Page:Paper and Its Uses.djvu/108



scheme for the analysis and testing of papers will include the following: Checking the weight of the ream and sheet; the thickness of the ream and sheet; examination of the physical and chemical constituents—fibre, sizing, loading, and colouring matter; testing the tensile strength and elasticity, the resistance to folding or crumpling, and microscopical examination of the fibres. It is not necessary to carry out all these tests on every paper, but it is well to be prepared, if required, to compare two samples, using appropriate tests.

Weight.—The weight of the ream is checked on the scales, and variation should not exceed 4 to 8 per cent, above or below the nominal weight. (See various kinds of papers under "Variations in Weight," on page 136.) A sheet of paper is weighed on a balance which gives a direct reading for a ream of 480, 500, or 516 sheets. The demy scale is a very useful little balance. A metal plate is supplied with the scale, a piece of paper is cut exactly to the size of the plate