74 THE PREPARATION OF RUBBER 



cavities. It is at first quite soft and can be readily torn, 

 but if allowed to stand for some time or if submitted to 

 pressure in order to squeeze out the contained liquid its 

 tenacity increases and it assumes the well-known physical 

 properties of rubber. On drying, rubber becomes trans- 

 lucent and develops more or less colour, the commercial 

 product varying from a very pale straw colour to black. 

 The development of the colour appears to be due to the 

 action of oxidising enzymes present in the latex. 



The form in which rubber is prepared by natives varies 

 widely according to the botanical source and the country 

 of origin. Thus Para rubber from South America comes 

 on the market in large, rounded masses, which have a 

 strong smoky odour ; Funtumia rubber from Africa and 

 Castilloa rubber from Central America are prepared in 

 the form of cakes or lumps which are often of considerable 

 size ; the Landolphia rubbers, again, are commonly made 

 into balls of various sizes, or into spindle-shaped or 

 sausage-shaped pieces, or into small cubes (see Plate I). 

 Most of the commercial rubbers prepared by natives have 

 distinctive forms which do not vary. 



On plantations the rubber is usually prepared either 

 in the form of " biscuits " or sheet, or, by means of 

 machinery, as sheet or crepe. The manufacture of 

 biscuits is a convenient method when only small amounts 

 of rubber are being obtained daily ; but when larger 

 quantities have to be dealt with, the use of machinery 

 becomes essential. 



The first step is to strain the latex, diluted with water 

 if necessary, in order to remove all solid impurities. 

 This is accomplished by passing it through sieves of fine 

 wire gauze or cloth, or by means of a centrifugal strainer. 

 In the manufacture of biscuits or sheet a definite quantity 

 of the strained latex is poured into shallow enamelled 

 vessels (which may be round, square, or rectangular) and 

 the requisite amount of a coagulant is added if necessary ; 

 the latex is then allowed to stand until coagulation has 

 occurred -and the cake of rubber is found floating on the 

 liquid. The rubber is lifted from the liquid, placed 

 upon a sloping table and pressed, at first with the hands 

 and finally with a wooden roller, in order to remove the 

 water as completely as possible. The cakes are then 

 washed with water and placed upon sloping tables to 



