To compare papers a more primitive method may be employed. It has the virtue of simplicity, and yet it gives a fair index to the amount of wear which the paper will withstand. Take a piece of the paper to be tested, about 6 inches square, roll it into a ball, then spread it out flat; repeat the performance, and notice how many such treatments the paper stands before perforation takes place. Papers which are very resistant, such as all-rag papers and air-dried browns, will assume a cloth-like appearance as they become softer, and it will be a long time before perforation takes place.
Sizing.—To test papers for efficiency of sizing write rather heavily upon the surface with ordinary pen and ink. Red ink is usually more penetrative than black, so it is better to use a good black ink as a standard test. As some papers, such as account book papers, have to stand erasure, they should be tested for ink bearing after abrasion of the surface.
To test for gelatine sizing cut up a small quantity of paper and boil for a few minutes in a beaker containing sufficient water to cover the paper. Pour off into a test tube, cool, add a few drops of a 2 per cent, solution of tannic acid. A flocculent precipitate indicates that the paper has been sized with gelatine. Heat the liquid, and the precipitate will coagulate and cling to the sides of the test tube. A comparative test is made by taking an equal quantity of each kind of paper, boiling in similar quantities of water for the same period, and adding the same amount of tannic acid solution, and comparing the results.
Resin sizing is determined in a different manner. A comparatively large quantity of paper is extracted in a small quantity of liquid. Take a strip of paper, about 8 inches by I inch, pleat it repeatedly until it can be placed in a test tube, and cover it with rectified
