Page:Paper and Its Uses.djvu/117

Rh better paper. The zone test is an elaboration of the ink test. A small quantity (1 c.c. or .5 c.c.) is allowed to fall a drop at a time upon the blotting paper, and when the blot is dry, the area of the outer non-absorbent zone, its proportion to the inner absorbent zone, and its regularity will serve as an index to the behaviour of the paper in use. Other factors in the choice of blottings are the resistance to wear, absence of fluff, and the resistance to surface dirt. A very rough blotting paper may not be entirely satisfactory in those respects, but, on the other hand, a very smooth paper may be produced at the expense of absorbency.

Copying papers are tested in the copying press with a document written with copy able ink, and the efficiency of the paper judged either by comparison with a standard sample, or merely by the clearness of the resulting copy.

Duplicating papers may be tested by drawing a fine pen charged with writing ink across the surface, and immediately rubbing the ink to see if it smears. Half-sized duplicating papers have the same method applied^but should be allowed five to ten seconds after writing. These methods are superseded by the use of the duplicating machine, if available.

Mineral Matter Loading.—A weighed quantity of paper—say 1 gm.—is torn into small fragments, placed in a porcelain crucible, previously weighed, and subjected to the intense heat of a Bunsen burner until the paper is consumed and the residue reduced to a white ash, or in any case until all carbonaceous matter is burnt off. See that any black deposit on the crucible is burnt away. Cool the crucible, weigh it with its contents, deduct the weight of the crucible, and the weight, multiplied by 100, will give the percentage of mineral matter present in the paper.