The weight of hurds which are capable of being charged into a rotary is a decidedly unfavorable factor.  The weight of a cubic foot of hurds varies somewhat with the proportion of bast fiber, but averages about 5.4 pounds, which, compared with a cubic foot of poplar chips at 8.93 pounds, represents a digester charge of 60.5 per cent of the weight of a poplar-wood charge, or, in terms of fiber capacity, the hurds charge would yield 38.6 per cent as much fiber as the wood charge.  The hurds upon being baled for transportation may be broken and crushed to such a degree that the weight of the charge may be increased, and it might be found possible to increase the charge weight by steaming or by the employment of tamping devices.  This small weight of charge constitutes one of the most serious objections to the use of hurds in paper manufacture.

In those tests in which the most satisfactory results were obtained, the cooking conditions were 29.5 per cent of caustic soda at a concentration of 107 grams per liter and a causticity of 84.0 per cent acting at a temperature of 170 deg.  C. for five hours, or a total time of seven hours.  The steam condensation in the rotary used for these tests was abnormally high, due to the fact that the steam supply pipe was uncovered for a considerable distance and the rotary was entirely uncovered.  It is believed, therefore, that a larger amount of caustic was necessary than would otherwise have been the case.  This belief is strengthened by the quality of the waste liquor from one of the later cooks, which gave on analysis 16.85 grams per liter of free caustic soda and showed a causticity of 27.75 per cent.  These data show that only 67.3 per cent of the total caustic employed was actually consumed in the cooking operation, which percentage is lower than obtains in practice.  The stock from this cook was bleached with 11.5 per cent of bleach.  But even as the figures stand, the comparison with poplar cooking practice is as follows:  29.5 per cent caustic soda used as against 22 to 25 per cent; 107 grams per liter as against 100 to 110; 84 per cent causticity is little different than obtains in practice; 170 deg.  C. is about commercial practice; five hours at pressure as against four to six hours; seven hours’ total time as against possibly six to eight hours; 11.5 per cent bleach as against 8 to 10 per cent.  Thus, it is evident that the cooking conditions employed were slightly more severe and expensive than those in commercial use with poplar wood.

The yield of total fiber obtained from the hurds may be placed at 35 per cent of bone-dry fiber calculated on the bone-dry weight of hurds used, or 33.1 per cent of air-dry fiber calculated on air-dry hurds.  The yield of bleached fiber was not determined in this preliminary work, but may be safely estimated as 30 per cent, which is low when compared with a yield of about 47 per cent of bone-dry bleached fiber from bone-dry poplar wood.  It is believed quite possible that satisfactory cooking conditions may be found which will give a higher yield than was obtained during these tests.  The stock should be classed as easy bleaching, and 11.4 per cent of bleach is a satisfactory figure, although a little high.