GUTTAPERCHA 423 



latex is then scraped from the incision, kneaded under hot water to 

 free it from accidental impurities, beaten with mallets, and finally 

 made into cakes which are bought up by Chinese merchants. 



At present Sumatra yields the bulk of commercial guttapercha, 

 but the destructive and wasteful method of collection has led to 

 numerous endeavours to cultivate the trees and obtain from them 

 the guttapercha by a more rational method. These endeavours have 

 met with some success. Burck has shown that by making V-shaped 

 incisions in the living tree large quantities of guttapercha can be 

 obtained, and that the tapping can be continued for three or four 

 years without apparent injury to the tree. It has also been found that 

 the leaves contain more guttapercha than the stem-bark, and that it 

 can be extracted by boiling the dried and crushed leaves with a suit- 

 able solvent, such as toluene or petroleum spirit ; from the latter solu- 

 tion the pure guttapercha is deposited on cooling (Obach's process). 

 Not only could the trees be preserved by this means, but the stools of 

 trees that have already been felled send up shoots, the leaves of which 

 could be utilised, although the stems are too young to fell. The gutta- 

 percha obtained by this means is, however, not equal to that produced 

 by incision, and the process has not yet established itself. 



The yield by felling has been variously computed at about 300 

 to 600 gm. from each tree, whereas by tapping 1,400 gm. has been 

 obtained annually ; the leaves are said to yield 10 per cent, of their 

 weight. 



Description. Crude guttapercha occurs in commerce in lumps or 

 blocks of very variable, often large size, of a brown or a greyish brown 

 colour externally, reddish yellow or reddish grey internally, and of 

 laminated or fibrous nature. It has (especially when rubbed) , an odour 

 that is not disagreeable and it is flexible though scarcely elastic. It 

 often contains mechanical impurities, from which it is freed by slicing 

 and washing it and pressing it whilst plastic through wire gauze, or by 

 softening in hot water and rolling into strips ; these are then torn by 

 machinery into shreds and the shreds kneaded into dark-brown lumps 

 (purified guttapercha). 



White guttapercha is prepared by dissolving purified guttapercha 

 in chloroform, decolorising the solution with charcoal, filtering, and 

 precipitating with alcohol. 



Purified guttapercha is firm, tough, and flexible, but scarcely 

 elastic ; it can be cut easily with a knife, and at a temperature of 

 45-60 it softens and can be rolled or drawn. It is soluble in 

 chloroform and carbon disulphide in the cold ; turpentine and benzene 

 dissolve it when warmed, alcohol and ether only partially, whilst 

 caustic alkalies and dilute acids have no action upon it. It is a very 

 bad conductor of heat and electricity, and upon the latter fact depends 

 its extensive use as an insulator. 



