From Paper-mill to Pressroom

by William Bond Wheelwright

5.—Folding endurance is determined on a machine which folds a strip of paper back and forth in a slot, the strip being clamped at either end to a spring device which maintains a uniform tension. The number of double folds which the strip withstands is automatically registered. This test is favorably regarded as an indicator of durability, but the apparatus is expensive and not easily available, hence this test fails of frequent use.

6.—The absorption tests are applied principally to blotting-paper, and consist in suspending equal widths of paper so their ends are submerged in a beaker of colored water. The height the water rises in a given time demonstrates the capillary attraction.

7.—Expansion is estimated by taking strips of uniform dimension, dipping in water and measuring the expansion.

Chemical tests are for the determination of (1) the percentage of mineral filler; (2) the percentage and nature of sizing materials; (3) qualitative test for starch, acid, sulphur, chlorine, glue, filler material, dyes, ground wood.

The amount of filler may be determined by incinerating a piece of paper of known weight. As the filler is non-combustible, the weight of the ash determines the percentage of filler, although allowance must be made for the amount of water of crystallization driven off from the mineral.

Tests for acids are important in papers used for mounting tarnishable substances, such as jewelry.

Tests for sulphur or chlorine are important in determining the chemical purity of the paper, since such residues militate against the permanency of color and strength of paper.

The presence of ground wood is easily determined by a drop of either strong nitric acid, which turns the paper brown, or a drop of phloroglucine, which gives a reddish-brown tint from contact with ground wood. Aniline sulphate produces a yellow tinge.

The presence of starch may be ascertained by using a dilute solution of Iodine which leaves a black stain in contact with starch.

Note.—For more technical information see “Paper Technology” by R. W. Sindall.