Chemistry of pulp and paper making . various fibres are measured in terms of the diameter of theobserved field. The magnification recommended is i6o diam-eters and an adjustable stage is essential in order to cover sys-tematically the entire sample on each slide. After all foursamples have been examined the figures are added together toget the total length of each kind of fibre present. This totallength multiplied by a weight factor, which varies with differentkinds of wood, gives a set of directly comparable results whichmay be converted into the per cent of each kind of fibre wei
Chemistry of pulp and paper making . various fibres are measured in terms of the diameter of theobserved field. The magnification recommended is i6o diam-eters and an adjustable stage is essential in order to cover sys-tematically the entire sample on each slide. After all foursamples have been examined the figures are added together toget the total length of each kind of fibre present. This totallength multiplied by a weight factor, which varies with differentkinds of wood, gives a set of directly comparable results whichmay be converted into the per cent of each kind of fibre weight factors given are as follows: rag pulp i; hemlockpulp ; poplar pulp ; birch pulp ; beech ; maple pulp Where a mixture of fibres fromdeciduous w^oods is under examination the number of counts ofeach kind to which the weight factor is to be applied may bedetermined from an examination of the number of ducts was found that the proportion of ducts and fibres in differentwoods was as follows:. 1 Spence and Krauss: Paper 20, 1917, May 23, p. 11. UNBLEACHED SULPHITE DETERMINATION 393 This method is too slow to be used where many routineanalyses are to be made daily, but its accuracy recommends itparticularly for settling cases of dispute between differentauthorities. Unbleached Sulphite Determination. The method given isthat worked out by Bright.^ *The principle of the method is first to stain the fibres withCross and Be vans ferric ferricyanide solution, which colors theunbleached sulphite green, on account of the lignin containedin it, and leaves the bleached sulphite colorless. This alonegives a good distinction, but by subsequently staining with ared substantive dyestuff, the green of the unbleached is changedto a very pure blue, the bleached being colored red, thus givinga most striking contrast. The problem is to adjust the treatment with the two solu-tions to bring out the sharpest contrast. If the treatment withred is too severe, s
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