Fibres, 



[November, 1909. 



are unsuitable for the manufacture of 

 any but the lowest classes of printing 

 paper. 



Mechanical pulp is placed on the 

 market in two forms ; as " wet mechani- 

 cal" and "dry mechanical." The bulk 

 of the mechanical pulp imported into 

 this country is shipped in the wet 

 condition ; of this quality the imports in 

 1908 were 422,957 tons. In the same 

 period, only 51,757 tons of the dry pulp 

 were returned. During recent years 

 very large shipments of mechanical pulp 

 have been received from Canada, which 

 is now an important source of supply. 



Chemical Pulp. 



The manufacture of chemical pulp is a 

 much more complicated operation. The 

 wood which forms the raw material 

 consists of about two-thirds pure 

 cellulose, with one-third non-cellulose 

 compounds. By removing the latter 

 bodies, a practically pure collulose fibre 

 is obtained, inferior only to that derived 

 from rags and Esparto grass. To attain 

 this object, various processes of chemical 

 treatment are in use, and the particular 

 reagent used gives its name to the 

 resultant product ; hence we have in 

 commerce soda pulp, sulphate pulp, and 

 sulphite pulp. In each of these pro- 

 cesses the wood undergoes the same 

 preliminary treatment. The trees are 

 sawn into small logs, and the bark is 

 removed. The logs are then passed 

 through a sloting machine, which turns 

 them into small boards ; the knots are 

 bored out, and the boards are passed 

 through a breaker, which resolves them 

 into chips, after which the chips are 

 screened to remove the dirt and dust. 



Tbe soda process consists in digesting 

 the chips for about twelve hours, with a 

 strong solutiou of caustic soda. The 

 high temperature and pressure involved 

 in this process affect the cellulose in- 

 juriously, the yield and quality of the 

 fibre being inferior to those obtained in 

 the sulphite process. In the sulphate 

 process, the digesting solution is a 

 mixture of sodium sulphate, sodium 

 sulphide, and caustic soda. The pulp 

 produced although uniform in strength 

 is also inferior to that obtained from 

 the sulphite process ; it contains more 

 of the outer substance of the wood, 

 and consequently is darker in colour, 

 and must be employed for the pro- 

 duction of inferior goods. It finds an 

 outlet in the manufacture of wrapping 

 papers, and for the production of these 

 it is well suited. Sulphate pulp is largely 

 used by Scandinavian paper-makers, 

 whose "Kraft" wrapping papers have a 

 high reputation in the trade. The 

 sulphate process is extensively adopted 



in the United States for the production 

 of pulp from poplar wood, and sulphate 

 pulp is also employed by British paper- 

 makers for maxing with Esparto grass, 

 which latter material it is now supplant- 

 ing to some extent. Its use as a sub- 

 stitute for Esparto, however, calls for 

 special care in the washing operation. 



The disadvantages of the two preced- 

 ing methods of treatment are overcome 

 in the sulphite process for the manu- 

 facture of chemical pulp. In this case a 

 solution of a bisulphite of lime or mag- 

 nesia is employed in the digesting oper- 

 ation. The Eckman process consists in 

 digesting the wood in a lead-lined revolv- 

 ing digester. In preparing the solution, 

 sulphurous acid gas is passed through a 

 tower containing the magnesia, the sul- 

 phurous acid and magnesia being kept 

 in the necessary proportions to form a 

 double sulphite, the resulting solution 

 containing about 1\ per cent, of magnesia 

 and 4^ per cent, of sulphurous acid. The 

 digesting process occupies about 11 

 hours, and the pressure employed is 

 about 90 lb. to the square inch. In the 

 Partington process, the sulphurous acid 

 gas is absorbed in milk of lime, and the 

 bisulphite solution is at once obtained ; 

 in this process the wood is digested for 

 about 18 hours. In the Mitscherlich 

 process a weaker solution is employed, 

 with a lower pressure, and the boiling 

 is continued for a much longer period, a 

 higher percentage yield of pulp being 

 obtained. 



In 1908, 315,941 tons of chemical pulp 

 were imported ; of this amount 288,655 

 tons were shipped in the ''dry" con- 

 dition, that is, containing 90 per cent, 

 of absolutely dry pulp and 10 per cent, 

 of moisture. Of "wet" chemical pulp, 

 only 27,286 tons were taken by British 

 paper-makers. The Scandinavian mills 

 supply about one-half of the output of 

 chemical pulp. 



In view of the fact that wood pulp i9 

 brought into the market in what is 

 known as the •' wet " condition, the 

 exact amount of moisture which it 

 should contain has been the subject of 

 much controversy. In order to preserve 

 the nature of the fibre, it is essential 

 that chemical pulp shall not be com- 

 pletely dried ; while in the case of 

 mechanical pulp, the cost of drying 

 would be greater than the additional 

 cost of carriage involved by shipping it 

 in the wet condition. Accordingly, 

 certain percentages of moisture are re- 

 cognized in the trade, and the pulp is 

 brought on this basis. In practice, 

 however, it very frequently happens 

 that the specified limits are considerably 

 exceeded, and therefore a careful system 



