360 CHEMICAL DISCOVERY AND INVENTION 



is left in the form of a pulp, which after washing free from soda 

 requires to be bleached. The bleaching is effected largely by 

 the use of so-called chloride of lime or bleaching powder, but in 

 some of the modern processes chlorine is produced electrolytically 

 from magnesium or sodium chloride solution in which the pulp is 

 immersed. 



In the second class of processes the acid bisulphite solution 

 required is obtained by passing through or over a milk of lime 

 or magnesia, the sulphur dioxide gas formed by burning sulphur 

 or iron pyrites in suitable kilns. The wood is digested with this 

 solution for many hours at temperatures running from 120 to 

 140 C. The yield of pulp is greater than in the case of the soda 

 process, and amounts to about 40 per cent. The brownish 

 product is then bleached as already described. 



The bleached pulp, however produced, is next subjected to a 

 process of " beating " by which the individual fibres are separated 

 and a perfectly smooth pulp is produced. With this is incor- 

 porated the size and the various colouring matters or loading 

 material, such as china-clay, which are required according to the 

 quality of the paper to be manufactured. The pulp is then ready 

 for the paper-making machine. 



In all these operations there is full opportunity and need for 

 chemical study and supervision in improvement of processes or 

 recovery of waste products, but in a superficial sketch it is 

 impossible to supply the details which, moreover, are to be found 

 in the several technical treatises to which the reader interested in 

 these matters is referred. (See Thorpe's Dictionary of Applied 

 Chemistry, Arts. Cellulose, Paper, etc.) 



For the production of the cheaper kinds of paper a large 

 quantity of wood pulp is produced without chemicals by 

 mechanical crushing in a stream of water which carries off the 

 pulp as it is produced. 



The importance of this branch of manufacture can be roughly 

 estimated from the figures to be found in the official publications 

 of the Board of Trade. We learn from the Report of the First 

 Census of Production of the United Kingdom (1907) that the 

 value of the paper produced in the United Kingdom amounted 

 at that time to about 13 J million pounds sterling. 



From the annual statement of the Board of Trade for 1913, 

 the following further figures have been gathered which show, at 

 any rate, that the consumption of paper in Great Britain is 



