The presse-pâte system, originally adopted for the treatment of straw, has of late years been extensively applied to esparto. The presse-pâte consists of the wet end of a paper machine, and is furnished with sand-tables and strainers. The pulp is allowed to flow on to the wire cloth, so as to form a thick web of pulp. The bulk of the water passes away through the wire cloth; a further quantity is removed by the {97} vacuum-boxes and couch-rolls. The pulp, containing from 50 to 60 per cent. of water, is wound round an iron rod until a sufficiently large roll is formed. The advantages of the presse-pâte system are the possibility of the removal of dirt and unboiled portions by means of the sand-tables and strainers, and the very complete washing and removal of the products of the action of bleaching powder. It also enables manufacturers to dispense with the somewhat costly methods of dry and wet picking. The presse-pâte system can also be applied to the unbleached pulp. It may be interesting at this point to say something about the substances which are removed from the esparto by the caustic soda. On referring to p. 57 it will be seen that the original grass contains nearly half its weight of extractive matter, the removal of which has to be effected. Only a small proportion of this is extractive matter in the ordinary sense of the term, i.e. that can be extracted by the usual solvents; the remainder is intimately combined with the cellulose. The action of the caustic soda is to resolve these bodies, the cellulose remaining behind, and the other constituents being dissolved as resinous bodies by the soda. A certain proportion of the mineral constituents, notably the silica, dissolves in the lye, the latter forming silicate of soda. On neutralizing the liquor with an acid, the bulk of the dissolved constituents is thrown down as a dark brown resinous mass. If this crude product be purified, it is found to consist of a definite body having the formula C_{21}H_{24}O_{8}. By the action of chlorine on this resin a bright yellow chlorine compound is formed, resembling the compound from jute described on p. 18. If the resin be treated with concentrated nitric acid, a bright yellow body is formed, which forms definite compounds with bases, and which has the property of dyeing animal fibres a bright orange colour. In addition to this body, a yellowish-white wax can be isolated. It sometimes happens that this wax is but imperfectly dissolved in the caustic lye; if the waste liquor be allowed {98} to stand, the wax is occasionally found to collect in small quantities on the surface.