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nent materials which are prone to decompose with the formation of acid.

The preliminary boiling or sour boiling is earned out in large

Figure 62. Nitrocellulose Fibers before Beating (132X).

wooden tubs heated by means of steam. At the beginning the nitrocellulose is boiled with water which contains 0.2br/o to 0.50c/o of acidity calculatcd as sulfuric acid. The first boil lasts usually for 16 hours during which time the acidity of the solution increases. The increase is due largely to actual sulfuric acid. After 16 hours the steam is shut off, the solution is decanted from the nitrocellulose, the tub is filled with fresh water, and the material is boiled again for 8 hours. The boiling is repeated until each tubful has been boiled for 40 hours with at least 4 changes of water. 262

The hollow fibers still contain an acid solution within them. In order that this acid may be washed out, they arc pulped or broken up into short lengths by means of apparatus like that which is used in the manufacture of paper. A Jordan mill cuts the fibers off rather sharply, leaving square ends, but a beater tears

Figur* 63. Nitrocellulose Fibers after Beating (132X). (Courtesy Western

Cartridge Company.)

Figur* 63. Nitrocellulose Fibers after Beating (132X). (Courtesy Western

Cartridge Company.)

them, leaving ends which appear rough and shredded under the microscope and which result on the whole in the better opening up of the tubular fibers. The two machines arc usually used in series. A weak solution of sodium carbonate is added during the pulping to neutralize the acid which is liberated. The pulping is continued until the desired fineness has been attained as shown by laboratory test.

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