Chemistry of pulp and paper making . t across and half with the speed of tearing of i^ ins. per minute was used and readingstaken every five seconds while making a tear of 3 ins. Thismethod was found to give good check results provided the speedof tearing was constant. A tearing tester recently devised by Thwing is shown in A small sample of paper is cut and punched by a special dieand attached to two pins one of which is attached to a movableweight on an arm carrying a recording pen while the other isattached to a motor driven, sliding record card holder. Thisholder is caused
Chemistry of pulp and paper making . t across and half with the speed of tearing of i^ ins. per minute was used and readingstaken every five seconds while making a tear of 3 ins. Thismethod was found to give good check results provided the speedof tearing was constant. A tearing tester recently devised by Thwing is shown in A small sample of paper is cut and punched by a special dieand attached to two pins one of which is attached to a movableweight on an arm carrying a recording pen while the other isattached to a motor driven, sliding record card holder. Thisholder is caused to move away from the pin on the weight arm,thus tearing the paper along the line of perforations. The record Veitch, Sammet and Reed: Paper, 20, 1917, May 30, p. Case; J. Ind. Eng. Chem., 11, 1919, 49. Wells: Paper, 23, 750, Feb. 12, 1919. 410 PAPER TESTING shows graphically the force in granas required to tear the paperbetween each two perforations, thus giving five peaks, theaverage of which is taken as the tearing Fig. 55. Thwing Tearing TesterCourtesy of Thwing Inslriimenl Company Absorbency. The absorbent power of a paper is generallymeasured by suspending strips vertically with their lower endsdipping into water and noting the height to which the waterrises in ten minutes. The average for several strips cut in bothdirections should be taken as the figure for absorption. This method is criticized by Reed ^ because it employs waterinstead of ink but stiU more because it is unaffected by the bulkor weight of the paper. He proposes allowing i of a standardink to fall from a pipette upon the surface of a 4-in. square of theblotting paper which is placed over a tumbler or beaker of Reed: J. Ind. Eng. Chem., 10, 191S, 44. PERMEABILITY TO AIR 411 such size that the edge of the spot will not touch the glass. Thetime for the complete absorption of the ink is recorded. In thistest attention must be paid to the temperature of the ink, thedeHvery time of the pipe
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