CELLULOSE. 551 



manure. Ashes when freed from earth and pieces of charcoal 

 yield the following percentages of potash : 



Silver-fir 39'9 



Oak 33-3 



Beech 28-6 



Birch 23-6 



Larch 23'6 



Spruce 19'7 



Scots pine ..... 14*3 



By washing the ashes, hoiling the solution so as to evaporate 

 the water and heating the residue, potash is obtained. 



SECTION IV. CHEMICAL AGENCIES FOR OBTAINING THE 

 CONSTITUENTS OF WOOD. 



(a) Cellulose. Cellulose is employed chiefly for making 

 into paper. Paper-pulp obtained from wood is not only 

 cheaper than that prepared from rags, hut gives clearer print 

 and wears away the type less. On the other hand paper that 

 contains much wood-pulp soon becomes brittle and yellowish ; 

 hence much of the paper made from wood is useless after 

 about ten years, and it cannot be used for important docu- 

 ments. Unmixed wood-pulp is, therefore, used chiefly for 

 pasteboard, packing paper and the coarser kinds of paper. 

 For superior paper some rag-pulp must be mixed with wood- 

 pulp. Nevertheless, the amount of rag-pulp used depends 

 essentially on the process employed in making wood-pulp, 

 and good wood-cellulose is considered as an alternative for 

 rags. 



The wood of aspen and lime are preferred for paper-pulp, 

 but as they are quite insufficient for the demand for this 

 material, coniferous wood is used, chiefly that of spruce. 

 Besides these woods those of poplar and birch, and in 

 America those of Liriodendron and Weymouth pine, are 

 employed. Poles and logs of 10 to 30 cm. (4 inches to 

 12 inches) in diameter, prepared as for firewood billets, were 

 usually chosen. At present wood of larger dimensions is 

 employed, as the cost of transport, etc., is considerably less. 



