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24. liberated during the cooking, there is usually more pressure within the digester than the pressure corresponding to the temperature of the charge, and since this false pressure is usually unknown it seems preferable to employ temperature as the control.

The results of the tests are shown in Table VII.

Table VII. Results of trials of four cooks of zacaton pulp.

The average yield of fiber at 90 per cent bone dry is 43 per cent of the air-dry grass, which would average 80 per cent bone dry. The excess caustic soda, 8.1 to 8.9 per cent of the bone-dry grass, doubtless higher than is necessary, and it would indicate that less soda could have been employed in the cooking.

Pulp charges from the four cooks were remarkably similar in appearance and feeling; they drained and washed with great ease, a property not shared by the pulp of many plants and a fact of great importance in a commercial sense, because of the necessity of washing out and recovering the spent soda.

On screening the pulp charges through a No. 10 cut screen there remained undercooked screenings to the extent of 2.05 per cent of the bone-dry pulp, or 1 per -cent of the bone-dry grass. The screened stock bleached easily and to a satisfactory color with the equivalent of 12.7 per cent of commercial bleaching powder.

After washing free from bleach residues, the stock was given four hours' medium brushing in a beating engine (fig. 13) and furnished with 24 per cent of clay, 1.8 per cent of resin size, and 2 per cent of alum.

At the close of the beating operation the charge was whitened by the addition of a small amount of blue or blue and red color, to offset the residual yellow tint invariably present in all bleached stocks.

The finished stock was run through a Jordan refiner and to a 30-inch Fourdrinier machine speeded to 85 feet per minute. Although the stock was as a little too "free" to get the maximum felting of the fiber it acted very well on the machine and gave a machine-finished sheet of good appearance and quality. Physical tests of this sheet, designated as No. 76, in connection with those of sheet No. 41 are given in Table VIII.