CHAPTER XIV. 

 PURIFICATION OF RUBBER. 



Analysis of washed and dried Para— Purification by the manufacturers 

 — Loss in brands of Para rubber — Plantation versus Wild Para — 

 Lawrence's apparatus — Loss on washing rubber — Oily and resinous 

 substances and ash in various rubbers — Determination of loss on 

 washing— High Ins- undesirable— Purification by the growers — 

 Rubber washing machines —Burgess's account of a washing machine: 

 construction and action— Illustration of a washing machine — 

 Advantages of washing rubber —Scrap and dirty rubber. 



HAVJX(! dealt with the properties of the latex and the various 

 methods of preparing rubber therefrom, it is now necessary to 

 consider the important question of the condition of the rubber when 

 it enters the market, and the processes through which it passes in 

 purification. It is possible that much time and trouble may be saved, 

 and at the same time a rubber of higher quality be produced, by carry- 

 ing out certain purification processes in the initial stages. The con- 

 dition of the rubber when it arrives in Europe is well-known to most 

 cultivators, as it undergoes no changes during transit if it has 

 been properly prepared. An ordinary sample of washed and dried 

 fine Para rubber may contain the following : — 



Rubber . . . . 94-0 per cent. 



Resinous matter .. 2*5 ,, 



Albumious matter . . 3-0 , , 



Mineral matter . . ■ 5 



Very often grades of washed rubber, prepared carelessly, contain 

 nearly 20 per cent, of impurities, and in the case of " scrap " rubbei 

 the question of purification may become a serious one. 



Purification by the Manufacturers. 



The scraps of fibre, particles of sand, abundance of resins, albu- 

 minoids, and mineral matter are not required in the finished product, 

 and the mechanical and soluble impurities are, as far as possible, 

 removed by the manufacturer. In Europe the rubber is first cut 

 into small pieces and placed in tanks containing hot or boiling 

 water. It is then put through the washing machines, the rollers of 

 which tear, cut. and expose all parts of it to a current of clean water. 

 The success of this method depends upon the rubber being cut into 

 sufficiently small pieces and soaked for the proper length of time in 

 water maintained at the desired temperature. The washing process 

 removes every kind of mechanical impurity, the fragments of fibre, 

 sand, &c, flying out of the softened rubber when it is stretched and 



( 17) 



