The conditions for boiling and bleaching esparto are varied by the paper-maker as circumstances require. A maximum yield of fibre is obtained when the least possible quantity of caustic soda is used, but a larger percentage of bleaching powder may be necessary to ensure a well bleached pulp. The use of an excess of caustic soda is probably the general practice for several reasons, amongst which may be noted the advisability of guarding against irregularities in the quality of the esparto, and consequent insufficient boiling, as well as the advantage of having some free caustic in the spent liquors to prevent the furring up of the tubes of the evaporating apparatus in the soda recovery department. The following experiments, given by a contributor to the _Paper Trade Review_ some years ago, are interesting as showing the effect of varying proportions of caustic soda used per unit of grass:-- EXPERIMENTS _RE_ YIELD OF AIR-DRY BLEACHED PULP FROM ORAN ESPARTO. Air-dry Pulp containing 10 per cent. water. ---+--------+----------------+------------------+-------+--------+------- |Esparto.| Soda Liquor. | Conditions of | | Dry | | | | Boiling. |Weight | Pulp |Bleach- ---+--------+-------+--------+------+-----+-----+ of |on Dry | ing No.| Wt. |Volume,| Per |Time. |Temp.|Pres-|Air-dry|Esparto.|Powder. | taken. | C.C. | cent. |Hours.|° C. |sure.|Pulp. | Per | Per | Grams. | |Na_{2}O.| | | Lbs.|Grams. | cent. | cent. ---+--------+-------+--------+------+-----+-----+-------+--------+------- 1 | 200 | 800 | 1·58 | 3 | 142 | 55 | 87·30 | 43·65 | 29·5 2 | 200 | 800 | 2·13 | 3 | 142 | 55 | 80·67 | 40·33 | 18·5 3 | 200 | 800 | 2·69 | 3 | 142 | 55 | 72·00 | 36·00 | 10·5 ---+--------+-------+--------+------+-----+-----+-------+--------+------- No. = No. of Experiment. PRACTICAL DATA CALCULATED FROM EXPERIMENTS. ---+------------+----------+------------+-------------+---------------- | Boiling. |Weight of |60 per cent.| Bleaching |For One Ton of No.+------+-----+Esparto to|Caustic Soda| Powder |Esparto used. |Time. |Pres-|give 1 ton|required to |required to +---------------- |Hours.|sure.| Pulp. | Digest |Bleach 1 ton | 60 per |Bleach- | |Lbs. | Cwts. | Esparto. |Air-dry Pulp.| cent. |ing | | | | Cwts. | Cwts. |Caustic.|Powder. | | | | | | Lbs. | Lbs. ---+------+-----+----------+------------+-------------+--------+------- 1 | 3 | 55 | 45·8 | 4·30 | 5·26 | 210 | 260 2 | 3 | 55 | 49·5 | 6·27 | 3·39 | 282 | 156 3 | 3 | 55 | 55·5 | 8·90 | 1·96 | 358 | 79 ---+------+-----+----------+------------+-------------+--------+------- No. = No. of Experiment.