Chemistry of pulp and paper making . (398) Fig. 46. Basis-weight ScaleCourtesy of Thwing Instrument Company THICKNESS 399 per 500 sheets is read off directly on the scale and no movementof weights is necessary. In the case of very small samples a piece of known areashould be weighed on a chemical balance and the ream weightcalculated by the following formula: (Wt. in grams) X () X (area of trade size desired)Area of sample in square inches= Weight on trade size desired. Thickness. The thickness of a paper may best be deter-mined by means of a spring micrometer having a hand that. Fig. 47.
Chemistry of pulp and paper making . (398) Fig. 46. Basis-weight ScaleCourtesy of Thwing Instrument Company THICKNESS 399 per 500 sheets is read off directly on the scale and no movementof weights is necessary. In the case of very small samples a piece of known areashould be weighed on a chemical balance and the ream weightcalculated by the following formula: (Wt. in grams) X () X (area of trade size desired)Area of sample in square inches= Weight on trade size desired. Thickness. The thickness of a paper may best be deter-mined by means of a spring micrometer having a hand that. Fig. 47. Thickness GaugeCourtesy of B. F. Perkins &• Son, Inc. travels around a circular dial which is graduated in thousandthsof an inch. One of the many such instruments is shown in 400 PAPER TESTING Fig. 47. This type of tester should not be read closer than halfa thousandth as this is about their limit of accuracy. Thickness may also be measured by means of an ordinarymicrometer caliper but the amount of pressure is not easily con-trolled unless it is supplied with a ratchet device which preventsan excessive pressure being applied. This is not so accurate asthe spring type but is useful for approximate work around themiU. It is advisable to have all thickness gauges tested before may be done by securing a set of standard sheet-metalleaf gauges which range from to in. These shouldbe used occasionally to make sure that the instrument formeasuring thickness remains accurate. It has been suggested by the Committee on Paper Testingthat the relative compactnes
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaperma, bookyear1920
