﻿96 RICHMOND. 



COMPARISON OF THE ACID AND ALKALINE PROCESSES OF PULP 

 MANUFACTURE. 



Some of the points of superiority claimed for the acid or bisulphite 

 method of treatment are : greater yields, stronger fibers and greater 

 economy in the cost of chemicals consumed. The adherents of the older, 

 or alkaline method of treatment claim applicability to a wider range 

 of raw materials, greater ease of manipulation and economy in cost of 

 chemicals and time. There is no doubt but that greater yields and 

 stronger stock are obtained by the bisulphite process, for as it is strictly 

 a hydrolytic chemical reaction performed in a reducing atmosphere, the 

 possibilities of oxidation are excluded, and therefore no loss of cellulose 

 or weakening of the fiber results from this cause. 



White pine wood, which is pulped by both processes, invariably in 

 commercial practice yields about 10 per cent more sulphite than soda 

 cellulose. Sulphite cellulose, in the common practice of blending dif- 

 ferent pulps to produce papers of certain qualities required by the trade, 

 is relied upon for the property which it possesses of giving strength to 

 the materials. 



That alkaline solutions exert a solvent action on vegetable fibers is well 

 known. Taus 13 in a series of carefully conducted experiments has shown 

 that purified cotton cellulose is attacked by alkalies at the high tempera- 

 tures and concentrations frequently employed for isolating paper cellulose 

 by the soda process, and assuming that a soft wood (pine wood) contains 

 54 per cent of cellulose and 46 per cent of other matter, the latter or 46 

 per cent will be dissolved after three hours of digestion with 3 per cent 

 caustic soda solution at a pressure of five to six atmospheres, but 70 per 

 cent of the. total cellulose and other matter would be dissolved with the 

 same strength of liquor in the same period if the digestion were to be 

 carried on at ten atmospheres, and approximately the same solvent action 

 is effected if the time (three hours) and the pressure (five atmospheres) 

 remain unchanged, but the strength of the alkaline liquor increased to 

 8 per cent. Now 8 per cent (12° Baume) liquor is the rule rather than 

 the exception in the actual practice of soda wood pulp production, and 

 for the purpose of facilitating the mechanical loosening of the fibers and 

 of effecting solution of the noncellular incrusting matters in the shortest 

 possible time, pressures which are more nearly ten than five atmospheres 

 are also adopted. In my opinion more thorough and better methods of 

 preliminary preparation of woody tissue or of other raw cellular materials 

 will accomplish the same purpose with an improvement both in quantity 

 and quality of the resulting product. In all the experiments I have 

 recorded on both soda and sulphite digestion of wood, the method of 

 preparation — that is, the barking and chipping which are employed in 



"Dingler's Polyt. Journ. (1890), 276, 411^28. 



