The two forms of boiler above described possess the obvious advantage of having the whole or nearly the whole of the interior available for holding grass; the boilers can therefore be made to hold more, and the boiling is moreover much more evenly accomplished. Washing.—The boiling being completed, the steam is allowed to escape and the liquor to collect at the bottom of the boiler where it is run away by the pipes placed at the bottom for the purpose. Water is then run in and steam turned on for a short time; this is also run off, and the grass drained as completely as possible. The boiled grass is then emptied into trucks and taken away to the washing engines. These resemble those already described under rags. During the process of washing, a certain amount of the shorter fibres find their way through the meshes of the wire-cloth. In addition to this a large proportion of the cellular tissue surrounding the fibro-vascular bundles (see Fig. 12, p. 57) is carried away. If the wash-water be examined under the microscope, it will be seen to consist largely of this cellular matter. Though this entails a certain loss of cellulose, its removal is in other respects advantageous, as it is possessed of hardly any “felting” properties, and it is moreover exceedingly difficult to bleach. The amount of fibre actually obtained in practice is but little below that contained in the grass. A certain loss is {96} inevitable, but this probably does not exceed 1 or 2 per cent. The percentage of cellulose in esparto is given on p. 57. The following numbers obtained by the authors are somewhat higher. They are calculated on the absolutely dry fibre; those mentioned are on the _air-dry_ samples:— Cellulose per cent. Spanish 58·0 Tripoli 46·3 Arzew 52·0 Oran 49·6 There is no doubt that considerable differences occur even between different specimens of the same kind of grass. It is the practice in some mills to wash the grass in a series of tanks connected together in the same way as the lixiviating tanks of an alkali works. They are so arranged that pure water flows in at one end, passes through fresh lots of grass in succession, and issues at the further end highly charged with the soluble products of the grass. By such an arrangement the grass can be washed without any loss of fibre, and with a minimum quantity of water. This latter feature is of great importance in mills where it is necessary to evaporate the whole of the waste liquors from the esparto, as they are then obtained in a very concentrated form. Even with such an arrangement it is advisable to give the grass a short final treatment in the washing engine. The washing having been completed, and the esparto having been broken up into “half-stuff,” it is now ready to be bleached (see Chap. VII.).