motive power, some four to six reams of paper being suspended in ball clip frames in the space between the two sets of fans. The air of the machine-room is circulated by the fans rapidly through the paper, and maturing takes place in two or three hours.
All paper, after it has been matured, must be stacked, a board and a heavy weight placed on the top of the stack, and the edges protected from getting dirty.
Stretching takes place when paper is subjected to tension or rolling. All cylinder printing machines exert these strains, from the pull of the cylinder and from the printing surface. Difficulty in register will be experienced when a paper stretches much under tension, but it is not so great a trouble as the expansion already referred to. All papers are elastic, and if stretched just within the bounds of the breaking strain of the paper, will show some elongation, permanent or temporary. If the paper returns to its original length there is no permanent stretch, but that is seldom found in practice. The greater expansion of paper is in the cross direction, and the direction of greater stretch of the sheet coincides with that of the larger expansion.
Careful tests of good litho. papers on the Leunig Paper Tester show them to have a mean temporary stretch of 2½ per cent, in the machine direction, with a stretch that is permanent of .68 per cent. The figures for the cross direction of the paper are 4 per cent, and 1½ per cent, respectively. It is the permanent stretch that may cause inconvenience, but the figures quoted must not be taken as an indication of what takes place when printing. A properly adjusted machine does not exert the tension that would be necessary to obtain the percentage of elongation
