240 TIMBERS AND THEIE USES 



The dark brown lye is treated for the recovery 

 of the soda by the process of evaporating and 

 calcining." 



A process which, in Europe, has almost en- 

 tirely superseded the above, consists in using a 

 lye consisting of three parts of caustic soda to 

 one part of sulphate of soda. It is used mainly 

 for obtaining chemical pulp from conifers. " A 

 direct function of the sodium sulphate may be 

 to limit the hydration of the cellulose of the 

 .fibre under the attack of the caustic alkali at 

 the high temperatures necessary for the resolu- 

 tion of the ligno-cellulose ; and this secondary 

 effect of the process favourably affects the yield 

 of cellulose which is about 10 per cent more 

 than that obtained with caustic soda alone ; 

 moreover the fibre is in a better state of preserva- 

 tion and of superior quahty." An unpleasant 

 part of the process is the evolution of evil- 

 smelling gases ; useful by-products, however, are 

 obtained, and " the recovery of methyl alcohol, 

 oil of turpentine and an inferior grade of resin, 

 suitable for the sizing of brown papers, is 

 practised on a commercial scale." 



" Soda or sulphate pulp is characterized by 

 the dull brownish shade in the unbleached con- 

 dition " ; it requires considerably more bleaching 

 powder than sulphite pulp for the production 

 of a fair white colour, but the brilUancy obtain- 



