3ii 



PREPARATION OF RUBBER. 



By P. J. Burgess. 



The Committee of the Agri-Horticultural Show held in Kuala 

 Lumpur early in August, 1904, invited me through the Government 

 of the Straits Settlements to give a lecture and demonstration on 

 the chemistry and the mode of preparation of marketable rubber. 

 The following account of the lecture I have written at the special 

 request of the Federated Malay States Government, and in it I have 

 tried to repeat as far as can be done those facts and ideas which 

 were then publicly stated and which were illustrated by experiment. 

 The lecture was not written out beforehand neither were formal 

 notes of it prepared and consequently I can, in this account of it, 

 only give the substance and not the form of what at Kuala Lumpur 

 was partly lecture, partly demonstration and partly discussion. 



The trees on which the attention of so many is now Hxed are of 

 two kinds Hevea Brasiliensis, the Para rubber tree, and Ficus 

 Elastica or Rambong. Those Irees I shall not describe, neither 

 shall I discuss the mode of extraction of the " latex " from the tree, 

 but suppose that the latex has been extracted and is now ready to 

 be examined. 



In appearance it is a white or pale yellow milky liquid — its 

 odour is pleasing and faintly aromatic, and if tasted it is found to 

 be slightly sweet. In reaction it is, when fresh and pure, the re- 

 verse of acid, that is to say, slightly alkaline. If greatly magnified 

 it is seen to consist of innumerable minute globules floating in a 

 colourless clear liquid. The globules are in size comparable to 

 bacteria, and though passing freely through ordinary filters can be 

 separated by means of Pasteur Chamberlain filter tubes. 



These globules consist of rubber mixed with a small but variable 

 percentage of oils and resins, the nature of which has not vet been 

 worked out. 



The liquid in which they are suspended is water carrying in 

 solution some gum, sugar, mineral salts and proteid or nitro- 

 genous matter. 



Some of this liquid was prepared by filtering the latex and shewn 

 during the lecture. This liquid when filtered from fresh latex 

 shews an alkaline reaction ; if an acid such as acetic acid be 

 added a chemical reaction takes place and the proteid is thrown 

 out of solution, appearing as a fine precipitate, at first barely visible 

 as a faint opalescence but which finally settles out and sinks, leav- 

 ing the clear liquid above. 



This reaction gives the key to the explanation of the coagulation 

 of the latex on the addition of acid, a method very generally 

 practised by rubber growers. The rubber globules in suspension 

 in the original latex do not interfere with the proteid precipitation 

 which occurs on the addition of acid, but they are caught and 



