Chemistry of pulp and paper making . planning a book which must not exceed a definitethickness. It is usually measured by making up a dummyor cutting out short strips, piling them up to the required num-ber and measuring its thickness with the ordinary graduatedsliding clamp. In using this the pressure used must be speci-fied as heavy, medium, or hght and this introduces an elementof uncertainty into the results. The so-called pressure bulker, Fig. 48, made by B. and Son has been made to ehminate these this instrument the dummy is put under a definite pres-sure which is r
Chemistry of pulp and paper making . planning a book which must not exceed a definitethickness. It is usually measured by making up a dummyor cutting out short strips, piling them up to the required num-ber and measuring its thickness with the ordinary graduatedsliding clamp. In using this the pressure used must be speci-fied as heavy, medium, or hght and this introduces an elementof uncertainty into the results. The so-called pressure bulker, Fig. 48, made by B. and Son has been made to ehminate these this instrument the dummy is put under a definite pres-sure which is read in pounds per square inch on the dial andthe thickness in inches is read on a scale at the side. Opacity. The opacity or translucency of a paper may bemeasured by the Contrast ratio method using a Martens OPACITY 401 photometer in a specially constructed box. This method in-volves a determination of the difference in photometric bright-ness, or contrast, between a black and white spot when coveredwith the material to be Fig. 48. Pressure Bulker Provided this apparatus is not available, good comparative tests can be made by cutting a small, sharp-edged opening in a piece of cardboard and placing this over a source of intense Ught. Pieces of the paper are then laid over the opening one Bureau of Standards Circular No. 63. 402 PAPER TESTING at a time and the number of sheets required to completelyobliterate the light is noted. By determining the thickness persheet the absolute thickness of the paper required to obliteratethe light can be calculated. Gloss or Glaze. An instrument to measure the gloss orglaze of paper has been devised by L. R. Ingersoll. It wasfound that hght specularly reflected from paper at an angle degs. was almost completely plane-polarized and workingon this basis the instrument was designed to measure the gloss
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaperma, bookyear1920
