THE CARBOHYDRA TES PRODUCED IN CROPS 129 



often lose from one-third to one-fifth of their weight through 

 the process of boiling, whilst inferior materials will lose much 

 more. After being boiled, the material is washed, and broken 

 up, so as to disintegrate all the fibres. When the materials 

 used for paper -making require bleaching, chlorine gas, 

 bleacliing powder or electrolyzed magnesium chloride is 

 used. The first named is the least satisfactory, and the last 

 the best. The paper pulp is then separated from the water 

 by some kind of sieve. Under old-fashioned systems this 

 was often done by hand, but it is now mostly done by 

 continuous machines, which separate the paper pulp from 

 the liquors, often with the aid of a certain amount of suction, 

 produced by a pump. The paper is rolled by rollers, some- 

 times with the aid of steam heat. 



Destructive Distillation of Cellulose.— All forms 

 of cellulose, when destructively distilled, produce char 

 coal, tar, acetic acid, water, gas, and a few other special 

 products. The crude forms of cellulose commonly used for 

 this process introduce many other substances in small 

 amounts. The form of cellulose most commonly used for 

 this distillation is some form of wood which is no longer 

 useful for other purposes. In felling timber the amount 

 of wood useless for any of the purposes to which timber is 

 commonly put will generally exceed in weight that 01 the 

 useful material. Probably each 1000 acres of wood produce 

 forty tons per annum of woody material of no value for 

 ordinary purposes, much of which can be destructively 

 distilled and converted into useful products. The distillation 

 of these materials can be divided into two separate systems, 

 that in which the wood is brought to the still, and that in 

 which the still is taken to the wood. Where it is possible 

 to convey the wood to the still, the still can be constructed 

 of fairly large dimensions. The best of these systems 

 needs a large retort, eight or ten feet in diameter, and fifty 

 or one hundred feet long. Two or more of these are set 

 in a big setting, and heated with flue gases from furnaces. 

 The temperature in the flues should be between 400** and 

 500° Cent., and the escaping products of combustion will 



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