ESPARTO PULP: MICROSCOPICAL FEATURES. The pulp of esparto when examined under the microscope is easily recognised, first by the characteristic appearance of the long slender cylindrical-shaped fibres, and secondly by the numerous cells always present. These cells consist of cuticular vessels with serrated edges, and also of small pear-shaped seed hairs, the shape of which is a ready means of identifying esparto. An examination of the transverse section of the raw material indicates the source of these pear-shaped vessels. _Test for Esparto in Papers._--Paper containing esparto fibre may be tested by means of a weak solution of aniline sulphate. The suspected paper is gently heated in the test reagent, and if esparto is present the paper turns a rose-red or pink colour, the depth of colour being a measure of the amount of esparto. Most of the modern book papers are prepared from chemical wood pulp and esparto mixed in varying proportions, and while this test can be used as a means of detecting a small or a large proportion of esparto, a microscopical examination is required for a more accurate estimation. The proportions used by the paper-maker depend upon the weighing out of the wood pulp and esparto more or less accurately, while the microscopical test is based upon the relative proportions as represented by the volume of fibres of each class on the glass slip placed under the microscope. Since the wood pulp consists of a number of broad flat ribbon-like fibres, and the esparto of small cylindrical fibres, considerable practice is necessary in making a proper analysis of the two constituents in paper. [Illustration: FIG. 25.--Esparto Pulp.] STRAW. The use of straw for the manufacture of paper was first brought prominently into notice about the year 1800 by Matthias Koops, who published a book printed on paper made from straw, but it was not until 1860 that this material was used in any large quantity. [Illustration: FIG. 26.--A Cylindrical Digester for Boiling Fibre.] Straw is now converted into a bleached paper pulp for news and printings, and is also utilised for the manufacture of straw boards. The production of a white paper pulp from straw is carried out in a manner similar to that used in the case of esparto fibre, viz., by digestion with caustic soda under pressure and subsequent bleaching. As the straw contains considerable quantities of siliceous matter, the chemical treatment necessary to reduce the material to paper pulp is more severe, a stronger solution of caustic soda being used, and the process of digestion being carried out at a higher temperature.