RUBBER 665 



the constituents of the fumes from the fuel, to the 

 elevated temperature in the presence of an atmosphere 

 deficient in oxygen or rich in carbon dioxide, or to the 

 preservative action of the fumes, due to some particular 

 constituent of the smoke, on the protein material in the 

 rubber, remains to be investigated. 



The form of rubber smoked now is almost entirely 

 sheet; the demand for smoked crepe has ceased, due 

 possibly to the fact that lower grades of rubber could, 

 by being smoked, be made to resemble closely first-grade 

 crepe, the various defects being obscured by the dark 

 colour of the smoked product. The best type of smoke- 

 house is the two-story building, resembling the Kent hop 

 kiln or drier; the sheets of rubber are hung on racks in 

 the top story and the fuel burnt in a hole in the ground 

 of the bottom floor, or preferably in shallow fire-boxes 

 on wheels. A wire-gauze box should be placed over these 

 fire-boxes to retain dust and sparks, or wire gauze may 

 be placed in the openings below the rubber racks. A 

 maximum and minimum thermometer should be kept in 

 the top story as a check on the temperature; if the tem- 

 perature rises above 120 F. during the day smoking 

 should only be carried out between 4 p.m. and 9 a.m. 



Sheet of average thickness (about J in.) is completely 

 dried in from ten to fourteen days, but smoking may be 

 carried beyond this period and, according to tests 

 carried out by the chemists of the Rubber Growers' 

 Association, appears to improve the quality of the rubber. 

 Fairly dry jungle wood or wood mixed with coconut 

 husks provides a suitable fuel; if the latter alone is used 

 the rubber has the appearance often attributed to " over- 

 smoking," as the fumes are rich in tarry and creosotic 

 substances. 



Other Processes of Preparation. 



I propose in this section to deal briefly with four of 

 the principal processes which have been tried on a more 

 or less commercial scale and which appear to be pro- 

 mising in several ways. These processes are all imita- 

 tions of the Amazonian smoke-curing process and are 

 as follows: (i) Berry's process; (2) Wickham's process; 



