Chemistry of pulp and paper making by Sutermeister Edwin b. 1876

Author:Sutermeister, Edwin, b. 1876
Language: eng
Format: epub, pdf
Tags: Paper industry, Wood-pulp, Papermaking
Publisher: New York : John Wiley
Published: 1920-03-25T05:00:00+00:00

Wochbl. Papierfabr., 39, 2273.

as well-bleached pulps which have already reached a good degree of whiteness are made distinctly gray by the addition of blue and pink. If any considerable amount of blue has been added to the pulp it is generally quite noticeable, especially on looking through the suspected sample. When a smaller amount has been used its presence may usually be detected by rolling the sample into a tube and looking through it, in which case the multiple reflections of the light before reaching the eye intensify the color.

There is a tendency with all bleached fibres to change somewhat in color when kept for any length of time and while the alteration which takes place is shght and the chemistry of the process obscure, yet experiments have brought out some interesting facts. It has been shown that bleached sulphite which has been stored in well-seasoned hard-wood or tin receptacles hardly changes in color within six months, while similar samples stored in pine-wood boxes became somewhat yellower in the same time. Direct exposure to sunlight gives sulphite a reddish tone while if part of the sheets are protected from the light by black paper the portions thus protected become much yellower than the fibre before exposure. Soda fibre is more susceptible to these changes than sulphite and the more highly bleached the fibre the more rapidly it appears to deteriorate. These facts have a distinct bearing on the preservation of standard samples of bleached pulps and indicate the precautions which should be taken in studying the changes which take place on exposure to light.

Testing Bleaching Powder. In testing bleaching powder the first requisite is a fair sample. This should be obtained by boring a hole through the side of the cask midway between the ends or through the head near the centre, and inserting a sampler two or three inches into the bleach. The first sample should be rejected and the sampler again inserted as far as it will go, the sample thus obtained should be placed at once in a glass fruit jar which must be closed until the next cask is sampled. Every third or fourth package should be sampled, according to

the size of the shipment, but in no case should less than 20 per cent of the total packages be opened.

The sample should be well and quickly mixed, breaking up any lumps with a stout glass rod, and 10 grams weighed out, put in a porcelain mortar, a little water added and the mixture rubbed to a smooth cream. More water is mixed in with the pestle, allowed to settle a little while and then poured off into a liter flask; the sediment is again rubbed up with water, and the process repeated till the whole of .the sample has been transferred to the flask and the mortar washed quite clean. The flask is then filled to the mark, thoroughly shaken and 50 c.c. at once removed with a pipette and placed in a beaker or cup.

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