THE PREPARATION OF RUBBER 75 



•drain ; whilst still soft they are usually branded with 

 the name of the estate. They are finally transferred to 

 the drying- chamber, where they are spread out on open 

 shelves formed of wire or wooden lattice, or they are 

 hung up on wires until they are perfectly dry. The 

 thin ckcular cakes obtained in this way are known as 

 " biscuits," whilst the square or rectangular cakes are 

 termed " sheets." This method of preparation is specially 

 suitable for Para and Ceara rubber. 



When large quantities of latex have to be dealt with, 

 however, the production of biscuits is rendered impossible 

 owing to the enormous amount of labour involved, and 

 machinery is now generally employed. The strained 

 latex is coagulated in bulk in large tanks by the addition 

 of a suitable reagent, and the freshly coagulated rubber 

 is at once rolled out into sheets by means of a washing- 

 machine similar to those employed in rubber factories. 

 This machine consists essentially of two horizontal steel 

 rollers which rotate at equal or different speeds and can 

 be set at varying distances apart. The rollers are some- 

 times smooth, but are more generally grooved in order to 

 give a grip on the rubber. A stream of hot or cold water 

 passes between the rollers whilst the rubber is being 

 treated, and thus submits it to a thorough washing. The 

 rubber is passed through the machine several times, the 

 distance between the rollers being gradually reduced 

 until a sheet of the required thickness is obtained. If 

 the rollers are not grooved, smooth sheet is obtained ; 

 if the roUers are grooved and rotate at nearly equal 

 speeds, sheets showing the pattern of the rollers are 

 produced ; whilst if the rollers are grooved and rotate 

 at unequal speeds, the rubber is subjected to a stretching 

 or tearing action whilst being rolled out and is converted 

 into the corrugated sheet known as crepe. The advan- 

 tages of the use of machinery are that large quantities of 

 rubber can be quickly prepared in a form which permits 

 of rapid drying and that the rubber is thoroughly washed 

 in the process. 



The crepe rubber, after drying, is sometimes converted 

 into blocks by submitting it to pressure in steel moulds. 



Drying of Rubber. — Freshly prepared rubber always 

 contains a considerable amount of water, the bulk of which 

 should be removed before shipment if the rubber is to 



