nearly white, or with a shade of red or yellow ; 

 when impure, it is of a reddish or dark color. It is taste- 

 less, and has a peculiar odor when warm. It can be cut 

 with a knife; it is not so elastic as Caoutchouc, and is a 

 poor conductor of electricity. It is partially soluble in 

 alcohol and ether, and completely so in warm oil of turpen- 

 tine and benzine. Its best solvent is a mixture of benzine 

 and carbon disulphide. It is not attacked by alkalies nor 

 weak acids. When examined with the microscope it is 

 found to be full of minute cavities. It is more complex in 

 composition than Caoutchouc, and contains pure gutta, 

 resins, acids, volatile-oil, casein, and coloring and mineral 

 substances. It is used in immense quantities to cover 

 sub-marine cables. It is also employed in the manufacture 

 of shoe-soles, bauds for machinery, tubes, vessels, water- 

 proof cloth, for taking copies or casts of objects, etc. Like 

 Caoutchouc, it also can be vulcanized. 



3. Balata Gijm has been used since the middle of the 

 present century as a substitute for Caoutchouc and Gutta- 

 Percha. It comes from Guiana, and is yielded by Sapota 

 Muelleri (family Sapoiacece). The milky juice of the tree 

 has been used for a long time as food by the natives. To 

 obtain the juice for the Balata Gum, the trees were at first 

 felled, placed on supports, the bark cut at short distances, 

 and the exuding juice caught iu vessels placed below. A 

 rational method is generally followed now, which is as 



