83 



As I have already had occasion to show,j this statement is incor- 

 rect, tor the heating continnes for too short a time ; ( u the rubber " is 

 not u dried in a few minutes " ) to evaporate off some 50 per cent, of 

 water, and further there is no loss of weight until the Hot begins to con- 

 tract and squeeze out water. Neither is " the supposition devoid of all 

 reason," for it is a well-known fact that the smoked rubber is far pre- 

 ferable to that obtained by chemical processes. A comparison of the 

 prices of " Para fine " and " sernambv " should be sufficient proof of 

 this. Why it is so, may be made dearer from the following experiment. 

 At the end of a dav's work I had several litres of latex left, to which an 

 equal volume of water had been added, which would not keep over night 

 without coagulating. To this a small quantity of acetic acid was added, 

 and in a short time the whole or it had formed a stiff card. On pressing 

 and drying, a poition of the water exuded from this mass of sernambv, 

 but it still remained full of cavities, and the proteid matter in it quickly 

 decomposed, so that ultimately a stinking, inflated mass was obtained. 



If this latex had been coagulated by smoking it would have yielded 

 a wet rubber, but the subsequent decomposition of proteids would not 

 have set in, for the creosote contained in the smoke would have acted as 

 an antiseptic and prevented decomposition, as it does when meat is pre- 

 served bv smoking. * 



Then again we find, ''the rubber thus prepared (by smoking) 

 acquires a darkish colour, due to the particles of coal which adhere to 

 the outer skin. Some people believe that this tends to improve it. but 

 such is not the case, for it is thus impregnated with impurity."§ Now 

 when these " bottles " of rubber are cut across, the fresh, laminated sur- 

 faces are a silvery grey colour, and as each layer is exposed to the same 

 extent to the action of the smoke it is difficult to account for the outer 

 layers only being so coloured. The freshly cut surfaces however soon 

 darken and become black in turn, so that the explanation of oxidation 

 seems far more probable, especially when taken in conjunction with the 

 fact that smoke is white * and not black, f for the nuts are simply dry- 

 distilled and not actually burnt. If the smoke of these heated urucuri 

 nuts is condensed, it forms two layers of liquid in the receiver, one a 

 clear limpid solution consisting mainly of acetic acid, the other, darker 

 in colour, A creosote. 



The hot vapour of acetic acid brings about the coagulation of the 

 proteids of the latex, as may easily be proved by direct experiment. 



A solution of alum is -aid to be in use for preparing rubber in some 

 parts of the Amazon valley. Morisse** states that alum solution ha< no 

 effect upon the latex of Hevea species however. 



The loss in the factories on making up Para rubber is as follows || : 

 (1) Para fine, 10 to 15 per cent. ; (2) Entre-fine, the carelessly smoked 

 pieces, 15 to 20 per cent. ; (3) Sernambv, rubber pulled from the cuts 



X Biffen, 4< Anns. Bot." 1898, p. 165. 

 % " Trinidad Bulletin." 1897. p. 38. 



* Compare the plate on page 757 of the " Journ. Soc. Arts." 1898. 

 + " Trinidad Bulletin," 1897, p. 37. 

 ** " Le Caoutchouc," &c. p. 67. 

 II " Le Caoutchouc," &c, p. 75. 



