CAOUTCHOUC AND ITS ALLIES. 183 



exceha, however, the outflow of resin apparently remains unaffected, 

 even if a portion of the heartwood is removed in making the blaze. 



Those of our conifers, the tapping of which is likely, in a near 

 future, to become a large and profitable exploitation, comprise the 

 three pines, EJiasya, Merkusii, and longifolia, and perhaps also the 

 excelsa. The aggregate areas covered by these pines are estimated 

 respectively at roughly 200, 50, 2,000, and 100 square miles ; but 

 in these figures is probably included a large proportion of poorly 

 stocked areas. The resin of the Khasya pine is the best, as it yields 

 a purer oil than any other conifer resin in the world. The oil of 

 Pinus longifolia is the least pure and has the least pleasant odour. 

 It has also the great defect of not drying quickly — a characteristic 

 which unfits it for the manufacture of varnishes. Excluding im- 

 purities, the turpentine consists of 18 per cent, oil and 82 per cent, 

 colophony. The corresponding figures for Pinus excelsa are 22 

 and 78 respectively. 



The utilization of the various turpentines will before long give 

 rise to an important forest industry from the borders of Afghanis- 

 tan to the frontier of Siam. A short account of the manufacturing 

 processes through which the raw product passes will hence be given 

 in Part III. 



Section III. — Caoutchouc and its allies. 



These substances are found suspended, in the form of small gra- 

 nules, in the latex of numerous plants belonging principally to the 

 Euphorhiacece, Apocynacece, Asclepiadece, Sapotacece, Lobeliacece, and 

 Urticacece. The latex, after a shorter or longer exposure to the air, 

 becomes coloured brown, and the granules separate of themselves 

 from the rest of the liquid and form a solid independent mass. 

 Caoutchouc is insoluble in water, acids, alkalies, and alcohol ; solu- 

 ble, but without any chemical change, in carbon disulphide. Its 

 composition is complex, but its market value depends upon a pro- 

 portionate abundance of the elastic substance, with a relative ab- 

 sence of a certain oxidized, viscid, resinous body soluble in alcohol, 

 whose formation is in great measure prevented by rapid evapora- 

 tion of the milk and other means of avoiding oxidation. 



In India the only species tapped on a large scale for caoutchouc 

 is the Ficus elastica. In Burma Parameria glandulifera is said to 

 yield a product equal to the best Para rubber, and Urceola esculenta 

 is described as very abundant, but not yielding as good a rubber. 

 Both are Apocynaceous climbers. They are not tapped, but cut 

 down, and the bark is at once stripped off and boiled. The hot 

 water, however, causes much of the milk to coagulate inside the 

 bark and thus reduces the yield very considerably. 



