660 RUBBER 



an estate is only just coming into bearing, the rolling is 

 carried out on hand machines. In the case of the lower 

 grades, e.g., tree scrap, and especially bark shavings, 

 hand machines are not sufficiently powerful, as such 

 rubber and debris 'require considerable maceration and 

 washing. When possible in such cases low grade 

 material is treated on a neighbouring estate till mechanical 

 power is available in the factory concerned. 



Before machining No. i sheet or crepe rubber from 

 first quality latex, the coagulum should be allowed to 

 stand from four to six hours after the coagulant is added 

 to the latex. As a general rule it is left overnight and 

 machined the following morning, the lower grades being 

 treated during the afternoon. 



On some estates, especially before the use of sodium 

 bisulphite became general, crepe rubber was prepared 

 from the freshly coagulated rubber by macerating and 

 washing about half an hour, or even less, after coagula- 

 tion, in order to avoid the darkening due to natufal 

 oxidation caused by oxidizing enzymes present in the 

 latex, which proceeds slowly after the latex is collected. 



Sheet Rubber. In the preparation of sheet rubber only 

 two machines are necessary, a plain even-speed roller 

 machine in which most of the moisture is pressed from 

 the rubber, and a diamond or a spirally grooved crepeing 

 machine to mark the plain sheet. Care has to be taken 

 while marking the sheets that the rollers of the crepeing 

 machines are not too close together, otherwise macera- 

 tion of the rubber takes place. To those who may not 

 be acquainted with the principle of marking sheet, it may 

 be stated that the sole idea of this ribbing of sheets is 

 to enable the sheets to be more easily separated from 

 each other when removed from the packing cases, as 

 they are not so liable to stick together as in the case of 

 plain sheet. 



Crepe Rubber. In the preparation of crepe rubber 

 one machine only could be used, namely, a machine with 

 spirally or diamond cut rollers running at uneven speeds; 

 crepe, however, which is only machined between 'such 

 rollers is very uneven in thickness, i.e., very corrugated, 

 and dries very unevenly, being thus more subject to spot 

 diseases caused by bacteria and fungi. For this reason 



