CH. XIIl] INDIARUBBER, GUTTAPERCHA, AND CAMPHOR 129 



coagulated, usually by the method introduced by Mr Parkin, 

 by the addition of a small amount of acetic acid, sufficient to 

 render the solution slightly acid. This brings about the coagu- 

 lation of the proteid in the fluid, which entangles the caoutchouc 

 and produces a clot. The rubber exists in the milk as an 

 emulsion of fine globules, which quite possibly are not pure 

 caoutchouc, but polymerise at the instant of coagulation to 

 form it. The clot is left till it has firmed somewhat, and may 

 then be prepared in various ways, the two most popular being 

 biscuit or sheet, made by pressing and drying, and crepe, made 

 by passing the clot between rollers that move at different 

 speeds and turn it out in a kind of crinkled sheet. Either of 

 these forms may be made into block. The great difference 

 between this rubber and the Brazilian is that it is quite dry, 

 instead of containing over 15 / of included water. 



Other species of rubber than Hevea brasiliensis are but 

 rarely cultivated. The most important cultivation is that of 

 Castilloa elastica in Mexico ; this tree, however, is very uncer- 

 tain in its yield, very delicate to grow, and very liable to 

 serious injury by overtapping. The various Manihots, and 

 especially M. Glaziovii and piauhyensis, are largely cultivated 

 in German East Africa and Brazil, and to a smaller extent in 

 other places, and Funtumia elastica is a little planted in West 

 Africa. But Hevea certainly forms 95 / of all cultivated 

 rubber. 



Guttapercha. This substance, allied to indiarubber, and 

 obtained from trees of the family Sapotaceae, especially species 

 of Palaquium, has as yet been mainly collected from the wild 

 trees in the islands of the Malay and Philippine Archipelagoes, 

 but of late attempts to cultivate it have been made in Java and 

 elsewhere, the gutta being obtained from the leaves by a process 

 of maceration. The yield however is very poor as compared 

 with that of the rubber trees, and a higher price cannot be 

 obtained, so that it is not likely that its cultivation will be 

 much taken up. Already new preparations of rubber are 

 beginning to take the place of gutta in cables, and rubber balls 

 have come into use in golf. 



w. 9 



