Oct. 1906.] 



281 



GUMS, RESINS, SAPS AND EXUDATIONS. 



Rubber Vulcanisation. 



By M. Kelway Bamber. 



A Lecture delivered at the Ceylon Rubber Exhibition, Royal Botanic Gardens, 



Peradeniya, on September 18th. 

 Dr. J. C. Willis, Director, Royal Botanic Gardens, presided at this lecture, and 

 there were also present :— Mrs. J. 0. Willis, Mr. and Mrs. Jas. Ryan, Mr. and Mrs. S. P. 

 Jeft'ery, Mr. and Mrs. W. H. Biddulph, Messrs. R. D. Tipping (S. Coorg), E. S. Campbell 

 (Lanadron Estate, Johore), I. Etherington, A. de Zilva, R. Hugh Pereira, A. M. 

 Fernando, 0- J. Bayley, G. Graham Clarke, A. C. Mathew, D. G. Brebner, A. J. Dawson, 

 R. L. Proudlock (Mysore), J. Cameron (Mysore), G. N. Pairhurst, J. P. Ireson, A. W. 

 Greig, G. A. Greig, F. W. de Hoedt, J. B. Carruthers (F.M.S.), P. H. Aste, R.K. Clark, 

 J. H. S. Rogers, H. F. Macmillau, E. Ernest Green, C. O.jMacadam, Thos.Tetch, J. H. 

 Betts, Dr. A. Lehmann (Mysore), J. Coryton Roberts, Herbert Wright, C. M. 

 Buckworth, Dr. Cuthbert Christy, Mr. A. N. Galbraith. Mrs. H. F. Tomalin, Messrs. 

 Edgar Turner, A. T. Rettie, C. H. E. Zacharias (F.M.S.), C. K. Smithett, H. M. Devitt, 

 C. L. Devitt, C. G. Devitt, G. Brnce Foote, W. A. Horn, W. A. Goodman and several 

 others. 



THE LECTURE. 



Mr. Bamber, who was received with applause, said :— Ladies and gentlemen, 

 before describing the vulcanisation of rubber it may be advisable to describe the 

 actual latex. Raw caoutchouc may be defined as the thickened or dried-up latex of 

 certain species of plants. Taking the latex of Hevea Brasiliensis as typical of 

 most latices, it is as it leaves the tree a white-looking milk-like fluid containing 

 variable quantities of minute globular particles, the diameters of which average 3'5 

 micro-millimetres, though the range is great. (One micro-millimetre is the one- 

 thousandth part of a millimetre.) The specific weight of latex containing 32 per 

 cent of caoutchouc is 1*018 at 60° Fahr. It is these microscopic globules that consti- 

 tute the real caoutchouc when caused to agglomerate into a mass, either by drying 

 and smoking, the addition of acids, or certain other chemicals, or by bacterial 

 decomposition of proteid matter, &c, in the latex with production of a free acid 

 causing coagulation somewhat analagous to the curdling of milk. The chemical 

 composition of the fresh latex from mature trees and for the first tappings during 

 more or less dry weather is as follows :— 



Caoutchouc ... ... ... 32*00 percent. 



Nitrogenous matter ... ... 2*03 ,, 



Mineral ... ... ... 9'07 „ 



Resinous ... ... ... 2*03 



Water (faintly alkaline) ... ... 55*56 ,, 



I noticed that in the lecture yesterday a question was raised as to 



THE AMOUNT OP CAOUTCHOUC IN BRAZILIAN RUBBER, 



and I now find from old analyses that Professor Faraday gives it as 37 7 per cent, 

 which is higher than anything we have had here. It is however liable to great 

 variation under different climatic conditions, age of tree, soil and numerous other 

 causes, which it is needless to enumerate here. When latex is coagulated in a vessel 

 by means of acid, the globules do not first rise to the surface like cream and then 

 amalgamate, but coagulation takes place throughout the mass of liquid, the rubber 

 at the moment of formation having the shape of the containing vessel. As soon as 

 coagulation has set in, the rubber instantly acquires its elastic property, and being 

 specifically lighter than water contracts on itself upwards, at first slowly, but with 



